摘要:

512 Analyst, July, 1973, Vol. 98, pp. 512-519 Pyridylazonaphthols (PANs) and Pyridylazophenols (PAPs) as Analytical Reagents Part 111." Formation of Copper(I1) Complexes and Their Determination in Alloys BY D. BETTERIDGE, D. JOHN? AND F. SNAPES (Chemistry Department, University College of Swansea, Swansea, Glamorgan, SA2 8PP) The reactions between copper(I1) and 2-(2-pyridylazo)-l-naplitliol (o-a-PAN) and 4- (2-pyridy1azo)phenol (p-PAP) have been studied by spectro- photometry and graphical analysis, and their equilibrium constants have been determined. A rapid and simple method for the spectrophotometric determination of copper in aluminium alloys has been devised. A solution of the alloy with pH 2 is extracted with an equal volume of a 5 x M solution of o-a-PAN in carbon tetrachloride and the absorbance of the extract is measured a t 590nm.The method has been checked by the analysis of standard alloys. The effect of interferences is discussed. The extraction behaviour of several cations with o-a-PAN is discussed and the sequential separation of copper(II), zinc(II), manganese(I1) and lead(I1) is outlined. IN Part I1 of this series1 and in unpublished studies (D. Betteridge and H. Freiser), the chelates of manganese(II), zinc(I1) and lanthanum(II1) with PANs and PAPs were considered. In this paper, the study of the chelates of copper(I1) with 2-(2-pyridylazo)-l-naphthol (0-a-PAN) and 4-(2-pyridylazo)phenol ($-PAP) is reported. The results provide guidance on the optimum use of these reagents and show that o-a-PAN can be used for the rapid.selective spectrophotometric determination of copper in aluminium alloys. EXPERIMENTAL SOLUTIONS- Copper(I1) solutions were prepared and standardised with EDTA. The buffer solution used in the solvent-extraction procedure had a pH of 2.05 and was prepared by diluting 25 ml of 0.2 M potassium chloride solution plus 26 ml of 0.2 M hydrochloric acid to 100 ml with de-ionised water. APPARATUS- The apparatus used was identical with that described previous1y.l PROCEDURES- Spectrophotometric determination of formation constants-The methods used were identical with those described previously.1 Absorbance curves of the chelates of o-a-PAN and p-PAP were obtained. Absorbance measurements were made at 546 and 580 nm for the p-PAP and o-a-PAN chelates, respectively.Solvent extraction-The procedure used was identical with that described previously.1 For extraction of the o-a-PAN chelate, the spectrophotometer was set at 590 nm. A calibra- tion graph of absorbance versus copper(I1) concentration in parts per million was also obtained by this method. Pyeparation of samples of alloys for analysis-The alloy was dissolved in a 1 + 1 mixture of 8 M nitric acid and 6 M hydrochloric acid (40 ml). The acidic solution was added dropwise because of the vigorous reaction. When all of the acid had been added, the solution was boiled for 1 hour so as to ensure complete dissolution of the alloy and to remove the oxides of nitrogen. Other solutions were prepared as described previous1y.l Duplicate results were obtained in all instances.* For particulars of Part I1 of this series, see reference list, p. 519. t Present address : BP Chemicals (U.K.) Ltd., Llandarcy, Swansea. $ Present address: Bausch and Lomb Co. Ltd., Toronto, Canada. 0 SAC and the authors. For Part IV of this series, see p. 520.BETTERIDGE, JOHN AND SNAPE 513 Determination of copper in alzmzinium alloys-Adjust the pH of an aliquot of the alloy solution containing 0.4 to 4 p.p.m. of copper(I1) to approximately 2. Add an aliquot of buffer of pH 2. Add a sufficient amount of a 5 x M solution of o-a-PAN in carbon tetrachloride so that the volumes of the aqueous and organic phases are equal and are convenient for manipulation. Extract the mixture for a fixed period of time (to be deter- mined by the operator, as described below), and, after the extraction is completed and the layers have separated, measure the absorbance of the organic phase a t 590nm against a blank of o-a-PAN solution.THEORETICAL COPPER(II) - o-a-PAN SYSTEM IN THE PRESENCE OF EXCESS OF REAGENT- The absorbance curve is shown in Fig. 1. The magnitude of the absorbances suggest that in the lower pH range a 1 : 1 chelate is formed, whereas a 1 :2 chelate is formed in the higher pH range. The Sornmer method as outlined in Part I1 of this series1 is used to confirm or disprove these postulates. 0.9 0.8 0.7 0.6 A Q 8 0.5 Y I= m 0.4 a 0.3 0.2 0.1 a 9 ~ - - - - - - - - - I / I I 1 I I I I 1 I 0 I 2 3 4 5 6 7 8 9 1 0 PH Fig. 1. Absorbance zlevsus pH for the copper - o-a-PAN system in the presence of excess of reagent Lower p H range-The formation of a 1 : 1 chelate is suggested according to the following reaction scheme : *KCuR Cu2+ + HR + CUR+ + H+ where rHRl rHRl and the symbols used are as defined previous1y.I514 BETTERIDGE, JOHN AND SNAPE : PYRIDYLAZONAPHTHOLS AND [Analyst, Vol. 98 Therefore, _ - 1 - 1 1 - - 1 a1 h'aL A =z [CUR] .. .. The total absorbance, A , is given by and the total metal-ion concentration, Ccu, by so that . . .. - (2) Ccu == [CU] + [CUR] . . .. .. .. * (3) From equations (l), (2) and (4) it can be shown that and that Higher PH range-For the formation of a 1 : 2 chelate, it is postulated that Cu2+ + 2HR + CUR, + 2H+ The algebra used is the same as that derived for the zinc(I1) and manganese(I1) chelates in the previous paper,l i.e., transformation IV.[HI2 .. .. (7) C R 1 1 -- - -__ A - E c m , + * ~ c u R , c C u R , CL and If the reactions postulated are correct, these functions should give straight-line graphs that yield values for the molar absorptivity and the stability constants. COPPER - @PAP SYSTEM- In this instance, the possibilities of the formation of a 1 : 1 or a 1 : 2 complex in the presence of excess of either metal ions or of reagent must be considered. It was found, by working through the algebra and plotting the experi- The absorbance curves are shown in Fig. 2. 6-0 7.0 8.0 9.0 10.0 11.0 PH Fig. 2. Absorbance vewws pH for copper - fi-PAP systems : (A) in the presence of excess of reagent; and (B) in the presence of excess of metal ionsJuly, 19731 PYRIDYLAZOPHENOLS AS ANALYTICAL REAGENTS.PART I11 515 mental results for the transformations, that the 1 : 2 complex was not formed in the presence of excess of metal ions. Excess of metal ions-1 : 1 complex-The proposed chelation reaction is Cu2+ + R- + OH- + CuROH i.e., only R- reacts as indicated by the maximum formation of the chelate at high pH values. It is also assumed that only HR and R- species are present in significant concentrations. [CUROH] 1 [RI [CuI[OHl KC~ROH = The total metal-ion concentration is given by The total absorbance, A , is given by The total reagent concentration, CR, isgiven by [CU] = ccu A = ER[R] + EHR[HR] + ECuROH[CuROH] CR = [R] + [HR] + [CUROH] = [CUROH] + [RI (1 + [H]/Ka,) By utilising the same type of algebraic manipulations as described previously, it is possible to obtain the following equations : .... * (9) -- CR - - 1 Ay - C R (ER + EHR[H]/Ka2) A - ECUROH + A[OH]KCuROHCCuECuROH where and Excess of reagent--l : 1 complex-The proposed reaction is The total metal-ion concentration, Ccu, is given by The total absorbance, A , is given by It can be shown that Cu2+ + R- + OH- + CuROH Ccu = [CU] + [CUROH] A = EC~ROH [CUROH] and Excess of reagent-1 : 2 complex-The proposed chelation reaction is As before, it can be shown that Cu2+ + 2R- + CUR, and Again, graphs of equations (9) to (14) should yield straight lines if the reactions postulated are correct.516 BETTERIDGE, JOHN AND SNAPE : PYRIDYLAZONAPHTHOLS AND [Arta@d, VOl. 98 RESULTS AND DISCUSSION ANALYSIS OF ABSORBANCE veysus pH CURVES- Copper - o-a-PAN system-The absorbance curve (Fig.1) can be divided into two main regions, the lower, steep portion corresponding to a 1: 1 chelate and the upper portion possibly to a 1 : 2 chelate. Equations (5) and (6) gave linear graphs and a value of log K c u ~ of 14.30 -& 0.20 and a molar absorptivity of 2-00 x lo4. This value of log KCuK is in good agreement with the value of 14.05 obtained by the method of continuous variations (D. Bet- teridge and H. Freiser, unpublished studies), and also agrees with the observations of Shun’ichiro, Carter and Fernando,2 who confirmed the formation of such a species by X-ray diffraction. The linearity of equations (7) and (8) was less good and suggested that a mixture of 1 : 1 and 1 : 2 chelates is formed and that the reaction is strongly dependent upon conditions.C?per - p-PAP system-The absorbance curves are shown in Fig. 2. Preliminary investigations by continuous variation,3 ~lope-ratio~,~ and mole-ratios methods demonstrated that chelates with either a 1 : 1 or a 1 : 2 ratio of copper to ligand may be formed. Straight-line graphs are obtained for equations (9) to (la), indicating that the equilibria suggested are reasonable. The values for the molar absorptivity and stability constants are shown in Table I. TABLE I MOLAR ABSORPTIVITIES AND STABILITY CONSTANTS FOR THE COPPER(II) - $-PAP SYSTEM Condition ‘CUROH KCuROH ‘CURS K C u R , Excess of metal ions . . 4-19 x 104 10.64 0.07 Excess of reagent . . . . 3.93 x 104 11.22 & 0.02 2-00 x 104 11.01 f 0.02 The results of these investigations suggest that the 1 : 1 chelate is more favoured and that the formation of the 1:2 chelate is most likely to occur in the presence of excess of reagent.SOLVENT EXTRACTION- using the established the0ry,~-9 the distribution ratio, D, is given by As the volumes of the organic and aqueous phases equilibrated were equal, then by where A,,,. is the maximum absorbance and Aobs. is the observed absorbance, and the per- centage extracted, E , is given by E=-------* 100 D + l The extraction of copper(I1) with o-a-PAN has been studied previous1y.l The pH dependence of the extraction of copper with this reagent has been published10 and it has also been used as an extractive indicator in titrations that involve the formation of com- plexes.11 This work serves to extend this application into a practicable analytical method for the determination of copper.Extraction curves for the copper(II), nickel(II), zinc(I1) and manganese(I1) chelates of o-a-PAN are shown in Fig. 3. No extraction of lead(II), iron(II), iron(II1) or titanium(1V) was observed in the pH range in which the extraction of copper(I1) occurred. Equilibrium was attained quickly (2 minutes) but the vials were shaken for 30 minutes so as to ensure complete extraction. The lowest pH for complete extraction as indicated by Fig. 3 is 2-05. The colour stability of the chelate was checked by absorbance measurements, when a constant value was obtained over a period of 24 hours. The calibration graph is shown in Fig. 4. A straight-line graph was obtained, which showed that Beer’s law was obeyed.The chelate has a molar absorptivity of 4-96 x lo4. The chelate was probably extracted as Cu(o-a-PAN),, and no evidence was found to support the view that the extracted species was CuR(0H) or, in the presence of ammonium thiocyanate, CuR(CNS), as have been proposed for the extraction of copper with o-/?-PAN.12,13July, 19731 PYRIDYLAZOPHENOLS AS ANALYTICAL REAGENTS. PART 111 51 7 PH Fig. 3. Extraction curves for the chelates of o-a-PAN (5 x M) in carbon tetrachloride. Left to right: eopper(II), nickel(II), zinc(I1) and manganese(I1) chelates INTERFERENCES- The extent of interference depends on pH and on whether the reaction is carried out in aqueous methanol or an extraction procedure is used. Fig. 5 shows the absorbance of various ions as a function of pH.Comparison with Fig. 3 shows that considerable im- provement in selectivity is gained by extraction of the copper( 11) complex. Nevertheless, in the absence of nickel(I1) and iron(II), the simpler non-extractive procedure would be satisfactory. We consider that the determination of copper is normally performed in the presence of these ions and accordingly we investigated the effect of interferences in the extraction procedure. The precise definition of the limits of interference is prevented because two important parameters are likely to be varied by individual workers, vix., pH and the rate of extraction. Fig. 3 shows that while it is feasible to use a pH of 2, the control of pH is less critical if the extraction can be carried out at pH 3. If the concentrations of nickel and zinc in a given sample are low in comparison with that of copper, then extraction at pH 3 is permissible and would be preferable to the procedure given.A guideline is provided by the simplified extraction equation for the system Kextract ;t2HR(, ;+ Mn+ + MR,,, + %H+ where the subscript (0) refers to the organic phase. 1 Copper, p.p.m= . Fig. 4. Calibration graph of absorbance ue~szcs concentration of copper518 BETTERIDGE, JOHN AND SNAPE PYRIDYLAZONAPHTHOLS AND [A?%@lySt, VOl. 98 Hence, for a bivalent ion, the extent of interference decreases 100-fold for a unit decrease in pH and increases 100-fold for every unit increase in pH, and for a tervalent ion there is a 1000-fold change for every unit change in pH. (These considerations are applicable, of course, only over the pH range for which D < lo2.) PH Fig.5. Absorbance of six metal ions in methanolic solutions of o-a-PAN (10-4 M) The variation in the rate of extraction is dependent upon the mode of shaking adopted by the operator. The extraction curves shown in Fig. 3 are for equilibrium conditions. Our studies showed that considerable improvement in selectivity can be gained by carrying out the extraction in the minimum time possible. It has been noted that a few minutes are necessary for the extraction of copper and a longer period of time is required to extract nickel(II), cobalt(I1) and zinc(I1) completely. A somewhat gloomy view of the extent of interferences was taken, and shaking was carried out for twice as long as necessary and a pH of 2-5 was used rather than 2.At a copper concen- tration of M, the following molar excesses gave an interference of 10 per cent. or less: cobalt(II), 15; nickel(II), 20; zinc(I1) and iron(III), 150; lead(II), 200; and manganese(II), chromium(III), vanadium(V) and vanadium(IV), above 1000. Most important, alumin- nium(II1) and iron(I1) did not give any interference over any practicable range of concen- trations. Hence, it would seem possible to determine copper in iron or steel if the sample were dissolved in such a way as to result in the iron being present as iron(I1). This possibility has not been explored. DETERMINATION OF COPPER IN STANDARD ALUMINIUM ALLOYS- The copper content of two British Chemical Standard aluminium alloys was determined Aluminium alloy “A” had the following composition (per cent.)- by the extraction and spectrophotometric procedure.Copper .. .. . . 4.68 Iron .. .. . . 0-51 Zinc . . .. * . . . 2.37 Silicon . . .. . . 0.39 Nickel . . .. . . 1.85 Tin . . .. * . . . 0.05 Lead .. .. . . 1-51 Aluminium .. . . 87.30 Magnesium . . .. . . 1-34 The average copper content found by extraction and spectrophotometric determination A 10 per cent. magnesium - aluminium alloy had the following composition (per cent.)- was 4.68 & 0-05 per cent. Copper .. .. . . 0-03 Zinc .. .. . . 0.05 Silicon . . .. . . 0.10 Chromium .. .. . . 0.06 Iron . . .. .. . . 0.19 Aluminium .. . . 88.84 Manganese .. .. . . 0.06 Magnesium . . .. . . 10.57 Titanium . . .. . . 0.10July, 19731 PYRIDYLAZOPHENOLS AS ANALYTICAL REAGENTS.PART I11 519 The average copper content found by extraction and spectrophotometric determination was 0-030 & 0-001 per cent. These results are in exact agreement with those quoted on the certificate of analysis, and confirm that this procedure for the determination of copper in aluminium is precise, sensitive and selective. The method is superior to the existing colorimetric procedure involving the use of sodium di~thyldithiocarbamatel~ because it is less time consuming, involves fewer chemicd manipulations and is therefore less likely to lead to error. A further advantage of the method is that copper can be quantitatively determined in the presence of a large excess of metals other than aluminium, e.g., lead, nickel, zinc and manganese, which react at higher pH.The low pH value used in the procedure is not only advantageous for promoting selectivity but it also minimises the occurrence of side-reactions such as hydrolysis. COUNTER-CURRENT EXTRACTION- The good extraction and spectrophotometric characteristics of several of the o-a-PAN, metal chelates suggest that the reagent might be useful for the sequential extraction of metal ions from a mixture. This possibility was explored by carrying out successive extractions and adjustments to the pH in a fourteen-tube, hand-operated, counter-current extraction apparatus. The mixture taken contained copper(II), zinc(II), manganese(I1) and lead(I1) ions. Lead ions remained in the aqueous phase but the other ions were extracted in the order copper, zinc, manganese at pH 4, 6.9 and 9-1, respectively, when the concentration of o-a-PAN in carbon tetrachloride was 5 x M. We are grateful to the T. and E. Williams Scholarship Fund and to the S.R.C. for maintenance grants to two of us (D. J. and F.S., respectively), 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. 12. 13. 14. REFERENCES Betteridge, D., and John, D., Analyst, 1973, 98, 390. Shun’ichiro, O., Carter, D., and Fernando, Q., Chem. Commun., 1967, 1301. Vosburg, W. C.,and Cooper, G. R., J . Amer. Chem. SOC., 1941, 63, 437. Harvey, A. E., and Manning, D. L., Ibid., 1950, 72, 4488. Yoe, J . H., and Jones, A. L., Ind. Engng Chem., Analyt. Edn, 1964, 16, 11. Morrison, G. H., and Freiser, H. F., “Solvent Extraction in Analytical Chemistry,” John Wiley, Starg, J ., “The Solvent Extraction of Metal Chelates,” Pergamon Press, Oxford, 1964. Laitinen, H. A,, “Chemical Analysis,” McGraw-Hill, New York, 1960. Betteridge, D., Todd, P. K., Freiser, H. and Fernando, Q., Anaiyt. Chem., 1963, 35, 729. Betteridge, D., Talanta, 1966, 13, 1497. Betteridge, D., Freiser, H., and Fernando, Q., Analyt. Chenz., 1963, 35, 294. Galik, A., Talanta, 1969, 16, 201. Meites, L., “Handbook of Analytical Chemistry,” McGraw-Hill, New York, 1963. NOTE-Reference 1 is to Part I1 of this series. > , Ibid., 1952, 74, 4744. New York, 1962. Received September 22nd, 1971 Accepted November 22nd, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800512

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

520 Analyst, July, 1973, Vol. 98, pp. 520-524 Pyridylazonaphthols (PANs) and Pyridylazophenols (PAPs) as Analytical Reagents Part IV.* Formation of Complexes with Titanium(1V) BY D. BETTERIDGE, D. JOHN7 AND F. SNAPE: (Chemistry Department, University College of Swansea, Swansea, Glamorgan, SA2 8PP) The formation of complexes of titanium(1V) with PANs and PAPs has been investigated in order to ascertain the types of complexes that are formed and to elucidate the optical and stability constants of such complexes. The competing effect of hydrolysis on these reactions has also been con- sidered. The reaction with 2-(2-pyridylazo)- 1-naphthol (o-or-PAN) has been examined in order to determine the analytical utility of this complex formation. PREVIOUS paper~l-~ have considered both theoretical and practical applications of pyridylazo- naphthols (PANs) and pyridylazophenols (PAPs) as analytical reagents.This paper presents the results of similar investigations with titanium(1V). EXPERIMENTAL SOLUTIONS- A standard solution of titanium(1V) was prepared by the method of Roseman and Thornton* and standardised gravimetrically with c~pferron.~ The solution was prepared shortly before use. Solutions that were more than 1 day old did not react with the reagents. Other solutions were prepared as described previously.1,2 APPARATUS- The apparatus used was identical with that described previously.192 PROCEDURES- Spectrophotometric determination of formation constants-The methods used were identical with those described previously.2 Absorbance curves of the chelates of 2- (2-pyridy1azo)- 1-naphthol (0-cc-PAN), 2-(2-pyridylazo)phenol (0-PAP) and 1-(2-pyridylazo)-2-naphthol (o-P-PAN) were obtained.Absorbance measurements were made at 582, 560 and 536nm for o-cc-PAN, o-P-PAN and o-PAP, respectively. Solvent extraction-The procedure used was identical with that described previously.2 Only the extraction of the o-cc-PAN chelate was considered, the absorbance measurements being made at 590nm. THEORETICAL The predominant titanium species presente in the pH range 0 to 5-5 is Ti02+, and the predominant reagent species in the pH range corresponding to the maxima of the absorbance curves is the neutral species HR (the protonated form H2R+ is of significance at lower pH values). The absorbance 'uersus pH curves shown in Fig.1 indicate a stoicheiometry of 1:2 for each chelate. Following through the Sommer method, as in the previous papers, the suggested chelation reaction is *KMR, .. - - (1) Ti02+ + 2HR + TiOR, + 2Hf . . d i e re * For Part 111 of this series, see p. 512. t Present address: BP Chemicals (U.K.) Ltd., Llandarcy, Swansea. Present address: Bausch and Lomb Co. Ltd., Toronto, Canada. @ SAC and the authors.BETTERIDGE, JOHN AND SNAPE 521 0.7 0.6 0.5 - W 5 0.4 $ 0.3 0.2 + 0.1 0 2 3 4 5 6 7 1 2 3 4 5 6 7 8 Fig. 1. Absorbance veYsws pH graphs for titanium(1V) chelates: (a) in the presence of excess of metal ions; and (b) in the presence of excess of reagent IN THE PRESENCE OF EXCESS OF TITANIUM(IV)- the total absorbance, A , is given by The symbols adopted in the previous papers are used.If it is assumed that [MI = CM, and then, by arguments similar to those used in Part 112 [transformation (111)l- where y = 2 + Ka,/[H], or in terms of the stability constant, K M R , , As [MI = CM and [MRJ/[HR] = AY(CKEMR, - 2A), I N THE PRESENCE O F EXCESS OF REAGENT- Under these conditions, [HR] == CR C M = [MI + LMR21 and .. .. .. .. .. .. Graphs of equations (5), (6), (7) and (8) should, if the initial assumptions are valid, yield straight lines, from which the molar absorptivities and stability constants can be calculated.522 d I x 41 &IT BETTERIDGE, JOHN AND SNAPE : PYRIDYLAZONAPHTHOLS AND [Analyst, Vol. 98 4 - I 1 1 1 1 1 1 1 I 1 J 10 12 14 16 18 20 0 2 4 6 8 - [HI2, 10-1 IH R1 Fig 2. Graph of equation ( 5 ) in the presence of excess of metal ions RESULTS AND DISCUSSION ANALYSIS OF THE ABSORBANCE vocysus pH CURVES- The reaction of o-p-PAN with titanium is very much weaker than that of the other two reagents, and consequently no further investigation of the reaction was carried out.The absorbance curves of the chelates of o-a-PAN and o-PAP were considered. Figs. 2 and 3 show the graphs of equations (5) and (8), which are straight lines, indicating that the initial assumptions made were correct. The molar absorptivities and stability constants are shown in Table I. If one assumes that a chelate species with a ratio of metal to reagent of 1 : 1 is W U ._ CY- .- w o L m Is) 29.2 28.8 - 28.4 - t 28.0 I I I 1 I I 1 I I 2.0 2.2 2.4 2.6 2.8 3.0 PH Fig. 3. Graph of equation (8) in the presence of excess of reagent formed instead of a 1 : 2 complex, it is possible to carry out similar algebraic manipulations so as to derive equations equivalent to equations (5) to (8) [cf. transformations (VIII) and (IX) in Part 117.Fig. 4, which is the graph of one of these equations, is not linear, thus showing that the initial assumption of a 1 : 1 complex is not correct. This example demon- strates the usefulness of this method for identifying possible species. TABLE I MOLAR ABSORPTIVITIES AND STABILITY CONSTANTS FOR CHELATES OF TITANIUM (IV) WITH o-a-PAN AND O-PAP Excess of reagent r Excess of metal ions ----LogR2 Reagent Log KMR, %R, o-R-PAN 1.74 x 10% 23-44 & 0.08 1-72 x lo4 23.46 & 0.02 o-PAP 9.89 x 103 20.50 f 0.08 1-04 x 104 20.21 &- 0.02 The results were obtained from different studies that involved the use of different reagent and metal-ion concentrations. The method of continuous vai-iation~~~~ confirmed that the stoicheiometry of the chelates is I : 2, and gave values for the stability constants that were in good agreement with those given above.At the upper pH levels, the absorbance decreases with increasing pH. This behaviourJuly, 19731 PYRIDYLAZOPHENOLS AS ANALYTICAL REAGENTS, PART IV 0.3 - 0.2 - 30 523 PH Fig, 4, Graph of equation to test for the 1 : 1 complex in the presence of excess of metal ions : log KMB f pH = logfA/L(CReMR - A)CIkfKa,] - log El) is similar to that observed for manganese(I1) and zinc(I1) chelates, and can be attributed to the occurrence of hydrolysis reactions.It is well known that the titanium species hydrolyse easily, and the decrease in absorbance may be caused by the preferential hydrolysis of the Ti02+ species according to the following equilibria- "* HTiO, + 3H+ H> TiO, + 2Hf KMR, / TiOR, + 2R+ + Ti02+ The existence of these equilibria can be verified by calculating the theoretical absorbance curves obtained by using the conditional coefficients a and ,!3 as described for lanthanum in Part 11.2 The values of the equilibrium constants involving the titanium species are6 Ti02+ + 2H,O F+ HTiO, + 3H+ and Ti02+ + H,O + TiO, + 2H+ log [TiOZf] = - 1.18 - 2PH It is now possible, by using these constants, to substitute in order to find values for 18, then C, and then the absorbance. The results for these calculations in the presence of excess of metal ions and excess of reagent are shown in Fig.5 . 0.81 I r - - - 2 4 6 8 10 PH Fig. 5 . Absorbance veysus pH graphs for the titanium(1V) - o-a-PAN chelate: (a) in Solid the presence of excess of metal ions; and (b) in the presence of excess of reagent. lines, experimental ; and broken lines, theoretical524 BETTERIDGE, JOHN AND SNAPE The agreement between the curves is evidence that the suggested equilibria are reasonably correct, but the discrepancies suggest that other equilibria may also be significant over part of the pH range investigated. We have tried the most likely permutations, e.g., TiOR,OH-, without success. ANALYTICAL UTILITY- The optical and stability constants indicate the possible use of o-a-PAN for the spectro- photometric determination of titanium(IV), but also that some ions will interfere, especially Cu2+, Zn2+, Ni2+, Fe2+ and Fe3+.The interference of iron could be overcome if the titanium complex could be extracted. Application of the methods described in Part 11, [equation (20)I and assuming a partition coefficient of lo4 for TiOR, and a reagent concentration of 1 0 - 3 ~ gives the pH range for extraction of 4 to 6. Copper(II), nickel(I1) and zinc(I1) can be extracted over this range and will interfere. In practice, the extraction of titanium was incomplete over the pH range 2 to 6 with o-a-PAN in n-butanol, carbon tetrachloride, n-octanol, isobutyl methyl ketone and chloroform as solvents. M were prepared by adding 10 ml of a 2-0 x lov4 M solution of o-a-PAN in 40 per cent.ethanol to an aliquot of titanium solution, adding 5 ml of phthalate buffer (pH 4 to 6) and making the volume up to 25 ml with water. The colour, which developed instantly, was stable for several hours and was measured at 582 nm in l-cm cells. The order of addition of reagents was not important, but the buffer was added last so as to minimise the possibility of hydrolysis of titanium. The presence of equal amounts of Fe2+, Fe3+, Cu2+, Ni2+ and Zn2+ ions made the determination impossible. The effect of masking reagents on this reaction was difficult to predict as values for stability constants for titanium complexes, other than for EDTA, are not available, but several reagents were tried in an effort to eliminate the interference of the above ions.Citrate, which has two donor oxygen atoms, and ethane-l,2-dithiol, which has two donor sulphur atoms, failed to mask either the interferences or titanium. Reducing agents, such as hydroxylammonium chloride, did not produce the required result. The possibility of producing mixed ligand complexes with different absorption maxima, such as TiR,O;- , by using hydrogen peroxide was also tried, but without success. CONCLUSIONS The optical and stability constants of the chelates of titanium(1V) with o-a-PAN and o-PAP have been determined and the results suggest that an analytical method for titanium based upon them would be sensitive. Furthermore, the colours, once they have been formed, are stable. Unfortunately the method is subject to interference from several common ions, which would have to be removed prior to the determination. We are grateful to the T. and E. Williams Scholarship Fund and to the S.R.C. for maintenance grants to two of us (D. J. and F.S., respectively). Calibration graphs for titanium concentrations in the range 5 x 10P to EDTA, as predicted, reacted preferentially with titanium(1V). 1. 2. 3. 4. 5. 6. 7. 8. REFERENCES Retteridge, D., and John, D., Analyst, 1973, 98, 377. -- , Ibid., 1973, 98, 390. Betteridge, D., John, D., and Snape, F., Ibid., 1973, 98, 512. Roseman, R., and Thornton, W. M., Amer. J . Sci., 1930, 20, 14. Vogel, A. I., “Quantitative Inorganic Analysis,” Third Edition, Longmans, Green and Co., London, Pourbaix, M. J . N., “Atlas of Electrochemical Equilibria in Aqueous Solution,” Pergamon Press, Job, P., Annls Chirn., 1928, 9, 113. Vosburgh, W. C., and Cooper, G. R., J . Amer. Chem. Soc., 1941, 63, 437. Note-References 1, 2 and 3 are to Parts I, I1 and 111, respectively, of this series. 1961. Oxford, 1966. Received September 22nd, 1971 Accepted November 22nd, 1972

ISSN:0003-2654    

DOI:10.1039/AN9739800520

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, July, 1973, Vol. 98, j!@. 525-528 525 An Ultramicro-scale Method for the Determination of the Uranyl Cation BY GLENN PETER WOOD (Department of Chemistry, University of San Andres, La Paz, Bolivia) A method that requires the use of very simple equipment has been developed whereby the uranyl cation can be determined at the micro-scale and ultramicro-scale levels with high precision. The method involves the use of the catalytic effect shown by the uranyl cation on the photo-decolorisa- tion of a naturally occurring carotenoid-type pigment. The interfering effects of several common anions and cations are also discussed. ANNATTO is the red colouring matter of the seed of the plant Bixa Orellana L.l and is a mixture of natural pigments that have similar chemical structures, the principal constituent being labile bixin- R = H ; R'=CH3 Solutions of bixin in acetic acid undergo photochemical decolorisation when irradiated with short-wave ultraviolet light.As nitrogen-purged solutions of bixin do not lose their colour when exposed to ultraviolet light, the reaction is thought to be based on its photo- chemical oxidation. As the catalytic oxidation of naturally occurring pigments has been used2 to determine ultramicro-scale amounts of cations, it was decided to investigate the possibility of discovering a cation that might catalyse the photochemical oxidation of labile bixin. About twenty cations were tested but only three had a noticeable effect on the velocity of the reaction, and of these three the uranyl cation had a much more pronounced effect than the other two cations.Investigation of this catalytic effect revealed that the reaction could be used to determine uranyl ions in the range 0.01 to 10 p.p.m. Several good techniques have been published for the determination of trace amounts of uranium by activation analysis,3 f l u ~ r i m e t r y , ~ ~ ~ fission-track counting6 and alpha-counting,' and although these methods offer good sensitivity a t low concentrations, all of them suffer from the disadvantage that they require the use of equipment or techniques, or both, not normally encountered in most chemical laboratories. Atomic-absorption spectroscopy is attractive but Perkin-Elmer only claim a lower detection limit of 30 p.p.m. for their Model 303 instrument. Florence and Farrar* described an excellent spectrophotometric method for the determination of uranium in ores that involves the use of the 2-(2-pyridylazo)-5-diethyl- aminophenol- zinc complex but their lower detection limit is 15 p.p.m.of uranium oxide (U,O,) in an ore. In our method, a standard graph of the bixin decolorisation gradients is prepared for the range of uranyl-ion concentrations of interest. Once this graph has been obtained a routine analysis can be completed in approximately 30 minutes (the time required to observe suitable decolorisation of the solution under ultraviolet irradiation) ; however, it should be realised that any number of solutions can be irradiated simultaneously according to the lamp facilities available. In the present work, one lamp was used to irradiate ten solutions simul- taneously and their final transmittance values were read consecutively. Each transmittance reading required approximately 30 s.EXPERIMENTAL cis-Bixin, in the form of the sodium salt, can conveniently be obtained by separation on a Sephadex columng and then precipitated as the free acid with dilute hydrochloric acid. @ SAC and the author.526 WOOD : AN ULTRAMICRO-SCALE METHOD FOR THE [Analyst, Vol. 98 In the present experiments the whole of the colouring matter from 40 g of Bolivian annatto was extracted into chloroform a t room temperature and the filtered extract was then mixed with anhydrous alumina (Merck, Extra Pure). The dyed alumina was then washed with chloroform until no further colouring matter could be removed. The only pigment that remains adsorbed on to the alumina is the cis-bixin, which was removed by placing the stained alumina on top of a chromatographic column containing clean alumina suspended in benzene.The column was then eluted with an acetic acid - ethanol mixture (1 + 9 V/V). The eluted product was recrystallised from glacial acetic acid (m.p. 185 to 186 "C and A,,, 468 nm). The yield was 400 mg, which was a sufficient amount to enable the entire set of experiments to be completed. 0.2 PREPARATION OF STANDARD DECOLORISATION CURVE- Previous experiments had shown that concentrations of water greater than 1 per cent. in the solutions to be decolorised reduced the rate of decolorisation and hence the sensitivity of the test, and so chromatographic acetic acid (99 to 100 per cent.) was used without further purification to prepare the bixin solutions containing uranyl ions in the following concen- trations: 0, 0.5, 0.1, 0.3, 0.7, 1, 2, 3, 4, 5, 7 and 10 p.p.m.In order to prepare these solutions, 0.00930 g of high-purity uranyl nitrate was weighed on a Mettler microbalance and then dissolved in 50 ml of the acetic acid, thus giving a standard solution containing 100 p.p.m. of uranyl ions. For the solutions containing from 1 to 10 p.p.m. of uranyl ions, aliquots of the standard solution (from 0.1 to 1 ml) were made up to 5 ml with the acetic acid and the solutions were then made up to 10 ml with a 2000 p.p.in. solution of bixin in acetic acid. In this way, an initial concentration of 1000 p.p.ni. of bixin was obtained for each solution, which ensured the presence of a large excess oi the pigment throughout the irradiations.The more dilute solutions containing from 0.05 to 0.7 p.p.m. of uranyl ions were prepared in the same way but by using aliquots of standard solutions containing 10 and 1 p.p.m. of uranyl ions. Kimax and Pyrex glassware (grade A) was used throughout; the temperature of the solutions was stabilised at 20 "C so as to ensure accuracy in volume measurement and all solutions were freshly prepared prior to exposure. 1 -4 - I I 1 I 1 *2 1.0 0.8 0.6 0.4 Irradiation time/minutes Fig. 1. Decolorisation graphs for bixin a t different uranyl concentrations: A, 0; B, 0.6; C, 1; D, 2; E, 3 ; F, 4; and G, 5 p.p.m.July, 19731 DETERMINATION OF THE URANYL CATION 527 Short-wave irradiations of the solutions were made with a Cromato-Vue 257.3-nm mercury lamp, which is operated at 0.36 A and 220 V; 2.7 ml of each solution were transferred by pipette into matched 1-cm quartz cells (Beckman), which were then irradiated at a distance of 25 cm from the lamp. After each 10-minute irradiation, the lamp was switched off and the cells were transferred into a Beckman DU-2 spectrophotometer, with which transmittance readings were taken at 468 nm.For the concentration range of uranyl ions above 7 p.p.m., the time of each irradiation was reduced to 1 minute or less. This step was found to be necessary in order to ensure that the corresponding transmittance - time graph was a straight line. For each concentration of uranyl ions the decolorisation graph of transmittance against irradiation time was plotted and found to be linear in each instance (Fig.1). In order to facilitate the use of these results for the practical determination of uranyl ions, it was decided simply to plot the gradient of each graph as a function of the uranyl-ion concentration. Four complete decolorisation series were run for each concentration of uranyl ions and the values shown in Table I are the mean values with the maximum divergence shown as the error. As expected, the greatest divergence was observed at low uranyl-ion concentra- tions. For the 0.05 p.p.m. solution the divergence was 3 per cent. and this error reduced to 2.7 per cent. in the 10 p.p.m. solution, although the error in the middle of the range was more frequently of the order of 1 per cent.TABLE I RELATIONSHIP OF URANYL-ION CONCENTRATION TO GRAPH GRADIENT [U022+], p.p.m. Gradient x lo3 [U022+], p.p.ni. Gradient x los 0.0 5.0 -J= 0.05 2-0 15.0 f. 0.15 0.05 6.0 rfr 0.10 3.0 17.5 f. 0.17 0.1 7.0 & 0.15 4.0 20.0 rfr 0.16 0.3 8.8 f. 0.15 5.0 22.5 & 0.2 0.7 11.0 f. 0.15 7.0 27.0 f 0.9 1.0 12.0 & 0.16 10 37.3 f. 1.0 By converting these errors into errors in uranyl-ion concentration the following con- clusions can be drawn: in the region of 10 p.p.m. an error of 2.7 per cent. in the decolorisation gradient indicates that the uranyl-ion concentration could be between 9-6 and 10-4 p.p.m., the deviation from the mean being of the order of 4 per cent. ; and in the region of 0.05 p p m . 35 30 25 20 15 10 5 I I I I I I I I I I 0 1 2 3 4 5 6 7 8 9 10 [uo22+1,p.p.rn.Fig. 2. Ursnyl concentration (0 to 10 p.p.m.) as a function of decolorisation gradient528 WOOD an error of 3 per cent. indicates that the concentration could be between 0.045 and 0.055 p.p.m., with a deviation of 10 per cent. These results are shown in Figs. 2 and 3, from which it can be seen that the relationship of gradient to concentration is linear between 1 and 10 p.p.m. of uranyl ions. P) z X 0 Fig. 3. Uranyl concentration (0 to 1 p.p.m.) as a function of decolorisation gradient In order to test for possible interfering effects of other ions, we carried out irradiations on a series of solutions, all of which contained 1 p.p.m. of uranyl ions, together with 500 p.p.rn. of any of the following cations : Fe2+, Cd2+, Pb2+, Ca2+, Naf, A13+, Mn2+, Co2+, Cr3+, Ni2+, Cu2+, Zn2+, Ag+ and Sn4+. As these cations were tested as the nitrate, sulphate, chloride, acetate or carbonate and no deviation was observed in any instance, we conclude that none of the above cations or anions interfere in the determination.Hg2+ and Mg2+, as the chlorides, caused an increase in the rate of decolorisation of about 5 per cent., but as they were present in a concentration 500 times greater than that of uranyl ions, we do not regard this increase as a serious interference. DISCUSSION The results show that uranyl ions have a catalytic effect on the photo-oxidation of labile bixin and that this effect can be used in the quantitative determination of the ions in micro- scale and ultramicro-scale concentrations. Although the relationship of decolorisation gradient to uranyl-ion concentration is non-linear at the parts per billion ( lo9) level, each point on the graph can be obtained simply and with a precision such that determinations of uranyl ions down to 0-05 p.p.m.can be made with a maximum error of 10 per cent. Four test decolorisations on a standard solution containing 0.01 p.p.m. of uranyl ions revealed that their concentration could be determined to an accuracy within 15 per cent. by using this method. The author is indebted to Justo Zapata and Jaime A d & for their help with the experi- ment a1 work. REFERENCES 1. 2. 3. 4. 5. Neumann, W. F., “National Nuclear Energy Series,” Div. VI, I, 11, McGraw-Hill, New York, 6. 7. 8. 9. Ingram, J. S., and Francis, B. J., Trop. Sci., 1969, 11, 97. Janjic, T. J., Milovanovic, G. A., and Celap, M. B., AnaZyt. Chem., 1970, 42, 27. Mackintosh, W. D., and Jervis, R. E., Rep. Can. Atom. Energy Cornm., AECL-481 and CRDC-704, Hoffman, J., Biochem. Z., 1943, 313, 377. April, 1957. 1949, p. 701. June, 1955. Carpenter, B. S., and Cheek, C. H., Anatyt. Chew., 1970, 42, 121. Campbell, E. E., Head, B. M., and Milligan, M. F., Rep. U.S. Atom. Energy Commn, LA-1920, Florence, T. M., and Farrar, Y. J., Analyt. Chem., 1970, 42, 271. Vera, H., and Wood, G. P., Trop. Sci., 1971, 13, 211. Received October 30th, 1972 Accepted February 12th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800525

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, July, 1973, Vol. 98, PP. 529-534 529 An Improved Plasma Jet System for Spectrochemical Analysis BY J. F. CHAPMAN, L. S. DALE AND R. N. WHITTEM (Australian Atomic Energy Commission, Research Establishment, Lucas Heights, New South Wales, Australia) The stability of a plasma jet has been improved by replacing the direct- injection nebuliser with a pre-mixed chamber - nebuliser arrangement of the type used in flame spectrometry. This arrangement has alleviated many of the operational problems that were experienced with the original system. As a result of the improved performance, the unit can be operated in con- junction with instantaneous photoelectric read-out. Details of the modifica- tion are given and the stability obtained is demonstrated. The sensitivity of the modified plasma jet has been investigated and detection limits for the most sensitive lines of sixty-seven elements are presented.These detection limits are compared with those obtained by using a nitrous oxide - acetylene flame with the same optical arrangement and detection equipment. THE plasma jet described by Margoshes and Scribnerl and later by Owen2 and Mittledorf and Landon3 has proved to be a significant development in the spectrochemical determination of elements in solution. The high-temperature environment provides f avourable conditions for exciting most elements. Unlike the lower temperature chemical combustion flames, the source is free from some chemical interference effects4 and is capable of exciting those elements which tend to form stable oxides in flames5 The plasma jet lacks the stability of a flame and in most applications either photographic recording6~~ or electronic integration of a photo- multiplier output4 is used.Photographic recording is tedious and time consuming and requires repetitive exposures in order to obtain precision data. Photoelectric read-out is a more rapid and convenient method of monitoring signals and the signal can be displayed as either instantaneous intensity or time-integrated intensity. In general, the former is preferred because it permits continuous monitoring of the emission stability of the discharge. The stability of the plasma jet as indicated by Lerners suggests that it is suitable for use with instantaneous read-out, and this aspect was investigated further.EXPERIMENTAL A plasma jet, which is commercially available from Spex Industries Inc. and is described as a spectrograph accessory, was operated in conjunction with a grating monochromator with non-integrated photoelectric detection similar to that used in flame spectrometry. We found, however, that the stability of the device was unsatisfactory for operation in this way. Lack of stability was attributed to the deposition of solids on the tip of the nebuliser, which resulted in rapid decay of the signal. Because the nebuliser nozzle was close to the discharge, it corroded rapidly and had to be replaced frequently. Other problems experienced with this sytem were the need to shut down the equipment in order to clean the capillary when blockages occurred and the need to use aqueous - organic solvent mixtures so as to prevent the build-up of solution on the upper graphite control ring.This latter problem indicated that the evaporation of the droplets was inefficient because of the unsatisfactory method of introducing aerosol into the discharge. In order to overcome these problems of introduction of the sample, and in an attempt to achieve adequate stability, the plasma jet was modified by replacing the direct-injection nebuliser with a pre-mixed aerosol chamber. The modification is simple and results in longer periods of continuous operation. The improved stability is satisfactory for operation with instantaneous photoelectric detection by using the equipment described. The improved performance of the modified system resulted in higher sensitivity and the detection limits for sixty-seven elements were obtained in order to assess the value of the system for spectrochemical analysis.These detection limits were, in general, an order of magnitude better than those previously obtained with @ SAC and the authors.530 CHAPMAN, DALE AND WHITTEM : AN IMPROVED PLASMA [Analyst, Vol. 98 the direct-injection system. In order to assess further the value of the system for spectro- chemical analysis, the detection limits were compared with those obtained with a nitrous oxide - acetylene flame by using the same optical arrangement and detection system. APPARATUS- A full description of the direct-injection plasma jet has been reported p r e v i ~ u s l y , ~ ~ ~ and a sectional diagram of the modified system is shown in Fig. 1.An EEL nebuliser (Evans Electroselenium Ltd.) was mounted on a Perspex screw-cap, which replaced the normal press-fit cap of an EEL spray chamber. The drain tube of the chamber was connected to a U-tube so as to maintain a positive pressure of 3 to 4cm (water gauge) inside. The spray from the nebuliser was directed past a baffle-plate and then through a 90" angle into the discharge via a glass tube of 3-5 mm i.d. The glass tube was positioned so that the lip was in contact with the lower graphite ring. A poly(viny1 chloride) tube between the ground- glass joint and the glass tube provided a flexible coupling between the spray chamber and the plasma jet. Scale : 0 1 2 inches - 0 1 2 3 4 5 c m Fig. 1. Sectional diagram of modified plasma jet.A, plasma jet; B, adjustable transfer electrode; C, flexible coupling; D, nebuliser; and E, spray chamberJuly, 19731 JET SYSTEM FOR SPECTROCHEMICAL ANALYSIS 53 1 The unit was mounted on an optical bar and light from the source (up to 4 mm above the upper graphite ring) was focused by a spherical lens on to the entrance slit of a 0.5-m plane grating monochromator (Jarrell-Ash Co.). The grating had 1180 lines per millimetre, giving a reciprocal linear dispersion of 1.6 nm mm-1 in the first order. The slits were 30 pm wide. The water-cooled transfer electrode holder was adjustable and permitted the electrode (a 3 mm diameter thoriated tungsten rod) to be advanced manually into the discharge so as to compensate for erosion of the electrode. This system permitted continuous operation for up to 2 hours.Emission signals were detected on an E.M.I. 6256s photomultiplier operating at 700 to 1000 V (variable) and were measured on a d.c. microvoltmeter connected to a 10-mV strip-chart recorder. Recently, a Keithley 414s picoammeter has replaced the microvoltmeter and permits considerable back-off of the high emission background of the source. The three-phase 415-V mains supply was rectified so as to supply direct current and a ballast network of 1-kW radiator bars in parallel was used so as to give a variableoutput of up to 30 A. The potential drop across the gap was 50 V and a Tesla coil coupling provided the spark ignition for the arc. It was essential to incorporate a small inductance in the ballast circuit so as to maintain stability of the current.The flows of the helium tangential gas and argon nebulising gas were controlled by pressure reducers and needle valves; the flow-rates of the gases were monitored by using precision-bore flow-rate meters. For the assessment of sensitivity, the plasma jet was operated under the conditions described below. The comparison with the nitrous oxide - acetylene flame was carried out by replacing the plasma jet with the burner and fog chamber from a Unicam SP900 flame spectrophotometer; the same optical layout was thus retained. The emission from the red “feather” of the flame immediately above the primary reaction zone was monitored. OPTIMISATION OF OPERATING CONDITIONS- In order to achieve satisfactory emission stability, the current, tangential flow-rate of the gas and flow-rate of the solution had to be optimised.Currents in excess of 15 A did not result in improvement but accelerated the rate of erosion of the transfer electrode, which limited the long-term stability and the length of the operating period. Tangential flow-rates in excess of 12 1 min-l (supply pressure 30 p.s.i.) caused deterioration of the intensity of the signal and increased the audible noise level of the discharge. The nebuliser was set to give a sample consumption of 4 ml min-1. With the baffle-plate in the spray chamber, the efficiency was found to be 5 per cent. The rate of spraying into the discharge was therefore about 0.2 ml min-l, which was considerably less than that obtained with the direct-injection system (1 to 1.5 ml min-l).The rate of spraying chosen was a compromise between the amount of solution reaching the discharge and the size of the droplets in the aerosol. The absence of build-up of solution on the upper graphite ring indicated that most of the droplets entered the discharge. Under these conditions (current, 15 A; tangential flow-rate of gas, 12 1 min-l; and flow-rate of solution, 4 ml min-l), the pitch of the audible noise of the discharge did not change when the aerosol was introduced, thus indicating that there was no significant disturbance in the behaviour of the arc. However, different results were obtained with the direct-injection nebuliser. The rate of erosion of the transfer electrode was very much reduced in the modified system and a three-fold increase in continuous operating time was achieved.EMISSION STABILITY- The stability of the new system is demonstrated in Fig. 2 , which shows a series of signals recorded for an aqueous solution of zinc of concentration 150 pgml-l at a wavelength of 213.9 nm. The coefficient of variation for the average values for each of the signals was 1.2 per cent. The average deviation between consecutive readings based on an estimate of the mean value for each individual signal was 0.05 PA. The direct-injection system was less stable : the average deviation between consecutive readings was approximately 0.2 pA for a set of signals of similar strength. The long-term stability was difficult to assess quanti- tatively because the transfer electrode had to be adjusted frequently. RESULTS532 CHAPMAN, DALE AND WHITTEM : AN IMPROVED PLASMA [Analyst, Vol.98 0 5 10 15 20 25 30 Ti me/m inu tes Fig. 2. Repetitive recordings of intensity of signals for zinc. Wavelength, 213-9 nm; concentration of zinc solution, 150 pg ml-1 SENSITIVITY- Detection limits obtained for sixty-seven elements are given in Table I. These limits are expressed as micrograms per millilitre in aqueous solution and are defined as that con- centration of an element which gives rise to a signal equal to twice the standard deviation of the background noise level at the appropriate wavelength. For comparison, the detection limits obtained for a number of elements with the nitrous oxide - acetylene flame are also given. These limits are also based on twice the standard deviation of the background noise level and were determined by using the same optical arrangement and detection equipment.DISCUSSION The incorporation of the pre-mixed aerosol chamber does not require any significant modification to the plasma jet itself. With simple workshop facilities, the remainder of the equipment can be manufactured at low cost. The system described has been in operation for about 2 years and the only occasional replacement has been of the glass tube that is in contact with the graphite ring. The life of these tubes is about 6 months in regular operation. The operation and performance of the new system have several advantages over the direct-injection system, namely: (a) elimination of corrosion of the nebuliser; (b) control over the rate of spraying; (c) production of a more uniform mist; (d) ease of cleaning the nebuliser capillary; and (e) longer operating periods with more stable emission.The stability achieved with the modified system is suitable for use with instantaneous photoelectric read-out. As well as giving higher sensitivity, this system permits continuous visible monitoring of the stability of the emission. A survey of detection limits with the modified system showed that the sensitivity was, in general, an order of magnitude better than that previously obtained with the direct- injection system. For example, the detection limits were aluminium, 3 ; barium, 0.1 ; boron, 0.5; copper, 1 ; gadolinium, 4; scandium, 0.2; strontium, 0.1; silicon, 2; titanium, 0.6; and vanadium, 2 pg ml-l.These detection limits, however, were obtained by using argon as both the tangential and the nebulising gas. The argon - argon system gives a much higher background than helium - argon, which is partly responsible for the reduced sensitivity.* Attempts to operate the original system with the helium - argon system were unsuccessful so that a strict comparison could not be undertaken. However, the major contributing factor in achieving the higher sensitivity is the greater stability of the emission in the modified system. Table I shows that the detection limits obtained with the modified system compare very favourably with those obtained with the nitrous oxide - acetylene flame. A major advantage of the plasma jet, however, is its ability to excite those elements which tend to form stable oxides in the high-temperature flame.This group of elements includes zirconium,Element Aluminium Antimony Arsenic . . Barium . . Beryllium Bismuth Boron . . Calcium . . Carbon . . Cerium . . Chromium Cobalt . . Copper .. Dysprosium Erbium . . Europium Gadolinium Gallium . . Germanium Gold . . Hafnium Holmium Indium . . Iridium . . Iron . . Lanthanum Lead . . Lithium . . Lutetium Magnesium Manganese Mercury Molybdenum TABLE I DETECTION LIMITS FOR THE MOST SENSITIVE LINE OF THE ELEMENT I N THE MODIFIED PLASMA JET AND I N THE NITROUS OXIDE - ACETYLENE FLAME 4 E ‘;c c, CD il W U .. .. .. ,. .. .. . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. Plasma-jet detection Wave- limit/pg ml-1 length/nm 0.3 0.2 0.5 0.2 0-003 5 0.05 0.008 15 2 0.4 0.8 0.2 0.3 0.6 0.1 0.7 0.1 0.2 0.2 0.6 0.3 0.3 1.5 0.2 0-5 0.2 0-08 0.06 0.02 0.04 0.3 0.1 396.2 259.8 235.0 553.5 313.07 306.87 249.8 393.4 247.9 415.0 267.7 228.6 324.8 353.2 400-8 382.0 342.2 417.2 265.1 242.8 264.1 345.6 451.1 254-4 259.9 394.9 283.3 670.8 261.5 279.7 257.6 254.6 281.6 NZO - w.2 flame detection limit/pg ml-1 0.06 -* - 0.03 - - - 0.002 - - 0.01 0.8 0.2 0.05 0.005 0.5 0.2 0.5 4 0.03 0.01 0.3 0.8 2 0.002 1 0.06 0.04 0.6 - - - - Wave- length/nm Element 369.2 Neodymium ,.- Nickel . . .. 553.5 Osmium .. .. Palladium . . Phosphorus . . - Platinum .. 422.7 Praseodvmium . . .. Niobium . . I - - Rhenium. . - Rhodium 425.4 Ruthenium 345.4 Samarium 327.4 Scandium 404.6 Selenium - Silicon . . 459.4 Silver . .440.2 Sodium . . 417.2 Strontium 265.1 Tantalum 267.6 Tellurium - Terbium . . 405.4 Thallium 451.1 Thorium . . Thulium . , 372.0 Tin . . 441.7 Titanium 405.8 Tungsten 670-8 Uranium 451-9 Vanadium 403.1 Ytterbium - Yttrium . . - Zinc . . - - 390.3 Zirconium * Not observed. t Second order. .. .. * . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. * . .. .. * . Plasma-j e t detection Wave- limitlpg ml-l length/nm 3 0.4 0.3 0.7 0.5 0.6 0.5 4 0.5 0.5 0.6 0.3 0.03 2 0.2 0.2 0.02 0.01 1.5 0.7 0.07 0-4 2 0.5 0.6 0.08 2 7 0.2 0.07 0.08 0.1 0.3 401.2 405.9 221.6 225.6 361.0 253.6 265.9 414.3 221.4 343.5 372.8 360.9 361.4 204.0 251.6 338-3 589.0 407.8 296.5 214-3 369.4 535.0 401.9 346.2 284-0 334.9 400.9 386.0 309.3 328-9 371.0 213.9 339.2 NZO - CzH2 flame detection limitlpg ml-1 - 0.1 0-2 - - - 0.05 0.0004 1 6 - Wave- lengthlnm - - 341.4 363.5 265.9 346.1 369.2 - - - - I 402.0 - - 328.1 460.7 481.3 431.9 - - - 371.8 399.8 - - - 437.9 398.8 362.1 360.1 - cn w W534 CHAPMAN, DALE AND WHITTEM beryllium, silicon, boron, titanium and some rare earths, and reference to Table I and other published detection limitsg indicates the greater sensitivity for these elements in the plasma jet.Phosphorus, uranium, thorium, iridium, cerium and osmium also have high sensitivities and are not appreciably excited in chemical combustion flames. The excitation of lines of high energy, such as that of phosphorus a t 253.6 nm (7.2 eV), indicates the high temperature of the source, which results in a high degree of ionisation, and it is generally found that the most sensitive lines are those which originate from ionised species.This effect is the reason for the poor sensitivity of the alkali metals sodium and lithium, for which ionic lines are inaccessible. The detection limits given in Table I for both tungsten and carbon were determined in the presence of a high background emission level for these elements in the discharge owing to the erosion of both the transfei- electrode and the graphite electrodes. By replacing the graphite electrodes with copper electrodes, the detection limit for carbon is reduced to 2 pg ml-l, taking into account the blank level that arises from contributions from carbon dioxide present in the water and gases, The plasma jet operates very satisfactorily with copper electrodes ; less erosion occurs than with graphite electrodes and only occasional replacement is required.The discharge is also characterised by a fairly high hydroxyl band emission (band head at 306.4 nm), and owing to this emission the emission lines of both bismuth and beryllium had to be recorded in the second order of the grating so as to minimise spectral interference. By using the system described, analyses that are not applicable to or readily accom- plished by flame spectrometry have been carried out. Some typical examples are the deter- minations of phosphorus in uranium compounds at the 100 p.p.m. level; low levels of rare- earth elements in association with solvent-extraction studies ; hafnium in reactor-grade zirconium; beryllium below the parts per million level; and total soluble carbon in aqueous effluent streams. These applications exemplify the usefulness of the plasma jet in the spectrochemical analysis of solutions. As the modified system can be operated in a manner similar to that with chemical combustion flames with the optical arrangement described and without the need to use integrated output, it can be conveniently interchanged with an air - acetylene or nitrous oxide - acetylene burner, thus permitting a wide range of elements to be determined with high sensitivity by selecting the appropriate excitation source. 1. 2. 3. 4. 5. 6. 7. 8. 9. REFERENCES Margoshes, M., and Scribner, B. F., Spectrochim. Acta, 1959, 15, 138. Owen, L. E., AppZ. Spectrosc., 1961, 15, 150. Mittledorf, A. J., and Landon, D. O., Spex Speaker, 1963, 8, 1. Webb, M. S. W., Wildy, I?. C., and Wordingham, M. L., Rep. U.K. Atom. Energy Auth., AERE- Jones, J . L., and Dahlquist, R. L., Proc. Pittsburgh Conf. AnaZyt. Chem. APPZ. Specfrosc., 1965. Collins, A. G., AppZ. SpeGtVOSG., 1967, 21, 16. Muntz, J. H., Ibid., 1967, 21, 300. Lerner, R., Spectrochim. Acta, 1964, 20, 1619. Pickett, E. E., and Koirtyohann, S. R., AnaZyt. Chem., 1969, 41, 28A. R4990, 1965. Received October 23rd, 1972 Accepted February 12th. 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800529

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, July, 1973, Vol. 98, $9. 535-541 535 A Method for Determining Free Azide Ions by Automatic Analysis in the Presence of a Covalent Cephalosporin Azide* BY R. E. WALLER (Glaxo Lnboratoifies Ltd., Greenford, Middlesex) An assay was devised in order to follow quantitatively the release of azide as free ions, N3-, from a cephalosporin azide when attacked by p-lacta- mase enzymes produced by specific strains of bacteria. Experiments were arranged to ascertain whether or not the azide cleavage occurred a t the same rate as the rupture of the p-lactam ring. The assay was required to determine free azide a t concentrations between 2 and 20 pg ml-l; other experimental limitations were imposed by the requirements of enzymolysis. The procedure adopted was based on the complete oxidation of azide ions to nitrogen by an excess of a standard aqueous solution of nitrite ions a t pH 4-6.The residual nitritc was removed by diazotisation with 4-amino- salicylic acid, followed by coupling of the product with a second molecule of the 4-aminosalicylic acid. The reaction mixture was then rendered alkaline by the addition of tetramethylammonium hydroxide solution. The final yellow colour was stable and had an absorption maximum a t 440 nm. It was not possible, however, to achieve sufficient operational reproducibility man- ually, and an AutoAnalyzer system was therefore used. The results show that cleavage of azide from the parent molecule occurs a t the same rate as the rupture of the p-lactam ring and parallels the decline in microbiological potency. THE antibiotic activity of cephalosporins is known to decline when they are attacked by /3-lactamase enzymes produced by organisms that infect the body. This decline is accom- panied by a decrease in ultraviolet absorption at a wavelength of 440 nm.An examination of the effect of such enzymes on derivatives of cephalosporin azides was undertaken as part of an investigation into the breakdown routes followed by these antibiotics. It was necessary to determine the free azide ions as they were produced in test preparations that contained both covalent cephalosporin azide and an enzyme inhibitor. Moreover, test solutions were also to be sampled for microbiological assay of their antibiotic potency and, simultaneously, for measurement of their ultraviolet absorption a t 260 nm.An analytical method for the deter- mination of free azide was therefore sought that was sensitive, reliable, rapid and practicable for use with a small amount of material. Azide is labile in the 3-position of the cephalosporin nucleus; it can readily accept an electron and leave the nucleus by the mechanism illustrated (Fig. 1). P-Lactamase would sever the carbonyl - nitrogen bond and release the lone pair of electrons into the dihydro- thiazine ring. Further electron displacement would result in the release of azide as N,- ions. i COzNa 0- Lactamase attack Fig. 1. Attack by /3-lactamase on the sodium salt of 3-azido- methyl-7 p-benzyl thi oacetamido- ceph-3-em-4-carboxylic acid * Based on a paper presented at the Third SAC Conference, Durham, July 12th to lBth, 1971.@ SAC and the author.536 WALLER: DETERMINATION OF FREE AZIDE IONS BY AUTOMATIC [ATZ@&St, VOl. 98 An aqueous solution containing 400 pg ml-1 of covalent cephalosporin azide could be expected to yield 40 pg ml-l of free azide on complete degradation. The analytical method was needed for concentrations of this order and, so that the earlier part of the breakdown could be followed meticulously, sensitivity had to be high, i.e., between 2 and 10 pg ml-l. At high enzyme concentrations, only 4 ml of the reaction solution could be spared. Additional limiting factors included buffer concentration, enzymolysis temperature and inhibitor efficacy. The concentrations of the P-lactamase preparations used were chosen so as to afford complete degradation in a reasonable time (Fig.2). At the highest concentration (E) they were solutions in 0.1 M phosphate buffer a t pH 7. Quantitative differences in enzyrnolysis and in azide release rates at temperatures of 4 and 37 "C were anticipated and were determined. I t I I I I I 1 10 20 30 40 50 60 70 80 Time/minutes Fig. 2. Azide release at different enzyme concentrations (E) An enzyme inhibitor was added in order to arrest the production of azide ions during the assay. This addition limited the assay time to 10 minutes, as the 7a- or 7P-naphthoic derivative of cephalosporin or penicillin finally used as inhibitor would not arrest the enzyme attack for a longer period of time. Many otherwise suitable inhibitors, such as phenyl- mercury( 11) salts, were discounted on grounds of solubility. Thus, adjustments to the temper- ture and pH of the sample in order to bring them within the time limits suitable for the assay had to be undertaken without delay.Various methods were considered, and included gasometric analysis, which required measurement of liberated nitrogen after the sample had been oxidised with sodium iodide and trichloroacetic acid1 ; distillation as hydrazoic acid and subsequent titration with standard alkali ; anodic polarography2 ; and precipitation of free azide as silver azide (AgN,) , measured p~tentiometrically.~ None of these methods was sufficiently sensitive. Titrimetric methods, based on the reaction between cerium(1V) and azide ions, were not attempted as they were already known to be very slow at low concentration^.^ Attention was therefore focused on colorimetry.REAGENTS- Potassium nitrite solution-A 0-03 per cent. m/V aqueous solution of AnalaR grade material is used (2 to 3 drops of Tween 20 are added to 500 ml of reagent so as to prevent any tendency to surge).July, 19731 ANALYSIS IN THE PRESENCE OF A COVALENT CEPHALOSPORIN AZIDE 537 Sodium 4-aminosalicylate solutio.12--A 2 per cent. m/ V aqueous solution of laboratory- reagent grade material is made up. Acetate bufer solution, 2 M-Equal volumes of 4 M acetic acid and 4 M sodium acetate solution are mixed. The pH is adjusted to between pH 4.50 and 4-70 by using, if necessary, acetic acid or sodium hydroxide solution. Tetramethylammonium hydroxide solution-A 25 per cent. aqueous solution of laboratory- reagent grade material is diluted with an equal volume of distilled water.All of the above reagents should be filtered through a fluted Whatman No. 541 filter-paper. Standard azide solution-A standard solution of sodium azide containing 1000 p.p.m. of free azide (NJ (1.548 g 1-l) is freshly prepared in 0.005 M phosphate buffer solution at pH 7.5. Suitable dilutions are made by using the same buffer. EXPERIMENTAL Methods of forming the red complex (FeNJ2+ by adding solutions containing azide ions to acidified iron( 111) nitrate4 or to perchlorate solution5 have been described, but cephalosporin derivatives, and especially their azides, interfere in the reaction. An otherwise promising alternative involving the use of diazotised sulphanilic acid coupled with 2-naphthylamine3 was considered to be unsafe for routine analysis.The procedure ultimately adopted was based on the complete oxidation of azide ions to nitrogen, by addition of excess of a standard solution of nitrite ions, in an aqueous solution strongly buffered at pH 4.6. The residual nitrite reacted with 4-aminosalicylic acid to form a diazo compound that coupled with another molecule of the 4-aminosalicylic acid. The reaction mixture was made alkaline with tetramethylammonium hydroxide solution so as to give a stable yellow - brown solution that had an absorption maximum a t 440 nm. A number of critical factors suggested that manual analysis would not be very satis- factory. Accordingly, an assay was developed that made use of an AutoAnalyzer system into which the required adjustments to pH and temperature could be incorporated.Each assay was completed in 7 minutes. The AutoAnalyzer accepted samples at the rate of twenty per hour and analysed solutions in the concentration range 2 to 20 pg ml-l. The enzyme purification process necessitated elution of the p-lactamase from a chromato- graphic column with 0.1 M phosphate buffer at pH 7-0 because the enzymes were insoluble in distilled water. A consequent advantage, however, was that the enzymolysis solution needed no further buffering to avoid loss of azide as hydrazoic acid. CI c 0 n C 0 L .- Temperature/"C Fig. 3. Transmission at 440 nm with continuous aspiration of a solution containing (A) 10 and (B) 0 pg ml-I of azide538 WALLER: DETERMINATION OF FREE AZIDE IONS BY AUTOMATIC [Analyst, VOl.98 The subsequent determination of azide required samples to be at pH 4.6, and because the diazotising and coupling reactions proceeded at a faster rate in an acetic acid - acetate medium than in phosphate or phthalate-buffered conditions, a strong acetate buffer (2 M) was used. The presence of this buffer also reduced the temperature dependence of the assay and interference from inorganic ions. Uniformity of temperature was achieved by imniersing all the AutoAnalyzer coils in a water-bath that was capable of controlling temperatures to within *0-1 "C. In addition, all of the reagents were brought to the azide assay temperature by passing them through suitable temperature-regulating coils also immersed in the constant-temperature bath.Fig. 3 illustrates the temperature dependence of the assay at concentrations of 0 and 10 pg ml-l of azide. This dependence is smallest between 18 and 26 "C and consequently represents a stable working temperature range while also ensuring almost maximum sensitivity. Problems arose at the final stage, when the product was made alkaline so as to stabilise the final colour. When, in the interests of speed and sensitivity, the assay was conductcd below pH 4, excessive amounts of tetramethylammonium hydroxide were needed to neutralise the acetate buffer, thus causing solubility problems. Above pH 4.6, the reaction became markedly slower; accordingly, 4-6 was selected as being the optimum pH. The most suitable temperature range was €ound to be between 16 and 22 "C.Lower temperatures, in the region of 4 to 10 "C, protracted the assay time beyond the working limit of the inhibitor and caused difficulties through the condensation of atmospheric water vapour on the colorimeter cell. To ensure a rapid reaction at pH 4.6, a large excess of sodium 4-aminosalicylate was used. In practice, a concentration of about 5 per cent. m/V was found to be the upper limit for this reagent; beyond that, absorption by excess of reagent at 440 nm became unacceptable. Further, above 5 per cent. nz/V the sensitivity was too low for small concentrations of azide to be measured. There was no interference from non-oxidising or non-reducing ions below concentrations of azide of 2 mg ml-l. A 40 per cent. reduction in sensitivity was observed with cephalosporin azide at 10 mg ml-l, but this level was twenty-five times greater than the normal working concentration.THE MANIFOLD- Initially, the air aspirated between the sample and wash solutions caused noisy recordings. To overcome this defect, a re-sample loop was incorporated in the AutoAnalyzer manifold (Fig. 4). The sample was segmented with air and brought to the reaction temperature by means of a small mixing coil immersed in the constant-temperature water-bath. The nitrite reagent, introduced into the sample stream at point A, was prepared and its temperature was regulated continuously by mixing equal volumes of potassium nitrite so1utio;i and acetate buffer (2 M) in another coil. When the buffer solution and sample were mixed, and the nitrite was then added, the results were not entirely reproducible.This imprecision was attributed to a varying loss of hydrazoic acid into the air bubbles. It was also noted that any segmentation cE an acidic nitrite stream at the preferred temperature led to a similar laxk of reproducibility. Hence, the diazotising mixture was prepared and added in a continuous stream. Sodium 4-aminosalicylate was added at point I3 after appropriate temperature regulation. Difficulties were incurred when the viscous tetramethylammonium hydroxicle reagent was added to the liquid stream. Mixing became difficult and, as a result, the irregular propor- tioning due to pump pulsing became critical. This problem was solved by including a pulse suppressor [Fig. 5 ( a ) ] , a chamber mixer [Fig.5 (b)] and a capillary side-arm T-piece of i.d. 0-05 mm at point C. The temperature of the tetramethylammonium hydroxide reagent was not critical. The whole manifold was assembled in a small thin-layer chromatographic tank (9 x 9 x 3 inches) filled with coolant. Greater sensitivity was obtained when the final reaction time was increased by using additional delay coils, and in order to eliminate any tendency to surge under these conditions the extra coils had successive turns of increasing diameter. The range and sensitivity of the method can be seen in Fig. 6, which shows peaks from eight standards within the concentration range 0 to 20 pg ml-l. The degree of discrimination between high and low peaks shows the negligible carry-over between sample and wash solu- tions.The reproducibility of the method is illustrated by peaks from replicate samples atJuly, 19731 ANALYSIS IN THE PRESENCE OF A COVALENT CEPHALOSPORIN AZIDE 539 ml min-' Single mixing coil 0.3 X o.3 V Buffer Potassium nitrite A * * A Wash reservoir " 3.4 / Single mixing Single mixing coil 0.8 0.3 Sample Resample Air Sod i um 4-am i nosal icy date ,, A 0.6 Tetramethylammonium hydroxide " 2.01 A Waste mi min-' Reaction mixture Single mixing coil '.O Sample +4 1 4 , Distilled water coil (b ) Fig. 4. (a) AutoAnalyzer manifold; and ( b ) diluent manifold concentrations of 7.5 and 15 pg ml-l of free azide, while a steady state is indicated by the peaks resulting from continuous aspiration of a 15 pgml-1 solution of azide. PROCEDURE FOR DISCRETE SAMPLING- The manifold is assembled as illustrated. The coolant is circulated a t 16 to 22 "C with a tolerance of not more than & O m 1 "C.The filtered reagents are pumped into the manifold (a) (b) Fig. 5. (a) Pulse suppressor; and (b) chamber mixer540 WALLER: DETERMINATION OF FREE AZIDE IONS BY AUTOMATIC [AndySt, VOl. 98 and a level base-line is established. The sampler unit operates at a rate of 20 per hour (2 : 1 sample to wash ratio), starting with two high and two low standards. The concentrations of the potassium nitrite solutions are adjusted until these preliminary standards give suitable transmissions at 440 nm. Further standards are prepared in order to establish a calibration graph. Daily calibration is necessary because the response curve is altered significantly by the inevitable small variations that occur in the reagents and the pump tubing.The necessary amount of inhibitor is added to samples that have been withdrawn from the experimental solutions, the solutions are mixed well and placed in a sample cup on the sampler module. They are immediately analysed for ionic azide. The concentration of free azide in each sample is then calculated by reference to the calibration graph. 90 80 70 + W 0 60 L a C .- 0 50 E t- v) .- 4 0 - 30 20 10 100 - - - - - - - - 15 15 I 20 20 10 Fig. 6. AutoAnalyzer recording of azide solutions. Values above peaks are azide concentrations in micrograms per millilitre PROCEDURE FOR CONTINUOUS SAMPLING- However, this can be effected only when a sufficiently large amount of solution is available.The manifold is assembled as in Fig. 4 (a), but omitting the re-sample loop and introducing an equal volume of the inhibitor (1.1 mM) into the sample line before splitting the stream [see Fig. 4 ( b ) ] . For circulating the coolant, pumping in the filtered reagents and establishing a base-line the method described under Procedure for discrete sampling is followed. A calibration graph is constructed by using six standards, taken over the complete working range, and sampling each until a steady state is achieved. Samples are taken from the reaction vessel in order to establish a base-line for the individual antibiotic, the enzyme preparation is added and mixed well, and the reaction is monitored, taking into account the delay time of the AutoAnalyzer system.RESULTS The logical method is to monitor the reaction continuously. Accuracy to within &l per cent. was demonstrated by recovery of the theoretical amount of azide from the covalent cephalosporin azide in six separate experiments. These experiments involved three different enzymes. The reproducibility was better than A0.5 per cent.July, 19731 ANALYSIS IN THE PRESENCE OF A COVALENT CEPHALOSPORIN AZIDE 541 The majority of the enzymolysis results are published elsewhere,6 and are considered in relation to other biological factors. However, the rate of enzyme attack at 37 "C was only 25 per cent. greater than that at 4 "C, with a similar temperature dependence for the rate of azide release. A typical graph, obtained with an enzyme produced from one specific strain of gram-negative bacteria to illustrate the above features, is given in Fig.7. The changes in ultraviolet absorption, in azide release, and in microbiological activity against Staphylococcus auuyeus, are plotted against time. The breakdown rates are identical within the limits of experimental error. Ti me/m i n Utes Fig. 7. Comparison of release of azide (O), loss of biological activity (0) and decrease in absorption at 260 nm (A) CONCLUSIONS The decline in antibiotic activity and the cleavage of azide from the parent molecule occur at the same rate and to the same extent, and are temperature dependent to the same degree, as the hydrolysis of the p-lactam ring. However, other semi-synthetic cephalosporins that have less labile groups than azide in the 3-position are also easily attacked by p-lacta- mase. In these instances rupture of the p-lactam ring takes place, and no loss of 3-terminal groups occurs, whereas the azide loss is directly dependent upon p-lactam ring hydrolysis. 'This fully supports the mechanism outlined in Fig. 1. I thank Mr. J. L. Martin and Mr. R. E. Duncombe for much helpful discussion. REFERENCES 1. 2. 3. 4. 6. 6. Carpenter, W. R., Analyt. Chem., 1964, 35, 2352. Masek, J., Colln Czech. Chem. Commun., 1960, 25, 3137. Staples, P. J., Chem. G. Ind., 1960, 1210. Robertson, C. E., and Austin, C. M., Analyt. Chem., 1957, 29, 854. Anton, A., Dodd, J. G., and Harvey, A. E., jun,, Ibid., 1960, 32, 1209. O'Callaghan, C., Kirby, S., Morris, A., Waller, R. E., andDuncombe, R. E., J . Bact., 1972, 110, 988. Received September 28th, 1972 Accepted January 22nd, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800535

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

542 Analyst, July, 1973, Vol. 98, pp. 542-5458 The Histochemical Detection of Soya “Novel Proteins” in Comminuted Meat Products BY M. COOMARASWAMY* AND F. OLGA FLINT (Procter De$vw+,rnerLt of Food and Leather Science, The University, Leeds 2) The enforcement of the regulations governing meat and meat products requires the determination of meat content. Meat content is assessed from the total nitrogen content, from which suitable deductions are made for the nitrogen contributed by the other ingredients of significant nitrogen content present in meat and meat products. The availability of “novel proteins” and the possibility of the addition of these proteins to meat products necessi- tates the detection and determination of “novel proteins” in such products for the true assessment of their meat content.A microscopical method that indicates the presence of “novel protein” of soya origin in meat products has been examined. This method involves the use of a specific technique to demonstrate the presence of carbohydrate material and is diagnostic for the cellular fraction of many processed soya products. PROTEIN has received much attention during the last two decades and the protein needs and supplies of the world have been the subject of much discussion. The Protein Advisory Group1 of the United Nations has concluded that the world protein deficit would be about 20 million tons per year in the early 1970s. The awareness of this great deficit, and the view that traditional sources, however developed, would be unable to meet the increasing shortage, has resulted in the search for non-traditional sources of protein, generally termed “novel proteins.” “Novel protein” research has been mainly directed towards oil-seed proteins, leaf protein isolate, field-bean (Vicia faba L.) protein isolate and single-cell proteins.Of the four oil-seed proteins (soya bean, groundnut, cotton seed and coconut), the first two are now available in commercial forms for human consumption : groundnut as protein concentrate and protein isolate2 and soya bean as full fat flour, defatted flakes, grits and flour, protein concentrate and protein The approximate protein percentage contents of the soya bean forms are: full fat flour, 42; defatted flakes, grits and flour, 50 to 55; concentrate, 65 to 70; and isolate, 90 to 95.394 Field-bean isolate is also commercially available for human consumption with a protein content of 85 per cent.These plant proteins have been presented as protein-rich foods, dried meat preparations, hydrolysed vegetable protein, protein drinks3 and textured vegetable proteins, which include extruded soya protein, spun soya protein5 and spun field- bean protein.6 It would appear that, for human consumption, only the soya-bean proteins are available in substantial and rapidly increasing amounts every year. These commercial products are available in the U.S.A., Europe and, more recently, in Great Britain. British food regulations7-10 require the quality of both meat and meat products to be assessed by their meat content. The meat content is calculated by using an experimentally determined value for total nitrogen from which appropriate deductions are made for the nitrogen contributed by other ingredients of significant nitrogen content .ll The presence of significant amounts of “novel protein” in meat products would increase the total nitrogen content value, unless its presence is detected, determined quantitatively and a correction made for its nitrogen contribution. The detection and determination of these “novel proteins,” whether declared or undeclared, intentionally or otherwise added to meat products, is becoming increasingly necessary, not only to control the addition of “novel protein” as a substitute for skeletal muscle protein, but also to aid the implementation of the regulations relating to meat products.A microscopical method for detecting “novel protein’’ in meat products has been examined in this investigation. The technique involves the controlled oxidation of the * Present address : Government Analyst’s Department, Colombo-7, Sri Lanka (Ceylon).@ SL4C and the authors.COOMARASWAMY AND FLINT 543 carbohydrate material present in plant protein products and demonstration of the presence of the resulting aldehydes. The method is capable of distinguishing between the carbohydrate material associated with plant proteins and that from soya beans and could be made semi- quantitative. METHOD REAGENTS- Bufered formaZinJixative-Dissolve 4.5 g of sodium dihydrogen orthophosphate dihydrate and 6.5 g of disodium hydrogen orthophosphate in about 700 ml of distilled water.To this solution add 100 ml of 40 per cent. formaldehyde solution. Dilute to 1000 ml with distilled water (the pH of this buffer is about 6.8). Periodic acid solution, 1 per ceizt.-Dilute 0.6 ml of 50 per cent. periodic acid solution to 50 ml with distilled water. Schif's reagent, stock solution-Dissolve 0-5 g of basic fuchsin (C.I. No. 42510) in 100 ml of distilled water and decolorise with a stream of sulphur dioxide. The solution is stable for a few weeks at 4 "C. Schif's yeagent, working solution-Dilute 1 ml of stock solution to 50 ml with distilled water. Protein counterstain-Prepare a 1 per cent. m/V solution of Procion Brilliant blue (C.I. No. Reactive Blue 4) in distilled water or a 0.5 per cent. m/V solution of Light green (C.I. No. 42095) in distilled water.SAMPLE PREPARATION PROCEDURE- Roll the comminuted meat product into balls approximately 1 cm in diameter or hydrate the dried protein products by soaking in distilled water and place them in buffered formalin fixative for a minimum of 48 hours. Cut cryostat sections by washing the fixed specimens in running water, rapidly freezing, and cutting 10-pm sections in a cryostat cabinet at - 18 "C. Alternatively, cut 10-pm wax sections. Details of the wax embedding and sectioning technique are available in standard textbooks on microscopy. Two distinct extruded soya protein products and one spun field-bean protein isolate were sectioned and stained as described above. As all the samples showed some orientation due to manufacture, sections were cut both parallel to this orientation (longitudinal sections) and at right angles to it (transverse sections).In addition, sections were prepared of a blend of raw pork sausage meat with firstly 10 per cent. mlm of defatted soya-bean flour and secondly 10 per cent. m/m of moist extruded soya protein. STAINING PROCEDURE- (Wax sections should be treated for 10 minutes in xylene followed by absolute ethanol, 90 per cent. ethanol and 70 per cent ethanol.) Oxidise the sections in periodic acid solution for 5 minutes, except the control sections, for which this step should be omitted, and wash them in running water for a further 5 minutes. Treat the sections with Schiff's reagent for 20 minutes and again wash them in running water for 5 minutes. Counterstaiii for 5 minutes in protein counterstain containing 3 to 4 drops of 1 N sulphuric acid per 50 ml of stain and rinse in water.Then, rinse the sections successively in 70 and 90 per cent. ethanol and dehydrate them in absolute ethanol for 1 minute. Clear in xylene, also for 1 minute, and finally mount the sections in neutral Canada balsam or DPX (refractive index 1.524). Carbohydrate material appears magenta on staining, i.e., periodic acid Schiff (PAS) positive, while protein appears blue or green, according to the counterstain used. The control shows only the colour due to the counterstain. Place the sections in water. RESULTS AND OBSERVATIONS All sections of extruded soya products showed regions of PAS positive material when viewed through a 16 mrn ( x 10) objective. The carbohydrate was present both in a charac- teristic cellular form consistent with being derived from the cells of the soya bean, and also as large areas of amorphous material.Soya-bean cells were clearly observed in the blends of sausage meat with soya flour and sausage meat with soya extrudate. In contrast, the protein isolate derived from field bean contained no distinct plant cells or discrete areas of carbohydrate material. When the PAS preparation was counterstained,544 COOMARASWAMY AND FLINT: THE HISTOCHEMICAL DETECTION OF [Analyst, VOl. 98 even lightly, only protein was observed. By omitting the counterstain it was seen that the whole preparation was weakly PAS positive. Photographs showing these results comprise Figs. 1 to 6, all of which are magnified 125 times.DISCUSSION Protein products of soya origin, although high in protein content, continue to be asso- ciated with some of the carbohydrate constituents of the soya bean. The soya bean is entirely different from other legumes and from cereals in its carbohydrate constituents. With the exception of a few strains, the bean has virtually no starch reserve and the carbo- hydrate present is composed of other polysaccharides, notably hemicelluloses and cellulose. These carbohydrates contain the lJ2-glycol grouping (CHOH-CHOH) , which can be selectively oxidised with dilute periodic acid to yield a dialdehyde (CHO-CHO). Periodic acid does not oxidise the aldehydes further, so that insoluble carbohydrates remain in situ and their presence can be demonstrated by use of Schiff’s reagent.12 It is claimed that the red colour produced is due to the combination of the basic fuchsin with the dialdehyde rather than a simple re-oxidation of the fuchsin sulphurous acid.13 Materials that give this reaction are known as PAS (periodic acid Schiff) positive and include compounds of carbohydrates with protein or lipids, so that a wide range of materials is involved. It was found with soya flour and soya extrudates that the strongly PAS positive materials occurred in a characteristic cellular form, easily recognised despite any processing that the material had undergone.In the samples examined, cells of the cotyledon were widespread and easy to identify, but other cells, including the hour-glass and endosperm cells, were also present. When the soya products were mixed with commercial sausage meat the plant cells were easily distinguished from other, less structured, carbohydrate material present , e.g., gelatinised starch derived from the sausage rusk.As many chemical groups oxidise Schiff’s reagent, control slides in which Schiff’s reagent is allowed to act but with the oxidation stage with periodic acid omitted, are essential, e.g., lignin or residual fixative both re-colour the Schiff’s reagent and it is desirable to be aware of such non-specific staining. Each photograph showing PAS positive material is therefore accompanied by a control. For contrast, and for ease of identification, the protein material present was counterstained. Light green and Procion Brilliant blue were both found to be effective for this purpose.They stain all of the protein present; in sausage sections, muscle tissue and flour protein (as well as soya protein) were coloured but it was observed that the soya protein was less intensely coloured than the other proteins. This differentiation is most useful in assessing the proportion of soya material present in comminuted meat products. The field-bean isolate (Figs. 5 and 6) contained only trace amounts of carbohydrate material, structured cellular carbohydrates being completely absent. This fact suggests that it might be difficult to detect soya isolates as distinct from flours, grits and extrudates. Spun soya contains more than 90 per cent. of protein, and hence much less carbohydrate than other soya products, and, in addition, the carbohydrate that is present is likely to be less structured.The high cost of production of the spun isolate has led to its use in declared forms of presentation, such as whole soya turkey in which the fibrous character is exploited, rather than to its declared or undeclared addition to comminuted meat products, in which the expense is not justified. This limited usage of the isolate suggests that it is the detection and determination of soya flour and extrudate that is currently the more pressing problem for the analyst. The authors thank Dr. J. E. McKay and Mr. R. A. Dalley, City Analyst, Leeds, for helpful discussions during the work, and Mrs. A. Sharples for technical assistance. REFERENCES 1. 2. 3. 4. Lock Miller, N. R., Fd Technol., 1972, 26, 66. 5. 6. United Nations Organisation, FAO/WHO/UNICEF.Protein Advisory Group, 1966. Anantharaman, K., Subramanian, N., Bhatiya, D. S., and Subrahmanyan, V., Indian Oilseeds J., Rakosky, J., jun., J . Agric. Fd Clzerva.. 1970, 18, 1005. Ashton, M. R., Burke, C. S., and Holmes, A. W., “BFMIRA Scientific and Technical Surveys,” Process Biochem., 1972, 7, 3. 1959, 3, 85. No. 62, August, 1970.Fig. 1. Transverse section of a cylindrical extru- date showing PAS positive palisade cells and areas of amorphous carbohydrate (magenta). Protein stained with Light green Fig. 2. Longitudinal section of a textured extru- date which macroscopically resembled meat chunks. A group of PAS positive cotyledon cells containing protein are surrounded by amorphous PAS positive material. Protein stained with Light green Fig.3. Control slide to Fig. 2 . The textured extrudate has beenstained as for Fig. 2 with omission of periodic acid oxidation. The only colour is the protein, stained with Light green [To face p . 544Fig. 4. Defatted soya flour present in pork sausage. Groups of palisade cells (PAS positive) sectioned longitudinally and transversely can be seen. Note PAS positive nature of the baked starch granules present in the rusk of the sausage. These are easily distinguished from soya carbohydrates. Protein counterstained with Procion Brilliant blue Fig. 5 . Spun protein stained with PAS and Light green. Only the protein fraction appears coloured and is identical with the control. Material cut to show fibres i n transverse section Fig. 6. Spun protein stained with PAS only. This shows a weak, uniform, diffuse, PL4S positive fraction, which is masked in the counterstain in Fig. 5. Material cut to show fibres in transverse section 70 face P. 5451July, 19731 SOYA “NOVEL PROTEINS” IN COMMINUTED MEAT PRODUCTS 545 8. 9. 10. 11. 12. 13. “The Meat Pie and Sausage Roll Regulations, 1967,” S.I. 1967 No. 860 as amended by S.I. 1967 “The Canned Meat Product Regulations, 1967,” S.I. 1967 No. 861 as amended by S.I. 1967 No. 1864 “The Sausage and Other Meat Product Regulations, 1967,” S.T. 1967 No. 862 as amended by “The Fish and Meat Spreadable Product Regulations, 1968,” S.I. 1968 No. 430 as amended by Stubbs, G., and More, A., Analyst, 1919, 44, 125. McManus, J. F. A., Nature, Lond., 1946, 158, 202. Pearse, A. G. E., “Histochemistry, Theoretical and Applied,” Third Edition, Volume I, Churchill, Received January 15tk, 1973 Accepted February 13th, 1973 No. 1864, H.M. Stationery Office, London. and S.I. 1968 No. 2046, H.M. Stationery Office, London. S.I. 1967 No. 1864 and S.I. 1968 No, 2047, H.M. Stationery Office, London. S.I. 1970 No. 400, H.M. Stationery Office, London. London, 1968, p. 309.

ISSN:0003-2654    

DOI:10.1039/AN9739800542

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

546 Analyst, July, 1973, Vol. 98, $9. 546-549 Interference of Carbon Dioxide, Resulting from the Schoniger Flask Combustion of Organofluorine Compounds, in the Titrimetric Determination of Fluorine BY WILLIAM F. HEYES (I1.ztevwatioizal Devclgjmaent Laboratory, E. R. Squibb t+ .So?as L t d . , Moreton, Cheshire) Carbon dioxide produced dm-ing the Schiiniger flask combustion oi organofluorine compounds has been found to interferc in the titrirnetric determination of fluorine. When thorium nitrate that had been standardised against sodium fluoride solution was used, the fluorine content found was consistently 93 per cent. of theory. This interference was overcome by adding sodium carbonate to the solution used for standardisation before titration. For detection of the titration end-point, an improved indicator, methylthymol blue, was used.By using this procedure, compounds containing between 4 and 30 per cent. of fluorine, either in a CF, or CF group, have been assayed satisfactorily. No interference from nitrogen, sulphur or chlorine containcd in some of the compounds was observed. IN assays of halogens bonded in organic molecules, the Schiiniger oxidation method can be usedl*2 to convert halogen atoms into ions, which can then be assayed by various techniques, e.g., colorimetry or titrimetry. In these procedures, it is customary to use as a reference standard an organohalogen compound of high purity. However, in this laboratory we required a method that did not rely upon the combustion of an organic compound as standard but, instead, involved the use of a true standard that did not require combustion, such as the sodium salt of the halogen.When this oxidative method, followed by colorimetry, was used to determine the amount of fluorine in nifluniic acid, I, it was found to be only 93 per cent. of theory. In the colori- metric procedure use was made of the coloured complex formed between fluoride ion and the cerium(II1) complex of alizarin complexan, 3- [di-(carboxymethyl)aminomethyl]-l,2-di- hydroxyanthraquinone, in acetate buffer. When a succinate buffer was substituted for the acetate bufferJ3 the fluorine content found was still only 93 per cent. of theory. ,COOH It was then decided to examine the possibility of using the thorium nitrate titration procedure. Soep4 had described the use of thorium nitrate solution, standardised against sodium fluoride solution, for the determination of the fluoride resulting from the combustion of an organofluorine compound.He found that use of this technique gave consistently low values for the fluorine content of the sample, thus requiring the use of a correction factor. In order to avoid the need to use this correction factor, we attempted to determine the cause of this apparent loss of fluorine. EXPERIMENTAL The determination of fluorine by titration with thorium nitrate solution is a well known analytical procedure for which a number of different end-point indicators have been used.j-’ An improved indicator was described by Selig,’ who used methylthymol blue at a solution pH of 3-35. Because the colour change of this indicator was much more definite than that of the commonly used alizarin red S, we adopted methylthymol blue for use in the titration.@ S!\C and the author.HEYES 547 The result of the application of this titrimetric method to the analysis of niflumic acid showed an apparent loss of 7 per cent. of the fluorine, as was expected from the work of Soep. ATTEMPTS TO TRACE THE APPARENT LOSS OF FLUORINE- so the factors that affected this combustion were studied as follows. It seemed most likely that loss of fluorine occurred during the Schoniger combustion, Replacement of the distilled water used to absorb the combustion products with sodium hydroxide solution failed to improve the assay results, which continued to indicate a fluorine content of about 93 per cent.of theory. The addition of oxidising agents (in this instance, sodium peroxide or potassium perchlorate) to samples before combustion, especially when fluorine is present as a CF, group (as in niflumic acid), had been suggested by some workers8 as a way of avoiding incomplete oxidation. Neither of these oxidising agents, when added, led to an increase in assay values for fluorine content above 93 per cent. of theory. Silica flasks were substituted for those made of borosilicate glass, because Johnson and Leonardg had shown that fluorine determinations by the Schoniger combustion technique carried out in borosilicate glass showed an apparent loss in fluorine content. The fluorine content found was still 93 per cent. of theory, but the assay results appeared to be much more consistent than those previously obtained with boro- silicate glass apparatus.When an aliquot of sodium fluoride solution was used as the absorbing liquid in a blank combustion by the Schoniger method (Le., by using only the paper-strip carrier and no sample), its titre of fluoride was lower than that of the sodium fluoride solution that was not subjected to the combustion procedure. The difference was attributed to carbon dioxide produced in the combustion; titres for carbon dioxide saturated and carbon dioxide free sodium fluoride solutions differed by about 9 per cent. Interference by carbon dioxide in the titration of fluoride was first reported by Banerjeelo and Schoniger.2 Banerjee showed that carbonate ions seriously affected the colour change of the indicator SPADNS [the trisodium salt of 2-(~-sulphophenylazo)-1,8-dihydroxynaph- thalene-3,6-disulphonic acid], but neither he nor Schoniger reported a decrease in titration value due to the presence of carbon dioxide.EFFECT OF DIFFERENT CONCENTRATIONS OF DISSOLVED CARBON DIOXIDE ON FLUORIDE TITRES- In order to determine whether the fluoride titre was dependent on the amount of carbon dioxide dissolved in the solution, various amounts of sodium carbonate were added to aliquots of sodium fluoride solution, which were equivalent to 2 mg of fluoride. After the pH had been adjusted to 3.35, the solutions were titrated with thorium nitrate solution, with methyl- thymol blue as indicator. The results obtained are shown in Table I. TABLE I EFFECT OF THE CONCENTRATION OF DISSOLVED CARBON DIOXIDE ON FLUORIDE TITRES Amount of sodium carbonate addedlmg 0 100 300 500 700 900 Titre for 2 mg of fluoridelm1 5.40 5-02 4.97 4.97 4-99 4.96 The amount of carbon dioxide produced by combustion of the paper carrier was equivalent to about 500 mg of sodium carbonate, and the effect on the titration value may be considered to be constant.Consequently, interference by carbon dioxide can be overcome by addition of sodium carbonate to the sodium fluoride solution before standardisation of the thorium nitrate solution. Schoniger2 avoided this interference by boiling the solution to expel carbon dioxide before titration. However, we have found the time of boiling to be extremely critical and therefore adopted the alternative procedure described above.548 HEYES: INTERFERENCE OF CARBON DIOXIDE I N THE [Ana,!ySt, VOl.98 The over-all combining ratio of fluoride to thorium in the presence of carbon dioxide was calculated to be 4-35: 1 when using the constant titration value given in Table I. METHOD APPARATUS- into which was fused a platinum basket on a platinum wire. Silica $ask, 500-ml capacity-This flask (Jobling Ltd.) was fitted with a glass stopper Paper-strip carriers-These were cut from Whatman No. 42 ashless paper. REAGENTS- All materials were of AnalaR grade, and distilled water was used throughout. Sodium $uoride solution-Dissolve 0.1 1 g (accurately weighed) of oven-dried (1 10 "C) sodium fluoride in water and dilute the solution to 50 ml. Thorium nitrate solution, 0.005 M-weigh 2.76 g of thorium nitrate tetrahydrate into a 1-litre calibrated flask.Dissolve it in and dilute to volume with water. Methylthymol blue (pentasodium salt) indicator solution, 0.2 per cent. mlV, aqueous- Eastman-Kodak. Bufer solution, pH 3-35-Dissolve 67 g of glycine and 110 g of sodium perchlorate in about 500 ml of water. Adjust the pH to 3.35 with 60 per cent. perchloric acid. Finally, dilute the solution to 1 litre with water. Sodium carbonate solution, 5 per cent. m/V, aqueous-Prepare by using the anhydrous salt. Perchloric acid, approximately 1.0 N-Dilute 105 ml of 60 per cent. perchloric acid to 1 litre with water. STANDARDISATION OF THORIUM NITRATE SOLUTION- With a pipette, transfer 2 ml of sodium fluoride solution into a 100-ml beaker and add, with a measuring cylinder, 10 ml of sodium carbonate solution.Adjust the pH to 3.4 with 1 N perchloric acid. Transfer the solution to a 500-ml silica flask (inconsistent titration values were obtained when using borosilicate glass conical flasks) and add 25 ml of buffer solution (pH 3-35). Add 1 ml of indicator solution and titrate with thorium nitrate solution to the first appearance of a blue colour. Repeat this procedure, omitting the sodium fluoride solution; this is the titration blank. PROCEDURE- Determination of juorine in a sample-Weigh on to a paper-strip carrier enough sample to contain about 2 mg of fluorine. Carefully fold the paper and place it in the platinurn basket of the combustion apparatus. Introduce 20ml of water into the silica flask, wet the ground-glass joint and flush the flask with oxygen.Ignite the paper strip and immediately insert it into the flask. Tilt the flask so that there is water in the neck, thus forming a barrier between the combustion products and the external atmosphere. When combustion has been completed, shake the flask vigor- ously for 5 minutes, then allow it to stand, with occasional shaking, for about 30 minutes. Wash down the stopper and platinum basket with distilled water and add 25 ml of buffer solution (pH 3.35) to the flask. Titrate the solution with thorium nitrate solution, using 1 ml of indicator solution. For the titration blank, repeat the above procedure omitting the sample, i.e., by using a paper-strip carrier only. RESULTS AND DISCUSSION Seventeen organofluorine compounds, mainly pharmaceuticals, were assayed for fluorine content by the above method.The compounds chosen represent different types of organo- fluorine groups that occur in pharmacologically active molecules ; some of them contain atoms other than carbon, hydrogen and oxygen, such as nitrogen or sulphur, which, on combustion, may form oxides that would interfere with the assay procedure, as does carbon dioxide. From Table 11, it can be seen that no difficulty was experienced in obtaining complete oxidation of the trifluoromethyl group, as had been reported by some worker^,^ and that no interference in the assay resulted from the presence of nitrogen, sulphur or chlorine.July, 19731 TITRIMETRIC DETERMINATION OF FLUORINE 549 TABLE I1 FLUORINE CONTENT OF ORGANOFLUORINE COMPOUNDS Type of Elements Theoreti- organo- present cal 99 per fluorine other fluorine cent.con- group than content, Actual fluorine Standard fidence Compound present C, H and 0 per cent. found, per cent. deviation limits 4-Fluorobenzoic acid Trifluoroace tanilide Fluphenazine hydrochloride Triflupromazine hydro- Trifluoperazine dihydro- H ydroflumethiazide Bendroflumethiazide Nifiuniic acid chloride chloride Flufenamic acid Triamcinolone Triamcinolone acetonide Fluocinolone acetonide Fluoxymesterone 9cc-Fluorohydrocortisone Research compound Research compound acetate C,,H,,FO, (SQ 15102) C,,H,,FO, (SQ 15112) m-Trifluoromethyl- benzoic acid C-F - 13-56 CF3 N 30-14 CF, N, S, C1 11.17 CF, N, S, C1 14.66 CF3 N, S, C1 11-86 N, s 17-21 13-53 N, s N 20.20 CF3 CF, CF, N 20.27 - 4.82 C-F C-F -- 4-37 C-F (tW0) - 8.40 C-F - 5.65 C-F - 4.50 CF3 C-F - 4.11 C-F - 3.83 CF, I 29-98 13.81, 13-61 - - 29-80, 30.50 - - 11.10, 11.32 14.71, 15.02 - - - - -- - 11.52, 11-66 17.38, 17.72, 17.82 - - 13-38, 13.69 20.10, 20-15, 20-05 0.17 &0*95% 20.10, 20.00, 20.15 19-75, 19.85, 19-72 20.25, 20.05 - - 4-94, 4.92 - - 4-26, 4.31 - - 8-21, 8.20 - - 5.50, 5.64 - - 4.39, 4.43 - - - - 4.04, 4.02, 4.18 - - 4.15 3.82, 3.73, 3.78 0.046 &1*24% 3.81, 3.88, 3.76 3.84, 3-82, 3-74 3.79 29-50, 30.15, 29.60 0-25 f 1.09% 29.50, 30.20, 29-60 30.00, 29.60, 30.10 The 99 per cent.confidence limits were calculated from the assay results obtained for niflumic acid, m-trifluoromethylbenzoic acid (the recommended standard for the determination of fluorinell) and the research compound C29H,,F0,. The confidence limits indicate the precision of the method to be &l per cent. REFERENCES 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. Schoniger, W., Mikrochim. Acla, 1955, 123. Hall, R. J., Analyst, 1963, 88, 76. Soep, H., Meded. Vlaarn. Chem. Vereen., 1959, 21, 49. Armstrong, W. D,, J. Amer. Chern. SOG., 1933, 55, 1741. Oliver, F. H., Analyst, 1966, 91, 771. Selig, W., Ibid., 1968, 93, 118. Belcher, R., Leonard, M. A., and West, T. S., J. Chern. SOC., 1959, 3577. Johnson, C. A., and Leonard, M. A., Analyst, 1961, 86, 101. Banerjee, G., Analytica Chinz. 14cta, 1955, 13, 409. Analyst, 1962, 87, 304. -, Ibid., 1956, 869. Received November loth, 1972 Accepted February 13th, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800546

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

550 Book Reviews [Awlyst, VOl. 98 QUANTITATIVE CHEMISTRY: AN EXPERIMENTAL APPROACH. By JOHN T. DONOGHUE. Pp. viii This book represents a collection of laboratory exercises used in a course of quantitative chemistry at the University of Arkansas. They are deemed to be suitable for a one-year course or, by selection of appropriate experiments, they may be the content of a half-year course. There are approximately thirty-five experiments in the book, ranging from polarography and ampero- metric titrations, through the colorimetric determination of formamide to the standardisation of aqueous sodium hydroxide solution against potassium hydrogen phthalate. Exercises in flame photometry and fluorimetry compete for space with sketches of Buchner funnels, magnetic stirrers and condensers and yet the book, and its implicit philosophy, are exciting.The author includes, for several of the experiments, additional exercises that require the student to show, through the calculations, that he has thoroughly understood the basic principles of the practical exercise. These calculations and problems also serve to indicate some of the scope of the practical techniques. It is time that modern teaching methods used modern analytical techniques and perhaps we may learn something from such an experimental approach. I do not agree with all of the author’s experiments and their arrangement, but it is a worth- while book and teachers of analytical chemistry should know of it. It presents perhaps a slightly unorthodox viewpoint but one which is nevertheless very acceptable.+ 136. New York and Belmont: Bogden & Quigley Inc. 1972. Price k3. L. S. BARK SPOT TESTS IN INORGANIC ANALYSIS. By FRITZ FEIGL and VINZENZ ANGER; Translated by RALPH E. OESPER. Sixth Edition. Pp. xxx + 669. Amsterdam, London and New York: Elsevier Publishing Company. 1972. Price Dfl. 125 ; $39 (approximately). In these enlightened days of sophisticated instrumental methods of analysis, it is an indis- putable fact that good use is still being made of conventional chemical reactions (spot tests) in qualitative analysis. Solid-source mass spectrometry and emission and atomic-absorption spectroscopy are examples of the powerful analytical tools used for resolving inorganic problems, but they have their limita- tions and, understandably, are not always to hand.Spot tests are simple to apply; they usually involve small samples, and often provide more information than can be obtained by instrumental methods. An outstanding advantage of these chemical reactions is that they are more likely to provide information on the “state” of the element in question, e.g., the presence of chlorine as the free element, chlorate or hypochlorite, etc. A typical example of the versatile nature of these reactions, and the simple innovations utilised and described in this book, is the test outlined on page 304 for detecting down to 0.3 pg of potassium permanganate in a saturated solution of alkali chromate. A drop of the test solution is placed on a filter-paper, the cellulosic paper is oxidised by the permanganate, and the manganese dioxide formed is deposited in the capillaries of the paper; the unaffected chromate is washed out.It is difficult to envisage an alternative instrumental or simpler chemical method for dealing with this problem. This brief introduction is not intended for the many analysts throughout the world who need no introduction to Feigl’s publications, and who will have eagerly awaited the appearance of this sixth edition. Since the previous edition of the book was published in 1958, many new analytical reagents and reactions have been mentioned in published papers ; these have been assessed by the present authors and, when appropriate, the essential details have been included in this latest, completely revised and enlarged edition of “Spot Tests in Inorganic Analysis.” Compared with the fifth edition of the book, more tests (899 instead of 649) and several new chapters have been added.Chapter 1 retains the title “Development, Present State and Prospects of Inorganic Spot Test Analysis.” Chapter 2, “Methodology of Spot Test Analysis,” has been completely revised and enlarged by Dr. G. Skalos. This chapter includes sections on, e.g., “Hand- ling of Vapors and Separation of Gases,” and “Conduct of Spot Test Analysis.” Chapter 3 has the title “Preliminary Orientational Tests.” Chapters 3, 4 and 5 of the earlier edition now appear as Chapter 4, “Tests for the Elements, Their Ions and Compounds,” which, with 430 pages, is the largest of the book’s six chapters. This chapter is divided into sections in which the elementsJuly, 19731 UOOIC REVIEWS 551 are dealt with indivitlually arid in alphabetical order.Thcse sections are further divided, the sub- sections corresponding to the form in which the element is present, e.g., in the free state, as an anion or cation, in a non-ionic form or organically bound. Numerous references are given in each of these sub-sections, and they are supported by a bibliography of published procedures in Ivhich the reactions referred to in the text have been applied on a quantitative basis. The chapter on ‘I-4pplication of Spot lieactions in Tests of Purity, Examination of Technical Materials, Studies of Minerals,” now Chapter 5 , contains an additional thirty-four sub-sections (now 129) under such headings, chosen at random, as “Detection of Traces of Nitrate in Alkali Molybdate, Tungstate and Vanadate,” and “Detection of Free and Polysulphide Sulphur in Mix- tures and Minerals.” Chapter 6 is a “Tabular Summary,” largely devoted to the limits of identi- fication attained by the spot tests recommended throughout the book.liegrettably, Professor Feigl did not live to see the release of this sixth edition; he died in January, 1971, and it is evident from the foreword to the book that the bulk of the revision was carried out by Dr. Anger. Perhaps, therefore, it is timely to modify an old clichk and ask, as the occasion demands, “What has Feigl - Anger to say on the subject ?” Apart from giving full inarks to Dr. Ralph E. Oesper for the excellence of his translation of this book into the English language, little more remains to be said in praise of the up-dating of a book that is already a recognised classic in its field of application. W.T. ELWELL INTRODUCTION TO MASS SPECTROMETRY. Second Edition. By H. C. HILL; revised by A. G. LOUDON. Pp. viii + 116. London, New York and Rheine: Heyden & Son Ltd. 1972. Price ;52-75; $7.25; DM25 (hardback) ; i l - 5 0 ; $3.90; DM13.50 (softback). It includes chapters on instrumentation and sample handling, basic aspects of organic mass spectrometry, fragmentation of positive ions and interpretation of the mass spectrum. It also includes a selection of unnamed mass spectra upon which the reader may try identification methods. There are also a selection of references, a subject index and two prefaces. The book has been skilfully revised by A.G. Loudon, who has kept to the spirit of the original text. Moreover, the publishers have taken this opportunity to modify the section on instrumen- tation as well as altering the format of the work. Although the book is deservedly popular, as is evidenced by its translation into German, Italian and Japanese, it is, alas, not without flaws. In particular, certain statements are made that should not be made without further qualification; ranking high amongst these are the more or less casual references to Stevenson. Stevenson’s rule lays down certain conditions that may lead to the production of a fragment ion in its ground state, but this is not made clear in the text. Equally important in an introductory text is the need to be precise about simple details, e.g.(page 5, line 4), E should be 21.21 eV. Another error appears on the same page: if in a single- focusing mass spectrometer the voltage varies while the field strength remains fixed, the field is represented by If, if the reverse is true the magnetic term is represented by B, the magnetic induction. A somewhat perplexing English phrase has also been noted: “at one time” (page 8, line 8) should surely be “one at a time.” Surprisingly, there is also the failure to use the symbol to indicate a rearrangement process. Finally, the reviewer regrets that there is no table to relate SI units, which are now being taught to students, with the traditional units used by their forebears. One looks forward to the correction of these rather trivial but irritating errors in the next edition.The book is well produced, eminently readable and is to be thoroughly recommended. This deservedly popular work has now appeared in a second edition. R. I. REED ANALYTICAL CHEMISTRY OF PHOSPHORUS COMPOUNDS. Edited by M. HALMANN. Chemical AHalysis : A Sevies of Monographs on Analytical Chemistry and its Applications, Volume 37. Pp. xii + 850. New York, London, Sydney and Toronto: Wiley-Interscience. 1972. Price Q6.80. This book commences with an introductory chapter on the r61e of phosphorus in the world, which is followed by chapters on methods of determining total phosphorus and the analysis of phosphorus compounds by separation and identification methods. Determination of compound groups and phosphorus in specific materials completes the remainder of the book.552 BOOK REVIEWS [Analyst, Vol.98 It is obviously difficult to cover such a wide range of topics in detail in only approximately 800 pages. One could, for instance, write a book on the analytical chemistry of the condensed phosphates whereas this, and other, subjects are treated very sketchily in this particular book. In Chapter 6, after a brief section on general considerations, the authors deal with the mass spectra of various functional types of phosphorus compounds. There is an abundance of examples, but in some cases they degenerate into little more than a description of the mass spectrum obtained. Errors such as Ph, for phosphine and [(CH,),SiO],PO, for tristrimethylsilyl phosphate are made more noticeable by the lack of readable material.Without questioning the accuracy of the data in the chapter concerned with vibrational spectroscopy, it can be said that some stamina is required in order to find the information sought, and spectroscopic data are scattered elsewhere in the book with consequent duplication. The presentation of the data is poor and the tables are, in some instances, far too long and consequently tedious to use. The authors could have used simple molecules in order to show the appearance of typical organophosphorus compounds. There are a number of printing errors in the notes to the spectra. The chapters on chromatography form a good reference source, provided that one has the patience to find what one is looking for. Why on earth did the editor not do some editing? On the credit side, the chapter on nuclear magnetic resonance spectroscopy is well balanced and up to date.Comments on the relevance of the latest advances in the field are particularly helpful. On page 157, P(OCH,),iscalled trimethylphosphine and the coupling range for CH,CP(O) < is surprisingly absent from the table of coupling constants on page 181. The gas - liquid chromatography of pesticides is very well covered with a full description of the various specific phosphorus detectors. Overall, of its type, this is a useful reference book for non-phosphate chemists and for those phosphate chemists who can afford to buy it for occasional use. The sections on classical analysis are adequate, considering the space available. S. GREENFIELD A PROGRAMMED INTRODUCTION TO INFRARED SPECTROSCOPY.By €3. W. COOK and I<. JONES. Pp. xvi + 192. London, New York and Rheine: Heyden & Sons Ltd. 1972, Price i1.50; $3.90; DM13.50. It presents the basic principles of infrared spectroscopy, its practice, and its use in routine analytical work in about the clearest and most elementary way possible. The book opens with a “Criterion Test” of twenty questions that the student can attempt to answer before and after reading the text; a ‘Validation Report” in the Preface claims that, in terms of this test, the efficiency of the book as a teaching programme is 67 per cent., 62 per cent. of a random group of students who scored less than 20 per cent. in the pre-test scoring 75 per cent. or more after reading the book. After reading the text carefully, a student should certainly be able to understand the terms used in infrared spectroscopy and the reasons why compounds exhibit infrared absorption ; under- stand the operating principles of the components of a commercial spectrometer ; identify and correct the faults that produce spectra of poor quality; prepare samples and obtain spectra for all the different physical forms of sample that commonly occur; calculate the thickness of cells; apply Beer’s law, make quantitative measurements and use internal standards ; use correlation tables of frequencies; and be able “to start building a working knowledge” of how to interpret spectra -a section that is particularly well presented, with many illustrative examples of reproductions of spectra and quiet inculcation of the basic fact that experience is essential.The price is very reasonable, but the purchaser must realise that the construction of this type of book leads to his having to buy a lot of plain paper : there are over fifty pages on which there are six or less lines of print saying, in effect, “sorry, but you are wrong, re-read page 123 then try again”; the basic information offered by this book is contained in about ninety pages. Those teachers and students who like to use modern programmed learning texts will nevertheless welcome the appearance of this one. It is a good example of its kind. This book is intended for the absolute beginner. D. M. W. ANDERSON

ISSN:0003-2654    

DOI:10.1039/AN9739800550

出版商:RSC    

年代:1973

数据来源: RSC