摘要:

APRIL, 1967 THE ANALYST Vol. 92, No. 1093 Heterocyclic Azo Dyestuffs in Analytical Chemistry A Review* BY R. G. ANDERSON AND G. NICKLESS (School of Chemistry, The University, Byisto1 8) SUMMARY OF CONTENTS General introduction and scope 1-( 2-Pyridylazo)-2-naphthol General properties Applications as a complexometric indicator Applications as a spectrophotometric reagent Other applications in analytical chemistry General properties Applications as a complexometric indicator Applications as a spectrophotometric reagent Other applications in analytical chemistry Other pyridylazo dyestuffs and related compounds Thiazolylazo and benzothiazolylazo dyestuffs Miscellaneous heterocyclic azo dyestuffs 4- ( 2-Pyridylazo) -resorcinol General Azo derivatives of 8-hydroxyquinoline Conclusions THIS review is concerned with the analytical applications of heterocyclic azo dyestuffs and closely related compounds, in which the heterocyclic atom is at least formally involved in chelation with a metal atom (see example below).The review will, therefore, include all dyes with a heterocyclic atom ovtho to the azo group, and also azo-derivatives of 8-hydroxyquinoline. It will, however, exclude certain dyes such as azo dyes of pyrazolone, which chelate through the keto oxygen atom. Ar I @ 0-M N 11 P-M either N - t M o r / Ar (i) X = OH (ii) X = N(CH3)z The review covers the literature up to the end of 1965, with a few early references from 1966. * Reprints of this paper will be available shortly. For details see Summaries in advertisement pages. 207208 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [Analyst, Vol.92 The earliest references to these heterocyclic azo dyestuffs were concerned with 8-hydroxy- quinoline azo dyes as test reagents for cations.1,2 In 1951, Liu3 investigated the reactions of l-(Z-pyridylazo)-Z-naphthol (PAN) with metal ions. However, the first major paper to be published was by Cheng and Bray4 in 1955, who recommended the use of PAN as a complexometric indicator in direct titrations with ethylenediaminetetra-acetic acid (EDTA). In addition, they observed that the chelates of PAN may be extracted into organic solvents, and described a few simple studies on this phenomenon. Initially PAN was used as an indicator, in indirect and direct titrations of metal ions with EDTA.5,6,7,8,9 Then about 3 years later applications were also found for the dye as a spectrophotometric reagent, especially for uranium.10911J2J3 Generally, such applications were used in conjunction with solvent extraction procedures.Since then PAN has been used in analytical procedures with about forty-five different metals. In 1957, Wehber14 recommended the use of 4-(2-pyridylazo)-resorcinol (PAR) in com- plexometric titrations, claiming it to be superior to PAN because of the solubility in water of the dye and its chelates. PAR was used in direct EDTA titrations for a variety of metals,15,16 being superior to PAN according to Wehber's observations, and also because of its sharper end-points. Pollard, Hanson and Gearyl7 used it as a spectrophotometric reagent for cobalt(II), uranium(V1) and lead(I1). No solvent extraction was required with this method, and PAR was found to be the most sensitive reagent for cobalt(II), the most sensitive water- soluble reagent for uranium(V1) and the first water-soluble reagent for lead(I1).PAR has now been used in analysis for about forty different metals. Azo dyes of thiazole can be prepared from a very wide range of phenolic substances, and have been used as potential metallochromic indicator^.^^^^^^^^^^^ In addition to these, azo dyes of 8-hydroxyquinoline have been synthesised for use in titrations with EDTA and found to give sharp e n d - p o i n t ~ . ~ ~ ~ ~ ~ r ~ ~ Dyes with a PAN-type chelating structure act as tridentate ligands complexing with most metals through the ortho-hydroxyl group, the azo nitrogen nearest to the phenolic ring and the heterocyclic nitrogen atom, giving two stable, 5-membered chelate rings.25 They form complexes with ions of small size carrying a large positive charge, such as the titanium (similar to salt-forming reagents) and with ions of the heavy metals and transition elements with nearly full d-shells (like other nitrogen-donor chelating agents) .z8 yz9 These two classes of metals may be compared with class A and class 13 acceptors, as described by Ahrland, Chatt and Da~ies.~O These heterocyclic azo dyes will complex well with both types of metal, and this may be regarded as the reason why it has been possible to find analytical uses for them with such a wide range of metals.Other reviews related to this subject have appeared by D a n ~ u k a , ~ ~ Busev and Ivan0v,~2 Sommer and HnilitkovA27 and Hsin-Chien Teng and Shui-Chieh Hung.33 A short leaflet on some analytical applications of PAR has been published by British Drug Houses Ltd.34 The most important dyes of this class are PAN and PAR, and about 200 papers have already been published concerning applications of these two dyes in analysis alone.GENERAL PROPERTIES OF THE DYE- PAN was first prepared by Chichibabin, by coupling sodium 2-pyridyldiazotate with /3-naphthol in ethanol under an atmosphere of carbon dioxide.35 Basically the same method is used to prepare the dye today. It is insoluble in water, dilute acids and alkalis, but is soluble in strong acid (pH > 2) to give a yellow - green cation, and in strong alkali (pH > 12) to give a red anion.It is soluble in alcohols, and also t o a slight extent in ethers, to give a bright yellow solution, and in concentrated sulphuric acid solution it is violet. 1-(2-PY RIDY LAZO)-2-NAPHTHOL (PAN) PAN is a bright orange solid with a melting-point of 137" C. 9 N = N 8-Q \ / N = N 8-Q \ / N = N 8 \ / H HO HO -0 I pH <2*5 II pH>2.5 to12 IIl pH > 12April, 19671 DYESTUFFS I N ANALYTICAL CHEMISTRY 209 The acid dissociation constants have been determined by Pease and Williams,36 who obtained values of 1-9 and 12.2 for pK,, and pKoH, respectively, in 20 per cent. aqueous dioxan with a spectrophotometric method. Corsini, Mai-Ling Yih, Fernando and Freiser3' obtained values of less than 2 and of 12-3 by potentiometric titrations in 50 per cent.dioxan at 25" C. Nakagawa and Wada,38 while studying the solvent extraction behaviour of PAN and the corresponding zinc(I1) and nickel(I1) chelates, obtained values of 2.9 and 11.5 in aqueous solution (see Table I). ABBREVIATIONS USED IN THE TABLES Abbreviation s p . . . r o t . . . SE. . . log K . . EDTA CHDTA EGTA Ext. . . isoPrOH DMF . . BuOH pptn. . . UBP . . TBP . . TNOPO OD . . EtOAc.. P * * IBMK REs .. Dye PAN .. PAR . . PAC . . PAAC $-PAN MAAR TAR . . TAN . . BTAN TAN 6s TAC . . TAM . . .. .. .. . . .. . . .. . . . . . . . . . . 4MeTAP-OMe p-TAN . . 9-BTAN . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . .. . . .. .. .. . . . . . . . . .. . . . . . . .. . . . . . . . . . . . . . . . . . . .. Explanation Spectrophotometric determination Potentiometric determination Determination by solvent extraction Log,, of stability constant (log,,K,, log,,K,, etc.) Ethylenediaminetetra-acetic acid 1,2-Cyclohexanediaminetetra-acetic acid Ethyleneglycolbis-(2-amicoethylester)-NNN'N'-tetra-aceiic acid Extracted Isopropyl alcohol Dimethylformamidc Butanol Precipitation Dibutyl phosphate Tributyl phosphate Tri-n-octylphosphine oxide Optical density or absorbance Ethyl acetate Ionic strength Isobutyl methyl ketone Rare carth elements TABLE I DISSOCIATION CONSTANTS OF AZO PKNH 1.9 (Sp.) <2 (Pot.) 2.9 3.1 2.3 (Pot.) 2-69 (Pot.in water) 2.41 (Pot. in 50% dioxan) 2.60 3.84 2.54 (Pot.) 1.03 - - - 5.83 5.6 6.9 (Pot.) 5.50 (Pot. in water) 7.15 (Pot. in 50% dioxan) - 5.35 6.15 6.4 5.9 (Sp.) - - 0.88 (Sp.) - 2.3 (Sp.) - - - 3.13 (Sp.) - 0.77 (Sp.) - - 7.19 - 6.94 DYESTUFFS PKOH (ortho) 12-2 (Sp.) 12.3 (Pot.) 11.5 12.5 11.9 12.4 (Pot.) 12.31 (Sp. in water) 13.00 (Sp.in 50% dioxan) 9-15. 10.16 10.74 (Pot.) 11-99 9.5 103 (Sp.) 10.5 9.0 (20% dioxan) 9.8 (60% dioxan) 9.10 (Sp.) 8-5 (Sp.) 7-86 (Sp.) 7.9 8.2 (Sp. and Pot.) 8.2 (Sp. and Pot.) 8.65 (Sp.) 7-98 (Sp.) - Reference 36 37 38 123 109 37 25, 108 25, 108 143 145 140 156 27 191 178 178 178 195 190 193 21 189 189 169 171 186 186 Note-For space considerations, ionic strength details have been omitted. The ultraviolet and visible absorption spectra of the dye have been studied as a function of pH, and it has been found that PAN shows hypsochromic and bathochromic shifts on protonation and ionisation, re~pectively.~~ In 20 per cent.aqueous dioxan, the peak210 ANDERSON AND NICKLESS HETEROCYCLIC A 2 0 [Analyst, Vol. 92 wavelengths are at about 440mp for the cation, 470mp for the neutral molecule and 495 mp for the anion. Busev and I v a n ~ v ~ ~ have shown that, under various conditions of pH, ionic strength and concentration, PAN shows no evidence of intermolecular association. Pollard, Nickless and Samuel~on~~ have used thin-layer chromatography to ascertain the purity of commercial PAN and other heterocyclic azo dyes of analytical interest. Because of the many applications of chloroform to the extraction of PAN chelates, the distribution coefficient of PAN between water and chloroform has been measured.39 A value of 105.1 was obtained, compared with 1040 found between carbon tetrachloride and water.41 It is fairly constant (about 2) so that the extraction conditions, predicted by D.Betteridge (private communication) from work with carbon tetrachloride or chloroform, may, to a first approximation, be applied to those solvent systems that might be more useful to, or favoured by, the analyst. These are red with the alkaline earths, rare earths, Al(III), Sc(III), Y(III), Ti(IV), Zn(II), Cd(II), Hg(II), Ga(III), In(III), Tl(III), Pb(II), Bi(III), Ni(II), Mn(I1) and U(VI), etc. With Cu(II), V(1V) and (V), Fe(I1) and (111) and Ru(III), they are of varying shades from red to violet, whereas with Co(III), Pd(I1) and Pt(I1) they are green. The sensitivity of the reagent is low with the alkaline earths. The alkali metals, Ge(IV), As, Se and Te do not react.These reactions are sensitive to changes in solvent, temperature, ionic strength and concentration of metal or ligand. The anion of the metal is not important unless it, itself, has a strong tendency to complex with the metal. The pH of the solution is of great importance, and the minimum pH for chelation with PAN varies from metal to metal. Correct pH control is of absolute importance in all analytical work with PAru’.42 Many of these chelates are insoluble in water but can be extracted into various organic solvents. This phenomenon has been investigated in detail by Berger and Elvers,41 Shibata42 943 and Betteridge, Fernando and F r e i ~ e r . ~ ~ All of these workers have shown that the formation of the chelates and their extraction into organic solvents is dependent on pH.By the correct choice of pH, organic solvent and masking agents, PAN can be made quite selective as a solvent extraction reagent. In the course of studying PAN as an analytical reagent, many workers have investigated the compounds formed between the dye and the metal. The most common metal-to-ligand ratios encountered are 1 : 1 and 1 : 2 . Shibata43 has proposed the following structures for these two types of complex- The ratio of logKD Z~(PAN), has been measured for several solvents. PAN forms coloured complexes with most metals. Oil+ ;2+ It has not always been possible to explain equilibrium results by these structures. There is evidence44 for complexes of the type M(PAN) (OH), especially for uranium,45 while Stanley and C h e n e ~ ~ ~ reported on Cu(TAR)(OH), which was suggested by potentiometry.The solvent extraction behaviour of nickel(I1) and cobalt (11) complexes has not been explained satisfa~torily.~89~4 Other types of complex are rare, and may occasionally occur with ions of high valency. An interesting complex of gallium has recently been rep~rted,~’ with a metal-to-ligand ratio of 1 : 5. Determinations of stability constants and stoicheiometries of many complexes have been made by various ~ o r k e r s . 3 7 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ Some values for the stability constants of PAN chelates are given in Table 11.April, 19671 DYESTUFFS I N ANALYTICAL CHEMISTRY 211 Ion Zn(I1) . . Cu(I1) . . Ni(I1) . . Co(1I) . . Mn(I1) . . Pb(I1) . . Cu( [I) In(II1) . . Tl(II1) .. Zn(I1) . . Cu(I1) . . Ni(1I) . . CO(1I) . . Mn(I1) . . Ta(V) . . Nb(V) .. Th(1V) V(V) . . U(V1) . . Zn(I1) . . Ni(1I) . . Zn(l1) . . Ni(I1) . . Hg(I1) .. Zn(I1) . . Ni(I1) . . Mn(I1) . . Pb(I1) . . Zn(I1) . . Cd(I1) . . Bi( 111) Ti(II1) . . Ga(II1) In(II1). . Cu(I1) . . Cu(I1) . . Cu(I1) . . Co(I1) . . CU(I1) . . TABLE I1 STABILITY CONSTANTS OF THE CHELATES Kl = - [ML1 for M + L = ML where L is the mono-anionic form of the ligand. K - -PZiL for ML + L = ML, 8, = K, K, or 2 for M + 2L = ML, [MI [LI - [MLI [LI [ML 1 [MI [LIZ .. .. . . . . .. .. .. .. . . . . .. . . . . . . . . . . . . .. .. .. . . . . . . . . . . . . . . . . . . .. . . . . . . . . .. . . . . . . .. Ligand PAN PAN PAN PAN PAN PAR PAR PAR PAR PAR PAR PAR PAR PAR PAR PAR PAR PAR PAR PAC PAC PAC R-PAN a-PAN a-PAN PAA PAA PAA PAA PAA PAA TAR TAR TAR TAR TAR TAR TAR TAR log10K1 11.2 10.9 12.6 15.5 17.0 12.7 14.0 8.5 6.5 8.6 10.0 (log K) 9-6 (log K) 13-6 9-8 (log K) 10.5 11.2 - -16 > 12 12.4 11-7 14.8 16.4 13.2 10.0 14.8 > 12 - 19.7 6.5 5-94 6.86 7-17 (log K) 12.5 16.2 8-36 13.70 - - 5.23 5-08 2.36 3-33 4.24 0.7 11-8 8.4 7.4 7.0 13.2 9.4 11.1 10.1 log10 l32 21.7 21.8 20.9 - - 23.9 25.3 27.5 16.4 - - - - 20.0 f 1.0 19-2 f 0-2 27.0 19.6 f 0.2 17.1 19.0 23.5 23.9 25.3 26.0 17-1 23-0 - - 19.7 18-9 - - - - 20.9 25.8 16.66 22-00 22-14 19 20 23 - - - - - - - - - - - - - - Method Pot.SE. SP. SP. SP. SP- Pot. SP- Pot. r o t . SP. Pot. in water SP. SE. - - - Pot. in water Pot. in 50% dioxan Pot. Pot. in water Pot. in 50% dioxan Pot. Pot. in water Pot. in 50% dioxan SP.- SP. SP. SP. SP. SP * r o t . Pot. in water Pot. in 50% dioxan - - - SP. SP- SP- SP. SP. SP. SP- SP. SP. - - - - - - - - Reference 37 44 38 36 44 50 139 37 38 37 37 240 24 241 241 242 241 25 25 37 123 25 25 37 25 25 37 243 37 244 118 118 111 25 25 144 144 144 140 140 140 110 110 110 110 110 110 27 27 27 27 27 27 27 27212 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [Analyst, Vol. 92 TABLE II-contin%ed Ion Ligand log10K1 log10K2 log10 /32 Method Reference U0,2+ . . .. TAR Cu(I1) . . .. TAN Zn(I1) . . .. TAN Co(I1) . . .. BTAN Ni(I1) . . .. TAC Ni(1I) . . .. TAM Cu(I1) . . . . TAM Cu(I1) . . . . 4MeTAP-OMe - Zn(I1) . . . . - 9.1 10.8 11-7 11.9 - 9.7 10.0 13.4 (log K) - 8.0 8.2 7.3 7.6 6.4 5.4 9.8 5.9 - - - 191 22-5 SE. 195 ._ SP. 188 19-7 SE. 195 193 - - - 16.2 Sp.and Pot. 189 14.9 Sp. and Pot. 189 170 173 174 11.8 - - - - - APPLICATIONS AS A COMPLEXOMETRIC INDICATOR- Applications of PAN as a complexometric indicator can be divided into three groups. Direct titrations of metals against EDTA with PAN as iadicator-This has been used for the titration of about eleven metals, of which the most important is c~pper.*,~~to 6o The colour change at the end-point is from red or red - violet to yellow or yellow - green. The stability constants of the metal - PAN complexes are high, but EDTA should displace the metal from its PAN complex at the end-point; the reaction, however, is frequently a slow one. This can be improved by heating the solution near the e n d - p ~ i n t . ~ ~ , ~ ~ ~ ~ Often in purely aqueous solutions the PAN chelate is present as a fine suspension of solid.Naturally this is not conducive to a fast reaction at the end-point. It has thus been found that the addition of an organic solvent, such as ethanol or acetone, can improve the end-point.50 These titrations are sensitive to the effect of pH and use has been made of this to make certain titrations more ~pecific.~ *61 Otherwise foreign ions may be masked or sometimes reduced to a lower, weakly complexing valency state.5 950961 Indirect titrations-This method consists in reacting the metal with excess of EDTA and titrating the uncomplexed EDTA with a standard metal solution. Standard copper sulphate is generally used for this p u r p o ~ e , ~ ~ ~ ~ ~ s ~ as it produces the sharpest and most clearly defined colour change at the end-point (yellow - green to red - violet).The direct titration of copper is one of the most satisfactory with PAN as indicator. Often heating is required near the end-p~int,~ and the addition of ethanol is beneficiaL61 The method, first used by Cheng and Bray for the titration of scandium,6 has since been used for the titration of about twenty metals. Interfering ions have to be masked or separated before the titration. Bismuth and thallium( 111) have been simultaneously determined by a combination of both methods.62 A direct titration at pH 4 to 5 gives the total metal content. Sodium sulphite is then added to reduce the thallium(II1) to thallium(I), which does not complex with EDTA at this pH. The liberated EDTA is then titrated with standard copper sulphate solution.Replacement titrations with copper - EDTA - PAN as indicator-This method is the same as the first method, except that a few drops of PAN and copper - EDTA complex solution are used as indicator. PAN displaces the copper from the EDTA to give a red - violet colour. During the titration the EDTA reacts with the uncomplexed metal in preference to the copper - PAN complex. The end-point is reached when the EDTA reacts with the copper - PAN causing a colour change to yellow. Boiling of the solution at the end-point is usually necessary. The method can be used for metals that form weak complexes with PAN and even for metals that do not react with PAN. The reaction has been used most frequently for the determination of aluminium in a variety of inorganic ~ ~ b ~ t a n ~ e ~ , ~ but has also been used for galli~rn(III),~~ indi~m(III),~' lead(II),68 vanadium6g and plut~nium.~O An interesting application is to the analysis of potassium in blood serum.71 The potassium is precipitated quantitatively as the cobaltinitrite and the cobalt in the precipitate determined by this method.Table I11 summarises the applications of PAN to complexometric analysis. Accounts of the use of PAN as an indicator are given el~ewhere.~~?'~ In conclusion, it can be seen that as an indicator PAN is more useful in indirect and replacement titrations than in direct titrations, in which its most important application is to the titration of copper. PAN suffers from the disadvantage of being, like its chelates, insoluble in water. Also many solutions require heating during titration with PAN as indicator.April, 19671 Ion Bi( 111) Pb(I1) .. Ga (I I I) In(1 TI(1 I) I) . . Zn(I1) . . Cd(I1) . . Hg(I1) . . Cu(I1) . . Ni(I1) . . Co(I1) . . Fe(II1). . Mn(I1) . . Cr . . v . . A1 (I I I) Mg(I1) . . Ca(I1) . . s c (I I I) Ce (I I I) Th(1V) .. .. .. .. .. . . .. .. .. .. .. . . .. .. .. . . .. .. Method 1 1 2 1 2 3 1 1 2 3 1 1 2 3 3 1 1 1 1 2 2 1 1 2 2 1 1 1 1 2 2 1 2 2 3 2 3 2 2 2 3 2 3 2 2 - - DYESTUFFS I N ANALYTICAL CHEMISTRY TABLE I11 PAN AS A COMPLEXOMETRIC INDICATOR Experimental conditions p H 4 t o 5 PH 1 - pH 4.5 to 7.5 In aqueous ethanol pH 5.0 pH 2 to 2.6 (70" to 80" C) pH 4 to 5 (70" to 80" C) pH 3.5 pH 2.3 to 2.5 p H 7 t o 8 pH 2.5 pH 2.5 to 2.7 p H 4 t o 5 - - pH 1.8 to 2.0 - pH 5 to 6 (70" C) pH 5 to 6, excess of EDTA titrated with standard lead solution - p H 5 t o 6 - - pH 2.5 PH 6 p H 4 t o 9 Acetic acid solutions Aqueous ethanol pH 4 (50" to 70" C) - pH 3 (cold) - - pH 4.5 to 5 in 33% meth- anol - pH 3 (boiling) - - pH 8 (heating) ..2 pH 2.5 . . 1 p H 5 t o 6 . . 2 in acid - p H 3 t o 4 213 Characteristics of method Reference Very specific Simultaneous determination with thallium - In PbTe and PbSe Iron masked with sulphosalicylic - acid - Fe(II1) and Tl(II1) interfere In(II1) does not interfere Very specific Interfering ions masked Ga(II1) does not interfere Photometric titration Simultaneous determination with - - bismuth - For analysis of hydrazine - - In CdS, for analysis of H,S - - Addition of organic solvent shar- pens end-point Equal amounts of Pb, Mn, Fe and Zn do not interfere in presence of Na,S,O, Applications to analysis of copper in various materials For standardisation of EDTA solutions Better than with PAR - - Copper masked with SZO3,- ions - For indirect determination of potassium in blood serum - With aluminium - 245 62 61 246, 247 8, 9, 61 68 248 249 8 67 5 5 8 67 250 62 251 252 4, 53 8, 9, 61 253 4, 53 107 8, 9 8, 61 4, 53 52 to 59 60 50 9 61 47 8, 9 8, 9 71 9, 61 254 8 61 8 69 61 254 32, 63 to 66 - 8, 61 - 8, 61 255 Many applications Excess of EGTA added to solu- tion and back-titrated with standard Ca(I1) solution with Zn - EGTA - PAN as indicator.Mg(I1) does not interfere - In rare earth mixtures After separation as iodide - 6 256 25 7 258214 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [AKtzalyst, VOl.92 TABLE III-cOfitifid Ion Method Experimental conditions Characteristics of method Reference U(V1) .. .. 1 pH 4.4 to 4.6 in 60% iso- Many ions do not interfere 259 2 pH 4.4 to 4.6 Many ions do not interfere 259 70 2 - Titrated solution masked with 70 propyl alcohol P u . . .. 3 pH 2.5 to 30 - F- ions and released EDTA titrated with CuS0,-more specific APPLICATIONS AS A SPECTROPHOTOMETRIC REAGENT- As PAN and most of its chelates are insoluble in water, applications in this class are generally associated with extraction of the metal into an organic solvent. Normally this is achieved by the use of PAN itself, as upon chelation the metal passes from the aqueous into the organic layer. However, sometimes the extraction is carried out first with a reagent such as tributylphosphate in chloroform for uranyl nitrate, the PAN solution then being added to the organic extract.12 Solvent extraction has been avoided either by using mixed solvent ~ystems~7,7~,7~ or by adding a coagulant such as gum a r a b i ~ .~ In solvent extraction procedures with PAN, it is important that the aqueous solution is at the appropriate pH. Correct pH control can be used to extract one metal in the presence of others.l* Back-extraction with acid or an aqueous complexing solution is sometimes possible and has been used for simultaneous determinations of two metals.sO~sl The choice of solvent is some- times important. Chloroform is the usual choice, but isopentyl alcoh01,~ benzene,s2983 o-di- chlorobenzene,ll 9 1 3 ether84,85*86 and carbon tetrachlorides2 have also been suggested.Addition of strong electrolytes to the aqueous layer has been used to bring about an otherwise im- possible extra~tion.~~ This effect has been studied in greater Most PAN complexes have absorption maxima lying between 530 and 570mp, but some complexes absorb at longer wavelengths, for instance, vanadium(V) (615 mp),88 cobalt(II1) (590 and 640 mp),4,89 palladium(I1) (620 and 675 mp),10976,77 rhodium(II1) (598 m , ~ ) ~ o and iron(I1) (765 mp).42943 These metals can be determined in the presence of others because their spectra do not overlap. Much of the work on solvent extraction procedures has been carried out by Berger and Elvers41 and Shibata.42 ,43 The applications of PAN as a spectrophotometric reagent are summarised in Table IV. It can be seen that PAN is a useful sensitive reagent finding applications with a wide range of metals.Rigid control of the experimental conditions causes PAN to become a very selective reagent as well. In other cases masking agents can be used to increase OTHER APPLICATIONS IN ANALYTICAL CHEMISTRY- PAN has been used as a chromatographic spray reagent by Pollard, Nickless and Jenkinsg1 The pale yellow background is unobtrusive whereas the spots contrast well, being pink, violet and green. PAN also has the advantage of being able to detect about forty-five different metals. It has subsequently been used for the detection, after chromatographic separation, of scandiumg2 and the rare earth elementsg3 Ion-exchange paper impregnated with PAN has been used for the detection of heavy metals.94 An interesting application is the use of PAN and cobalt nitrate solutions for the detection of conjugated steroid glucosiduronates after separation by thin-layer chr~matography.~~ Spot tests for nanogram amounts of heavy metals have been devised by impregnating beads of ion-exchange resin with 1 drop of buffered test solution and 1 drop of PAN solution.Different colours are produced for the various ions.96 In ethanolic solutions PAN gives a fluorescent complex with aluminium, and therefore it has been used as a simple qualitative and semi-quantitative test for this meta1.97,98 A method for the analysis of uranium has been studied, whereby the metal is precipitated quantitatively from alkaline solution with PAN.The complex is hydrolysed with acid and the absorption of the free PAN produced is measured at 440 mp. The method is claimed to be 50 per cent. more sensitive than the normal solvent extraction procedure, and to require less stringent .conditions.99 ,loo The sprayed chromatograms are stable indefinitely.April, 19671 Ion Ga( 111) In( 111) TW) T1( 111) Zn(I1) Cd(I1) Cu(I1) DYESTUFFS I N ANALYTICAL CHEMISTRY TABLE IV PAN AS A SPECTROPHOTOMETRIC REAGENT 215 Method a t pH 3.6 to 3.0 Ext. into CHC1, - Ext. into CHC1, a t pH 4.3 Aqueous DMF solu- tions a t pH 5 to 6 Aqueous DMF solu- tions a t pH 5 to 6 - Ext. into CHCl, a t pH 5.4 to 6-7 Absorbance measured a t 560 mp - 550 mp 545 mp 545 mp - 560 mp Aqueous dioxan solu- 550 mp tions a t pH 4-3 to 6-0 Ext.into CHCl, pH 2.2 Ext. into isopentyl Ext. into CHC1, a t alcohol pH 10 - Ext. into CHC1, at pH 6.6 Ext. into CHCl, a t Ext. into CHC1, a t pH 8.7 to 10 pH 10 - Ext. into CHC1, a t pH 6 to 7.5 Ext. into CHCI, a t pH 7.5 to 11-5 Aqueous EtOH at pH 6.5 to 8.3 Ext. into isopentyl alcohol - Ext. into isopentyl alcohol - - - 555 mp 540 mp - - - - 555 mp 540 mp - - 560 mp 555 mp 550 mp - - 560 mp - - - 560 mp Sensitivity, pg per cm2 characteristics of method Reference OD per General - 0.308 - 0.357 0.214 0.132 0.171 0.1 - - 0-439 0-42 - - - - 0.435 - - - 0.176 - 0.2 - - - 0.34 - - - 0.15 43 - Study of solvent extraction be- 41, 42, 201 For 1 to 15 pg per 5 ml. Ga(II1) 260 haviour extracted from Al(II1) previ- ously with isopropyl alcohol as chloro complex Small amount of isopropyl ether added to enhance sensitivity.Cd(I1) masked by I- Simultaneous determination with 47 Ga (I I I) Study of solvent extraction be- 41, 42, 43, haviour 201, 261 For 5 pg per ml. Also for simul- 262 taneous determination with Fe(I1I) and isopentyl alcohol 47 1 : l complex soluble in BuOH 74 - 263 General study 48 Study of solvent extraction be- 38, 41, 42, hahour Ni(I1) masked with CN-. Cd(I1) can be back-extracted with Et,NCS,Na for simultaneous determination. Fe(I1) and Mn(I1) should be removed. In copper In iron ores. Other metals re- In nickel and nickel alloys Study of solvent extraction be- moved by extraction or masking haviour - In nickel. Simultaneous deter- In copper Study of solvent extraction be- haviour mination with zinc - Many ions interfere, but mercury removed by distillation.For up to 5 pg per ml. For up to 2.5 pgper ml. Many ions interfere. Separation described 43, 44 4 so 81 264 265 33, 42 43 80 81 42 43 266 75 Study of solvent extraction be- Spectrophotometric studies 36, 49, 267 41 to 44 haviour 4 - Study of solvent extraction be- Study of solvent extraction be- 38, 41 to 44 Spectrophotometric study 267 4 268 haviour haviour -216 Ion "1) Pd(I1) Co(I1) Rh( 111) Ir(II1) Fe( I I I) Mn(I1) V ANDERSON AND NICKLESS : HETEROCYCLIC A20 TABLE IV-continued [Analyst, Vol. 92 Sensitivity, Absorbance OD per General Ext. into CHCl, a t 570 or 530 0.85 For 0.2 to 1-5 mp per ml. CC14 269 Method measured a t pg per cm2 characteristics of method Reference pH 4 to 10 after mtL and C,H, also used.A t pH 4 pptn. of chelate only Cu(II), Fe(T1) and Co(I1) by boiling interfere. First two masked. Co absorbs a t 630 mp and can be simultaneously determined determination with Mn(I1) by back-extraction of latter with acid cobalt and W Ext. into CHC1, a t 575 mp - For 0.05 to 1 p.p.m. Simultaneous 270 pH 5 to 9 Ext. into CHC1, 570 mp - For up to 20 pg. In presence of 271, 272 - - - For 5 to 100 p.p.m. In pure Mo 273 - - - In thin films 274 - - - Study of solvent extraction be- 41, 43 - - - Spectrophotometric study 267 Ext. into CHC1, at 620 and 675 0.15 For 0.15 to 0.35 mg. Specific at 10 haviour pH 2.5 m P this pH for platinum metals. Of others only Co interferes Ext. into CHCl, a t 678and 626 0.132 For up to 20 pg per ml. Co 76 Ext. into CHC1, a t 675 mp 0-146 In Ti alloys.Interfering ions 77 pH 2 to 5 mP masked with EDTA pH 3-0 to 3.5 masked with EDTA haviour - - - Study of solvent extraction be- 41, 43, 44 4 Ext. into isopentyl 640 mp 0-29 - Aqueous solution 640 mp 0.61 Gum arabic added to stop pptn. 4 alcohol Ext. into CHC1, at 640 or 590 - For 0-1 to 2.4 pg per rnl. 640 mp 89 pH 3 to 6 at mP more selective. Cu(I1) inter- feres - - - In thin films 274 - - - In molybdenum metal and titan- 275 Ext. into CHCl, at 598 mp 0.19 For 1.1 to 3.8 p.p.m. Simul- 90 ium hard materials pH 5.1 taneous determination with Ir(II1). Complex precipitated by boiling with PAN first Ext. into CHC1, a t 550 mp 0.056 For 3.6 to 12.5 p.p.m. Simul- 90 pH 5-1 taneous determination with Rh(II1). Complex precipitated by boiling with PAN first haviour - - 0.277 Study of solvent extraction be- 42 - 43 - - - In thin films 274 - - 1.06 Study of solvent extraction be- 41, 42, 44 Ext.into CHCl, a t 775 mp - p H 4 t o 8 haviour 43 Ext. into ether at 560 mp - - Ext. into CHC1, 575 mp - Followed by back-extraction with 270 - - - In beryllium 276 pH 9 to 10 from basic solution acid for simultaneous deter- mination with Ni(I1) - - - In Nb, Ta, Mo and IV alloys 277 Ext. into CHC1, at 615 mp 0.332 For 9 to 61 pg. Fe interferes but 88 pH 3 in presence of 560 mp - For 10 to 300 pg per 50 ml. In 278 - - Study of solvent extraction be- 43 pH 3-5 can be determined simul- acetone and steel. Separation of other taneously at 765 mp components described haviour (NH4)2S208 -April, 19671 DYESTUFFS I N ANALYTICAL CHEMISTRY TABLE IV-continued 217 Ion Zr(1V) Y(II1) REs UVI) Sb Ca(I1) Pb(I1) Absorbance Method measured at Ext.into CHC1, - Ext. into CHC1, - In organic phase 555 mp Ext. into ether a t 560 mp pH 8.5 to 11 Ext. into ether at 570 mp pH 9 to 10 Ext. into ether from 530 or 560 alkaline solution pH 3-20 with CU(II) - EDTA - PAN Ext. into CHCI, - Ext. into o-dichloro- benzene at pH 10 UO,(NO,), ext. into UO,(NO,), ext. into TBP - CHC1, TNOPO Red precipitate in NH, solution, ext. into CHCI, if NaCl or Na,SO, added - Ext. from acid solu- tion containing KI and thiourea with C,H, solution of PAN With Cu - EDTA - - PAN At pH > 6 in meth- anolic solutions 530 mp Sensitivity, General characteristics of method T ” Zr(1V) previously extracted with DBP. For 10 to 65 pg per 25 ml Can be separated from La(III), Ce(II1) and Sc(II1).PO,,- and Zr(1V) interfere La(lII), Ce(II1) and Sc(II1) not extracted. CCI,, CHC1, and C,H, can also be used Following separation by ion- exchange chromatography. RE replaces Cu(I1) from Cu - EDTA and Cu(I1) reacts with PAN Study of solvent extraction be- haviour - Study of solvent extraction be- haviour For (0.1 to 5) x mmoles per ml. EDTA masks foreign ions In presence of Th(1V) masked with EDTA For 40 to 400 pg. EDTA useful for masking foreign ions From plutonium. For 1 to 20 p.p.m. Removal of interfering ions EDTA or CN- masks most foreign ions In CaF,; CHDTA masks most In organic and inorganic materials foreign ions Can be used at lower pH values For 0.8 to 6.6 pg per ml. Best with PAN in 50-fold excess PAN has been used successfully as a mercurimetric indicator for chloridelol Keterence 200 279 200 43 84, 85 82, 86 280 268 200 41, 43 11 13 12 281, 282 78 79 283 83 284 285 (titration of chloride with standard mercury solutions).Titration of mercury with standard‘ chloride solutions is also possible. The dye has also been used in precipitation titrations for anions. Molybdatelo2 and tung- statel03 ions have been determined by titration with standard lead solutions with copper - EDTA - PAN as indicator. The titration reaction is slow and heating is generally required. Sulphate ions have been determined by a similar method,1O4 or by precipitation with excess of lead solution and back-titration with EDTA in the presence of copper - EDTA - PAN indicator.lo5 Many cations and anions interfere with these titrations. Niobium has been determined by co-precipitation with zinc, and titration of the zinc with copper - EDTA - PAN as indicator.lo6 Hydrazine is determined indirectly as it reduces standard thallium(II1) solutions to thallium(1). Back-titration of excess of thallium(II1) with EDTA and PAN as indicator is then possible.lo7 GENERAL PROPERTIES- PAR was first prepared by Chichibabin, by coupling resorcinol with sodium Z-pyridyl- d i a ~ o t a t e .~ ~ Originally the conditions used in the preparation were the same as those for It is necessary to add ethanol to the titrate. 4-(2-PY RIDYLAZ0)-RESORCINOL (PAR)218 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [Anzazyst, VOl. 92 PAN, but in more recent preparations the use of carbon dioxide is dispensed with, and the dye is obtained as the mono-sodium or di-sodium salt.17 The sodium salts are more water soluble than the free dye itself, and in analysis are used in preference for this reason.The aqueous solutions are orange. The dye as a sodium salt is soluble in acid and alkaline solutions, and to a lesser extent in alcohol. Geary, Nickless and Pollardlos made a complete investigation of the visible spectrum of the dye as a function of pH in aqueous and 50 per cent. aqueous dioxan solutions. They were able to identify the following four chromophoric species- It is insoluble in ether. Q I N= H H d H d I pH < 2.5 I1 pH 3 to 5.5 H d -0’ 111 pH 6 to 12.5 IV pH > 12.5 It is believed that the 9-hydroxyl group ionises first, as the o-hydroxyl proton is hydrogen- bonded to the azo group. The peak wavelengths of all four forms were found to be as follows- Aqueous dioxan solution, Aqueous solution 50 per cent.I . . . . 395 rnp (E = 15,500) 420 mp ( E = 14,750) I1 . . . . 383 mp (E = 15,700) 392 mp (e = 15,240) I11 . . . . 415 mp ( e = 25,900) 414 mp ( e = 23,100) IV . . . . 485 rnp ( E = 17,300) 502 mp ( e = 17,800) HniliEkovk and Sommerlog carried out a spectrophotometric study of the dye and estab- lished the existence of six chromophoric forms of PAR. In addition to those above, they found H,R3+ (Amax. = 433 mp) and H,R2+ (Amax. = 390 mp) in 90 and 50 per cent. sulphuric acid. The extra protons are thought to be attached to a hydroxyl group and to the azo group. Similar to PAN, PAR shows no signs of intermolecular association under most normal conditions met with in analy~is.3~ The purity of the reagent can be tested by using thin-layer chromatography .4O The complex with palladium is green in acid and red in neutral solutions. PAR does not react with the alkali metals, chromium(VI), antimony(III), molybdenum(VI), tungsten(V1) and arsenic(II1) or (V). The formation of these complexes is very dependent on pH. HniliEkovA and Sommerlog have investigated the formation and stoicheiometry of some metal - PAR complexes as a function of pH, and have shown that in acid solution M(PAR)H was formed, and in alkaline solution, M(PAR) 2. Geary, Nickless and Po11a1-d~~ measured the stability constants of some metal chelates for the following compounds : PAR, benzeneazo-resorcinol (I), salicylidene- 2-aminopyridine (11) and 2-pyridylidene-o-aminophenol (111).Examination of both these o\, = , q p o H QLHQ Q c H = NQ PAR reacts with metals to give red or red-violet complexes. HO HO HO I II 111 results and those published by Klotz and MingllO on the chelates of 4-(2-pyridylazo)-dimethyl- aniline, showed that only the stability constants for I11 were of the same order as those of PAR. The other ligands formed less stable complexes. From this it was concluded that PARApril, 19671 DYESTUFFS I N ANALYTICAL CHEMISTRY 219 chelates with metals through the pyridine nitrogen atom, the azo-nitrogen atom furthest from the heterocyclic ring, and the o-hydroxyl group. PAR thus acts as a tridentate ligand forming two stable 5-membered chelate rings, and the commonest chelates are of the type, M(PAR) and M(PAR),.Other types are rare, but Th(PAR),lll and Ga(PAR),45 have been reported. An interesting and important point to note about the chelation of PAR concerns the ionisation of the two hydroxyl groups. Normally the $-hydroxyl group ionises first, because of the internal hydrogen bonding in the molecule. However, on chelation, which often occurs at pH values lower than either pKoH, protons are released preferentially from the o-hydroxyl group. This means that, theoretically, PAR chelates in the thermodynamically unfavoured form- for which the dissociation constant is not known. Corsini, Mai-Ling Yih, Fernando and F r e i ~ e r ~ ~ considered this problem in calculating the stability constants of metal - PAR chelates, and pointed out that pKoH (ortho) was almost the same for PAR and PAN.They therefore considered it safe to assume that the ionisation of the $-hydroxyl group had no effect on pKoH (ortho). The effect of chelation on pKoH ($ara) has also been studied by Corsini, Fernando and Freiser.l12 Although the values given by Geary, Nickless and P01lard~~ may be open to considerable doubt, following the values given by Corsini, Fernando and Freiser,l12 the general approach is in no way invalidated. Further evidence from crystallographic results on the structure of copper-(benzene-a~o-fl-naphthol)~~~ showed that the metal is co-ordinated through the nitrogen atom, alpha to the naphthalene ring. Some values for the stability constants of metal - PAR chelates are given in Table 11.APPLICATIONS AS A COMPLEXOMETRIC INDICATOR- Wehber14 was the first to suggest PAR as an alternative to PAN in complexometric titrations. The immediate advantage of PAR over PAN is that this reagent and most of its complexes are water soluble. Thus it is not necessary to add organic solvents to the solution to be titrated. Also in many instances the end-points are sharper, the colour change being from orange - red to yellow. PAR can also be used at lower pH values than PAN. As with PAN, heating of the solution is often necessary. In most of the titrations the direct method is used. However, back-titration of excess of EDTA with standard lead solutions, with PAR as indicator, has been recommended for a1umini~m.l~~ Also standard lead, bismuth and zinc solutions have been recommended for use in back-titrations with PAR.115 Table V summarises the main applications of PAR in EDTA titrations.APPLICATIONS AS A SPECTROPHOTOMETRIC REAGENT- Again the immediate advantage of PAR over PAN is the water solubility of both it and its complexes.l7 Spectrophotometric analyses with PAR involving mixed solvent systems or solvent extraction are few and far between.ll67ll7 However, butanol has been used to extract excess of PAR from an aqueous phase in order to increase selectivity.lls But normally, although the metal may previously have been extracted to separate it from interfering ions,119,120 the analysis is carried out in an aqueous phase. The sensitivity of PAR for metals is greater than that of PAN, as can be seen by consulting Tables I11 to VI.In the first application to spectrophotometric analysis,17 it was reported to be the most sensitive reagent for cobalt, and the most sensitive water-soluble reagent for uranium, being 30 per cent. more sensitive than PAN. Except in the determination of palladium, all optical densities are measured at wave- lengths between 494 and 550 mp. With PAN, a wider range of wavelengths was used, which gives a greater possibility of choosing a part of the spectrum in which the interference of foreign ions is at a minimum. This increases the selectivity of PAN and makes possible220 Ion Bi (111) Pb(I1) Ga (111) In(II1) T1( 111) Zn(I1) Cd(I1) HgW) Cu(I1) Ni(I1) Mn(I1) Al( I I I) REs Er (111) ANDERSON AND NICKLESS : HETEROCYCLIC A20 TABLE V [Analyst, Vol.92 PAR AS A COMPLEXOMETRIC INDICATOR Experimental conditions pH 1 to 2 - pH 1 to 2 p H 5 t o 9 pH 6.5 to 7 p H 8 t o 9 pH 2 to 2.6 (70" t o 80" C) pH 2.3 to 2.5 (60" t o 70" C) p H 4 t o 5 Weakly acidic pH 6 t o 11.5 p H 8 t o 9 pH 6 to 11.5 p H 8 t o 9 pH 3 to 6-9 pH 5 to 11.5 p H 5 t o 9 pH 5 (90" C) pH 3 (100" C) p H 5 t o 7 - pH 9 General characteristics (all titrations are of the direct method unless otherwise stated) Can also be used in back-titrations For 4 to 600 pg per ml. PAR gave better results than PAN For 2.5 to 64 mg Can also be used in back-titrations Also used for back-titration of AI(II1) For 3 to 80 mg Al, Cd, Zn, Mn, Mg and Ca do not interfere Initial separation into ether from 1.5 N H,SO, - and NKI - For indirect determination of organic hydrazines Can also be used in back-titrations (pH 5 to 6, For 1 to 26 mg For 3 to 80 mg For the indirect analysis of H,S 10 to 12) - - - Inferior to PAN - - Indirect method. Excess of EDTA titi-ated with Heat required if excess standard lead solutions. of nitrate is present - For 0-3 to 0.8 mg.Other rare earths interfere Reference 115 286 109 115 114 109 248 16 287 62 130 115 109 115 109 107 115 115 50 115 115 115 114 115 288 certain simultaneous determinations. Also, selective solvent extraction is not applicable. These facts show that PAR is a less selective reagent than PAN, and more involved schemes for the separation or masking of ions are necessary. Applications are listed in Tables V and VI, and no further comment is required.Such methods are not possible with PAR. OTHER APPLICATIONS IN ANALYTICAL CHEMISTRY- As a chromatographic spray reagent, PAR is as sensitive as PAN.Q1 The reagent has a pale yellow background and the spots stand out with a fairly consistent red colour (vanadium is violet). For the detection of metals on ion-exchange paper, it was noticed that PAR gave a uniform reddish purple colour as opposed to the variety of shades produced by PAN.Q4 As a colour producing reagent, PAR can be used for detecting nanogram amounts of heavy metals absorbed on resin grain~.~6 PAR produces a colour sensitive to 1 pg with yttrium and zirconium,121 0.1 pg with niobium122 and 5 x pg for copper in a resin spot test.l23 The reaction with titanium has been studied more f ~ 1 l y . l ~ ~ PAR and methylthymol blue have been used to detect the formation and evaluate the stabilities of peroxy complexes of niobium and tanta1~m.l~~ The reactions of these metals and titanium, in the presence of hydrogen peroxide with many dyes, including PAR and PAN, have been studied as a function of pH.126 The dye has been used as an indicator in precipitation titrations with standard lead solutions, for orth~phosphate,~~~ arsenate,128 molybdate and t ~ n g s t a t e .~ ~ ~ PAR has also been used for the indirect determination of organic hydrazine derivatives with thallium(II1) ions.130 An interesting method involving spectrophotometric titration has been used for copper.131 The solution containing about 0.1 M copper(I1) in 10 ml of acetate buffered medium is titrated against standard PAR solution in 0.05-ml aliquots, the absorption being measured after each addition.A sharp inflection in the titration curve marks the end-point. The method also works for lead and cobalt and does not require a calibration curve.April, 19671 Ion Pb(I1) Sn(I1) Ga(1 I I) In(II1) TI(II1) Ni(I1) Pd(I1) Cu(I1) Co(I1) Fe (111) 0 s (IV) V(V) Method pH 10 pH 10 - pH 4.7 to 6.7 DYESTUFFS I N ANALYTICAL CHEMISTRY TABLE VI PAR AS A SPECTROPHOTOMETRIC REAGENT PH 4 PH 7 - PH 3 pH 4.3 to 6 - pH 7.05 - PH 4 PH 4 - pH 8.6 to 10 Sensitivity, Absorbance OD per measured at pg per cm2 520 mp 520 mp - 512 mp - 514 mp 504 mp 530 mp - 530 mp 510 mp - 500 mp 500 mp - 496 mp - 530 mp 530 mp 517 to 532 mp 494 mp In strong acid heat 440 or 630 to 70" to 80" C and mp extract into EtOAc 510 mp p H 7 t o 8 500 mp pH 6.8 510 mp - PH 8 - pH 6.8 to 8.2 510 mp pH 5-25 to 6.50 545 mp pH 6.5 540 mp 0.171 0.19 I 0.35 - 0.20 1.47 - - - - 0.753 - 0.286 0.5 - - - - - - 1-24 0.172 or 0.0847 0.93 0.951 0.965 - 1.0 - - - 0.69 - 221 General characteristics of method Reference For up to 5 pg per ml Spectrophotometric titration Separated from interfering ions by extraction into IMBK and back-extracted into NH, solu- tion For (C,H,),PbCI, as (C,H,),PbPAR.Also for PbCI, in (C,H,),PbCI, Application t o steel, brass and bronze For (C,H,),SnCI, as (C,H,),SnPAR For 1 to 15 pg per 25 ml. Many ions interfere For up to 1 pg per ml. Extraction of HGaCI, into ether from 6 N HC1 removes most ions except Fe and Sn For 2 to 12 pg per 50 ml. Up to 600-fold excess of oxalate tolerated For 6 to 48 pg per 50 ml.Organic solvents and Br- ions have no effect For 1.0 to 2.0 p.p.m. For 2 to 30 pg per 25 ml. Many ions interfere - For 5 to 120 pg per 25 ml. Fe, Co, Ni, V(V), Zr, Bi, Sn(II), F, NO,-, P,Og4- and C,O,,- inter- fere. Separation from these described Cations interfere For 20 to 120 pg per 50 ml. Or- ganic solvents and Br- ions have no effect Best molar concentrations of metal to ligand are 4-75:5.25. Conditions by Box and Wilson's method298 - For 1.0 to 2.0 p.p.m. For 1.0 to 8.0 p.p.m. Spectrophotometric titration For 0.005 to 1.0 pg per ml. Inter- fering ions masked with EDTA, citrate, etc. 44 ions listed as not interfering For up to 1.4 pg per ml Spectrophotometric titration EDTA masks foreign ions For 4 to 32 pg per 50 ml.In presence of EDTA only Fe(II1) and Ni(1I) interfere In soils, water and plants, citrate and EDTA mask other ions For 0.3 to 5 pg per ml In the presence of CHDTA, very specific For up to 1.0 p.p.m. Co, Cu, Ni, Fe, Hg, Cr, Ag and Bi interfere For 1 pg per ml. Many ions inter- fere - 17 131 119 289 120 289 290 291 2 92 293 294 295 261 296 74 293 297 242 294 294 131 299 116 17 131 243 300 301 302 303 304 305 306222 ANDERSON AND NICKLESS : HETEROCYCLIC A20 TABLE VI-continued [Analyst, Vol. 92 Ion W V ) Ti(1V) Th(1V) Sc(II1) La( I I I) Ce (I1 I) Er (111) REs U W ) NP (V) Method pH 5 to 8 in tartrate media pH 5.8 to 6-5 in pH 5 to 8 in tartrate media tartrate media pH 5 in the presence of 30% H202 pH 5.5 to 7.0 in tartrate media pH 5.5 in oxalate media - pH 5 to 6 in acetate tartrate medium In presence of C,042-, H202 and BuOH a t pH 6 to 8 In presence of C2042- at pH 5.5 In H,02 medium pH 6.4 to 6.7 pH 6 to 7.3 pH 3.5 to 4.5, p = 0.4 pH 5.1 pH 5.1 pH 8.5 - pH 6.2 Aqueous solution at PH 8 p H 7 t o 8 pH 9 to 10 Absorbance measured at - 550 mp 540 mp 550 mp - - 530 mp 540 mp - - 536 mp 535 mp - - - 515 mp 530 mp 510 mp 510 mp 540 m p 515 mp 530 mp 540 mp - - Sensitivity, pg per crn2 characteristics of method Reference OD per General OTHER PYRIDYLAZO In presence of Cr04,-, Mo,O,,~-, W042- and NO,- For up to 7 pg per ml.EDTA masks most metals except V(V) and UWI) In presen'ce bf Ta(V), Ti(1V) and Zr (IV) For up' to 1 p.p.m. CN- and EDTA mask all ions except U(VI), V(V) and PO,3-. De- tails for masking these EDTA masks Ti(IV), Zr(1V) and Fe( 111) In steel (without separation from Fe, Cr, Ni, Co, Mo, W, Ti, A1 and Zr) In presence of Mo, W, Ti, Al, Fe, Co and Ni In presence of Mo, W, Zr and U In rocks In presence of EDTA or CHDTA only V(V) seriously interferes. Mo, Ti, U and Th interfere in 7 to 10-fold excess BuOH extracts excess of PAR to prevent reaction with other ions.In presence of Nb(V), Ti(1V) and Zr(1V) For 5 to 80 fig U, Zr, W, Mo masked For 2 to 60 pg per ml. with C,O?-, Fe masked with EDTA CO,2-, F-, NO,-, C2042- and organic anions forming stabIe complexes interfere For 0.05 to 2.0 pg per ml. Many ions interfere Many ions interfere - For lo-, to 10-4g Conditions for determination of La, Nd, Sm, Gd, Y , Dy and Er Optimum conditions described For up to 6.0 pg per ml For 0.04 to 16 pg per ml.Masking agents or chromatography re- move all interfering ions - DYESTUFFS 307 122 118 308 309 310 122 311 312 313 118 314 315 316 111 317 318 319 319 288 320 321, 322 17 323 324 Although sodium 2-pyridyldiazotate couples with phenols only with difficulty, other pyridylazo dyestuffs have been prepared and used in analytical chemistry. Sommer and HniliCkovA,15 when they reported PAR as a possible metallochromic indicator, also mentioned 2-(2-pyridylazo)-l,8-dihydroxynaphthalene-3,6-disulphonic acid (PACh) and 2- (2-pyridylazo)-l-hydroxy-8-aminonaphthalene-3,6-disulphonic acid (PA-H) . These dyes are less sensitive than PAR, and their applications are more limited. PACh, however, is interesting in that it contains a peri-dihydroxy grouping, a useful chelating system in its own right.Thus two types of chelate formation are possible. Certain metals that form stable chelates with chromotropic acid complex at a lower pH witli PACh than with PAR or PAN. It is possible that in these instances chelation is via the two hydroxylApril, 19671 DYESTUFFS I N ANALYTICAL CHEMISTRY 223 groups. PACh, together with 2- (3-pyridylazo) - 1,s-dihydroxynapht halene-3,6-disulphonic acid has been used for the colorimetric determination of berylli~m(I1)~~~ and copper(I1) .I33 With beryllium(I1) at least, the stoicheiometry of the complexes and the general similarity of behaviour of the two dyes suggests that chelation may only be via the oxygen atoms. Sommer and HniliCk~vAl~~ have also used 4- (2-pyridylazo)-orcinol (PAO) and 1- (2-pyridyl- azo)-2,3-dihydroxynaphthalene-6-sulphonic acid (PADNS) as indicators for chelometric titrations.PADNS produces red colours with metals (similar to those of PAN), unlike PACh which produces blue-to-violet colours. Theoretically, PADNS can also complex either like PAN or via the two hydroxyl groups (cf. catechol-3,5-disulphonic acid). S ~ m m e r ~ ~ ~ has reported the reaction of titanium( IV) with several polyphenols and dyes, including 1-(2-pyridylazo)-2,7-dihydroxynaphthalene (2,7-PAN). Except that the extra hydroxyl group makes the dye more water soluble, it is similar to PAN. 7- (2-Pyridylazo)-8-hydroxyquinoline (PAOx), which can be prepared from sodium 2-pyridyldiazotate and 8-hydroxyquinoline, forms coloured complexes with a similar range of metals to those which react with PAN.135 However, PAOx chelates at a lower pH than either PAR or PAN. It has been used in the complexometric determination of thalli~m(II1)~36 and also of copper(I1) in al10ys.l~~ Theoretically this dye, which has both PAN and S-hydroxy- quinoline chelating systems, can complex in two different ways, either as a bidentate or trident ate ligand.Pollard, Nickless and Anderson138 9139 have synthesised a new series of pyridylazo dyestuffs by coupling 2-hydrazinopyridine with various quinones. They have prepared by this method 4-(2-pyridylazo)-phenol ($-PAP), and 2-(2-pyridylazo)-phenol (0-PAP) . The former is a weak complexing agent, only forming strong colours over a narrow range of pH with metals in groups VIII and Ib, whereas the latter reacts with many cations over a wide range of pH.The behaviour of these two compounds illustrates the relative rdles played by the two hydroxyl groups in PAR. These workers also prepared 2-(2-pyridylazo)-l-naphthol (cc-PAN) and some of its water-soluble sulphonated derivatives. This is the compound prepared by Betteridge, Todd, Fernando and Freiser140 by the Chichibabin and Rj asanzew reaction35 and designated on the basis of a low pKoH value compared with P-PAN, as $-PAN. The evidence provided by D. Betteridge and A. Kawase (private communication) of organic synthesis and infrared spectra leaves no doubt that the compound was incorrectly described. There is, at present, no satisfactory explanation why the pKoH is almost the same value of free 1-naphthol and apparently is not shifted by the hydrogen bonding that would be expected for a hydroxyl group in an ortho position to an azo-group.The reagent reacts with many ions to give complexes, with colours ranging from purple to green, many of which can be extracted. The stability constants are almost the same as those with P-PAN for the same metal ion, a notable exception being copper, which forms a 1 : 2 ~omp1ex.l~~ The reagent has recently been recommended as an extractive indicator in the titration of EDTA with and for the complexometric and spectrophotometric (by solvent extraction) determination of indium.142 PACh and water-soluble sulphonated derivatives of a-PAN, which is also a derivative of cc-naphthol, form blue - violet complexes with many ions, and ionise and chelate at lower pH values than /3-PAN. Their properties as chromatographic spray reagents have been discussed .I38 Nakagawa and Wada143 have prepared 2-(2-pyridylazo)-4-methylphenol (PAC) and in- vestigated its reactions with metal ions.This reagent reacts with a wide range of metals giving blue-to-violet extractable complexes. They have used it for the complexometric determination of copper, zinc, cadmium and lead, for which it appears to be better than PAR or PAN, giving a sharp colour change from violet to yellow at the end-point. The same workers144 have made a spectrophotometric study of the copper, nickel and zinc chelates and conclude that the reagent acts as a bidentate ligand. However, its behaviour, which is similar to that of 2-(2-pyridylazo)-phenol, suggests to us that it is tridentate.Gusev and Shch~roval~~ have prepared 5-(2-pyridylazo)-2-monoethylamino-$-cresol (PAAC) and have used it for the complexometric determination of bismuth, indium and zinc, and for the spectrophotometric determination of thallium and cobalt. They have made a full investigation of the bismuth - PAAC system, and recommend the dye as an indicator for this meta1.146 The reaction of this dye and 3- (2-pyridylazo)-4-ethoxy-6-monoethylamino- toluene with indium has been studied with respect to use in the analysis of this metal.147 Recently three new dyes have been prepared as possible analytical reagents by coupling224 ANDERSON AND NICKLESS: HETEROCYCLIC A20 [Analyst, Vol. 92 diazotised 2-amino-N-methylanabasine with resorcinol,l48 oc-naphth0114~ and P-naphthol.150 These dyes are similar to their pyridyl analogues, but are more specific.4-(2-1L7-Methyl- anabasineaz0)-resorcinol (MAAR) has been used for the complexometric determination of t h a l l i ~ m ( I I I ) , ~ ~ ~ indium(III),152 g a l l i ~ m ( I I 1 ) ~ ~ ~ and bismuth(III),148 and also for the spectro- photometric determination of bismuth(II1) .154 The reagent's acid dissociation constants have been measured.155 1-(2-N-Methylanabasineaz0)-2-naphthol (MAAN) has been used for the spectrophotometric determination (in aqueous solutions) of the rare earths156 and of zinc(I1) .157 4-(2-ili-Methylanabasineazo)-l-naphthol (@-MAAN) has been used for the spectrophotometric determination of vanadium(V).157 Klotz and MingllO studied the metal complexes of 4-(2-pyridylazo)-dimethylaniline (PAA) and evaluated an order of stability for some common metal ions.The stabilities are low compared with those of PAR, and are of the same order as those of 4-(2-pyridylazo)- phen01.l~~ This dye has found use as an acid - base indicator in non-aqueous media.158,159 Chiswell, Lions and TomlinsonlG0 condensed 2-hydrazinopyridine with benzil, acenaph- thenequinone and o-phenanthraquinone. For each, only one molecule of hydrazine would condense with the diketone, and the hydrazones obtained reacted with metals in a similar manner to PAR and PAN, forming highly coloured complexes. Pollard, Nickless and Jenkinsg1 prepared a series of pyridylazomethines related to PAR for use as chromatographic spray reagents. These were easily obtained by condensing o-aminophenol with pyridine-%aldehyde and pyridine-2,6-dialdehyde, and by condensing salicylaldehyde with 2-aminopyridine and 2,B-diaminopyridine.The first two give red-to- brown colours with many metals, whereas the second two are far less s e n ~ i t i v e . ~ ~ 5 l ~ ~ The compound from salicylaldehyde and 2,6-diaminopyridine, however, was found to be selective for copper and iron(II1). All of these compounds showed some fluorescence with certain metals. Pollard, Nickless and Anderson138 9139 prepared some 2-pyridylhydrazones such as salicyl- aldehyde-2-pyridylhydrazone, and compared them with the pyridylazo dyestuffs. Although these compounds formed stable metal chelates, the colour changes produced on chelation were not striking.The above-mentioned compound did produce some good fluorescence reactions when used as a chromatographic spray reagent. 2-Pyridylidene-o-aminothiophenol was also prepared138J39 and found to be more selective than its oxygen analogue. THIAZOLYLAZO AND BENZOTHIAZOLYLAZO DYESTUFFS 2-Aminothiazole, unlike its pyridyl analogue, requires no special conditions for diazotisa- tion, and hence thiazolylazo dyes are easily prepared from a wide range of phenols, naphtholsl61 and other non-phenolic substance^.^^^^^^^ The same is true for 2-aminoben~othiazole.~~~~~~~ It was inevitable, therefore, that soon after the introduction of pyridylazo dyestuffs as analytical reagents, parallel work should be undertaken on their thiazolyl analogues, as these also will provide a chelating system similar to that of PAN.In 1958, Boni and Hemmelerls coupled diazotised 2-aminothiazole with catecliol, resor- cinol, phloroglucinol, P-naphthol, chromotropic acid, 8-hydroxyquinoline, alizarin and salicylaldoxime. They showed that the dyes produced could be used for the detection of metals, either in solution or on paper, and worked out qualitative methods for identifying cobalt, copper and zinc, by using l-(2-thiazolylazo)-2-naphthol (TAN) .19 Later, Hemmeler and Scattolari166 used 2-(2-thiazolylazo)chromotropic acid (TACh) as an indicator in both direct and indirect titrations of zirconium and thorium. Jensen21 3167 prepared thiazolylazo dyes of resorcinol, orcinol, 9-cresol, m-dimethylamino- phenol, /3-naphthol and 2-naphthol-6-sulphonic acid.These reagents were used as com- plexometric indicators, and it was found that in direct titrations they were most useful for cobalt, nickel and copper (addition of ethanol and heating were required for the end-points to be sharpest), although the use of the copper - EDTA - dye system increased the range of titratable metals. 2-(2-Thiazolylazo)-5-dimethylaminophenol (TAM) was found to be a sensitive reagent for the spectrophotometric determination of uranium,168 and has been investigated further as a possible analytical reagent,169 especially for copper.17o Much of the important work on these compounds has been carried out in Japan, in particular by Kawase. Initially, with Yanagihara and Matano, Kawase prepared 2-(4-methyl- 2-thiazolylazo)-4-methoxypheno1171 ,172 and used it for the spectrophotometric determination of copper,173 zinc,174 nickel and cobalt,175 and iron.176~~7~ He then prepared about twenty-three derivatives of 2-(2-thiazolylazo)-pheno1178 and studied their copper cornple~es,17~ showingApril, 19671 DYESTUFFS IN ANALYTICAL CHEMISTRY 225 that two chelates were formed with metal-to-ligand ratios of 1 : 1, water soluble and suitable for complexometric titrations, and 1 : 2, soluble in organic solvents and suitable for extraction.Kawase used these dyes for the spectrophotometric determination (with or without extraction) of nickel,180 cobalt(II)ls1 and cobalt(III).182 Of the dyes studied, TAN seemed to be the most useful, and was used for the spectrophotometric determination of zincls3 and nickel in chromium,184 both by extraction into chloroform.Studies on the stability constants and spectra of the metal complexes have shown that the dyes are tridentate.ls5 Derivatives of 4-(2-thiazolylazo)-l-naphthol ($-TAN) are almost specific in their reaction towards palladiurnls6 and $-TAN itself has been used for the determination of this metal by extraction into isopentyl alcoh01.l~~ Only iron and silver interfere. Nakagawa and Wada have used azo dyes of thiazole in analysis, for the complexometric determination of copperlss and nickel,ls9 and in solvent extraction.lgO Kaneniwa has also used these dyes in complexometric titrations20 as well as carrying out some spectrophotometric studies on their ~he1ates.l~~ 31923193 Although it has been shown that these dyes act as tridentate ligands,ls4 the lower basicity of the thiazole nucleuslg4 will cause the chelates to be less stable than their pyridyl analogues.However, this in turn means that the thiazolylazo dyes will be more s e l e c t i ~ e . ~ ~ ~ ~ ~ One or two dyes have been shown to be highly selective, such as l-(6-bromo-2-thiazolylazo)- 2-naphthol ( I ‘bromobenzothiazo”) , a reagent for the solvent extraction of and 4-(2-thiazolylazo)-l-naphthol reagent for palladium.1863187 The lower stabilities of these chelates also make the dyes particularly useful in EDTA titrations.18 ,20 *21y166 $5’ ?188 Js9Jg8 3 1 g 9 9200 The dyes and their chelates are less soluble in water than their pyridyl analogues, and are easily extracted into organic solvents.Various workers have studied the solvent extraction of thiazolylazo dye ~he1ates.l~~ ,170 3173 to l s 4 3 1 s 6 9 l S 7 919031933195,197 7201 Results from these investi- gations show that, for bivalent ions such as copper, with insoluble dyes, the 1 : 1 chelate is soluble in water and suitable for use in EDTA titrations and the 1 : 2 (metal-to-ligand) chelate, which is insoluble in water, can be extracted into organic solvents for spectrophotometric determinati011s.l~~ 917431753195 As chromatographic spray reagents they are inferior to their pyridyl analogues because the strong orange background colour of the dye causes the chelates to appear less distinct.91 OTHER HETEROCYCLIC AZO DYESTUFFS By far the most important group of dyes in this class are the azo derivatives of 8-hydroxy- quinoline.Very few applications for other heterocyclic azo dyes in analytical chemistry have, as yet, been found. These few will be discussed first. Pollard, Nickless and A n d e r ~ o n , l ~ 8 - ~ ~ ~ by condensing a quinone with a heterocyclic hydrazine,202 have prepared a series of pyrimidylazo dyes that they were able to compare with the corresponding pyridyl compounds. The former dyes were found to be superior in several ways for the following reasons- They are more water soluble. They are more sensitive towards cations of groups IIa and IIIa of the periodic table. The bathochromic shifts observed in the visible spectrum on ionisation and chelation of the dyes are larger with the pyrimidyl derivatives. Pyrimidine is a weaker base than pyridine,lg4 and thus the acid dissociation and chelate stability constants were found to be lower.The dyes formed chelates in more acidic solution, and were also found to be more suitable for the titration of copper, giving faster colour reactions at the end-point. These same workers have also prepared some 8-quinolylazo dyestuffs and hydra- zones,138 showing that metals gave sensitive colour reactions only with ligands forming two 5-membered rings on chelation, such as PAR and PAN; but the most stable complexes contained a 5-membered and a 6-membered chelate ring (cf. salicylaldehyde-2-pyridyl- hydra~one13~ ,139). 2- (8-Quinolylazo)-l-naphthol-4-sulphonic acid gives a good colour change with cobalt and iron, and was also found to be a useful fluorescence reagent.At this point it is interesting to note that Dziomko, Markovich and Zelichenok203 have226 ANDERSON AND NICKLESS : HETEROCYCLIC A 2 0 [Analyst, Vol. 92 investigated the colour reactions of some multidentate quinazoline derivatives, including some possibly tetradentate ligands of the types shown below- CH3 CH3 I I CH3 CH3 H K OH N CH3 TABLE VII THIAZOLYLAZO AND BENZOTHIAZOLYLAZO DYESTUFFS IN ANALYTICAL CHEMISTRY Dye Ions Method TAN .. .. - Indicator Cu(I1) Indicator - Solvent extraction ZntII) Solvent extraction Ni(I1) Solvent extraction - Solvent extraction Co(I1) Solvent extraction Co(II1) Solvent extraction Ag(I), REs Solvent extraction - Spray reagent Co(II), Cu(II), Detection Zn(I1) TAR .. .. - Indicator Cu(I1) Indicator REs Indicator Co(I1) Indicator Ni(I1) Spectropho tometric - - TAM .... Ni(I1) - Cu(I1) UOZ+ - TAC .. .. Ni(I1) TAP-OMe . . Co(I1) Ni(I1) 4MeTAP-OMe Cu(I1) Zn(I1) Ni(I1) - Co(I1) Spectrophotometric - Spray reagent Indicator Indicator Solvent extraction Solvent extraction Spectrophotometric Indicator Indicator Solvent extraction Indicator Solvent extraction Solvent extraction Solvent extraction Solvent extraction Solvent extraction General remarks References General investigations 18, 20, 21, pH 3 to 8 188 167, 198, 200 General investigations 190, 195 into CHC1,. Absorbance a t 600mp 183 Also for Zn(I1) in Mg and Tho, into 180 in high purity chromium 184 into CHC1, a t pH 5 to 9. Absorbance 181 into CHCl,. Absorbance maximum 182 General investigations 268 - 19 CHC1, at pH 7 measured a t 508 mp between 600 and 700 mp Blue-to-violet colours given by 91 numerous metals General investigations 18, 19, 20, pH 3 to 8 better than with TAN 188 Better than with PAR 199 - 181 Absorbance measured a t 473mp, 180 167, 198 pH 6-0 - In rocks.Absorbance measured a t 550mp in an aqueous tartrate medium at pH 5 to 6. Foreign ions masked with EDTA or CHDTA Less satisfactory than with PAR General investigations pH 6 to 10 General investigations with CHC1, at pH 5 to 10. Absorb- UO,(NO,), first extracted into IMBK General investigations pH 6 to 10 with CHCl,, pH 7 with CHCl,, pH 7 with isopentyl alcohol, pH 9. Absorb- with isopentyl alcohol, pH 7 to 9. Ab- with isopentyl alcohol, pH 7 to 9. Ab- ance measured a t 570 mp - - ance measured a t 612 mp sorbance measured at 620 mp sorbance measured at 607 mp 325 326 91 21, 167 189 169 170 168 20, 21, 167 189 180 181 180 173 174 175 176April, 19671 Dye p-TAN TACh TAN-6S TAN-3,6S TAO .. BTRN BTAR .. . . .. . . .. .. . . “Bromobenzo- thiazo” BTANa and sulphonated derivatives Derivatives of O-TAP Ions Fe(1I) c o (I1 I) - Pd(1I) - Th(1V) and Zr(1V) - - Co(I1) c o (I 11) Co(I1) Ni(l1) - - - Cd(I1) - Cu(I1) c u (I I) Co(l1) co (I 11) Ni( I1 I) DYESTUFFS ’IN ANALYTICAL CHEMISTRY 227 TABLE V I I-contimed Method Solvent extraction Solvent extraction Indicator Solvent extraction Indicator Indicator Indicator Indicator Indicator Spectrophotometric Spectrophotometric Indicator Detection Spray reagent Spray reagent Solvent extraction Spray reagents Indicator Indicators and Solvent extraction General remarks References with isopentyl alcohol, pH 5.5 to 7.Absorbance measured a t 777 mp with CHCI,. Absorbance maximum 182 between 600 and 700mp measured at 635 mp 176, 177 General investigations 20 General investigations 18,198 with isopentyl alcohol. Absorbance 187 pH 2.5 to 3.0 Th(IV)), 1.5 to 2.5 166 General investigations 21. 167, 198 (ZWV)) General investigations General investigations pH 6.0. Absorbance measured at 515 m p - General investigations For 0.21 pg or more Slightly better than TAN Not as good as TAR From alkaline tartrate solution into xylene. Absorbance measured a t 600 mp Blue -green spots on a pink back- ground pH 4.5 to 6. General investigations Very good Spectrophotometric Spectrophotometric 1 Others used in solvent extraction Spectrophotometric J Soluble dyes used in aqueous media 198 181 180 182 21, 167 193 91 91 197 138 139 179 18Q 18l! 182 The pH values between which compounds of this type will extract metals into chloroform have been listed.Heterocyclic amines containing &membered rings are, on the whole, capable of under- going diazotisation and coupling with phenols.204 to 207 However, except for the thiazolylazo dyes, few applications have been found for the products in analytical chemistry. Kurbatov and Kazarinova208 have prepared 1-(2-thiadiazolylaz0)-2-naphthol and measured its acid dissociation constant, which was found to be 7.3. They recommend its use as an acid - base indicator, stating that it was yellow in acid and pink in alkali. Dziomko201 investigated the solvent extraction of metals with a wide range of chelating agents, including l-(6-nitro-2-benzothiazolylazo)-2-naphthol, PAN and 2-(2-hydroxyphenyl- azo) -4,Ei-dimeth ylimidazole.Tanaka and Y amauchi209 coupled diazotised 4-amino-5-methylimidazole with P-naphthol and dimethylaniline, and investigated the reactions of the dyes with metals, with regard to their use in complexometric titrations and solvent extraction procedures. Cherepakhin210 has used 3-methyl-5-propylpyrrole-(2-azo-2’)-phenol as a reagent for the spectrophotometric determination of cobalt. A20 DERIVATIVES OF 8-HYDROXYQUINOLINE- These are easily prepared by coupling the diazotised amine with 8-hydroxyquinoline or one of its derivatives. Coupling takes place either in position 5 or position 7 of the quinoline ring, thus giving rise to two series of compounds.5-Arylnxo-8-~ydroxyq~~~zoZ~~e~-These were the first to be prepared, and have been used mainly as test reagents for the detection of very small amounts of metals.1y2.211 to 217 Proce- dures have been described for the detection of bismuth, zinc, mercury, copper, silver, gold, nickel, palladium, chromium, molybdenum, vanadium and magnesi~rn.2~ All of these tests are best carried out in nitric acid solution by spotting either on filter-paper or on a white porcelain tile. The test for magnesium is carried out in alkaline solution. 5-(4-Carboxyphenylazo)-8-hydroxyquinoline has been successfully used for the gravi- metric determination of zinc and lead, and 5-(2-carboxyphenylazo)-8-hydroxyquinoEne has228 ANDERSON AND NICKLESS : HETEROCYCLIC A20 [A.naZyst, Vol.92 been used for the colorimetric determination of zinc and mercury.215 A method has been devised for the indirect determination of metals colorimetrically, by precipitating them quantitatively as their 8-hydroxyquinolinates, dissolving the precipitate in hydrochloric acid and allowing the solution to react with a diazotised amine. The absorption of the dye produced is then measured. The method has been used for the determination of calcium with diazotised sulphanilic and y-acids,218 gallium with diazotised sulphanilic and naphthionic acids2I9 and aluminium with diazotised sulphanilic220 and naphthionic221 acids. The fact that these dyes complex at low values of pH has been put to good use by Kuznetsov and Fang,222 who used azo dyes of diazotised picramic acid and dinitroaniline coupled with 8-hydroxy- quinoline for the solvent extraction of zirconium and thorium from acid solutions below the pH at which these metals hydrolyse.Although these dyes have not found any applications as EDTA indicators, they have been used in mercurimetric titrations for c h l ~ r i d e . ~ ~ ~ , ~ ~ ~ The most suitable dyes for this purpose were found to be 5- (3- and 4-nitrophenylazo)-8-hydroxyquinoline, and these dyes could also be used for the colorimetric determination of chloride. Both methods are carried out in acidic solution (pH about 2).223 8-Hydroxyquinoline violet is 5-(4-nitroplienylazo)-7-nitroso-8-hydroxyquinoline, and can complex either as a derivative of 8-hydroxyquinoline or nitrosonaphthol.I t is reported as being specific towards copper and selective towards nickel. Its copper complex is not easily broken up by many common complexing agents, including 8-hydroxyquinoline itself .225 The acid dissociation and chelate stability constants of 5-(benzeneazo)-8-hydroxyquino- line and 5- (2-, 3- and 4-hydroxyphenylazo) -8-hydroxyquinoline have been measured by Takamoto, Fernando and Freiser.226 They discussed the results obtained in relation to the position of the aromatic hydroxyl group, and showed that the heterocyclic hydroxyl group ionises at a lower pH than in 8-hydroxyquinoline itself. Chelation also took place at a lower pH than with 8-hydroxyquinoline, and the advantages of this in analytical chemistry were discussed. 7-AryZaxo-8-hydroxyquinoZi.nes-These are mainly derivatives of 8-hydroxyquinoline- 5-sulphonic acid and are used primarily as indicators in titrations, either with EDTA or with standard metal solutions in various applications.8-Hydroxyquinoline itself will couple either in the 5- or in the 7-position, the dye produced depending on the diazo component and on the conditions of coupling. Sometimes a mixture is obtained and separation of the isomers is necessary.227 However, with 8-hydroxyquinoline-5-sulphonic acid, coupling can only take place in position 7. The first workers to use these dyes as indicators for EDTA titrations were Fritz, Lane and Bystroff ,22 who coupled diazotised aniline, p-chloroaniline, p-nitroaniline and cc-naphthyl- amine with 8-hydroxyquinoline-5-sulphonic acid.The dyes thus obtained were suitable for the direct titration of many metals, although the addition of a small calculated amount of copper salt just before the end-point was reached was necessary to ensure a correct result for some of the weaker complexing ions. Within a short time of each other, Guerrin, Sheldon and Reilley introduced 7- (4-sulpho-l-naphthylazo)-8-hydroxyquinoline-5-sulphonic acid (“SNAZOXS”),23 and Fritz, Abbink and Payne introduced 7-(6-sulpho-2-naphthylazo)- 8-hydroxyquinoline-5-sulphonic acid24 as indicators for the titration of a wide range of metals with EDTA. These two dyes were found to be similar, and could be used in both direct and indirect titrations. The addition of a small amount of copper salt near the end-point was again sometimes necessary. They could also be used over a wider range of pH than those mentioned previously.22 Busev, Talipova and Skrebkova have since used dyes of this type for the direct titration of 9229 indium230y231 and thalli~m.~32 With 7-arylazo 8-hydroxyquinolines as indicators, the colour change at the end-point is from yellow to orange, red or violet.00’-Dihydroxyazo dyes of 8-hydroxyquinoline have been studied by Badrina~,~~’ 9233 who prepared 7-(2-hydroxy-4-sulpho-l-naphthylazo)-8-hydroxyquinoline and its analogues and recommended them as metallofluorochromic indicators for chelometric titrations. 7-Arylazo-8-hydroxyquinolines have been used as mercurimetric indicators,234 9235 the best dyes for this purpose being 7-(4-sulphophenylazo)-8-hydroxyquinoline and 7- (2-naphthyl- azo)-8-hydroxyquinoline. Arsenic has also been determined as arsenate ions by titration with standard lead solutions, with “SNAZOXS” as indicator.12* Scandium has been determined spectrophotometrically in aqueous solution with threeApril, 19671 DYESTUFFS IN ANALYTICAL CHEMISTRY 229 azo derivatives of 8-hydroxyquinoline-5-sulphonic a~id.2~6 The selectivity of the method is low, and the absorbance is measured at 420mp, the free dyes absorbing at 520mp.The mechanism of chelation of these dyes is interesting, as they can co-ordinate either as an o-hydroxyazo dye or as a derivative of 8-hydroxyquinoline. Ishibashi and Yamarn~to~~' studied the copper complex of 7-(benzeneazo)-8-hydroxyquinoline-5-sulphonic acid spectro- photometrically, and proposed the following structure for the chelate- Cherkesov, on the other hand, showed that 7-arylazo-8-hydroxyquinoline in neutral solutions complexed via the hydroxyl group and heterocyclic nitrogen atom (yellow complexes), and in acid solutions via the hydroxyl group and azo nitrogen atom (red complexes).This leaves the heterocyclic nitrogen atom free to be protonated by the a ~ i d ~ ~ ~ y ~ ~ ~ - yellow red v Cherkesov also observed that 5-arylazo-8-hydroxyquinolines only gave yellow chelates with metals, because of the inability of the metal to co-ordinate with the azo g r o ~ p . ~ 3 ~ Heterocyclic azo dyes of 8-hydroxyquinoline have been prepared with diazotised 2-arninop~ridinel~~ ~ ~ ~ 6 % ~ ~ ~ and 2-aminothiazole.1s These have already been discussed, and their behaviour seems to suggest, at least with the pyridine compound, that they complex as derivatives of PAN rather than of 8-hydroxyquin01ine.l~~ CONCLUSIONS The analytical applications of heterocyclic azo dyestuffs, in which the heterocyclic atom is involved in co-ordination with a metal ion, have been reviewed.A few related compounds, whose properties have been compared with those of the azo dyestuffs, have also been included in this review. The most important dyes of this type are 1-(2-pyridylaz0)-2-naphthol for solvent extrac- tion procedures, and 4-(2-pyridylazo) -resorcinol for determinations in aqueous media. These two dyes are also useful as indicators for complexometric titrations, although modified procedures are often required because of slow reactions at the end-point.Some other azo dyes of pyridine have also been prepared, but the same number of uses for them has not as yet been found, despite the fact that some of them show quite promising properties. Because of their ease of preparation, many azo dyes of thiazole have been tested for analytical uses. On the whole they do not appear to be as promising as the pyridylazo dyes, being more strongly coloured themselves, less water soluble and producing less stable complexes. h'evertheless, some specialised applications have been found for these reagents. Dyes with a PAN-type chelating structure have been shown to complex via the o-hydroxyl group, the heterocyclic nitrogen atom and the azo nitrogen atom nearest to the phenolic half of the molecule giving rise to two stable, 5-membered chelate rings.The main charac- teristic of these dyes is the strong bathochromic shifts observed in their visible spectra on chelation with a wide range of metals. This phenomenon is not observed to the same extent with any related compound in which this chelating structure has been modified.230 ANDERSON AND NICKLESS HETEROCYCLIC A20 [Analyst, Vol. 92 Several applications have been found for the azo derivatives of 8-hydroxyquinoline as spot reagents and as indicators. These dyes show hypsochromic shifts on chelation, especially if it is the heterocyclic nitrogen atom that is involved in co-ordination. Heterocyclic azo dyestuffs thus constitute an important and relatively new class of analytical reagents with a wide range of applications.Further research in this field should be fruitful, if directed to investigations on the mechanism of chelation of these dyes and the factors affecting their usefulness in analytical chemistry in order to anticipate the potentials of new dyes, especially dyes containing new heterocyclic systems. PYRIDYLAZO DYESTUFFS r- Name A 4- (2-Pyridylazo) -resorcinol OH 1- (2-Pyridy1azo)-orcinol OH 2- (2-Pyridylazo) -phenol OH 2- ( 2-Pyrid ylazo) -4-methylphenol OH 5- (2-Pyrid ylazo) -2-monoethylamino-p-cresol OH 4- (3-N-Methylpiperidyl-2-pyridylazo) - OH 4- (2-Pyridylazo) -phenol H 4- (2-Pyridylazo) -dimethylaniline H resorcinol* Position of substitution B C H OH H OH H H H OH H H H NHC,H, H 1 E H c:, H H H H H Abbreviation PAR P A 0 0-PAP p-PAP PAC PAAC PAA MAAR Position of substitution Name A B C D 1- (2-Pyridylazo) -2-naphthol O H H H H 1- (2-Pyridylazo) -2,3-dihydroxy- OH OH H H 1-(2-Pyridylazo) -2,7-dihydroxy- O H H H H 4- (2-Pyridy1azo)- 1-naphthol H H OH H 1-(3-N-Methylpiperidy1-2-pyridyl- OH H H H 4- (3-N-Methylpiperidyl-2-pyridyl- H H OH H naphthalene-6-sulphonic acid naphthalene azo) -2-naphthol azo)-1-naphthol* \ E F G Abbreviation H H H PAN SO,H H H PADNS H OH H 2,7-PAN H H H p-PAN H H H MAAN H H H p-MAAN * Contains grouping in 3-position on pyridyl ring.April, 19671 DYESTUFFS I N ANALYTICAL CHEMISTRY G .F 231 B C Position of substitution Name ‘A B C D E F G‘ Abbreviation 2- (2-Pyridylazo) - 1, S-dihydroxy- OH SO,H H H SO,H H OH PACh 2-(2-Pyridylazo)-&amino-l-naph- OH SO,H H H SO,H H NH, PA-H naphthalene-3,6-disulphonic acid thol-3,6-disulphonic acid 2-(2-Pyridylazo) -1-naphthol OH H H H H H H CX-PAN 7-(2-Pyridylazo)-8-hydroxyquinoline OH H H H H H N* PAOx * Substitution of naphthalene ring sytem by quinoline.THIAZOLYLAZO DYESTUFFS E D A B Position of substitution f A \ Name A B C D E F G 4- (2-Thiazolylazo) -resorcinol O H H O H H H H H 2-(2-Thiazolylazo)-5-dimethylamino- OH H N(CH,), H H H H 2-(2-Thiazolylazo)-4-methylphenol OH H H CH, H H H 2-(2-Thiazolylazo)-4-methoxyphenol OH H H OCH, H H H 2-(4-Methyl-2-thiszolylazo)-4-meth- OH H H OCH, H H CH, phenol ox yphenol 4- (2-Thiazolylazo) -orcinol OH H OH H cg3 g H 2- (2-Thiazolylazo) -phenol O H H H H 4-(2-Benzothiazolylazo)-resorcinol OH H OH H H \-y--* * Benzene ring fused across F-G Abbreviation TAR TAM TAC TAP-OMe 4-MeTAP-OMe TAO o-TAP BTAR D C I A \ I Abbreviation H TAN H fi-TAN l-(2-Thiazolylazo)-2-naphthol- OH H H H SO,H H H H H TAN-6S l-(2-Thiazolylazo)-2-naphthol- OH SO,H H H SO,H H H H H TAN-S,6S Position of substitution Name A B C D E F G H l-(2-Thiazolylazo)-2-naphthol OH H H H H H H H 4-(2-Thiazolylazo)-l-naphthol H H OH H H H H H 6-sulphonic acid 3,6-disulphonic acid 2-naphthol 1-( 2-Benzothiazo1ylazo)- O H H H H H H H H< >CH BTAN c-c H H l-(6-Bromo-2-benzothiazolyl- OH H H H H H H / \ * “Bromobenzo- azo) -2-naphthol HC\\ ,,CH thiazo’ ’ C-CH Br’ * Benzene ring fused to H and I positions.232 ANDERSON AND NICKLESS: HETEROCYCLIC A20 MISCELLANEOUS REAGENTS [Amdyst, Vol.92 2 - (2 - Thiazolylazo) - I, 8 - dihydroxy naphthalene - 3, 6 - disulphonic acid TAC h 2 - (Benzothiazolylazo) - I - naphthol BTAN u HO QN = NQ 0 , q H - N = c H o PN N = N+ 2 - (2 - Pyrimidylazo) - I - naphthol Salicylaldehyde - 2 pyridyl- 2 - (8 - Quinolylazo) - I - naphthol - SO3 H / HO HO hydrazone 4 - sulphonic acid N = N - A r I I Salicylaldehyde - 8 - quinolylhydrazone OH 1.2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 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ISSN:0003-2654    

DOI:10.1039/AN9679200207

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, April, 1967, Vol. 92, $9. 239-246 239 The Determination of Plutonium in Refractory Materials by Electrometric Methods after Dissolution by Fusion with Ammonium Hydrogen Sulphate BY G. W. C. MILNER, A. J. WOOD, G. WELDRICK AND G. PHILLIPS (Analytical Sciences Division, Atomic Energy Research Establishnze%t, Harwell, Didcot, Berks.) A fusion with ammonium hydrogen sulphate at 400" C has been developed for the dissolution of refractory materials containing plutonium dioxide. On cooling, each melt is leached with sulphuric acid to produce a solution suitable for analysis for plutonium by electrometric methods. Plutonium concen- trations (about 2 mg per ml) are determined either by a potentiometric titration based on the reduction of plutonium(V1) to plutonium(IV), or by a controlled-potential coulometric method, the PUS+ - Pu4+ couple being used.Both techniques are suitable for the accurate determination of plutonium with a precision of better than 0-20 per cent. (coefficient of variation) for about 5-mg amounts or less. The behaviour of many other elements in these methods has been studied in some detail. The fusion technique has been found to be suitable for the dissolution of several refractory materials, including samples of PuO, - UO, fired a t 1550" C, and also samples of PuO, - Tho, produced by the ignition at 900" C of the carbides of these elements coated with pyrolytic graphite. The determination of the plutonium contents of these samples was then completed directly by the electrometric methods. CERAMIC materials containing plutonium are being studied as potential fuels for nuclear reactors, and oxide and carbide systems are being investigated for this purpose.In this work specimens are prepared to cover a wide range of compositions, and final materials are then checked by chemical analysis. With oxide samples, difficulties can occur in the chemical analysis because of the refractory nature of plutonium dioxide, particularly after ignition at temperatures greater than 850" C. Many of the oxide samples for analysis had been ignited at temperatures greater than 850" C, and some reached 1550" C in the ignition process. In the analysis of carbides for plutonium, the usual practice is to ignite them to oxide to remove carbonaceous matter before proceeding with the dissolution.The temperature in this process can be controlled at less than 850" C. The present methods for the dissolution of low-fired plutonium dioxide include the use of various acids, such as nitric acid plus hydrofluoric acid,l halogen acids,2 or perchloric acid and hydrochloric acid at high press~res,~ but, unfortunately, these methods are unsatisfactory for the complete dissolution of high-fired plutonium dioxide. A need occurred therefore for the development of new methods of dissolution that were compatible with the solution requirements of the techniques for the plutonium determination. In earlier work4 a sodium peroxide sinter was developed for the dissolution of plutonium dioxide, and differential spectrophotometry proved to be suitable for the determination of the plutonium content of the resulting solution.The differential spectrophotometric method requires, however, that the plutonium concentration is not less than 2 mg per ml, and that at least 15ml of solution are available for each determination. Electrometric methods for plutonium offer the advantage of improved precision for smaller concentrations, but they are more readily applied to solutions in sulphuric acid medium. Controlled-potential coulo- metry is suitable for the determination of 4-mg amounts of plutonium in M sulphuric acid with a precision of 0.25 per cent.,5 whereas a potentiometric titration procedure6 can be used for the determination of 2 to 10-mg amounts in M sulphuric acid with a precision of 0-1 per cent. Both techniques have been applied successfully to the analysis of cermet and alloy samples that could be dissolved in mineral acids, but their application to solutions produced by the sodium peroxide sinter technique proved less suitable.A fusion with ammonium hydrogen sulphate has been recommended by Feldman' for the dissolution of small amounts (about 2 mg) of plutonium dioxide, and the results of preliminary experiments with this240 MILNER et al.1 DETERMINATION OF PLUTONIUM I N [Analyst, VOl. 92 technique in our laboratory were encouraging. The complete dissolution of plutonium dioxide, ignited at 1350" C, was achieved by fusing with ammonium hydrogen sulphate at 520" C and extracting the cooled melt with M sulphuric acid. Moreover, the resultant solution was suitable for analysis by electrometric techniques.In fact, the behaviour of this type of solution in controlled-potential coulometry was superior to that of solutions prepared by other methods. The further development of this procedure for the dissolution of larger amounts of high-fired plutonium dioxide was therefore undertaken, and the results of this investigation are reported here. EXPERIMENTAL FUSION CONDITIONS WITH AMMONIUM HYDROGEN SULPHATE FOR THE DISSOLUTION OF Feldman succeeded in dissolving 2-mg amounts of an impure specimen of plutonium dioxide by fusing it with ammonium hydrogen sulphate in a small quartz beaker. This tech- nique needed scaling up, however, before it could be used successfully for the dissolution and analysis of oxide samples containing plutonium. The feasibility of achieving this was tested on a sample of finely powdered plutonium dioxide that had been ignited at 1350" C.A suitable sample weight (about 100 mg) was mixed with 2 g of ammonium hydrogen sulphate in a glass beaker, and then the covered beaker was heated at 500" to 520" C on a hot-plate for 2 hours. Visual examination of the melt at this stage indicated that a little unattacked plutonium dioxide remained, and so more ammonium hydrogen sulphate (2 g) was added and heating was continued for a further 18 hours. On cooling, the melt was leached with sulphuric acid, and the solution was diluted to 50 ml to give a solution M in sulphuric acid. The plutonium content was determined by analysing suitable volumes of solution by the electrometric techniques. The following results, expressed as percentage recoveries, assuming stoicheiometric Pu02.00, showed that the plutonium dioxide was dissolved completely by the above fusion procedure.PLUTONIUM DIOXIDE- Plutonium taken, Plutonium found, Recovery, Coefficient of variation, per cent. per cent. mg mg Coulometry . . 9.966 9,964 100.0 0- 17 (2 determinations) Potentiometry . . 3-986 3.983 99.9 0.15 (8 determinations) Information on the efficiency of the fusion with time was next obtained by carrying out experiments with fusion times of 30 minutes, 2 hours and 4 hours. The resultant solutions were then analysed for plutonium content by potentiometry. The following results showed that although 99 per cent. of the plutonium dioxide is dissolved after 2 hours, a fusion time of 3 to 4 hours is needed for complete dissolution- Time of fusion Plutonium taken, Plutonium found, Recovery, Coefficient of variation, 30 minutes .. 3.074 2-924 95.1 0.16 (6 determinations) 2 hours. . . . 3.62 1 3.596 99.3 0.22 (6 determinations) 4 hours. . . . 3.260 3.260 100.0 0.08 (6 determinations) per cent. per cent. mg mg Although ammonium hydrogen sulphate boils quietly at 520" C, losses of reagent from a covered beaker eventually cause the melt to evaporate to dryness, and care is needed to prevent this from taking place. There is also a risk of some loss of plutonium resulting from carry-over in the spray. It was considered that these problems might be overcome by using a lower temperature for the fusion and a condenser to deal with any spray. Tests showed that ammonium hydrogen sulphate remained in the molten state even at 400" C, and so dissolution experiments with plutonium dioxide were carried out at this temperature.The plutonium dioxide and ammonium hydrogen sulphate mixture was placed in a 50-ml conical flask and an air condenser, 5 inches in length, was fitted. A small watch-glass was used to cover the open end of the air condenser. Under these conditions it was possible to take 200 mg of plutonium dioxide into solution with 5 g of ammonium hydrogen sulphate, provided that the fusion process was allowed to proceed for 3 hours or longer. A little difficulty was experienced with the removal of the air condenser, but this was overcome by moistening the ground-glass joint with M sulphuric acid and allowing it to stand for some time before removing.The condenser was washed with M sulphuric acid and the washings were addedApril, 19671 REFRACTORY MATERIALS BY ELECTROMETRIC METHODS 241 to the sample solution before making up to volume (100 ml). A series of plutonium deter- minations carried out by potentiometric titration following this dissolution technique gave a mean recovery of 100-0 per cent., with a coefficient of variation of 0-20 per cent. METHOD APPARATUS- Conical Jasks-Capacity, 50 ml, fitted with C19 ground-glass joints. Glass tubes, 5 inches long and 0.5 inch i.d.-Fitted with C19 ground-glass cones to serve Grade A 100-ml graduated $asks. Controlled-potential coulometev8 ,9--Iiitted with a digital voltmeter (type LM1010-2, Electrolysis cell for coulometry-As described previ~usly.~ Automatic potentiometric titmtor.6 as air condensers. Solartron Laboratory Instruments Ltd., Chessington, Surrey).REAGENTS- Ammonium hydrogen sulphate-B.D.H. laboratory reagent. Szlver(I1) oxide-Prepare by adding 100ml of 3 per cent. w/v potassium persulphate to 10 ml of 10 per cent. w/v silver nitrate. Allow to stand for 1 hour. Filter the precipitate, wash well with water and allow it to dry in a desiccator. Sulphuric acid, 9 M and M. Silver sulphate, 1 per cent. w/v in M sulphuric acid. Cerium(1V) sulphate, 0.1 N in M sulphuric acid-Standardise potentiometrically against 0-1 N potassium dichromate.6 Ammonium iron(11) sulphate, 0.025 N in M sulphuric acid-Standardise against cerium( IV) sulphat e. Potassiziin dichromate, 0.1 N-Dissolve 4.903 g of potassium dichromate (dried at 110" C> in water and dilute to a volume of exactly 1 litre at 20" C.Use AnalaR reagents, including the distilled water. RADIOCHEMICAL SAFETY- Operations on dry samples containing plutonium dioxide, up to the point of complete dissolution, should be conducted in a glove-box. Aliquot portions for completion of the analysis may be handled in a fume cupboard with an efficient extraction and filtration system. PROCEDURE- Prepare a solution (100 ml) of the sample to contain 1 to 2 mg of plutonium per ml by transferring a suitable weight of sample to a 50-ml conical flask and adding 2 g of am- monium hydrogen sulphate. Fit an air condenser, and cover its open end with a small watch- glass. Stand the flask on a small temperature-calibrated hot-plate, and adjust the rheostat to raise the melt to 400" C.Maintain at this temperature for at least 3 hours, and add more ammonium hydrogen sulphate if the melt solidifies. Then cool the flask, moisten the ground-glass joint with M sulphuric acid and allow to stand (preferably overnight). Carefully remove the air condenser and wash it with M sulphuric acid, adding the washings to the flask. Allow the melt to dissolve and add more M sulphuric acid for this purpose, if necessary. Transfer the solution to a 100-ml graduated flask and dilute to the mark with M sulphuric acid. Take suitable aliquots containing about 4 mg of plutonium for determination by either potentiometric titration or controlled-potential coulometry as follows. Potentiometric titration-Transfer the aliquot of sample solution to a 15-ml squat beaker, and adjust the solution to be 2 to 3 ml in volume and M in sulphuric acid.Add 3 ml of 1 per cent. silver sulphate solution, and then 25 mg of finely powdered silver(I1) oxide. Stir the mixture and allow it to stand for 5 minutes. Add two further portions (25 mg each) of silver(I1) oxide at intervals of 5 minutes, and allow to stand for a total of 20 minutes while agitating at frequent intervals. Then cover the beaker with a watch-glass and warm it at 95" C for 5 minutes to destroy the excess of oxidant. Cool, rinse the watch-glass and beaker with 1 ml of water, and then add 3ml of 9 M sulphuric acid. Accurately add 2 ml of 0.025 N ammonium iron(I1) sulphate solution to reduce plutonium(V1) to plutonium(IV), and leave some reagent in excess (Note 1).Place the electrode system, consisting of a platinum elec- trode and an S.C.E. in the sample solution, and allow the potential to stabilise while stirring242 MILNER et al.: DETERMINATION OF PLUTONIUM IN [Analyst, Vol. 92 the solution smoothly. Dip the end of the Agla burette in the solution and slowly titrate the excess of iron(I1) with standard 0.1 N cerium(1V) sulphate solution with the automatic potentiometric titrator. Calculate the plutonium content of the sample from the expression- (C - B) N x 239-1 x V A x 2 Plutonium, mg = where C is the titre for the total ammonium iron(I1) sulphate added, B is the titre of the iron(I1) in excess, N is the normality of the cerium(1V) sulphate solutions, A is the volume of the aliquot taken for analysis, and Vis the total volume of the sample solution.NOTE 1- The strength of the ammonium iron(I1) sulphate should be such that the titration of the excess will require less than 0.5 ml of 0.1 N cerium(1V) sulphate. This is because the total capacity of the burette is 0.5 ml. Coulowzetric determination-Transfer the aliquot of sample solution to the coulometer cell, and add sufficient M sulphuric acid to cover the working electrode. Remove oxygen from the solution by passing a stream of nitrogen through it. Then reduce the plutonium to the tervalent state by electrolysing at a potential of +0.30 volt against an S.C.E. until the current attains a low constant value ( < l o PA). After adjusting the coulometer to zero, carry out the quantitative oxidation of plutonium to the quadrivalent state by electrolysing at +0.70 volt against an S.C.E.until the cell current reaches its previous low value (<lo PA). Correct the digital-voltmeter reading, Q, for a blank determination carried out in exactly the same way with only M sulphuric acid in the cell. Calculate the weight of plutonium from the expression- Q (corrected) x F x 239.1 x V 96,487 x A Plutonium, mg = where F is the calibration factor in millicoulombs per millivolt for the coulometer range used, and V and A are the same as for the potentiometric titration. THE BEHAVIOUR OF OTHER OXIDES IN THE SOLUTION PROCESS- In experiments to study the behaviour of other oxides, a suitable weight of each oxide in the range 50 to 200 mg was transferred to a 50-ml flask, then 2 g of ammonium hydrogen sul- phate was added and the fusion carried out. Several oxides gave clear melts which produced complete solutions in RI sulphuric acid.Oxides in this category included B,O,, CeO,, CuO, HgO, MnO,, MOO,, NiO, NpO,, Tho, (ignited at 2000" C), UO,, U,O,, V,O, and 21-0,. The clear melts of a few oxides failed to give clear solutions in M sulphuric acid. These oxides included beryllium oxide, niobium pentoxide, silicon dioxide, tantalum pentoxide, titanium dioxide and tungsten trioxide (WO,). This difficulty was overcome with beryllium oxide, niobium pentoxide, tantalum pentoxide and titanium dioxide by extracting the melts with concentrated sulphuric acid before diluting with water. The melts of tungsten trioxide and silicon dioxide failed to produce clear solutions.The oxides of barium, calcium and lead did not produce clear melts, and insoluble sulphates of the elements precipitated from M sulphuric acid solutions. Calcium sulphate was incompletely precipitated under these conditions. The oxides of the rare earths were unattacked during the ammonium hydrogen sulphate fusion, but clear melts could be obtained by including ammonium nitrate in the fusion mixture. The oxides of iron and magnesium were also unattaclced by ammonium hydrogen sulphate, and ammonium chloride was needed to achieve clear melts. The resultant solutions containing chloride and nitrate ions required evaporating to fumes of sulphuric acid to remove these constituents before proceeding with the plutonium determination.INTERFERENCES IN THE PLUTONIUM DETERMINATION- As many oxides of other elements are dissolved by the solution procedure developed for plutonium dioxide, a knowledge of the behaviour of these elements in the electrochemical procedures for plutonium is important. Possible interfering elements are those that are able to undergo oxidation - reduction reactions similar to plutonium. However, as the redoxApril, 19671 REFRACTORY MATERIALS BY ELECTROMETRIC METHODS 243 reaction for plutonium is not the same in both procedures, elements interfering in the potentio- metric method may not necessarily interfere in the coulometric method. The behaviour of elements in these methods was therefore considered separately with the following results.POTENTIOMETRIC TITRATION- Any element capable of oxidation by silver(I1) oxide and then reduction by iron(I1) will give high results for plutonium by this method. Elements in this category include chromium, cerium, vanadium and manganese, and the first three react quantitatively. Manganese is oxidised to permanganate by silver( 11) oxide, but then precipitation of manganese dioxide occurs during the destruction of excess of oxidant. Lloyd and PickeringlO have reported that when manganese in sulphuric acid solutions is not fully oxidised by silver(I1) oxide, the remaining manganese( 11) ions reduce permanganate with the precipitation of manganese dioxide. From electrochemical considerations there should be negligible interference from many elements. No difficulties were encountered from equal amounts of the following elements in the determination of plutonium at the 4-mg level: B, Be, Bi, Ca, Cu, Eu, Mg, Nd, Ni, Sm, Ti, Th, U and Zr.The presence of mercury made the precision of the determination worse, and low results were obtained in the presence of equal amounts of molybdenum, niobium and tantalum. These elements were precipitated on heating the solution to destroy excess of silver( 11) oxide and removed some plutonium from solution. Difficulties might be expected from elements precipitating as sulphates from M sulphuric acid, and although quantitative results were obtained for plutonium in the presence of an equal amount of calcium, some plutonium was carried down on the sulphate precipitates of lead and barium. In the case of iron, iron(II1) sulphate was precipitated on fuming the solution with sulphuric acid to remove chloride ions.Unfortunately this precipitate did not re-dissolve in M sulphuric acid, and it retained some of the plutonium on it. At a 10 : 1 ratio of the oxide of the other element to plutonium dioxide, the list of elements causing no interference is reduced to boron, copper, magnesium, thorium, uranium and zirconium. It proved impossible to produce satisfactory solutions for the increased amounts of bismuth, europium, neodymium, samarium and titanium, and although nickel gave a clear solution initially, a precipitate began to form fairly soon after preparation. Both beryllium and mercury gave satisfactory solutions. However, the titration curves were poorly defined in the presence of beryllium, and the precision of the plutonium determination was poor.Mercury also caused inferior titration curves with a positive bias of a few per cent. for the determination of plutonium. With calcium, the increased amount of calcium sulphate pre- cipitated from solution at the 10: 1 ratio resulted in the removal of some plutonium from solution, and hence interference in the determination. CONTROLLED-POTENTIAL COULOMETRY- This technique is more specific for plutonium than the potentiometric titration, and earlier work5 showed that no interference occurred from chromium, molybdenum, thorium, titanium and uranium in the analysis of alloys, cermets and ceramic materials. Interference from electro-active elements is limited to those that undergo oxidation - reduction reactions in the voltage range required for the plutonium determination (i.e., +0.3 to +0.7 volt against an S.C.E.), and possible interfering and non-interfering elements can be identified by reference to tables of standard potentials of half-reaction for the elements.Iron, mercury, silver and vanadium were considered to be the elements most likely to cause difficulty in the electrolysis. The Eb value for the Fe2+ - Fe34- couple is almost identical with that for the Pu3+ - Pu4+ couple, and so interference from this element is serious. Mercury interfered seriously by depositing as the metal on the platinum electrode during the electrolysis. It also proved difficult to determine the completion of the plutonium determination under these conditions. Similarly, silver caused difficulties by reducing to the metal and plating on the working electrode.For vanadium, Eb values for the various couples are +0.119 volt against an S.C.E. for V3+ - V02+, and +0.76 volt against an S.C.E. for VO2+ - VO;, and clearly interferences can be expected in the plutonium determination on electrolysing at 1-0.7 volt against an S.C.E. This was confirmed experimentally in the analysis of a synthetic solution with a 1 : 1 ratio of plutonium dioxide to vanadium pentoxide, as a high background current persisted at +0.7 volt, resulting in a plutonium recovery of about 105 per cent. Investigations with a pure vanadium solution showed that V02+ ions oxidised slowly at +O-7 volt, but that244 MILNER et al.: DETERMINATION OF PLUTONIUM IN [Afialyst, Vol.92 this reaction did not take place on reducing the voltage to +Om62 volt against an S.C.E. It was concluded that it should be possible to oxidise Pu3+ to Pug+ to 99 per cent. completion at +0-62 volt against an S.C.E. and avoid interferences from vanadium. This was attempted experimentally with satisfactory results, a recovery of 99-9 per cent. being obtained for plutonium in the 1 + 1 mixture of plutonium dioxide with vanadium pentoxide on correcting for the 1 per cent. plutonium unoxidised at this potential. From electrochemical considerations most of the remaining elements should not interfere. Investigations were therefore limited to those elements with Eb values fairly near to the voltage range for the plutonium determination, and to those elements hydrolysing or precipitating from solution.From elements in the first category, copper was found to give no interference with plutonium for 1 : 1 and 10 : 1 ratios of its oxide to plutonium dioxide, and although bismuth did not interfere at a 1 : 1 ratio of the oxide, it proved impossible to produce satisfactory solutions for a 10 : 1 ratio of bismuth trioxide to plutonium dioxide. In the second category of elements, work by Shultsll indicated that difficulties might uise from elements not in true solution in M sulphuric acid. This worker reported interference 'rom zirconium, even in small amounts, in the coulometric determination of plutonium. The :iature of this interference was similar to that from organic matter in causing extended iitration times and hence poor results.This behaviour was identified as being caused by louling of the electrode by hydrolysed zirconium in the solution. In consequence, any element that can hydrolyse from M sulphuric acid containing ammonium sulphate may cause difficulty i i the plutonium determination. n'iobiuni and tantalum could be included in the same category as zirconium. The interference of zirconium was confirmed by us. A small positive tias was obtained for a 1 : 1 ratio of the oxides, and this increased to about 10 per cent. for a 10: 1 ratio of zirconium dioxide to plutonium dioxide. For freshly prepared solutions of niobium and tantalum, negligible interference occurred for 1 : 1 ratios of each oxide to p utonium dioxide. At 10 : 1 ratios of niobium pentoxide or tantalum pentoxide to plutonium d oxide, however, it proved impossible to prepare satisfactory solutions. The difficulties with elements forming insoluble sulphates (e.g., barium, calcium and lead) were the same as fc r the potentiometric titration method. Beryllium resulted in a slight positive bias being 01 ltained for plutonium. This was caused by a persistent background current occurring di .ring both the reduction and oxidation of plutonium.RESULTS A standard plutonium solution was used to test the procedures and to give information on accuracy and precision. It was prepared from a sample of high purity plutonium dioxide th;tt had been ignited at 1300" C to produce stoicheiometric PuO,.,,. This material was grclund to a fine powder and 200 mg were taken for dissolution by fusing with ammonium hy irogen sulphate at 400" C.The recoveries for plutonium shown in Table I were obtained by both the coulometric and potentiometric titration methods. The mean recovery values an( L the precisions (coefficients of variation) obtained for the determinations by both procedures wei'e considered to be satisfactory. TABLE I RESULTS FOR PLUTONIUM AFTER DISSOLUTION OF PLUTONIUM DIOXIDE WITH AMMONIUM HYDROGEN SULPHATE Method of Plutonium taken, determination mg Pc tentiometric . . 2.818 3.654 4.135 ( oulometry . . 5-181 5-691 6.180 Co itrolled-potential Mean recovery, per cent. 100.0 100.1 100.0 99.96 99.95 99.95 Coefficient of variation, per ccnt. 0.18 0.19 0.10 0.09 0.18 0.10 Number of deterininations 6 6 6 8 5 6 The value of this method of dissolution for samples containing refractory plutonium dioxide has recently been demonstrated in this laboratory for the analysis of PuO, - UO, samrles and PuC - ThC spheres coated with graphite.In a metallurgical study of PuO, - UO, fuels it was necessary to determine the plutonium contents of a series of refractoryApril, 19671 REFRACTORY MATERIALS BY ELECTROMETRIC METHODS 245 samples covering a range of compositions from 70 per cent. UO, - 30 per cent. PuO, to 99 per cent. UO, - 1 per cent. PuO,. All of the materials in this work had been sintered a t a temperature of 1550" C either in argon, or in a mixture of carbon dioxide and carbon monoxide. The ammonium hydrogen sulphate fusion procedure proved to be satisfactory for the dissolution of all samples, and the controlled-potential coulometric and the potentiometric titration methods were applicable to the analysis of the resultant solutions.Although uranium caused no interference, slight difficulty was encountered from iron in the analysis of samples at the 1 per cent. level of plutonium dioxide by controlled-potential coulometry. These samples were found to contain iron as an impurity, and a correction was needed for the iron in solution. Results for plutonium from the analysis of samples in this range of compositions are given in Table 11. Very good agreement was found to occur between the results for plutonium by both methods of analysis. TABLE I1 THE DETERMINATION OF PLUTONIUM IN REFRACTORY PuO, - UO, CERAMIC SAMPLES Plutonium content by analysis, per cent.Potentiometric Coulometric Sample weight, r--A--- _7 Nominal composition Sample conditions mg PuO,, 3076 - UO,, 70% Sintered a t 1550" C in argon 248-9 25.4 25.4 PuO,, 10% - UO,, goo/;, Sintered a t 1550" C in carbon 489.0 9.06 9.00 PuO,, 15% - UO,, 85% 562.2 13.2 13.2 monoxide - carbon dioxide PuO,, 1% - UO,, 9976 Sintered a t 1550" C in argon 901.9 0.98 0.99* * Result corrected for iron in solution. For the analysis of the PuC - ThC spheres, which had been fired at 1500" C in an inert atmosphere during preparation, it proved necessary to ignite the samples at 900" C in air to remove the graphite coating and oxidise all carbonaceous material. This resulted in a refractory mixture of PuO, - Tho, for subsequent analysis for plutonium. In the analysis of a typical sample, 1.0077 g of sample was ignited to give 0.3746 g of oxide, which was then dissolved in ammonium hydrogen sulphate to give 100 ml of solution.Aliquots (5 ml) con- taining about 2-23 mg of plutonium were taken for analysis by the electrometric methods with the following results for the percentage of plutonium in the coated spheres. Potentiometric method: 13.6 per cent. of plutonium, with a coefficient of variation of 0.6 per cent. for three results. Coulometric method: 13.5 per cent. of plutonium, with a coefficient of variation of 0-2 per cent. for four results. The suitability of the above method was confirmed on a synthetic sample with a similar composition. A recovery of 99.92 per cent. was obtained for the plutonium by the coulometric method as a mean of six results, with a coefficient of variation of 0-07 per cent.CONCLUSIONS Fusion with ammonium hydrogen sulphate has proved to be a successful method for dissolving refractory plutonium dioxide, either alone or in the presence of other refractory oxides. The need to reduce the sample to a fine state of subdivision and to mix it thoroughly with the fusion mixture, which is so essential for the sodium peroxide sinter, is unnecessary for the ammonium hydrogen sulphate fusion. As a consequence the latter method is readily applicable to very high-fired materials that cannot be dissolved completely by the sodium peroxide sinter, However, the ammonium hydrogen sulphate fusion is not rapid by com- parison with the peroxide sinter, but the resultant solution is more suitable for the deter- mination of plutonium by electrometric methods.Although a glove-box is necessary for the hydrogen sulphate fusion, the solution can then be transferred to a fume cupboard and the determination completed there because of the small amount of plutonium needed for the electrometric methods. This gives greater flexibility in handling sample solutions after dissolution. By comparison, the sohum peroxide sinter followed by differential spectro- photometry must be carried out completely in a suite of glove-boxes because of the higher concent rations of plutonium involved. We thank Mr. I. G. Jones for assistance in some of the preliminary experiments.246 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. MILNER, WOOD, WELDRICK AND PHILLIPS REFERENCES Katz, J. J., and Seaborg, G. T., “The Chemistry of the Actinide Elements,” Methuen and Co. Cleveland, J. M., J . Inorg. LVucl. Chem., 1964, 26, 1470. Kolthoff, I . M., and Elving, P. J., Editors, “Treatise on Analytical Chemistry,” Interscience Pub- Milner, G. W. C., Crossley, I)., Jones, I . G., and Phillips, G., Analyst, 1965, 90, 732. Phillips, G., and Milner, G. W. C., in Shallis, P. W., Editor, “Proceedings of the SAC Conference, Milner, G. W. C., Wood, A. J., and Cassie, G. E., U.K. Atomic Energy Authority Research Report, Feldman, C., Analyt. Chem., 1960, 32, 1727. Rockett, J. J., U.K. Atomic Energy Authority Research Report, AERE-R 3784, H.M. Stationery Milner, G. W. C., and Edwards, J. W., l J . K . Atonzic Energy Authority Research Report, ,4 ERE-R 3772, Lloyd, C. P., and Pickering, W. F., Talawta, 1964, 11, 1409. Shults, W. D., Ibid., 1963, 10, 833. Ltd., London; John Wiley and Sons Inc., New York, 1957, p. 279. lishers Inc., New York, 1962, Part 11, Volume 9, p. 251. Nottingham, 1965,” W. Heffer & Sons Ltd., Cambridge, 1965, p. 240. AERE-R 4975, H.M. Stationery Office, London, 1965. Office, London, 1961. H.M. Stationery Office, London, 1961. Received November 30th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200239

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, April, 1967, Vol. 92, pp. 247-252 247 The Spectrophotometric Determination of Ampicillin BY J. W. G. SMITH, G. E. DE GREY AND V. J. PATEL (Beecham Research Laboratories, Clarendon Road, Worthing, Susse.v) A method is described for the determination of Ampicillin (a-amino- benzyl penicillin) based on the spectrophotometric measurement a t 320 mp of a compound formed by acid degradation of the penicillin a t 75" C in the presence of buffer solution a t pH 5.2 and a trace of a copper salt. Results obtained on samples of Ampicillin, Ampicillin Trihydrate and Ampicillin Sodium show good agreement with those recorded by the cup-plate micro- biological method. FOLLOWING the isolation of the penicillin nucleus, 6-aminopenicillanic acid in 1959, several semi-synthetic penicillins with a wide range of antibacterial properties have become available in this country (Table I).SEMI-SYNTHETIC PENICILLINS Several methods have been published for the determination of these compounds. The British Pharmacopoeia monographs for Ampicillin and Ampicillin Trihydrate specify a pro- cedure based on the cleavage of the p-lactam ring to the corresponding penicilloic acid by controlled hydrolysis with standard alkali. This method is also included in the B.P. monographs for Cloxacillin Sodium and Methicillin Sodium, and in the B.P.C. monograph for Phenethicillin Potassium. The B.P. monographs for Cloxacillin Sodium and Methicillin Sodium also include additional assays based on chlorine and methoxyl determinations, respectively. An iodimetric assay procedure has been specified for Ampicillin Sodium B.P.Alternative methods have been examined in these laboratories with a view to establishing a routine general procedure that would be applicable to the assay of large numbers of samples and, if possible, specific for the intact penicillin molecule in the presence of 6-aminopenicillanic acid, side-chain compounds and the usual penicillin degradation products. The method selected for detailed study was that originally described by Herriottl and later modified by Stock2 and by H~lbrook.~ Herriott found that benzylpenicillin could be determined by acid degradation under controlled conditions of pH, time and temperature to a stable intermediate with an absorption maximum at 322 mp. Stock recognised this intermediate as the penicillenic acid, and showed that reproducible results could be obtained by incorporating trace amounts of a copper salt in the buffer solution.The method was further investigated by Holbrook and has been applied by Weaver and Reschke4 to the determination of Met hicillin Sodium. Our preliminary experiments indicated that an intact penicillin molecule was essential for this determination. No acid degradation products, as indicated by absorption maxima above 300 mp, were observed when solutions containing 6-aminopenicillanic acid side-chain compounds and penicilloic acids were subjected to acid treatment for prolonged times and at elevated temperatures. The method, therefore, appeared promising for the determination of the semi-synthetic penicillins. It was, however, realised that the experimental conditions described for benzylpenicillin and Methicillin might not be applicable to all of the compounds in Table I, in view of their different stability characteristics in acidic solution.It was clearly necessary to examine each penicillin individually to determine optimum assay conditions. This paper describes the work carried out in these laboratories to establish a suitable assay procedure for Ampicillin. METHOD REAGENTS- dilute to 1 litre. Copper sdphate solution-Dissolve 3.93 g of copper sulphate pentahydrate in water, and248 SMITH, DE GREY AND PATEL: SPECTROPHOTOMETRIC [Awlyst, Vol. 92 B?Jl$eer solution p H 5-2-Mix together 464 ml of 0-1 M citric acid solution and 536 ml of 0.2 M disodium hydrogen phosphate solution.Adjust the pH, if necessary, to 5-2 & 0.05 with the citric acid or disodium hydrogen phosphate solution. To 15 ml of the copper sulphate solution add the mixed buffer at pH 5.2 to a volume of 1 litre. (1 ml of this solution contains 15 pg of copper.) TABLE I SEMI-SYNTHETIC PENICILLINS /s\ RI-CO-NH-CH-CH C(CH,), I l l CO-N--CH. COOR, Compound R, Phenethicillin Potassium . . . . CGH5-0-CH- I CH, I Propicillin Potassium . . . . . . CGH5--O-CH- CH,-CH, Ampicillin . . . . . . .. C,H,-CH- I NH, I NH, I Ampicillin Trihydrate .. .. CCH5-CH- Ampicillin Sodium . . . . .. C,H,-CH- K H H.3H20 Na h T H ,OCJI, /cl /-L * . L/ Methiciliin Sodium . . . . \OCH, Cloxacillin Sodium . . . . . . ey--;- N C-CH, \o' Phenbenicillin Potassium . . . . C6H5-0-CH- I I< Na.H,O Na.H,O C,H5 PROCEDURE- Prepare a solution of the sample in distilled water at a concentration of about 1-0mg per ml of Ampicillin.Place 2.0 ml of this solution into a 100-ml calibrated flask and dilute to volunie with the pH 5.2 buffer solution. Transfer 10.0 ml of this solution to a calibrated test-tube, lightly stopper the tube and place in a thermostatically controlled bath at 75" C. After exactly 30 minutes, remove the tube from the bath and cool to room temperature in ice. If necessary, adjust the volume to 10.0 ml with water and determine the optical density at 320 mp in a 1-cm cell with the unheated buffered Ampicillin solution in the reference cell. Determine the Ampicillin concentrat ion of the original sample by reference to a calibration graph prepared by carrying out the above procedure on known dilutions of the standard Ampicillin preparation.EXPERIMENTAL A Hilger H999 Ultrascan recording spectrophotometei- was used for most of the experi- mental work described, and a Unicam SP500 instrument was used for measuring optical densities during subsequent routine assays. Unless otherwise stated, all experiments were performed on buffered solutions containing a nominal Ampicillin concentration of 20 pg per ml.April, 19671 DETERMINATION OF AMPICILLIN 249 WAVELENGTH OF MAXIMUM ABSORPTION- Under the specified conditions of assay, Ampicillin was found to develop an absorption maximum at 320 mp (Fig. 1 ) . Under other assay conditions studied, the wavelength was found to vary in the range 320 to 340mp. Wavelength, mp 0 10 20 30 40 50 60 Time, minutes Fig. 1.Ultraviolet absorption spectrum Fig. 2. Time of heating; pH 5-2, 15pg per ml of copper in buffer solution of degraded Ampicillin; pH 5 . 2 , temperature 75" C, 16 pg per ml of copper in buffer solution, 30 minutes' heating time TIME OF HEATING- Under the optimum conditions of pH , temperature, Ampicillin and copper concentration, the absorption at 320 mp increases with time to a maximum at 30 minutes (Fig. 2). During the following 40 minutes a t 75" C, it was found that the optical density decreased slowly at about 0.2 per cent. per minute. The solution held at room temperature after reaction for 30 minutes at 75" C was found to exhibit the same optical density for 1 hour. EFFECT OF pH ON ABSORPTION AT 320mp- The effect of pH on the absorption at 320 mp, at a temperature of 75" C, was examined with phosphate - citrate buffer solutions in the pH range 2-5 to 7-5.Copper sulphate reagent was added to all buffer solutions to produce a copper concentration of 15 pg per ml. The optimum pH of 5.2 was selected from these observations (Fig. 3). a o.lk 0 pH of buffer solution Fig. 3 , Effect of pH; 30 minutes' heating time 0.7 o . 6 1 5 10 15 20 25 30 Concentration of copper in pH 5.2 buffer, pg per mi Fig. 4. Copper concentration; temperature 75" C, 30 minutes' heating time EFFECT OF COPPER CONCENTRATION- the pH 5.2 buffer solution within the range 0 to 30pg per ml. of 15.0pg per ml in the buffer solution was selected. Fig. 4 illustrates the effect on the optical density of varying the copper concentration in A copper concentration250 SMITH, DE GREY AND PATEL: SPECTROPHOTOMETRIC [Analyst, Vol.92 0.6 - 0.5 - x 'j; 0.4 c -0 - - .g 0.3- 4-l 0" Temperature of heating, "C Fig. 5 . Effect of temperature EFFECT OF TEMPERATURE- The optimum temperature of 75" C was selected from a series of results obtained by heating a 20 pg per ml solution of Ampicillin at pH 5.2 for 30 minutes at temperatures in the range 50" to 100" C (Fig. 5). BEER'S LAW- Buffered solutions of the standard Ampicillin at a range of concentrations up to and including 50pg per ml were assayed by the specified procedure. Beer's law was obeyed over the range (Fig. 6). A working concentration of 20 pg per ml of Ampicillin in the buffer was selected for optimum sensitivity.Concentration of ampicillin, pg per ml Fig. 6. Beer's Law; pH 5.2, temperature 75" C, 15 p g per mlof copper in buffer solution, 30 minutes' heating time RESULTS Table I1 shows results obtained by the specified procedure on routine samples of Ampicillin, Ampicillin Trihydrate and Ampicillin Sodium. The results are expressed in terms of the free acid and are compared with those recorded by the quadruplicate (8 x 8 Latin square) cup-plate microbiological assays (B. Subtilis A.T.C.C. 6633 as assay organism) with fiducial limits of error (P = 0.95) estimated as k3 per cent. of the quoted average potencies.April, 19671 DETERMINATION OF AMPICILLIN 251 TABLE I1 COMPARISON OF SPECTROPHOTOMETRIC AND BIOLOGICAL ASSAYS Expressed as pg per mg of Ampicillin Compound Sample No.Spectrophotometric assay Bioassay -4mpicillin . . . . . . .. 1 964 961 2 967 960 3 958 962 4 976 971 5 978 970 6 978 990 Ampicillin Trihydrate . . . . 7 755 755 8 77s 773 9 811 815 10 814 s10 11 829 830 12 823 825 13 837 834 14 835 840 15 546 844 16 847 545 17 847 837 18 851 s45 Ampicillin Sodium . . . . . . 19 765 770 20 790 793 21 830 833 22 837 534 23 s52 857 24 S51 s44 The spectrophotometric assay results quoted in Table I1 represent the mean of duplicate A standard deviation of less than 1 per cent. was indicated. determinations. DISCUSSION The method described is considered to be the most specific at present available for the As no interference has been observed due to direct chemical determination of Ampicillin. 6-aminopenicillanic acid and a-aminobenzylpenicilloic acid, the structure R-CO-NH-CH-CH- I 1 CO-N- appears to be essential for the reaction to proceed.Thus the spectrophotometric method is clearly more specific than procedures based on the determination of either the p-lactam ring, e.g., alkaline or penicillinase de-activation, iodine absorption or hydroxamate colour formation, or the side-chain entity. The optimum assay conditions for Ampicillin, i.e., pH, temperature, time of heating and wavelength of measurement, differ somewhat from those specified in previous papers for benzylpenicillin and Methicillin Sodium (Table 111). TABLE I11 ASSAY CONDITIONS FOR AMPICILLIN, BENZYLPENICILLIN AND METHICILLIN Penicillin Wavelength, Temperature, heating, in buffer, Compound mtL PH "C minutes pg pcr ml Benzylpenicillin .. . . 322 4.6 100 15 40 to 50 Rlethicillin . . . . . . 330 3-8 70 30 10 Time of concentration Ampicillin . . .. . . 320 5.8 75 30 20 i.u. per ml ASSAY CONDITIONS FOR AMPICILLIN, BENZYLPENICILLIN AND METHICILLIN The optimum copper concentration in the pH 5.2 buffer for the Ampicillin assay (15.0 pug per ml) is considerably higher than that found by Stock2 for benzylpenicillin, i.e., 0.33 pg per ml. The effect of The importance of copper in the reaction has been confirmed.252 SMITH, DE GREY AND PATEL varying the copper concentration in the Methicillin Sodium assay was not reported by Weaver and Re~chke,~ but a figure of 0.5 pg per ml in the buffer solution was specified; in the absence of added copper, a lower absorptivity was obtained. The method is simple and accurate, and because of the stability at room temperature of the solution after reaction many samples can be assayed simultaneously. The procedure should be amenable to automation, and this aspect is currently being investigated, together with the possibility of extending the method to the assay of the other semi-synthetic penicillins listed in Table I. The procedure described for Ampicillin has been used in these laboratories for the routine assay of samples covering a wide potency range. The method has given satisfactory repro- ducibility and results have shown good agreement with those recorded by the cup-plate bioassay method. REFERENCES 1. 2 . 3. 4. Herriott, R. M., J . Biol. Chevn., 1946, 164, 725. Stock, F. G., Analyst, 1964, 79, 662. Holbrook, A., J . Phavn?. Pharmuc., 1958, 10, 762. Weaver, W. J., and Reschke, R. F., J . Plzarin. Sci., 1963, 52, 362. Received November 9th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200247

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, April, 1967, Vol. 92,pp. 253-256 253 An X-ray Spectrographic Method for Determining Barium BY S. A. PROKOPOVICH AND E. R. McCARTNEY (Department of Ceramic Engineering, School of Chemical Technology, The University of New South Wales, Kensington, N.S. W., Australia) An X-ray spectrographic method is described in which a Philips 50-kV universal X-ray spectrograph with a chromium tube is used for the quanti- tative trace analysis of barium in aqueous solutions. The method involves the use of the barium Lcc, line, and is suitable for concentrations of up to a t least 0.5 per cent. w/w of barium. A limit of detection of 0.002 per cent. w/w of barium is achieved. The extension of the method to the neighbouring elements in the periodic table is suggested. SEVERAL methods have been developed for the X-ray spectrographic analysis of barium in various systems.Davis and Van Nordstrandl have described the determination of barium, calcium and zinc in lubricating oils, Lewis and Goldberg2 have determined barium, titanium and zinc in sediments, Gulbransen3 has developed a procedure for the analysis of barium in barite ores, and Toussaint and VOS~ have used X-ray spectrometric determinations for barium in ion-exchange clay effluents. The purpose of the present work was to investigate yet another approach to the quantitative determination of barium with a view to lowering the practical limit of detect- ability, thus permitting the extension of the useful range of the trace analysis. The system of interest in this investigation was the filtrate, resulting from the hydrothermal formation of barium titanate, and consisting of the solution of barium hydroxide in water.The barium hydroxide solution is difficult to handle owing to the rapid absorption of carbon dioxide from air, and it was expected that the X-ray spectrographic analysis of the filtrate solutions, immediately acidified with the hydrochloric acid, would enable more convenient handling of the reaction filtrates and result in a considerable time saving. INSTRUMENTATION The equipment used in this work was a Philips 50-kV universal X-ray spectrograph provided with a pulse height discriminator. In the preliminary work, tungsten and chromium X-ray tubes were used in conjunction with the scintillation and flow proportional counters and lithium fluoride and pentaerythritol analysing crystals.However, the final combination and the operating conditions that were found to give the most satisfactory results are- X-ray tube . . .. Tube operated a t . . Analysing crystal. . . . Analytical line . . .. X-ray path . . . . Parallel blade collimator. . Counter . . . . .. Counting technique . . Pulse height discriminator .. . . Chromium .. . . 44kV, 22mA .. . . Lithium fluoride . . . . 480 p, 10 cm long .. . . Flow proportional .. . . BaL,,, 87.13" (28) .. . . Air . . . . Fixed count . . . . Adjusted to give maximum P/B ratio EXPERIMENTAL Preliminary work carried out with the scintillation counter, lithium fluoride crystal and tungsten indicated that the BaKcc, line is not a satisfactory choice owing to the very high background in this angular region, which results in a low peak-to-background ratio.The high background intensity encountered when analysing liquid specimens is caused by scatter- ing of the white continuum from the light elements of which most liquids consist. The pulse height discrimination for BaKg, was found to be ineffective, as scattered radiation from the tungsten tube is about the same wavelength as the line of interest.254 [Analyst, Vol. 92 The BaLs, line is, then, the logical choice because the background in this region is much lower, resulting in an increased P/B ratio. A flow proportional counter was selected for the analysis of BaLa, radiation (2.775 h;) as it is very sensitive to radiation softer than 2-3 A. The use of the chromium tube under these conditions resulted in the net intensity of the BaLa, line being about three times larger than for the tungsten tube at the same loading, and the peak height discriminator was found to be effective for both.Results with the pentaerythritol crystal were similar to those obtained when using lithium fluoride, with essentially the same P/B ratio. However, because of the temperature dependence of the pentaerythritol crystal and also because the full range of the data for it was not available, a lithium fluoride crystal was selected. PROKOPOVICH AND MCCARTNEY : AN X-RAY SPECTROGRAPHIC PROCEDURE- The Perspex cells for the analysis of liquids were made from standard Perspex sample bottles (l# inch in diameter), provided with tightly fitting polythene lids.The bottles were shortened to about 1; inch in height, and were provided with a supporting circular edge made of $-inch thick Perspex. New bottoms were glued on and holes, 1 inch in diameter, were cut in the polythene lids. The Mylar foil was placed on the top of the bottle, and the lid was slid over, thus forming a satisfactory seal. The reaction filtrate was found to contain no titanium; this permitted direct determina- tion of barium. A barium calibration graph was prepared by using barium hydroxide solutions containing fixed amounts of hydrochloric acid in a given volume. Standards were checked by chemical analysis. The ratio technique was used to take care of fluctuations of the instrument sensitivity that occurred over a period of time and that may have invalidated the calibration graph.For this purpose a solid reference sample was prepared by mixing the measured amount of the barium carbonate powder with boric acid and pressing the resultant mixture at 15 tons per sq. inch. The resultant pellet was sprayed with transparent lacquer known to contain no barium. Immediately the counting on the solution was completed, another count was carried out on the reference standard, BaLccRs. The correction for the background was made by counting the intensity of the scattered radiation at 87.13" (28) from distilled water containing the same amount of hydrochloric acid as the samples, This method allows some time saving because the counting on the unknown, the reference standard and the distilled water can be carried out at the same angular position without re-setting of the goniometer.The intensity ratios BaLM,/BaLa,,, where BaLa, is the net intensity from the solution, were plotted against the percentage of barium w/w. The resultant straight line was used as a calibration graph for the analysis of unknowns. This graph was found to pass through the origin, indicating a satisfactory estimation of the background intensity. Barium, per cent. w w Fig. 1. Effect of the target on the intensity of the barium La, line in aqueous solutions. Operating con- ditions are as given in Table IApril, 19673 METHOD FOR DETERMINING BARIUM 255 RESULTS AND DISCUSSION The results obtained for both tungsten and chromium tubes are plotted in Fig. 1. The range of concentrations studied extended to 0.5 per cent.w/w of barium; only part of these results are plotted in Fig. 1. A setting of 44 kV and 22 mA was selected as giving a high intensity, and at the same time being within the permissible loading for the tubes. The runs carried out at 40 kV and 20 mA resulted in slightly reduced P/B ratios. The graph indicates that the chromium tube is more efficient than the tungsten tube. The fact that the chromium tube gave the more satisfactory results is not unexpected. The chromium tube was especially developed for the analysis of elements lighter than chromium (KE, = 2.29OA). The increased intensities of the analytical lines of these elements are achieved, partly because of the location of the characteristic lines in respect to the absorption edges of these elements, but mainly because the combined energy reaching the sample is higher than, for example, that of the tungsten tube in this wavelength region. This is a consequence of the chromium tube having a thin window whose absorption is lower than that of the tungsten tube.I t therefore seemed likely that the chromium tube would be at least as efficient as tungsten for the excitation of the L spectrum of elements 38 to 57 in the periodic table, with LIII absorption edges extending from 6-39A for strontium, to 2-26A for lanthanum, It must be noted that some of the angles involved are very large and beyond the normal instrument range at present. The work reported here applies these ideas to the analysis for barium, and shows them to be valid. Of the targets tested, the chromium gave the lowest background intensity as this originates mostly from the continuum, and is therefore dependent on the atomic number of the target material.The use of a pulse height discriminator to improve the P/B ratio was found to be more effective for the tungsten tube. However, the final results obtained with the tungsten and the chromium tubes at the same operating conditions indicate that the chromium tube is superior because the net intensity of the BaLcc, line is increased by a factor of 3, and the P/B ratio by a factor of 2, in comparison with the tungsten tube. An attempt was made to use an asymmetrical setting of the channel height, as described by Dowling, Hendee, Kohlet and Parrish5; however, this did not improve the P/B ratio, indicating that the remain- ing wavelengths are close to the BaLa, radiation.For example, Friedman and Birks6 indicate that it is inadvisable to attempt to detect a line intensity of less than one-tenth of the background, that is, setting the limit of detectability as one-tenth of the background intensity. However, from the practical point of view, the definition given by Birks7 is more satisfactory. He defines the practical limit of sensitivity as the intensity of the line which exceeds the background by at least three standard deviations of the back- ground. Several definitions of the practical limit of detectability are available. In terms of the latter definition, the following sensitivities were obtained- Chromium tube operated at 44 kV and 22 mA-0.002 per cent. w/w of barium. Tungsten tube operated at 44 kV and 22 mA-0.004 per cent.w/w of barium. The use of a chromium tube in a given instrumental arrangement therefore doubled the sensitivity obtainable with a tungsten tube. It is not clear why the sensitivity obtained with a tungsten tube was not as high as that obtained under apparently similar conditions by Toussaint and VOS.~ When a more complicated matrix is encountered and interference from other elements is expected, resort may be made to the internal standard method which is well described by Adler and Alexrod.8 For barium, several investigators2 y 4 found lanthanum to be a satisfactory internal standard. CONCLUSION It has been established that, for the analysis of barium in solution, the use of the LEI line results in a much higher sensitivity than the use of the KE line. The advantage of using the LEI line was further enhanced by exciting the specimen with a chromium-target tube rather than a tungsten-target tube. A sensitivity of 0.002 per cent. w/w ol barium was achieved in standard X-ray spectrographic equipment. Changing the X-ray tube as a method of increasing the sensitivity is more convenient than, for example, the use of a helium atmosphere.256 1. 2. 3. 4. 5. 6. 7. 8. PROKOPOVICH AND MCCARTNEY REFERENCES Davis, E. N., and Van Nordstrand, R. A., Analyt. Chem., 1954, 26, 973. Lewis, G. J., jun., and Goldberg, E. D., Ibid., 1956, 28, 1282. Gulbransen, L. B., Ibid., 1955, 27, 1181. Toussaint, C. J. G., and Vos, G., Philips Sevv. Sci. Ind., 1964, 11, (6), 2. Dowling, P. H., Hendee, C. F., Kohler, T. R., and Parrish, W., Philips Tech. Rev., 1956/1957, Friedman, H., and Birks, L. S., Rev. Scient. Instrum., 1948, 19, 323. Birks, L. S., “X-ray Spectrochemical Analysis,” Interscience Publishers Inc., New York, 1959, Adler, I., and Alexrod, J. M., Spectrochim. Acta, 1955, 7, 91. 18, (9), 262. p. 54. Received May 23vd, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200253

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

Analyst, April, 1967, Vol. 92, p$. 257-259 257 The Loss of Elements during the Decomposition of Biological Materials with Special Reference to Arsenic, Sodium, Strontium and Zinc BY E. I. HAMILTON, MISS M. J. MINSK1 AND J. J. CLEARY (Radiological Protection Service, Clifton Avenue, Belmont, Sutton, Surrey) The problems encountered during dry ashing of biological materials are discussed, and an attempt has been made to show the variability of results quoted in the literature. Special reference has been made to sodium, arsenic, zinc and strontium, which have been incorporated into rat tissue by injection. These are representative of the various groups of elements when considering their stability towards heat. It is concluded that each biological sample must be treated individually when considering losses of elements during dry ashing.IT is accepted that, unless the appropriate precautions are taken, many elements are partially or totally lost during the decomposition of biological tissues. Although this subject has been studied in considerable detail, the results are inconclusive for losses incurred as a result of using dry-ashing procedures. In most instances negligible losses occur during wet ashing and this technique will not be discussed in this paper. The losses of elements when using dry-ashing procedures occur as a result of the following factors. MATRIX EFFECTS- In many instances the matrix of a sample influences the volatility of the various elements that are present in a variety of chemical forms. Gorsuchl used an inorganic matrix to which lead nitrate was added; the volatility of lead was enhanced by the presence of chloride ions, if converted to hydrogen chloride, but depressed by sodium phosphate.The influences of varying concentrations of chloride and phosphate ions are undoubtedly responsible for the differences in lead losses, as shown in Table I, for blood and bone. These pose the problems of losses from intermediate tissues such as connective tissue and cartilage, or from young bone, in which calcification is incomplete. TABLE I LOSSES OF LEAD AT DIFFERENT TEMPERATURES AS FOUND BY VARIOUS WORKERS Author Matrix Ashing temperature, "C Losses Losses for temperatures > 600" C Petrov and Cover2 . . Human bone Holtzman3 . . .. Human bone 900 None Hursh4 . . . . Human bone 900 None Hasson and Cherry5 .. Human blood 100 50 per cent. Hasson and Cherry5 . . Human blood 600 90 per cent. Animal bone } to 'O0 The addition of a carrier-free radioactive tracer is a method commonly used to determine chemical yields. For this method to be valid, the tracer must be mixed completely with the stable element at the start of the experiment, and both must be present in the same chemical form. For biological tissues, it is further required that the tracer is incorporated into the same structural position as the stable element. A comprehensive study by Gor- S U C ~ ~ , ~ , ~ was made on a matrix of cocoa. In our limited study we have injected sodium-22, zinc-65, arsenic-74 and strontium-85 into live rats so that, before sampling various organs, the radiotracer has become incorporated into the organic tissue matrix; this is considered to be closely related to true biological conditions.After ashing, the losses of these elements were compared with the losses of the same tracers that had been added to dry ox blood. Measurements were made by determining the total y-activity by scintillation counting of the dish before and after the ashing. The results are given in Table 11, in which losses are divided258 HAMILTON, MINSK1 AND CLEARY: LOSS OF ELEMENTS [A%a@t, Vol. 92 into two types: those occurring as a result of the retention of the radionuclide to the inner walls of the silica dishes during the ashing, and which could not be removed by washing with 6 M hydrochloric acid; and those caused by volatilisation that occurred during the ashing.560L 550 c 540 520 I 510 5301 2 500 490 x 480 + a c : 460 470 I\+- 450 I 1 I I I I I I I 0 10 1 Front Bac Position in furnace, inches Fig. 1. Relationship between temperature and position in a furnace as determined with standard sentinels ASHING TEMPERATURE- A general survey of the literaturel16,7,* would indicate a maximum temperature of 450" C to produce negligible losses for the majority of the elements, exceptions being com- pounds of arsenic, mercury and the halogens. The point that is not emphasised is that in a muffle furnace, with a thermocouple projecting 4 inches from the back of the oven, there is usually a considerable temperature gradient, as shown in Fig. 1, and although the thermo- couple may indicate 450" C, there could be a deviation of 50" C from the actual temperature at this setting.Some samples could, therefore, be at 500" C and losses would thus be increased. This problem has been investigated in this laboratory by using standard melting-point sentinels for five different melting-points between 420" and 900" C. At high temperatures the range becomes more pronounced, and at 900" C a difference of &200° C in some parts of the furnace is possible. TABLE I1 LOSSES OF VARIOUS ELEMENTS FROM DIFFERENT MATRIXES ASHED AT VARIOUS TEMPERATURES Loss, per cent. -7 Com- Tem- Byvola- By pound Radio- Condi- pers- tilisa- reten- used for nuclide Element tions* ture, "C tion tion Total test used Matrix Strontium . . 7 450 9 Slight 9 SrCl, Strontium-85 Dry ox blood Sodium . .I Blood 450 Slight Slight Slight Na,SO, Sodium-22 Dry ox blood Dry ox blood Arsenic-74 Dry ox blood Dry ox blood Dry ox blood Dry ox blood )Zinc-65 Dry ox blood Human blood Arsenic . . I spiked 450 28 0 28 Na3As0, 850 0 45 45 450 0 Slight - Rat-Bone 450 16 7 23 Strontium-85 Blood 1 cxternally 550 29 Slight 29 1 with 850 35 8 43 Zinc . . 1 radio- 450 0 Slight Slight ZnC1, I nuclide 550 0 5 5 ! J Kidney Rat-Bone Elood Kidney Rat-Bone 450 Slight 6 8 Sodium-22 Blood J I Slight 0 0 Kidney I Slight 0 Slight SrC1, I Rats 5 Slight 5 )- with 450 86 0 86 49 Na3As04 1 Arscnic-74 44 5 i Strontium.. Arscnic . . 1 injected Sodium . . I nuclides 0 0 0 Na,SO, I radio- 82 Slight 82 J * The samples were ashed for 16 hours in Vitreosil dishes. All results are to within f5 per cent.April, 19671 DURING THE DECOMPOSITION OF BIOLOGICAL MATERIALS 259 MATERIAL OF VESSELS USED FOR ASHING- If chemical or physical reaction is likely to occur between the sample and the material of the vessel during various stages of decomposition, then losses of some elements are to be expected.Magnesium, copper and zinc are lost to the walls of porcelain or silica dishes as a result of chemical reaction at the surface, while gold and lead can be readily deposited or absorbed on to platinum surfaces.l~ The age and previous use of a dish has to be considered; a new silica dish tends to retain some elements (q., zinc) more readily than a well used dish.lS8 LITHIUM TETRABORATE FUSION METHOD- In X-ray fluorescence analysis, matrix problems can often be reduced by the distribution of a small aliquot of the sample into a large volume of material with a homogeneous matrix.Lithium tetraborateg is commonly used, and as the technique requires at least two periods of heating to about 1100” C, it is conceivable that some elements will be at least partially lost by volatilisation from the borate melt. Losses occurring as a result of volatilisation and reten- tion by the dish were determined as before by using sodium, zinc, arsenic and barium radio- active tracers. The results given in Table I11 show that the losses of the selected elements are surprisingly small. TABLE I11 LOSSES OF RADIONUCLIDES ON FUSION WITH LITHIUM TETRABORATE Volatilisation losses Retention losses & -- Mean, Mean, Total losses, Radionuclides per cent.Range per cent. Range per cent. Arsenic-74 . . . . 6 4 to 7 9 3 to 16 15 9 Barium-133 . . .. 9 5 to 17 0 Sodium-22 . . * . 1 1 to 5 0 - Slight Zinc-65 . . .. .. 2 2 to 3 0 - Slight - LOW TEMPERATURE ASHERS- A low temperature asher,1° such as that supplied by Tracerlab, produces a gaseous plasma by applying radio-frequency voltage to a copper coil surrounding a vacuum chamber in which the sample is placed in an atmosphere of oxygen. Oxygen at low pressures is produced in highly excited states and reacts with the sample, and oxidises at low temperatures of about 100” C. Although low and consistent volatilisation losses have been reported for some seventeen elements, the studies have been limited to a matrix of dry ox blood. From this brief survey of problems encountered when dry ashing biological samples, it is obviously essential to treat each type of sample individually. It is not advisable to accept losses for a particular element that have been obtained on a significantly different matrix. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. REFERENCES Gorsuch, T. T., Analyst, 1959, 84, 135. Petrov, H. G., and Cover, A., Analyt. Chem., 1965, 37 (13), 1659. Holtzman, R., Hlth Phys., 1965, 11 (6), 477. Hursh, J., Science, 1960, 132, 1666. Hasson, V., and Cherry, R. D., Nature, 1966, 210 (5036), 591. Gorsuch, T. T., Analyst, 1960, 85, 225. -, Ibid., 1962, 87, 112. -, i n Kolthoff, I. M., and Elving, P. J., Editors, “Treatise on Analytical Chemistry,” Interscience Publishers, New York and London, 1965, Volume 12, Part 11, p. 295. Glaisse, F., Quebec Department of Mines, P.R. 327, 1956. Gleit, C. E., and Holland, W. E., Analyt. Chem., 1962, 34, 1454. Received September 8th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200257

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

260 Analyst, April, 1967, Vol. 92, Pp. 260-263 Determination of Arsenic by the Uranyl Salt Method Part II.* The Radiometric Determination of Microgram Aniounts of Arsenic by a Filter-spot Technique BY A. D. WILSON AND D. T. LEWIS (Ministry of Technology, Laboratory of the Government Chemist, Cornwall House, Stamford Street, London, S.E. I) A development of the uranyl salt method for the gravimetric deter- mination of arsenic is described. Gravimetric manipulations are conducted on a filter-paper base and the arsenic content of the ammonium uranyl arsenate precipitate is determined indirectly by measuring the alpha count- rate of the associated uranium. The method has been demonstrated to be applicable in the range 1 to 8 p g of arsenic. THE use of uranyl salt as a precipitant for arsenic(V) has been reported by Pullar,l and Lewis and Davies., As the ammonium uranyl arsenate precipitate is bulky and gelatinous, rendering filtration difficult, Wilson and Lewis3 prefer precipitation from homogeneous solution, which yields a compact coarsely crystalline material.Following the collection of arsenic from solution as ammonium uranyl arsenate the determination may be completed by a titrimetric or gravimetric procedure. The weighing forms of the precipitate on ignition have been discussed by Wilson and LewisJ3 who have established that the method is capable of a high degree of accuracy. In applying this method to the quantitative determination of microgram amounts of arsenic by spot analysis on filter-paper, an alternative finish based on the radioactive properties of uranium is now proposed.Arsenite must initially be oxidised to arsenate with bromine. Precipitation is carried out at the centre of a filter-paper and excess of uranyl salt reagent is removed to a peripheral zone by washing, an operation conveniently carried out by the use of a Weiss ring oven. After removal of the filter-paper by ignition, the uranium content of the precipitate is determined by alpha counting and will be proportional to the count- rate, provided the material is dispersed in a thin layer so that no self-absorption occurs. As the chemical composition of the precipitate may be represented by the formula, NH,.UO,.AsO,.nH,O, so that arsenic is equivalent to uranium, the arsenic content of the precipitate can be calculated.Such a calculation is independent of the subsequent thermal history of the precipitate, for, provided uranium is not lost the exact composition is of no consequence. Because the relationship between the alpha count-rate and the uranium content of the precipitate is dependent on the specific disintegration rate of the uranium source used, it follows that the sensitivity of the method is a function of isotopic composition. The specific disintegration rates of various uranium sources differ considerably; natural uranium con- taining the alpha-emitting radioisotopes uranium-238, uranium-235 and uranium-234, exhibits a rate of 2.504 x lo4 disintegrations per second per gram. As the corresponding figure for pure uranium-235, 7.89 x 104, is 3.15 times greater, the use of a uranium source enriched with this isotope will increase the sensitivity of the method up to this limit.However, such sources are not generally available ; most commercially available uranium salts are derived from the residues of isotopic separation plants and are of diminished activity compared with natural uranium. In the present work the uranium source used had a specific disintegration rate of 2-326 x 104 disintegrations per second per gram, i.e., 0.930 of that of natural uranium. The sensitivity of the method is also dependent on the efficiency of the counter, but it is not necessary to determine experimentally either this factor or the specific disintegration rate of the particular uranium source used. Provided a pre-calibration is made of the alpha count-rate associated with a given amount of arsenic by using known * For details of Part I of this series, see reference list, p.263.WILSON AND LEWIS 261 equivalent amounts of uranium, any subsequent analysis for arsenic may be interpolated within these values. The uranium used must, of course, be derived from the identical source with that used in the preparation of the precipitant; other experimental conditions must also remain unchanged. This procedure was adopted in the work now described. The method rests on the basic assumption that the activity of the uranium source remains unchanged over the experimental period and this is clearly so when natural uranium is used. The method is also valid for any isotopic mixture of uranium-238, uranium-235 and uranium-234 as these are all long-lived, and although they yield radioactive decay pro- ducts, the first alpha-emitting daughter in each chain is also long-lived and will therefore not grow to significant proportions for a century or so.METHOD REAGENTS- acetate and 2 ml of acetic acid in 100 ml of water. acetate and 8 ml of acetic acid in 100 ml of water. acid in 100ml of water. Uranyl salt @reci@itad (1)-Prepare a solution of 2 g of uranyl acetate, 2 g of ammonium Uranyl salt precipitant (2)-Prepare a solution of 8 g of uranyl acetate, 8 g of ammonium Wash solution (A)-Prepare a solution of 0.5 g of ammonium acetate and 0.5 ml of acetic Wash solution (B)-Prepare a solution of 0.5 ml of acetic acid in 100 ml of water. Standard uranium solution for alpha counter calibration-Dissolve 0.1873 g of tri-uranium octoxide (derived from the uranyl acetate used in preparing the precipitating reagent) in a little nitric acid and remove the excess of acid by gentle evaporation to dryness.Dissolve the residue in water and dilute to 50ml exactly. 1 pl of solution = 3.746 pg of tri-uranium octoxidz (= 1-0 pg of arsenic). PROCEDURE- Preparation of a calibration graph-By clsing a Hamilton pipette (0 to 10 pl) transfer measured amounts of the standard uranidm solution, in the range 0 to 8 p1, to separate 1-4-cm diameter circles of Schleicher and Schiill 58g2 filter-paper. Allow to dry and add about equivalent amounts of arsenic(II1) solution. (This addition is made to simulate those counting conditions that will exist during an actual determination of arsenic by this method, and to correct for any minor differences in count-rate that the presence of arsenic may induce.) Allow the filter-paper to dry over bromine water vapour and expose to ammonia fumes.Place the paper disc at the centre of an aluminium 2-inch alpha counting Equivalent arsenic (asAs),yg 2 4 6 0 I I I I ! 1 1 6 1 Fig. 1. Calibration of an alpha counter with uranium reagent262 WILSON AND LEWIS: DETERMINATION OF ARSENIC [Analyst, Vol. 92 planchet. Cool, moisten with 1 drop of 0.1 per cent. Teepol and spread the ignited material around the centre of the planchet with a glass rod to ensure that the precipitate is dispersed evenly in a thin layer so as to avoid self-absorption. Wash down the rod with one or two drops of water.Evaporate to dryness and re-ignite. Transfer to an alpha counter. From the known weights of uranium applied to each disc, and by using the relationship of uranium equivalent to arsenic, calculate the theoretical concentration of arsenic. Plot these values against the alpha count-rate, less the background. Detemination-By using a Hamilton pipette (0 to 10 1.1) transfer not more than 2 pl of solution to the centre of a Schleicher and Schiill No. 58g2 filter-paper, 5.5 cm in diameter. Allow the spot to dry over bromine water vapour. Add 5 pl of precipitant solution; for amounts of arsenic not exceeding 4 pg, use solution (l), and for amounts in the range 4 to 8 pg, use solution (2). Place the filter-paper in a Weiss ring oven and wash the precipitate four times with wash solution ( A ) and four times with wash solution (B), by using 0-02 to 0.03 ml of wash solution each time.Punch out the centre of the filter-paper containing tlie washed precipitate with a cork borer (diameter 1.4 cm). Place this disc at the centre of an aluminium 2-inch alpha counting planchet and ignite at 600" C. Cool it and moisten the residue with 1 drop of 0.1 per cent. Teepol; spread the ignited material evenly around the centre of the planchet with a glass rod and wash down the rod with one or two drops of water. Evaporate to dryness and re-ignite. Cool, transfer the planchet to an alpha counter and estimate the alpha count-rate. Read the arsenic content from the calibration graph and subtract from this value that of the blank obtained by using reagents only in the procedure.Ignite at 6OOOC and carefully remove it from the furnace. A linear calibration graph should be obtained, as shown in Fig. 1. For routine determinations a convenient period is lo4 seconds. RESULTS AND DISCUSSION An automatic alpha counter (supplied by Isotopic Development Limited) of about 30 per cent. efficiency was used throughout this work and calibrated with known amounts of uranium derived from the same source as the uranyl salt used in the precipitant solution. Values obtained over the entire working range of 0 to 30.0 pg of tri-uranium octoxide (equivalent to 0 to 8.0pg of arsenic) were represented graphically after subtraction of the background TABLE I DETERMINATION OF ARSENIC BY THE PROPOSED METHOD Alpha count Arsenic added, Pg 8.0 8.0 8.0 4-0 4.0 4-0 2.0 2.0 2.0 2.0 2-0 2.0 1.0 1.0 0.2 0.2 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 Precipitant Total count (observed) 5080 5260 1279 2364 4478 1218 304 1373 2229 644 1310 1499 645 769 506 181 85 227 30 177 618 180 298 109 108 158 Time, lo4 seconds 4 4 1 4 7 2 1 4 6 2 4 6 4 4 7 3 3 6 1 3 7 3 3 2 2 2 Count per lo4 seconds 1270 1315 1279 59 1 640 609 304 343 37 1 322 327 250 161 192 72 60 Arsenic found, Pg 8-2 8.5 8.2 3.8 3.9 3.7 1.9 2.1 2.1 2.0 2.0 1.5 0.9 1.1 0.3 0.2 Background 32 for precipitant (1) 593 67 I Background 60 ' Error + 0.2 + 0.5 + 0.2 -- 0.2 -0.1 - 0.3 -0.1 +0.1 t o .1 0.0 0.0 - 0.5 -0-1 + 0.1 +0*1 + 0.0 - .-April, 19671 BY THE URANYL SALT METHOD. PART I1 263 count. The best straight line was drawn through the plotted points (Fig.1) and a factor of 1.00 pg of arsenic (equivalent to 147 alpha counts per lo4 seconds) was obtained. To confirm that there was no possibility of self-absorption within this working range, the cali- bration was checked at a point well above it (equivalent to 50 pg of arsenic). A factor of 1.OOpg of arsenic (equivalent to 150 alpha counts per lo4 seconds) was obtained, the agreement between these two factors confirming the linearity of the calibration graph. The behaviour of the method with solutions containing known amounts of arsenic is illustrated by the results presented in Table I. Inspection of this table reveals that the method has been demonstrated to be applicable in the range 1 to 8 pg of arsenic, as at lower levels (0-2 pg of arsenic) relative error is considerable. The total analytical error associated with a determination by the proposed method is composed of manipulative error and the random error inherent in the statistics of alpha-particle counting. At an arsenic level of 0-2 pg of arsenic the count-rate is low and, in addition, only about twice that caused by the reagent blank. As the variance of counting errors is the sum of sample and blank variances, the counting error is considerable. The method can only be expected to be approximate at the low level (0.2 pg of arsenic). Gutzeit’s well known chemical method is usually used in the range 5 to 10 pg of arsenic, with an estimated error of 10 per cent.4 REFERENCES 1. 2. 3. *Wilson, A. D., and Lewis, D. T., Analyst, 1963, 88, 510. 4. Pullar, R. E. O., 2. analyt. Chem., 1871, 10, 72. Lewis, D. T., and Davies, V. E., J . Chem. SOC., 1939, 284. Kodama, K., “Methods of Quantitative Inorganic Analysis,” Interscience Publishers, a division Received May 9th, 1966 of John Wiley and Sons Inc., New York and London, 1963, p. 194. * The paper referred to may be taken as Part I of this series.

ISSN:0003-2654    

DOI:10.1039/AN9679200260

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年代:1967

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264 Analyst, April, 1967, Vol. 92,pp. 264-267 Direct Injection Enthalpimetry in the Routine Determination of the Hydroxyl Value of Alkylphenols BY F. L. SNELSON, W. R. ELLIS AND J. VILKAULS (Shell Chemicals U. K. Ltd., Laboratory Department, Stanlow Refinery, Ellesrnere Port, Wirral, Cheshire) A thermometric method in which the heat of reaction is used as a quantitative measure of the hydroxyl value of alkylphenols is in routine use. This method has replaced a lengthy acetylation procedure that necessitated measuring the difference between two titrations. By catalysing the acetylation reaction with perchloric acid and then measuring the temperature rise resulting from the heat of reaction, a method has been developed that takes less than 5 minutes to carry out. Standardiss- tion of reagents is unnecessary and only one volumetric measurement is important to the result.The advantages of this method are simplicity and speed, and also a repeatability equal to that of time consuming conventional titration techniques. IN the manufacture of alkylphenols the measurement of the hydroxyl value is an important control analysis which is required at various times during the 24 hours of the day. It is, therefore, desirable to have a simple and fast method of analysis that can be used on the plant by plant-operating personnel. The laboratory method in use was based on the acetylation of the hydroxyl group with an excess of acetic anhydride and the subsequent hydration of the excess with water. The acetic acid produced was then titrated with standardised sodium hydroxide.A blank deter- mination carried out without sample gave the total amount of acetic anhydride available for the reaction, and the difference between the blank and sample titrations was proportional to the hydroxyl value of the sample. This whole procedure took 2 to 2; hours (elapsed time) and required a certain amount of analytical skill for good precision to be achieved. Recently, Wasilewski, Pei and Jordan1 showed that various analyses, i.e., EDTA titra- tions, acid - alkali titrations and anionic - cationic detergent titrations, could be carried out by using direct injection enthalpimetry. This same principle has been applied to the hydroxy-acetylation reaction. EXPERIMENTAL The heat produced by a chemical process is a quantitative property proportional to the number of molecules of product formed by the reaction.Under conditions of constant heat capacity this heat of reaction can be measured as a change in temperature, AT. If the reaction is rapid and stoicheiometric, and if the amount of one of the reactants is constant and in excess, the measured temperature change, on adding a standard amount of one reactant, is proportional to the concentration of the second reactant. APPARATUS- To establish the principle of the method, a simple apparatus was made from readily available components. As previously mentioned, AT should be measured under conditions of constant heat capacity, and in the laboratory this condition was most readily achieved by standardising the reaction vessel and stirring conditions by using fixed volumes of reagent and sample, and insulating the reaction vessel effectively from its surroundings.The change in temperature, AT, was detected by a thermistor sensing element situated in the reaction vessel and connected as one arm of a Wheatstone bridge. Out-of-balance signals across the bridge were measured by a standard Sunvic, potentiometric, strip chart recorder with a sensitivity of 50-mV full-scale deflection. Fig. 1 shows the reaction cell, and a schematic wiring diagram of the simple circuit is illustrated in Fig. 2.SNELSON, ELLIS AND VILKAUh 265 G \ A = 50-ml Tall beaker D = Reagent inlet B = Sample and suction probe inlet E = +-inch Perspex C = Thermistor sensor F = Foam plastic insulation G = Magnetic stirrer Fig. 1.Direct injection enthalpimetric reaction cell The resistance of the thermistor (a Stantel F2311/30C) was about 2000 ohms at ambient temperature, and its rate of change with temperature was 43 ohms per “C. Hence, with a %volt supply to the bridge, a 1” C change in temperature produced an out-of-balance signal of about 20 mV (equivalent to 40 per cent. of the recorder response or 100-mm deflection). The routine plant instrument was designed for simplicity of operation and to minimise operator variability. The reagent is introduced by a “Zipette” manually operated dispenser, and the sample is injected into the magnetically stirred reaction cell with a Struer automatic dispenser (obtainable from H. Struers Chemiske Laboratorium, Copenhagen, Denmark). The cell is emptied by suction through a water-pump operated probe.In laboratory models of the instrument the reagent may be dispensed with pipettes and the sample by a hand-operated 1-ml hypodermic syringe. THE APPLICATION OF DIRECT INJECTION ENTHALPIMETRY TO THE DETERMINATION OF HYDROXYL For direct injection enthalpimetry to be applied successfully to the determination of hydroxyl value, it was necessary to accelerate the reaction so that it became almost instan- taneous. The use of perchloric acid2 as a catalyst for the acetylation produced a reaction that was both rapid and stoicheiometric. VALUE- Battery R,, R, and R, = 1500-ohm Resistors Battery = Two Mallory cells RM- Rv = 1000-ohm 10-turn Vari- 42, each 1.35 volt RT = Stantel thermistor able resistor F23 I I /30C Fig. 2.Schematic wiring diagram of thermistor bridge266 -l? ' 8 - d SNELSON et d.: DIRECT INJECTION ENTHALPIMETRY I N [Lt?$a&st, Vol. 92 - A y l p h e n c l 2-Pro~an-2-01 E 2000 Dodecanol U U E A Phenol To test the validity of the method, the temperature rise caused by the acylation, as indicated by the recorder deflection in millimetres (equivalent to AT), was measured for a variety of commercially available alcohols and phenols. A regression curve of the results is shown in Fig. 3 where millimetres deflection per gram of sample is plotted against hydroxyl value. The results show a significant correlation between hydroxyl values and AT measure- ments, although individual calibration would be necessary for different compounds. Because pure alkylphenols of high molecular weight were not available as calibration standards for the particular analysis which it was desired to standardise, it was decided to calibrate the apparatus by using actual samples for which average hydroxyl values had been determined by repeated analyses with traditional methods.The resultant calibration graph covering the range of hydroxyl values of 1.5 to 2.4 milli-equivalents per gram was linear with respect to recorder response. Extrapolated line Recorder response, mm Fig. 4. Typical enthalpigram PROCEDURE- It can be seen from the enthalpigram shown in Fig. 4 that the recorder deflection is measured from the injection point to the point of intersection of the main rise and the extrapolation of the steady-state temperature line. The peak that occurs above this inter- section is caused by a transient heating of the thermistor probe as a result of a brief period of incomplete mixing.April, 19671 ROUTINE DETERMINATION OF HYDROXYL VALUE OF ALKYLPHENOLS 267 The method, which has been in routine use on the plant for 12 months, is briefly outlined as follows.Rinse the reaction vessel with acetylating reagent, empty it and transfer into it 20 in1 of the acetylating reagent. Balance the bridge with the variable potentiometer. Inject 1 ml of the sample into the reaction vessel, and measure the deflection of the recorder in millimetres. Read from the calibration graph the hydroxyl value corresponding to this deflection. (Measurement of the deflection and the calibration reading can be combined by calibrating a ruler in hydroxyl values.) The acetylating reagent is made up by mixing together 720 ml of ethyl acetate, 120 nil of acetic anhydride and 4 ml of perchloric acid (sp.gr.1.70). The mixture should be allowed to stand for 24 hours before use. RESULTS The repeatability of the method (2 standard deviations) was determined (see Table I) and was found to be 0.07 absolute or 3.6 per cent. relative, which is better than that achieved when using the traditional method. TABLE I COMPARISON OF REPEATABILITY Sample B Sample A Direct injection Traditional method enthalpimetric method 1.82 1-92 1.80 1.93 1-83 1.94 1-81 1-91 1.73 1.93 1.88 1.92 1.92 1-88 1-84 1.92 1.90 1.89 1.88 1.90 1.82 1.89 1.81 1-89 1-79 1.93 1.77 1.93 1-78 1.93 1.81 1.92 1-78 2.00 1.77 1.98 1-75 1.99 1-79 1.99 Repeatability Repeatability Mean value 1.82 2 standard deviations 0.10 Mean value 1.93 2 standard deviations 0.07 DISCUSSION Direct injection enthalpimetry has simplified the analysis as follows.The acetylating reagent is present in considerable excess and therefore does not require standardisation. Only reasonable care is required in the measurement of the 20 ml of reagent, to achieve the constant heat capacity conditions necessary for the AT measurement. The only volumetric measurement critical to the analysis is the 1 ml of sample. This was achieved by using an automatic dispenser or a l-ml hypodermic syringe used with care. A permanent record of the AT deflection is obtained on a recorder chart, and this can be measured easily with a ruler calibrated in millimetres or, if desired, in hydroxyl values. The reaction vessel does not require cleaning between tests. A suction probe connected t o a water pump is adequate to remove the reactants after each analysis. The reaction vessel is rinsed with reagent and sucked dry immediately before an analysis. An approximate but consistent strength is all that is required. The analysis is completed in less than 5 minutes. REFERENCES 1. 2. Wasilewski, J. C., Pei, P. T. S., and Jordan, J., Analyt. Chew., 1964, 36, 2131. Stelzler, R. S., and Smullin, C. F., Ibzd., 1962, 34, 194. Received May 13th, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200264

出版商:RSC    

年代:1967

数据来源: RSC

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268 Analyst, April, 1967, Vol. 92, p p . 268-270 A Note on the Determination of Vapour-Liquid Equilibrium for Multi-component Systems BY K. A. PIKE AND D. C. FRESHWATER (Imperial Smelting Co. Ltd., Avonmouth) (Loughborough University of Technology, Loughborough, Leicestershire) The use of a gas chromatograph connected to a data-logging system is described for analysing samples taken in the determination of ternary vapour - liquid equilibria. Data are produced in a form that is ready for processing by digital computer, and therefore their accuracy may be determined within a short time of sampling. There is a distinct improvement in the accuracy of the method over more traditional methods for ternary system analysis. ONE of the major hindrances to experimental investigation of the vapour - liquid equilibrium of multi-component systems is the time-consuming and usually tedious analysis of experi- mental samples.Many of these difficulties disappear if gas - liquid chromatography is used, but by itself this is still a lengthy technique for the many samples that have to be examined. However, we have developed a method that not only reduces the time of operation to a minimum but also gives the actual composition results directly from the detector output. These results can also be produced in a one-step operation from sample injection, in a form suitable for immediate processing by digital computer. The method has been developed for a three-component system which was of particular interest for other purp0ses.l The method can be easily adapted to analyse four or more components.The main components of the equipment used are shown in the form of a flow-chart (Fig. l).. The data-logging system is multi-purpose and is used for recording experimental results in the Chemical Engineering Laboratories of Loughborough University of Technology. ANALYSIS PROCEDURE A = Air supply t o combustion chamber B = Carrier gas supply, 75 per cent. hydrogen and 25 per cent. nitro- gen (as recommended by Shandon Scientific Co. Ltd.) C = Sample introduction point D = Thermocouple E = Combustion chamber F = Jet G = Chromatograph column H = Output from thermocouple t o I = Sunvic recorder J = Signal voltage t o data-logging system K = Data-logging system L = Data scanner unit M = Digital voltmeter N = Paper tape punch recorder Fig. 1.Flow-chart of analytical equipmentPIKE AND FRESHWATER 269 The gas-liquid chromatograph used was a Shandon universal model with a flame thermocouple detector. The chromatograph column (20 feet x $ inch, external diameter) was packed with Celite, and diglycerol was used as the stationary liquid phase. This column was maintained at 100" C. The detector output was fed simultaneously to a chart recorder and also the data-logging system. At the conditions chosen, samples of the system, acetone - methanol - isopropyl alcohol, which were to be analysed, gave three well separated peaks on the recorder chart. The areas of these peaks were measured by recording several peak height values, read at regular time intervals and then performing an integration to obtain the area. A trans- mitting potentiometer was incorporated in the chart recorder, which enabled the alterations in the thermocouple output to be read and then recorded by the data-logging system.The peak height was recorded at precise 1-second intervals by the data-logging system. Each peak had a duration of about 100 seconds, and considerably more readings for each peak were obtained to ensure that the whole peak was sampled. Peak areas were obtained by integrating the precisely recorded peak heights by using a form of Simpson's rule- h h h f (4 dx = 3 (Yo + 4% + YZ) + 3 (9% + 4y3 + y4) + 3 (y4 + 4y5 + y6) + error function (1) (where h = increment 1 second, and y = peak height above base-line), which gives- h f (x) dx = 3 (yo + 4y1 + 2y2 + 4y3 + 2y4) + error function .. By sampling the peak height above a base-line, which is calculated for each peak in turn, the method allows for the slight drift of base-line that can occur when using an amplifier over an extended period. For the type of peak obtained with the signal voltage equal to the base-line voltage immediately before and after a peak, the first and last terms of equation (2) tended to zero and were neglected. The error function was also negligible for the size of increment being considered. The peak areas so obtained were normalised by using heats of combustion, with methanol being considered as the basic component. The normalised peak areas were then converted into mole fractions of the components present. All of the computations necessary to produce an analysis result were carried out by a digital computer programme compiled in Fortran for the I.B.M.1620 data processing system. Other functions of the programme were to compare an analysis result with previously defined accuracy limits. If the results were of the required accuracy a data tape was compiled for use in other programmes. Data of insufficient accuracy were simply printed out and not punched out as a data-source tape. When operating the analysis procedure for the systems composed of acetone - methanol - isopropyl alcohol, it was necessary to accumulate a number of vapour - liquid equilibrium samples that required analysing to make optimum use of the system. The peak height information was then accumulated as a continuous reel of paper tape that could be stored until processing time was available on the digital computer.The processing time for the longest reel of data containing some thirty ternary analyses was about 20 minutes. The same programme as that used for ternary samples was also used for binary samples. This was possible because the programme would integrate the signal voltage Less the base-line voltage for a period where a peak should have occurred and obtain an area of zero, as during this period the base-line voltage was equal to the signal voltage. ACCURACY OF THE METHOD- Besides the distinct advantage of the convenience of the method over more traditional techniques, there are significant improvements in other directions. With the physical property measurement technique for a ternary system, Jones2 has quoted an accuracy of analysis of k0.2 per cent., while the procedure outlined here has an accuracy of better than k0.1 mole per cent.This is a small but significant improvement when considering vapour - liquid equilibrium results. The gas - liquid chromatograph was calibrated with standard samples made up by weight to the fourth decimal place, the total weight of a sample being about log. In the event of a contaminant entering the system, which is unlikely in a vapour - liquid equilibrium study where very high purity components are required, the digital computer270 PIKE AND FRESHWATER programme would identify the whole analysis result as being of insufficient accuracy for further processing. Again in a vapour - liquid equilibrium study this would not be too serious as the experimental point could be repeated.OTHER APPLICATIONS- In addition to its use for analysing complex multi-component mixtures, gas - liquid chromatography can be used to obtain, by direct measurement, activity coefficients under conditions tending towards infinite dilution. The method depends upon obtaining retention volume data, which, in turn, require the determination of retention times. Retention times are variously defined as being the time taken from actual sample injection to the emergence of the maximum peak height, or as the time between emergence of an inert-gas peak and the emergence of the maximum peak height. A feature of the analysis procedure described in this paper is that the emergence of peaks can be accurately recorded to small time intervals. Thus the timing operation for retention volume determination can be carried out auto- matically and to a high degree of accuracy. The technique could also be used advantageously linked to an equilibrium still along the lines of the suggestion by Wichterle and HAk3 Resides providing analyses of a high accuracy, the continuous analysis of the mixture could be used to ensure that equilibrium between liquid and vapour phases was being achieved. REFERENCES 1. 2. Jones, T. H., Ph.D. Thesis, University o f Birmingham, 1962. 3. Pike, K. A., Ph.D. Thesis, Loughborough University of Technology, 1965. Wichterle, I., and HAlB, E., Ind. Engng Chew. Fundamentals, 1963, 2, 155. Received Augztst lst, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200268

出版商:RSC    

年代:1967

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Analyst, April, 1967, Vol. 92, pp. 271-272 271 The Preparation of Analysis Samples of Hard Materials with a Boron Carbide Mortar BY J. F. BOULTON AND R. P. EARDLEY (British Ceramic Research Association, Queens Road, Penkhull, Stoke-on-Trent) Boron carbide has advantages as a grinding medium for hard ceramic materials. Owing to its hardness the contamination is slight and does not interfere with the normal chemical analysis. Contamination that occurs when grinding fused alumina, sillimanite, silicon carbide and magnesite has been determined by a spectrometric method. The degree of contamination introduced by the boron carbide appears to be an order of magnitude lower than when a 95 per cent. alumina mortar is used. THE analysis of harder ceramic materials is usually complicated by the problem of preparing a pure powdered sample, as severe contamination must be experienced if the sample is ground in agate (as much as 5 per cent.of silicon dioxide for a sample of corundum). The usual technique is to prepare two samples, one ground in alumina and the other in iron. The analysis is carried out on the iron-ground sample, the true iron content being determined on the alumina-ground sample. With the purer and harder materials this correction is not usually sufficiently stringent, as the alloy content of the iron and the minor constituents of the alumina become significant, and therefore two full analyses are required. Even then the analyst has to accept the assumption that the minimum content of impurity determined is that of the pure sample. Boron carbide mortars have been available for some time from American sources, but prototype production in this country led to the experiments to be described. Boron carbide is extremely pure, and contributes to the material two elements that are not usually deter- mined in the analysis, do not interfere with the normal analytical method, and are easily determined.EXPERIMENTAL Samples of 0.5 g of the materials of interest were ground in a boron carbide mortar of 2 inches diameter for varying periods of time from 5 to 30 minutes. The samples obtained were analysed by using a direct-reading spectrometric powder technique with dilutions of boron carbide in the base material as standards. When the original material was too coarse to allow adequate mixing of the standards, the latter were ground in an alumina mortar and the degree of contamination evaluated.The materials examined and the results obtained are shown in Table I. To aid comparison with other methods of grinding, some samples were ground in an alumina mortar known to have contents of about 0.8 per cent. of chromium trioxide and 4 per cent. of silicon dioxide. The chromium was a useful monitor for determining the contamination of the coarse alumina grain by this mortar, and the results obtained are shown in the fourth column. The result for magnesite was determined directly, and that for the sillimanite could easily be in error owing to the high (0.03 per cent.) content of chromium trioxide of this material. Comparative results were not attempted for silicon carbide because of the risk of serious damage to the mortar, and because it was not thought that this would be attempted in practice.It should be noted that the results for a 30-minute grinding are really only of theoretical interest, as all of the samples were reduced to a satisfactory degree of fineness after grinding for 10 to 15 minutes As this grinding was accomplished with a pestle roughly fashioned from a piece of stock rod, it is fair to conclude that this period could be reduced by the use of a pestle of profile matched with that of the mortar. A larger mortar would have been useful in that it would allow the preparation of sample increments larger than 0-5 g. It was found that boron carbide powder was readily decomposed by the fluxes used in routine analysis, such as sodium carbonate and the mixture with boric acid.The use of sorbitol or glycerol272 BOULTON AND EARDLEY [Aizalyst, Vol. 92 as a complexing agent should remove risk of interference with the silicon determination. The extent of contamination should be easily determined, if not by direct-reading spectro- metry, then either by emission spectrography or colorimetric methods. TABLE I CONTAMINATION INTRODUCED BY GRINDING IN BORON CARBIDE Alumina produced by grinding in an Boron carbide alumina mortar Grinding time, introduced, (for comparison), Material ground minutes per cent. per cent. Alumina powder, less than 80 B.S. mesh . . Alumina grain, about & inch diameter Silicon carbide, less than 80 B.S. mesh . . . . Sillimanite, about + inch diameter . . .. 5 0.13 10 0.10 15 0.18 30 0.16 15 0.18 5 0.45 10 0.65 15 0.70 30 0.55 5 0.03 15 0.04 30 0.05 hfagnesite, dead-burnt, less than 80 B.S. mesh 15 <0*01 30 0.01 - 5 about 0.25 - 0.4 - CONCLUSION Boron carbide is a useful mortar material for the preparation of hard ceramic samples. The degree of contamination is low, easy to determine, and should have little effect on the normal analysis. Increase in the capacity of the mortar should make it more generally useful, and improvement in the profile of the pestle should make it more efficient. The authors thank the Carborundum Co. Ltd. for making the prototype mortar available for these experiments, and the Director of Research, Dr. N. F. Astbury, for permission to publish this work. Received Octobev 3rd, 1966

ISSN:0003-2654    

DOI:10.1039/AN9679200271

出版商:RSC    

年代:1967

数据来源: RSC

摘要:

April, 19671 BOOK REVIEWS 273 Book Reviews KIRK-OTHMER ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY. Volume 9. FERRO-ELECTRICS TO FOAMS. Edited by HERMAN F. MARK, JOHN J. MCKETTA, jun., DONALD F. OTHMER and ANTHONY STANDEN. Second Edition. Pp. xvi + 901. New York, London and Sydney: John Wiley & Sons Inc. 1966. Price Ll6 18s.; price per volume for subscribers to the complete set of 18 volumes k13. This, the ninth volume of this series, corresponds with the half-way point in its publication (see Analyst, 1963, 88, 899 et seq.). Statistically, this means about 8200 pages, and almost six letters of the alphabet in three years. It is interesting to note that the subject matter of chemical technology falls chiefly in the first quarter of the alphabetical sequence. Over one-third of the present volume, i.e., 341 pages, is taken up with the treatment of fluorine the element, inorganic fluorine compounds and organic fluorine compounds, under these three separate headings.Of this total, 159 pages deal with inorganic fluorine compounds, which in itself is a significant reflection of the importance of this element in modern chemical technology. Sub- stances dealt with in some detail include aluminium trifluoride, which is used in the electrolytic process for refining aluminium; cryolite, which can be a natural or synthetic product these days, and in this connection i t is important to note that different methods of analysis apply accordingly; boron trifluoride, which is a catalyst, and whose manufacture and analytical methods are described ; and fluorobordtes (used as a flux, for grinding and in electroplating), which also present certain analytical problems, but can be precipitated quantitatively as nitron fluoroborate.Another interesting analytical problem is raised by chlorine trifluoride, which reacts violently and incon- sistently with water. This precludes the classical chemical methods for determining chlorine, but physical methods depending on freezing-point depression, infrared absorption or gas chromato- graphy have been suggested with more satisfactory results. As might be expected there are sections dealing with the toxicity of the various fluorine compounds, and also with the often specialised and difficult problems of handling and transport. The class of organic fluorine compounds (described collectively as “fluorochemicals”) is regarded as of sufficient importance to justify an historical introduction, which is followed by a detailed treatment of the surface chemistry of these compounds.This leads to a theory of adhesive action, which is also invoked to explain adhesion, i.e., release properties. This part of the subject is treated on a theoretical basis, and will be of value to those interested in adhesives as distinct from fluorine compounds as such. The numerous other usual and unusual technological applica- tions of organic fluorine compounds include the surface treatment of textiles, the separation of olefins by preferential reaction, the eradication of lampreys from lakes, uses in inhalant anaesthetics, and (for the inert compounds) in gaseous dielectrics. In addition there is, of course, the wide range of polymers based, for instance, on polytetrafluoroethylene; and the manufacture of a wide range of solvents. It is not difficult, therefore, to justify the large proportion of this volume devoted to this element of many derivatives and applications, and indeed the monograph is probably unique in its coverage.Many of the other monographs in this volume, although shorter, are of equal importance although in a more restricted sense. Perhaps the most outstanding are those dealing with man-made fibres (20 pages) and vegetable fibres (15 pages). Closely allied to the latter subject, and conveniently near it alphabetically, is the monograph on film materials (24 pages); and this in turn links up with the monograph on film deposition techniques, a short but informative account of the more important methods now being employed.The monograph on vegetable fibres has as its author D. Himmelfarb, of the Boston Naval Shipyard, and its contents may be described as of a textbook nature supplemented by some statistical data. As is to be expected, the bias of the monograph is towards uses as cordage and textiles rather than for other purposes, such as papermaking pulp. There is a useful table of properties, but it is remarkable that a monograph on this subject should make no reference, either in the text or pictorially, to appearance under the microscope. The monograph on man-made fibres is by H. F. Mark (of the Polytechnic Institute of Brooklyn) and S. M. Atlas. The first part is also descriptive and of a textbook nature, but Professor Mark’s views (well known to his colleagues in this field) on the future of such fibres are set out in the second half of the monograph, and make interesting and stimulating reading.The production of conjugate fibres (which is based on the principle of the use of two polymers having sufficiently similar characteristics to make spinning them into bi-component fibres a possibility) is an example.274 BOOK REVIEWS [A~talyst, Vol. 92 The monograph finishes with a section on research possibilities in connection with the fully synthetic fibres, e.g., polyesters; this continues the theme of future developments. There is nothing of analyti- cal interest in this monograph, but it will serve nevertheless as a valuable contribution to the general knowledge of any chemist on this subject.The monograph on films (described as a flat section of thermoplastic resin or regenerated cellulose material) deals with a wide variety of familiar (and some unfamiliar) materials, including the fluorochemicals already mentioned. In this connection the term “Cellophane” is used in such a way as to give the impression that it is a generic description of regenerated cellulose of the rayon type, and not the product of a particular company. It is also stated that it burns a t a rate similar to that of newsprint, which may be accurate in theory in view of its cellulosic com- position, but is hardly so in practice because of the presence of additives such as plasticisers. Another important monograph is that on fertilisers (126 pages).As its author points out, this industry is in a phase of rapid change. It is no longer an industry concerned primarily with the mixing and handling of materials, but is a major division of the chemical industry and it is becoming more and more based on chemical engineering technology. The increasing world-wide pressure of population and the necessity to find food to sustain it will undoubtedly accentuate this trend. The monograph deals with the various types of fertilisers and methods of winning, handling and processing them both from a practical and an economic point of view. There is also a section on evaluation, although the subject is dealt with more from the point of view of the chemical constituents than that of chemical analysis.Individual fertilisers are then discussed, and there is a special and interesting reference to micro-nutrients, the term used to describe certain inorganic compounds that sometimes have spectacular effects on the efficiency of fertilisers containing them. It is interesting to note that the greatest consumption of any one micro-nutrient in the United States in 1962 to 1963, was that of zinc sulphate, and this totalled only about 6000 tons; so that the use of the prefix “micro” in this connection is fully justified. Another monograph of special interest to analysts is perhaps that on flavour characterisation (11 pages). As it happens, this is followed by the monograph on flavours and spices. The former difficult subject is dealt with from the point of view of isolating the volatile flavouring compounds from certain solid foods, followed by their fractionation and chemical identification.Gas chromatography, infrared spectrophoto- metry and mass spectrometry all play an important part in this work, which can be applied to fruits of all kinds, beverages, meats, dairy products, spices, fats, oils, vegetables and starch products. The procedure, therefore, is quite distinct from organoleptic evaluation, although the two methods should be used together rather than independently; and there is a cross-reference to a monograph to come on organoleptic testing. The remainder of the monographs in this volume likely to be of interest to the analyst can be mentioned only by name. They include fire-resistant textiles, fish, filtration, flotation and foams ; for the more mechanically minded there are fluid mechanics, fluidisation and ferro-electrics.It will be seen that the half-way milestone in the publication of this work fully maintains the high standard of its predecessors. JULIUS GRANT HANDBUCH FUR DAS EISENH~~TTENLABORATORIUM. BAND 2. DIE UNTERSUCHUNG DER METAL- LISCHEN STOFFE. Edited by CHEMIKERAUSCHUSS DES VEREINS DEUTSCHER EISENHUTTEL- LEUTE. Pp. xxiv + 441. Verlag Stahleisen mbH: Dusseldorf. 1966. Price DM 88. This is the second edition of Volume 11, Analysis of Metallic Materials, of the comprehensive “Handbook for the Iron and Steel Works Laboratory” issued by the V.d. E-h (the other volumes being I-Analysis of Non-metallic Materials, 111-Sampling, and IV-Referee Methods).The first edition appeared in 1941 after a delay due, said the editors with remarkable restraint, “to the political developments of the last two years.” Difficulties of the post-war years have likewise delayed the second edition, but the delay has made it possible to include recent developments such as the application of X-ray fluorescence to the analysis of steel and ferro-alloys. After a general introduction and a section on reagents, a chapter is devoted to methods for removing large amounts of iron, chromium and other elements from solution; this includes a useful account of the application of mercury-cathode electrolysis. The longest section (150 pages) is on the determination of alloying elements and residuals, including gases, in iron and steel. Although anyone who wants to determine beryllium, thorium or uranium will have to refer to the first edition, it is hard to think of anything else even rarely addcd to steel which is not covered here.For most elements alternative methods are given.April, 19671 BOOK REVIEWS 275 The next hundred pages on the analysis of ferro-alloys provide the best treatment of the subject I have seen. Methods are given not only for the main elements in all of the most important ferro- alloys (including some that are often omitted, such as ferro-phosphorus), but also for impurities that are of increasing interest to the steel maker today. Under ferro-tungsten, for example, we have methods for determining C, Si, Mn, P, S, Al, As, Cr, Cu, Mo, Ni and Sn. Ferro-niobium - tantalum is fully dealt with, although sulphurous hydrolysis as a method of obtaining mixed oxides should now be scrapped.Anyone interested in the analysis of tungsten metal will want to know more than the iron and oxygen contents. There is a brief section on the analysis of hard metals. Perhaps no other technique offers quite the same combination of benefits and headaches as X-ray fluorescence. This must be the first work of its kind to devote more space (39 pages) to X-ray fluorescence than to emission spectrography ; the possibilities are indicated, and 119 references are given to papers on the subject. Sections on micro-chemical analysis and identification of structural constituents follow, and a full treatment of the analysis of metal coatings is given.There is a detailed list of contents and a full index. The book is excellently printed on high quality paper and strongly bound, and is worth ,@ to anyone who can make full use of it. G. M. HOLMES QUALITATIVE ORGANIC ANALYSIS. Second Edition. By B. HAYNES. London, Melbourne and As long as examining bodies continue to rely on the identification of organic compounds as a basis for assessing ability in practical organic chemistry, there will remain a need for books of this kind. Much care and thought has been given t o the writing of this manual, which can be thoroughly recommended. The importance of a thorough preliminary examination and the necessity for a logical collation of all the observations are well stressed. The student who uses this book intelligently will soon realise that functional tests, valuable as they are, cannot be regarded as the organic chemist’s equivalent of the inorganic group tables.In this way, he will avoid the pitfalls that frequently arise from hasty or haphazard use of functional or specific tests, or even through a cursory scanning of a table of melting-points. The various types of compounds are grouped into eight sections, with the corresponding generic tests for the different types in the relevant chapters. A table giving the characteristic ultraviolet and infrared absorption frequencies of the principal organic functional groups (e.g., carbonyl, ethylenic) could well have been included in this part of the book. The preparation of appropriate derivatives is dealt with in a separate chapter, which is followed by a comprehensive table of melting- (or boiling) points of compounds and their derivatives. The instructions for carrying out the tests are clear and unambiguous, while the hazards involved in certain laboratory manipulations are duly emphasised. Finally, as is most desirable in a laboratory manual, the book is clearly printed on high quality paper, and is very good value for money.Toronto: Macmillan, incorporating Cleaver-Hume Press. 1966. Price 25s. I;. G. ANGELL PROGRAMMED TEMPERATURE GAS CHROMATOGRAPHY. Pp. xvi + 305. By WALTER E. HARRIS and HENRY W. New York, London and Sydney: John Wiley and Sons Inc. Gas chromatography must rank as one of the most significant developments that has ever occurred in analytical science, and in the course of its widespread application to the problems of chemical manufacture it has inevitably encountered mixtures of components with a wide range of boiling-points.Columns operating a t a fixed temperature cannot deal conveniently with mixtures of this kind, and the device of raising the column temperature during separation, so as to speed up the higher boiling components, was an obvious step. Programmed temperature gas chromatography, as this is called, has been used empirically on many occasions, and so successful has it been that freedom to vary column temperature is now a most important factor in comparing the merits of commercial instruments. Walter E. Harris, Professor of Analytical Chemisty in the University of Alberta, and Henry W. Habgood, Chief of the Fuels Branch of the Research Council of Alberta, have collaborated since 1958 in developing the theoretical treatment of programmed temperature gas chromatography, and in the book that they have published jointly they have attempted to give a unified and HABGOOD.1966. Price 83s.276 BOOK REVIEWS [Analyst, Vol. 92 consistent presentation of the theoretical equations that have been produced, both by themselves and by other workers in the same field. Retention temperature is presented as the most important parameter in programmed tempera- ture gas chromatography, and the first four chapters of the book contain a detailed and mathe- matical treatment of the theory of retention, leading to the development of characteristic equations from which the retention temperature can be calculated for any component of a mixture, provided that one knows the isothermal retention volumes of that component over a range of temperatures on a column containing the same stationary phase; the fifth chapter deals with the factors affecting resolution of components having similar retention temperature, and the sixth with the use of reten- tion indices as a method of identifying unknown cornFonents.In the last three chapters, the authors turn to the practical application of these theoretical equations and to the apparatus required for programmed temperature gas chromatography, and they conclude with a section on preparative and pyrolysis gas - liquid chromatography carried out under programmed temperature conditions. The book is not, therefore, an exclusively theoretical treatise, and the later chapters on practical aspects will undoubtedly be of value to everyone concerned with the use of programmed temperature gas chromatography : nevertheless, it must be recognised that the real challenge is presented by the mathematical treatment given in the first part, and it is the challenge of the theoretical approach compared with the instinctive, experimental approach to a problem that is adopted by most commercial analysts.While countless problems have been solved by the empirical method, a fundamental understanding of the separation process must be beneficial, and may well become the preferred method of attack in the future. Many will find this book rather tough going, but those who do are recommended, in the preface, to read the easy parts first and come back to the more difficult ones later.This, one feels, is good advice, and if it is heeded it should enable all concerned in the field of gas - liquid chromatography, expert and novice alike, to benefit from the painstaking labour of these two authors. The book is clearly printed, well bound and apparently free from tyFographica1 mistakes ; each chapter is neatly summarised, and both subject and authors indexes are included. 13. E. STAGG POLAROGRAPHY 1964. PROCEEDINGS OF THE THIRD INTERNATIONAL COKGRESS, SOUTHAMPTON. Volumes 1 and 2. Edited by GRAHAM J. HILLS, Ph.D., D.Sc., F.R.I.C. Pp. xxviii + 685 (Volume 1 ) ; xxviii + 687-1164 (Volume 2). London and Melbourne: Macmillan. 1966. Price Ll5 15s. per set. These two volumes are a record of the Third International Congress of Po!arogi-aphy held in Southampton, under the auspices of the Polarographic Society.The 89 papers presented were grouped into five main categories: Theory, Methods and Instrumentation ; the Analysis of Inorganic Systems ; the Analysis of Organic Systems ; the Analysis of Biological Systems; and the Study of Non-aqueous Systems. Professor Kolthoff gave a classical account ol the iunda- mentals of organic polarography in inert organic solvents, and a lucid picturc of the current trends in organic polarography was provided by Dr. Zuman. Electrochemical methods for determining the kinetics of fast electrode processes was the subject of Fleischman’s paper, while Barker des- cribed the study of fast electrode processes by non-linear relaxation techniques.A brave attempt t o introduce a new and confusing electrochemical terminology was made by Milazzo with his paper “Temperature Coefficients of the Electrode Tension of Individual Electrodes.” In the final introductory lecture, Breyer described some practical applications of a.c. polarograpliy. A large proportion of the papers either describe or have some bearing on analytical methods. In view, however, of the increasing application of polarographic methods, particularly in the field of rapid automated analysis, many of the more theoretical contributions, especially those dealing with the r81e of the various factors that influence the electrode process, also have some practical importance. Although it is invidious to pick out a single contribution, the excellent paper by Fisher, Relew and Kelley, in which recent advances in d.c.polarography are described, is a very valuable and readable treatment of the subject. It is evident that these proceedings cover the whole spectrum of polarograpliic and related techniques. This fact, together with the large number of references quoted, makes it a valuable reference book. Although the price is rather high, the book can be recommended to all those wishing to keep abreast of developments in this field. Six principal lectures were given. B. FLEETApril, 19671 BOOK REVIEWS 277 ADVANCES IN X-RAY ANALYSIS. Edited by GAVIN R. MALLETT, MARIE FAY and WILLIAM M. MUELLEK. Proceedings of the Fourteenth Annual Conference on Applications of X-Ray Analysis.August 25-27, 1965. Pp. x + 544. New York: Plenum Press. 1966. Pricc $22.50. This volume contains 46 of the papers presented a t the Denver Conference on the Applications of X-Ray Analysis, held in August, 1965, and they are arranged in the now familiar format. Aspects of a wide range of subjects are considered, including electron-probe microanalysis, uses of soft X-rays in emission analysis, X-ray diffraction and fluorescence analysis. Several papers on X-ray diffraction topograpy are included. A group of 8 papers on the effects of chemical combination on X-ray spectra and on X-ray absorption fine structure, together with a record of an open discussion a t the Conference on the first of these topics, will be of special interest to chemists. These papers show clearly that, in addition to its use in determining the elemental composition of a sample, X-ray spectrochemical analysis can be used to investigate bonding.Significant effects are detected in K and L spectra of elements of low atomic number arising from changes in the state of bonding, and results are reported for silicon, boron, carbon, nitrogen, chlorine and sulphur. Reviving interest in high intensity, rotating-anode X-ray tubes is reflected in a paper describing a de-mountable tube dissipating 7a kW. The publishers have maintained their good standard of production and the time that has elapsed between conference presentation and publication is again relatively short. The work is recommended for Chose whose interests lie in X-ray analysis. Volume 9.E. A. KELLETT ELECTRONIC ELECTROCHEMICAL MEASURING INSTRUMENTS. By D. DOBOS. Translated by T. DAMOKOS and 2. ERDOKUKTY. Pp. 449. Budapest: Akadbmiai Kiad6. 1966. Price 105s. It is intended primarily for those who use electronic instruments in the chemical field. There must be many who require a book on basic electronic principles with the emphasis on electrochemistry rather than com- munications, and in the choice and arrangement of the subject matter this book should be well suited to fill that need. It starts with sections on the construction and properties of the various components used, and proceeds to basic circuit configurations: amplifiers, stabilisers, oscillators, etc., followed by sections on the principles of electrochemical measurements. Unfortunately, it falls far short of the standard of clarity and orderly presentation of informa- tion that is so essential in an introductory work.It seems likely that this is due largely to inadequate translation; much of the English is clumsy, explanations are often devious where they should be concise and clear, and various words and phrases appear which are certainly not in common use. Difficulties of this sort are bound to arise when translating into a foreign language, but much of it could have been avoided had the proof bcen checked by an Englishman with even a superficial knowledge of the subject. He might also have noticed some of the printing errors, which are quite numerous, and corrected the author’s few mistakes, such as the parallel connection of stabilisers in Fig.160, which is quite impracticable. It is a pity that the publishers who have produced a very attractive volume in layout, printing and illustrations do not seem to have taken this step. There is a large section occupying nearly half the book in which commercially available instruments are described in detail. The instruments are selected from many European countries, including a fair proportion from Britain. The information appears to be drawn mainly from manufacturers’ instruction manuals which are usually only available to purchasers, rather than from sales literature. In some cases it is quoted in extreme detail, including full circuit diagrams, component schedules, operating instructions and fault finding procedure. All of the instruments are illustrated.Including nearly 60 pH meters and titrators, also 14 conductance meters and instruments for high frequency measurements, polarography and coulometry, this section provides the reader with an opportunity to compare instruments from many countries on the basis of much more detailed information than he could hope to acquire himself. In this lies the chief value of the book; the reader seeking instruction in basic electronics would do better to look elsewhere. This is an English edition of a work first published in Hungary. Continental symbols are used in circuit diagrams throughout the book. There is an extensive international bibliography classified by subject. G. Ross TAYLOR27 8 BOOK REVIEWS [Analyst, Vol. 92 PROGRESS IN NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY.Volume I. Edited by J. W. EMSLEY, J. FEENEY and L. H. SUTCLIFFE. Pp. viii + 386. Oxford, London, Edinburgh, New York, Toronto, Sydney, Paris and Braunschweig : Pergamon Press. 1966. Price 105s. Should nuclear magnetic resonance be new to any reader of this journal, it is best stated early that n.m.r. is predominantly a technique for the analytical chemist. I use the word technique carefully, for the progress reported in this volume is largely progress i n techniques. This is the first of two volumes. The editors point out on the dust jacket that the first volume is concerned with basic theory and spectral analysis, and the second with the correlation of spectral parameters with molecular structure. It is also noted that the two volumes have been written as a single entity, with extensive cross-referencing.Volume 1 of this new series contains four chapters and is best judged, initially, by considering them separately. Dr. Haworth and Professor Richard’s chapter on the use of modulation in magnetic resonance gives a clear understanding of this technique and is applicable to both nuclear magnetic and electron paramagnetic resonance. The theory of modulation is considered in some detail, and this chapter will be of interest and of practical use to all radio-frequency and microwave spectroscopists. In order not to mislead the reader, I should point out that this chapter forms only a very small part of the book, although its size in no way detracts from its quality. Chapter 2 is concerned with high resolution nuclear magnetic double and multiple resonance and explains how these techniques lead to more powerful methods of obtaining additional informa- tion in the interpretation of the single resonance spectrum.Many practical examples of double resonance experiments are given, and instrumentation is dealt with very clearly. 0 ther sections cover the theory and applications of the technique. The glossary, appendices and references are extremely comprehensive. Since the acceptance of computer techniques to facilitate identification of spectra there has been a need for a review which could fully explain and exploit this, and which is also understandable to the non-computer expert. This review achieves many of these requirements. The approach is clear and systematic, and the references are good. The four appendices are particularly useful, and include problems dealt with by various computer programmes, a complete sample problem, and, particularly useful to the non-specialist, a good explanation of computer terminology. Chapter 4 deals with the progress achieved in the n.m.r. field on phosphorus compounds with special emphasis on organic compounds. A comprehensive account is given of the information derived from the resonance spectra of proton, fluorine and other nuclei, with the exception of phosphorus-31. From an exhaustive literature survey, all of the significant features have been well tabulated and a complete formula index is givcn. Besides providing bibliographical information to those concerned with the structural chemistry of phosphorus, a rationalisation of available data is also given, in relation to molecular features. This book will be very useful to n.m.r. specialists, and comes a t a time when there is need for full coverage of this rapidly expanding branch of chemistry. This particular volume, I might ven- ture to add, by the nature of its contents relating to techniques, is equally applicable to those concerned with the sister subject to n.m.r., namely, electron spin resonance. The complete volume has a good index, is extremely well bound, has clear print and is easy to read. The price of this book is L5 5s., which I think is rather a high price to pay to keep abreast of new developments. This should not stop readers from buying a copy. The third chapter deals with computer techniques in the analysis of n.m.r. spectra. Typographical errors are a t a minimum. H. M. ASSENHEIM

ISSN:0003-2654    

DOI:10.1039/AN9679200273

出版商:RSC    

年代:1967

数据来源: RSC