摘要:

168 Analyst, March, 1974, Vol. 99, @. 168-170 Automated in situ Preparation of Azomethine H and the Subsequent Determination of Boron in Aqueous Solution BY W. D. BASSON, P. P. PILLE AND A. L. Du PREEZ (Defiartnaent of Inorganic and Analytical Chemistry, University of Pretoria, Pretoria, Republic of South Africa) A procedure for the preparation of azomethine H and the use of the reagent in the same system for the determination of boron in solution is described. A DRAWBACK to the automated procedure recently described for the automated determination of boron in plant tissue1 is the time needed to prepare the required reagent, azomethine H, and the fact that, unless stored in a desiccator, it is unstable, resulting in changes in the calibration graphs. Moreover, aqueous solutions of the reagent tend to hydrolyse rapidly, unless they are refrigerated, and should not be stored for longer than 1 day because of their loss of sensitivity. In continuous-flow procedures, this tendency towards hydrolysis leads to considerable drift during the determination, In this paper a procedure is described whereby the azomethine is prepared in sit% in a continuous-flow system and is subsequently used for the determination of boron in aqueous solutions. This procedure results in a system in which the above-mentioned problems are overcome, thus increasing the effectiveness of the basic method.The formation of Schiff's bases from a carbonyl compound and a primary arnine is catal- ysed by the presence of an acid, a carbinolamine (I), being formed first, which rapidly elimin- ates water to give the Schiff base (11)- RR'CO+ R"NH2 + R- E" -NHR"* RR'C=NR" -I- HzO I R' I I t From studies with semicarbazide Hammett2 concluded that the addition of a proton to the carbonyl group gives a carbonium ion, RR'COH+ (R' is hydrogen or an alkyl radical), which adds rapidly to the base.Deprotonation of this adduct is the rate-determining stage, leading to the formation of the carbinolamine (I). The condensation between benzaldehyde and aniline has been shown to be first order with respect to aldehyde, amine and acid cataly~t.~ It appears, therefore, that the reaction between aldehydes and amines is rapid. The possibility of preparing azomethine H from salicylaldehyde and H-acid (8-amino-1 -naphthol- 3,6-disulphonic acid) in a continuous-flow procedure, and then utilising it to determine boron in the same system, is reported here.EXPERIMENTAL APPARATUS- Technicon AutoAnalyzer-11 equipment. REAGENTS- All reagents are of analytical-reagent grade, unless otherwise specified. METHOD AND RESULTS- In view of the work carried out by Deming and Morgan4 on their optimisation, the reaction conditions for the determination of boron with azomethine H were studied on the basis of the @ SAC and the authors.BASSON, PILLE AND DU PREEZ TABLE I . - - 169 I COMPARISON OF RESULTS FOR BORON CONTENT OBTAINED BY USE OF ORIGINAL AND MODIFIED PROCEDURES Automated procedure,l Suggested procedure, 2-90 0.42 I 1 -60 ,.oo 0-42 p.p.m. 38 9 84 24 33 6 Sampler wash Air Sal icy 1 - aldehyde H-acid p.p.m. 36 10 81 26 33 5 27-turn MDC Recorder - Colorimeter suggested simplex model.Three variables, viz., pH, concentration of H-acid and concentra- tion of salicylaldehyde, have to be considered in order to optimise the reaction conditions for the preparation of the azomethine. By using the earlier flow system1 the optimum conditions for the determination of boron were found to be a pH of 6.35 (previously established1 as 5.1) and an azomethine H concentration of 9.5 g dm-3. The following reactant conditions were finally selected. H-acid-A 2.5-g amount of H-acid was dissolved in 250 cm3 of distilled water and the pH was adjusted to 2-25. L t Air '.O0 Azomethine, 3 3.90 1 420nm 1 I 27-turn D D D 27-turn c c c 37-turn -P- IO-turn double mixing coils Waste- lao0 Azomethine I 0.42 Air 0.62 Sample Buffer EDTA 1 moo 1 -20 1 -00 , Waste4 1 I 1.00 I Fig.1. Flow diagram for the preparation of azomethine H and the determination of boron in aqueous solution. MDC = mixing delay coil170 BASSON, PILLE AND DU PREEZ SaZicyZaZdehyde solution-A 1 -O-cm3 volume of salicylaldehyde was dissolved in 250 cm3 of 80 per cent. ethanol. Samples of plant material were analysed by the procedure previously reported1 and the results compared (Table I) with those obtained by the system described in the present paper and illustrated diagrammatically in Fig. 1. CONCLUSION A more effective automated azomethine procedure for the determination of boron in a variety of materials is described in which the preparation of the azomethine is incorporated into the flow system. REFERENCES 1. 2. 3. 4. Basson, W. D., Bohmer, R. G., and Stanton, D. A., Analyst, 1969, 94, 1135. Hammett, L. P., “Physical Organic Chemistry,’’ McGraw-Hill Book Co., New York, 1940, p. 333. Porai-Koshits, B. A., Problemy Mekhanizma Org. Reaktsii, Akad. Nauk. Ukr. S.S.R., Otdel. Fiz.- Mat. Khim. Nauk, 1953, 238; Chem. Abstr., 1956, 50, 16686. Deming, S. N., and Morgan, S. L., Analyt. Chem., 1973, 45, 278A. Received April 30th. 1973 Accepted October 15tlz, 1973

ISSN:0003-2654    

DOI:10.1039/AN9749900168

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

AnaZyst, March, 1974, Vol. 99, $9. 171-177 171 Determination of Polyoxyethylene p - t-Nonylphenyl Ethers in Pomades BY C. CALZOLARI, L. FAVRETTO AND F. TUNIS (Istituto d i Merceologia, Universitii d i Trieste, 34127 Trieste, Italy) A method is proposed for the determination of polyoxyethylene p-t- nonylphenyl ethers, RO(CH,CH,O),H (R = fi-t-nonylphenyl), in pomades. The method is based on the evaluation of the number average degree of polymerisation of the polydispersity ( E ) by vapour pressure osrnometry and by thin-layer chromatography, and on the spectrophotometric determination of the apparent mean molar absorption coefficient ( E ) at 620nm of the bisammonium tetrathioisocyanatocobaltate(I1) complexes extracted into 1,Z-dichloroethane. The method has been tested for values of E in the range 6.5 to 21.5 and for Weibull distributed polydispersions. Significant systematic errors arise only in mixtures of polydispersions with very different values of E.The accuracy and intralaboratory reproducibility have been evaluated by analysing samples of a pomade of known composition. POLYOXYETHYLENE oligomers derived from alkylphenols, RO(CH,CH,O),H (where R is an alkylphenyl group and n is the degree of polymerisation), are often determined in products containing them by the method of Brown and Hayes,l which is based on the extraction of the complexes, formed by the polyoxyethylene chain with bisammonium tetrathioisocyanato- cobaltate(I1) [(NH,),Co(NCS) J, into an organic phase, followed by spectrophotometric deter- mination in the visible or ultraviolet region.This method gives relative concentration values with respect to a polyoxyethylene compound taken as a standard, as, under similar conditions, the apparent specific absorbance of the complexes in the organic phase varies with the degree of polymerisation of the oligomers and with the nature of the hydrophobic group (R) and that of the extracting solvent. If, for homogeneous oligomers with a definite R group, a relationship can be found between n and the apparent molar absorption coefficient (E), within a certain range of n values, this relationship can, in principle, be made use of for the determination of the oligomers in this range, provided that n can be determined with the aid of other systems. The commer- cial polydisperse products are characterised by the number average degree of polymerisation (G).Their determination involves many accurate operations because of the presence of variously reacting oligomers. For example, with polyoxyethylene 9-t-nonylphenyl ethers (PENPEs) (R = $-t-nonylphenyl), the curve 2 (apparent mean molar absorption coefficient) as a function of ii shows an increasing trend for the value of E to be greater than 5 to 6, with a maximum at about 20 to 25, which is controlled by the solubility of the complexes in the organic phasee2 Observations made on homogeneous compounds (0 < n < 9) substantially confirmed this trend.3 Within a limited range of G values (G always higher than 6) a linear relationship may fit the results, provided the sample is homogeneous or characterised by a narrow distribution of relative molecular masses, as occurs in the Weibull distributed oligomers.4 Suitable choice of solvent and of experimental conditions are important factors for extending the practical applicability of this empirical relationship.Within the above limitations, a method for the determination of PENPE with 6-5 < +i < 21.5 in a typical pomade is suggested and discussed. The method is based on the extraction and determination by absorption spectrophotometry of the complexes formed with bisammonium tetrathioisocyanatocobaltate( 11), in conjunction with the evaluation of Ti for the polyoxyethylene compound by vapour pressure osmometry and by thin-layer chromato- graphy, coupled with direct photometry of the layer.5-7 The matrix generally contains hydrophobic substances such as stearic acid, which are first eliminated so as to avoid interferences in the vapour pressure osmometry and in the thin-layer chromatography. @ SAC and the authors.172 CALZOLARI et al.: DETERMINATION OF [Analyst, Vol. 99 METHOD APPARATUS- 1-cm glass cells for measurement of the absorbance of solutions in the visible range. A Perkin-Elmer 402 ultraviolet - visible recording spectrophotometer was used with REAGENTS- Ethanol, 95 per cent.-RP, Erba. Bisammonium tetrathioisocyanatocobaltate(II)-This reagent was prepared according to the method of Greff, Setzkorn and Leslie2 by dissolving 620 g of ammonium thiocyanate (Fisher, Certified) and 280 g of cobalt(I1) nitrate hexahydrate (Fisher, Certified) in water and making the volume up to 1 litre. Standard aqueous solutions of polyoxyethylene p-t-nonylphenyl ethers, 250 mg 1-l-These solutions were prepared by using compounds with E values of 6.5, 7-5, 8.6, 9.7, 10.8, 12.9, 15.0 and 21.5 (Chemische Werke Huls), which had previously been dried at 50 "C and at a pressure of 0.5 mm of mercury for 2 hours. The solutions should be freshly prepared.The value of +i was controlled by vapour pressure osmometry, by using a Hewlett-Packard Mechrolab vapour pressure osmometer. 1,2-Dichloroethane-RP, Erba, freshly distilled. Sodium chloride-AnalaR grade. Sodium hydroxide solution, 2 M-This solution was freshly prepared from Merck pro DiethyZ ether-Merck pro analysi reagent. Chloroform-Merck pro analysi reagent. analysi reagent. PROCEDURES- Preparation of the sample and extraction of the complexes-Weigh exactly 0.500 g of pomade into a 25-ml beaker, add 4.0 ml of ethanol and heat the mixture for a few minutes at 40 "C in order to dissolve the pomade almost completely.Transfer the solution into a 500-ml calibrated flask, wash the residue in the beaker with 1.0 ml of ethanol and then with 10 to 20 ml of water (40 to 50 "C), adding the wash liquids to the contents of the flask. Finally, wash the beaker with 20 to 25-ml portions of cold water, and add these to the liquid in the flask until a total volume of at least 300ml is obtained. Mix the contents of the flask for a few seconds and make the volume up to the mark, thus obtaining a relatively stable, opalescent aqueous suspension. With a calibrated pipette, transfer 30.0 ml of suspension into a 50-ml calibrated flask, together with 10.0 ml of bisammonium tetrathioisocyanatocobaltate(I1) reagent.Mix the solution and allow it to stand for at least 1 hour. Add 10.0 ml of lJ2-dichloroethane (accurately measured with a calibrated pipette), and extract by shaking the flask vigorously for 3 minutes. Transfer the contents into a 100-ml separating funnel the tap of which is lubricated with water, and, after separation of the phases, transfer the organic layer dropwise into a 15-ml centrifuge tube fitted with a polyethylene tap and centrifuge it for 5 minutes at 3000 r.p.m. Determination of PENPE by absorption spectrophotometry-Measure the absorbance of the clear organic extract at 620 nm in 1-cm cells against a blank consisting of the pure solvent.Taking the dilution into account, the percentage (m/m) of PENPE in the pomade is: A 4aP PENPE, per cent. m/m = 133.3 -=-- (for 6.5 < fi < 21.5) where A is the absorbance, p g is the amount of sample in 1000 ml of solution, a' 1 g--l cm-l is the apparent mean specific absorption coefficient, which is calculated for a given value of fi by means of the expression a' = Z/E = (BE + ct)/(220 + 44.05%), where /3 = 130-0 1 mol-l cm-1 per oxyethylene group, and a = -335.8 1 mol-l cm-l at 20 "C. ii? is calculated from the number average degree of polymerisation found by vapour pressure osmometry and by thin-layer chromatography. Determination of fi by vapour pressure osmometry and by thin-layer chromatography-Ex- tract the PENPE from 250 ml of sample solution by introducing 40 g of powdered sodium chloride and 20 ml of 2 M sodium hydroxide solution, followed by extraction twice with 50 ml ofMarch, 19741 POLYOXYETHYLENE p-t-NONYLPHENYL ETHERS IN POMADES 173 diethyl ether that has been saturated with water.Combine the extracts, evaporate the solution in a small conical centrifuge tube and take up the residue with 5 ml of anhydrous diethyl ether. Centrifuge the solution for 5 minutes at 3000 r.p.m., transfer the clear liquid to another tube, evaporate to dryness at 60 "C and a pressure of 0.1 mm of mercury, and determine the ii? value of the residue in 1,2-dichloroethane by vapour pressure osmometry in a concentration range of 2 to 8 x Take up the residue of another sample with 2.00 ml of chloroform and use this solution (approximately 1 to 2 per cent.m/m of PENPE) for thin-layer chromatography. M. DISCUSSION OF THE METHOD PREPARATION OF THE SAMPLE- The experiments were carried out with a pomade that had the following composition: stearic acid 17.5, propane-1,2-diol 5.0, benzoic acid 0.10, PENPE (5 = 9.7) 5.25, gum tragacanth 1.2 and water 70.75 per cent. m/m. The preliminary dissolution of stearic acid with ethanol and its precipitation by addition of an excess of water allows the preparation of a dispersion, which is stabilised by the surface-active agent, from which it is possible to take a representative aliquot. EXTRACTION OF THE COMPLEXES AND PREPARATION OF CALIBRATION GRAPHS- Compared with other organic phases previously used, 1,2-dichloroethane has the following general advantages : it has lower volatility (with good reproducibility of results), a density greater than that of the aqueous phase, resulting in easy separation by centrifugation, and is a more suitable solvent for insoluble complexes.s The last feature is illustrated by Fig.1, in which absorbances obtained with various organic phases (other conditions being identical) are compared. With 1 ,Zdichloroethane absorbances are enhanced and limiting factors due to the solubility are avoided. 1.2, 1.0 eO.8 - 0.6 - C m - % n a 0.4 - 0.2 - C /- I 1- 10 15 20 25 5 Fig. 1. Absorbances ( x 5 ) at 620 nm and at 20 "C (b = 1 cm) of extracts with various solvents (A, 1,2-dichloroethane; B, chloroform; and C, benzene) as a function of the number average degree of polymerisa- tion ( f i ) of PENPEs.Ratio of organic to aqueous phase 1: 4 V / V . Concentration of PENPE in aqueous phase 25 mg 1-1 Blank tests show that 1,2-dichloroethane reacts slowly with the thiocyanate ions to give ethylene thiocyanate, NCSCH,CH,SCN (see Note), which is extracted into the organic solvent. As this compound absorbs at 240 nm, with a broad band, in lJ2-dich1oroethane, its presence makes the measurement at the maximum for the complexes in the ultraviolet region (321 nm) less reproducible. Therefore the maximum at 620 nm was preferred, although its sensitivity is five times lower than at 321 nm. At 620 nm, interferences caused by ultra- violet chromophores are also avoided. NOTE- This substance was crystallised from organic extracts and identified by i t s melting-point (90 "C, in agreement with that given in the literature@), by elemental analysis, and by infrared and nuclear magnetic resonance spectroscopy.174 CALZOLARI et aE.: DETERMINATION OF [Analyst, VOl. 99 TABLE I POLYNOMIAL REGRESSION ANALYSIS OF E' vcysus .ii RELATIONSHIPS Coefficients of the polynomial 2 = a + /3fi + p? A r > l-degree polynomial 2-degree polynomial I A I U a Y 0.4325 1,2-Dichloroethane - 335.85 130-01 -266.18 1 18-20 Chloroform -683.16 110.79 - 650.62 105-53 0.1832 B P Analysis of the variance A \ Number of observations 1,2-DicAloroetha~e- l-degree polynomial- 35 2-degree polynomial- 35 Chloroform- 10 l-degree polynomial- 2-degree polynomial- 10 Degrees of Sum of Source of variation freedom squares F Due to regression 1 9 762 610 12 830 Deviation about regression 33 25 110 Total 34 9 787 720 Due to regression 2 9 765 263 Total 34 9 787 720 Deviation about regression 32 22 457 6958 Due to regression 1 3 191 217 1299 Deviation about regression 8 19 647 Total 9 3 210 864 Due to regression 2 3 191 387 673 Deviation about regression 7 19 477 Total 9 3 210 864 For every PENPE considered, Beer's law at 620 nm holds at least in the concentration range 5 to 25 mg 1-1 in the aqueous phase, with an intralaboratory reproducibility of 2 to 3 per cent., expressed as the coefficient of variation of the results from the interpolating line. In order to define analytically the empirical relationship 2 versus .ii, polynomial regression analysis has been applied to the results.E has been calculated as follows: ii = (A/4c)/ (220 + 44.05G), taking into account the ratio (V/V) of the organic to the aqueous phase; c g 1-1 is the concentration of PENPE in the aqueous phase. Table I shows the statistical TABLE I1 ACCURACY AND PRECISION' IN THE DETERMINATION OF THE NUMBER AVERAGE DEGREE OF POLYMERISATION (G) BY THIN-LAYER CHROMATOGRAPHY (3 OPERATORS) Sample 1 2 3 4 5 3 S 100 (sp) J- observed theoretical t-value ( (P = 0.99) fi = 6.5 (by vapour pressure osmometr y) Standard 6-28 6-85 6-98 6-99 6.77 f 0.34 f 5.0 3 1.59 5.84 - 6 = 7.5 (by vapour pressure osmometry) Standard 8.04 7-55 7-81 7.72 7.78 f 0.20 f 2.6 3 2.30 8-84 - Extracted 7.59 8.04 7-91 - 7-86 f0.23 f 2.9 2 2-64 9.93 6 = 9-7 (byvapour pressure osmometry) r Standard Extracted 10.50 9.53 9.77 9.79 9.63 9.64 10.27 9-66 10.09 - 9-96 9.63 f0.26 f0-14 f2.6 f 1.5 4 3 2-24 1.00 4.60 5.84 9, average of N determinations; s, root mean square deviation; 100 (s/Z), coefficient of variation, per cent.; f = N - 1 degrees of freedom.March, 19741 POLYOXYETHYLENE p-t-NONYLPHENYL ETHERS I N POMADES 175 results calculated by using an IBM 7044 computer.Comparison of F values shows that a straight line fits the results better than a parabolic curve. The equation Z = -335-8 + 130.0ii is the empirical relationship that is valid for Weibull distributed PENPEs in the range of ii values from 6-5 to 21.5. Fig. 2 shows the regression lines observed in 1,2-dichloroethane and in chloroform. I I I 10 15 20 25 0 ' "- 5 if f i i u 9 T ; n n ~ r rnmncc;nnc nf +ho Q n n a r o n C -=r-'U- I '6.Y. Y l l l V U I I"~LUUU'""U "I *Il" mean molar absorption coefficient ( 2 ) as a function of number average degree of polymerisation ( R ) a t 20 "C, in two-phase extraction of PENPEs with 1,2- dichloroethane (line A) and chloroform (line B). Regression equations: A, Z = - 335.8 + 130.0 +i ( s = f 2 8 and N = 35); and B, 'E =- 683-2+ 110-8 2 (s = f 49 and N = 10). s is the root mean square deviation of the estimate and N is the number of results (in the diagram many of the results are superimposed) EXTRACTION OF PENPE AND DETERMINATION OF 3- Diethyl ether was used for the extraction of the PENPE from the pomade, in combination with salting-out. In order to minimise the extraction of interfering organic acids, the aqueous phase was made strongly alkaline.The results obtained by thin-layer chromatography and vapour pressure osmometry in the determination of 3 for the standard PENPEs are shown in Table 11. The significance of the difference between the value for 3 found by vapour pressure osmometry, and taken as a true value, and the average value found by thin-layer chromatography was evaluated by the Student t-test.1° In every instance, the observed t-values were smaller than the critical values at the 99 per cent. probability level, so that it is justifiable to assume that there is no significant difference. PRECISION AND ACCURACY OF THE METHOD- Table I11 shows the results of the analysis of two samples taken from the pomade that contained 5-25 per cent. (m/m) of PENPE (ii = 9.7). The accuracy of the method is accept- able, as shown by the t-test applied to the comparison of the true value and the average value found.In both samples, the t-value, calculated from N observations, is smaller than the theoretical critical value tabulated at 99 per cent. probability and forf = N - 1 degrees of freedom.176 CALZOLARI et al. : DETERMINATION OF [Analyst, VOl. 99 TABLE I11 EVALUATION OF THE PRECISION AND ACCURACY OF THE RESULTS OBTAINED FROM 5.25 PER CENT. mlm OF PENPE (G = 9.7) THE ANALYSIS OF TWO SAMPLES (A AND B) OF A STANDARD POMADE CONTAINING PENPE, per cent. Analysis No. - 1 5.34 5-36 2 5.39 5-25 3 5.27 5.22 4 5-25 5.29 2 5.3 1 5-28 S f 0.064 f 0.058 observed 1.88 1.04 theoretical 5.84 5.84 (P = 0.99) f 3 3 100 (S/Z) 1.2 1.1 t-value { 3, average; s, root mean square deviation; 100 (s/2) , coefficient of variation, per cent.In Table IV some examples of the systematic errors that arise with a PENPE sample from a mechanical mixture of two polydispersions that had different fi values are reported. In the range 6.5 to 12.9 the polydispersity can be controlled by thin-layer chromatography. Fig. 3 illustrates some distributions obtained by this method, which are plotted on Weibull probability logarithmic paper. * Weibull distributed samples appear as nearly straight lines. Unfortunately, thin-layer chromatography is not very efficient in resolving broad poly- I I 1 I 1 5 10 20 0.1: n Fig. 3. Cumulative distributions of the degree of polymerisation (n) observed in Weibull distributed PENPE samples. Polydispersions are character- ised by their number average degree of polymerisa- tion (ii), which is immediately read out on the abscissa a t the 60 per cent.value. Analyses per- formed by thin-layer chromatography: A, 6.5; B, 9.7; and C, 12.9 @Available from W. Heffer & Sons, Cambridge.March, 19741 POLYOXYETHYLENE P-t-NONYLPHENYL ETHERS IN POMADES 177 dispersities owing to the limited peak capacity of this technique. Further studies are in progress on the determination of 5 in truncated distribution by thin-layer chromatography. TABLE IV ANALYSIS OF MIXTURES AT A CONCENTRATON OF 25 mg 1-l OF PENPE I N THE AQUEOUS PHASE +i for the fi A -value oligomers in (by vapour) - Difference 0 (1 + 1 m/m) osmometry) (Z f $1 (XI [loo ( X - $)/XI (P = 0.99) the mixture pressure Observed Calculated (per cent.) Observed Theoretical 8.6 + 10.8 9.7 0.1443 f 0.0019 0-1429 - 1.0 1.5 6.84 7.6 + 12.9 10.2 0.1463 f 0.0017 0.1479 + 1.1 1.9 6-84 8.6 + 21.6 14.2 0.1695 f 0.0013 0.1785 + 5.0 13.8 5.84 3, average; s, root mean square deviation calculated from N = 4 analyses; A , absorbance at 620 nm (b = 1 cm).The authors are grateful to Dr. E. Cebulec of the Institute of Chemistry, University of Trieste, for his assistance in the measurements by vapour pressure osmometry. Thanks are also due to Chemische Werke Hiils, Marl, Kreis Recklinghausen, West Germany, for supplying PENPE samples. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. REFERENCES Brown, E. G., and Hayes, T. J., Analyst, 1955, 80, 765. Greff, R. A., Setzkorn, E. A., and Leslie, W. D., J. Amer. Oil Chem. Soc., 1966, 42, 180. Crabb, N. T., and Persinger, H. E., Ibid., 1968, 45, 611. Shachat, N., and Greenwald, H. L., “Mechanism of Ethylene Oxide Condensation,” in Schick, Favretto, L., Pertoldi Marletta, G., and Favretto Gabrielli, L., J. Chromat., 1970, 50, 304. Favretto, L., Riv. Ital. Sostanze Grasse, 1970, 45, 187. Pertoldi Marletta, G., and Favretto Gabrielli, L., Tec. Ital., 1969, 34, 649. Weber, J. R., Degner, E. F., and Bahjat, K. S., Analyt. Chern., 1964, 36, 678. Weast, R. C., Selby, S. M., and Hodgman, C. D., Editors, “Handbook of Chemistry and Physics,” Nalimov, V. V., “The Application of Mathematical Statistics to Chemical Analysis,” Pergamon Received February 2Sth, 1972 Amended July 26th, 1973 Accepted September 7th, 1973 M. J., Editor, “Nonionic Surfactants,” Marcel Dekker, New York, 1967, p. 34. The Chemical Rubber Co., Cleveland, Ohio, 1964, p. C-309. Press, Oxford, 1963, p. 47.

ISSN:0003-2654    

DOI:10.1039/AN9749900171

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

178 Analyst, March, 1974, Vol. 99, ++, 178-183 Determination of iota- Carrageenan with 2-Thiobarbituric Acid BY W. ANDERSON AND W. BOWTLE (Department of Pharmaceutical Technology, University of Strathclyde, Glasgow G1 1X W ) A colorimetric method for the determination of iota-carrageenan is des- cribed, based on the measurement of the yellow colour developed by the reaction of the 3,6-anhydro-~-galactose residue with 2-thiobarbituric acid and hydrochloric acid. The method has a sensitivity equivalent to 0.01 mg ml-1 of carrageenan and can also be used to determine carrageenan in blood and urine in concentrations of 0.02 and 0.01 mg ml-l, respectively. The method has advantages of sensitivity, relative specificity, a small sample-volume requirement and convenience over previously published methods for the determination of sulphated polysaccharides, thus providing a means of ex- tending quantitative biological investigations of this group of substances.THE determination of sulphated polysaccharides still presents difficulty and is normally subject to appreciable error, especially when their determination in biological material is required. Several methods have been suggested for the determination of sulphated poly- saccharides; the toluidine blue1 and azure A2 methods can be used, in which the excess of cationic dye, after completion of a metachromatic reaction between the dye and the macro- anionic sulphated polysaccharide, is determined. These methods lack specificity and require carefully standardised conditions, particularly of salt concentration, rendering them unsuitable for routine, accurate determinations in complex media in which the salt concentration varies, when mixtures of macro-anions occur and when dialysis is not always possible.The determination of sulphated polysaccharides from the amount of the sulphate ester or their identification by infrared spectroscopy in media other than simple solutions requires prior removal of the sulphated polysaccharide by precipitation with a quaternary ammonium compound from the m i x t ~ r e , ~ followed by isolation and characterisation of the sulphated polysaccharide prepared from the macro-anion - quaternary ammonium complex and there- after determination with one of the methods referred to.1,2. Such methods have obvious dis- advantages for the routine determination of sulphated polysaccharides in boilogical media in which they are likely to occur in small concentrations.Some of the difficulties can be resolved for certain sulphated polysaccharides by adapting the resorcinol m e t h ~ d , ~ , ~ in which 5-hydroxymethyl-2-furaldehyde, produced from fructose or 3,6-anhydro-~-galactose that has been liberated from the polysaccharide, reacts with resorcinol in the presence of l,l-dieth~xyethane~,~ to form a coloured reaction product, which can then be determined. However, we have found that this method presents certain difficulties when applied to the determination of sulphated polysaccharides containing 3,6-anhydro- D-galactose, not only in biological fluids but even in aqueous solution. The continuing need for a rapid, convenient method for the determination of sulphated polysaccharides containing 3,6-anhydro-u-galactose has been intensified by a recent report on the intestinal toxicity of sulphated polysaccharides after oral administration to experi- mental animals8 and the demonstration that gastrointestinal absorption of certain members of this group of substances with low relative molecular mass can O C C U ~ , ~ ~ ~ ~ together with their traditional and apparently continuing use in foodstuffs, beverages and medicines.In order to provide a more accurate and sensitive method for the determination of sulphated poly- saccharides containing 3,6-anhydro-~-galactose, the use of 2-thiobarbituric acid, previously suggested as a reagent for the quantitative determination of fructosides,ll has been investi- gated, and is now reported.REAGENTS AND MATERIALS- Sul+hated +olysaccharide containing 3,6-anhydro-~-galactose-Both native and degraded iota-carrageenans were used. The native carrageenan was obtained by extraction with hot 0 SAC and the authors.ANDERSON AND BOWTLE 179 water from the red seaweed Eucheuma spinosum ; degraded carrageenan was prepared from native carrageenan by treatment with 0.001 N hydrochloric acid followed by neutralisa- tion with 0.001 N sodium hydroxide solution (after a predetermined degree of depolymerisa- tion, monitored viscosimetrically, had occurred), precipitation with ethanol, dialysis and freeze-drying. Results for these carrageenans are summarised in Table I. Lambda-carra- geenans were obtained by extraction from Chondrus crispus and Gigartina 9istiZlata in the usual manner.For purposes of spectrophotometric calibration crystalline methyl-3,6-anhydro-~-galacto- pyranoside was used. TABLE I PROPERTIES OF SULPHATED POLYSACCHARIDES CONTAINING 3,6-ANHYDRO-D-GALACTOSE Sulphate ester 3,6-Anhydro-~- Mass average content (-OS0,Na) galactose content?, relative molecular per cent. per cent. mass: Native r-carrageenan . . .. .. 37.7 18.70 f 0.21 800 000 Degraded r-carrageenan . . .. 36.1 21-01 f 0.21 25 000 chloride and a gravimetric finish. * Determined by complete acid hydrolysis with 10 N hydrochloric acid followed by addition of barium t Determined by 2-thiobarbituric acid method described herein. 1 Determined by light scattering. 2-Thiobarbituric acid, 1, l-diethoxyethwe and resorcinol-Laboratory-reagent grade.Charcoal-This was Norit A (Sigma), washed with 10 per cent. acetic acid followed by Sugars-The sugars used were D-glucose (AnalaR) , L( +)-rhamnose, D-XylOSe, D-arabinose, Heparin. Chondroitin sulphate. Blood-The blood was obtained by exsanguination from the ox, rat and guinea-pig; 4 parts of fresh blood were collected into 1 part of 3-8 per cent. m/V trisodium citrate solution. The plasma was used after centrifugation and removal of particulate sediment. Urine-Freshly voided normal human urine was used. distilled water and heated to redness in air for 15 minutes. L-fucose, D-galactose , D-mannose, D-fructose (glucose-free) and D-ribose. EXPERIMENTAL COLOUR DEVELOPMENT WITH 2-THIOBARBITURIC ACID- (a) Determinations of monosaccharides and polysaccharides in a series of 2-ml aqueous solutions (the concentrations of which are noted below) were carried out by adding 2 ml of 2 x 10-2 M thiobarbituric acid solution and 2 ml of 10 N hydrochloric acid to each, heating them for 6 minutes at 100 "C, followed by cooling for 2 minutes in an iced water bath and measuring the absorbance at 432nm within 30 minutes.Concentrations of the test sub- stances used were: carrageenans, 1 to 40 mg per 100 ml; heparin and chondroitin sulphate, 10 to 2000 mg per 100 ml; methyl-3,6-anhydro-~-galactose, 0.025 to 0.25 x M; fructose, 0.1 t o 0-25 x l o - 3 ~ ; and other monosaccharides, (b) The determination of degraded carrageenan in blood and urine was carried out as follows.Blood-A l-ml volume of plasma was shaken for 60 minutes at 37 "C with 8 ml of saturated potassium chloride solution so as to dissociate the carrageenan - protein complexes. Protein was precipitated by adding 0.3 ml of 30 per cent. trichloroacetic acid and removed by centri- fugation. The carrageenan in 2 ml of the supernatant liquid was determined by adding 1 ml of 3 x M thiobarbituric acid followed by 1.5 ml of 10 N hydrochloric acid and the method conducted as described in (a) above. The final concentrations of the reagents in the reaction mixture were the same as in the procedure described in (a). Urine-A l-g amount of charcoal was added to 1 O m l of fresh urine and shaken for 30 minutes. After filtration, 0.5 ml of 4 N sodium hydroxide solution was added to 2 ml of the filtrate and the mixture was then placed in a bath at 100 "C for 10 minutes, cooled in an iced water bath, 0-2 ml of 10 N hydrochloric acid added and a 2-ml aliquot treated as in (a) above.to 5 x l o - 3 ~ .180 ANDERSON AND BOWTLE : DETERMINATION OF IOTA-CARRAGEENAN [Analyst, Vol. 99 MODIFIED RESORCINOL METHOD- This method, intended for the determination of fructose and 3,6-anhydro-~-galactose, was carried out as described,"' except that the 1, l-diethoxyethane concentration was varied. 1.6 2 1.2 a -e s1 2 0.8 0.4 RESULTS 8-THIOBARBITURIC ACID METHOD- Colour development-The spectra obtained with the products of the interaction of Z-thio- barbituric acid with iota-carrageenan, methyl-3,6-anhydro-~-galactose and fructose are shown in Fig. 1, which shows a single peak at 432 nm in each instance.Beer's law is obeyed over the ranges of direct application and graphs of the absorbance at 432 nm versus the concentra- tion of the substance in aqueous solution yield the equations shown in Table 11. As would be expected, the lambda-carrageenans from Chondrus crisp~s and Gigartina pistillata con- tained less 3,6-anhydro-~-galactose than iota-carrageenan, which was verified by infrared studies. Colour stability-The first-order rate constants for loss of absorbance at 432 nm for thiobarbituric acid and degraded carrageenan (taken as being representative) in dark and light conditions were 12.4 x lov4 and 29.8 x lo4 min-l, respectively, at 36-5 "C and 06_x and 1.1 x min-l, respectively, at 20 "C. TABLE I1 EQUATIONS FOR COLOUR DEVELOPMENT BETWEEN 2-THIOBARBITURIC ACID AND CARRAGEENANS, METHYL-3,6-ANHYDRO-D-GALACTOSE AND FRUCTOSE Degraded &-carrageenan .. .. .. .. y = 0.0715~ Native L-carrageenan .. .. .. . . y = 0.0633~ Carrageenan from C. crispus . . .. .. y = 0.0463~ XCarrageenan from G. pistillata . . .. .. y = 0.0185~ Degraded X-carrageenan from G. $istillata . . y = 0.0132~ Methyl-3,6-anhydro-~-galactose . . .. .. y = 0.3390~ Fructose . . .. .. .. .. . . y = 0.3110~ y = absorbance a t 432nm; and x = concentration/mg per 100 ml. XCarrageenan from C. crispus . . .. .. y = 0.0121X Specificity-The ratios of the colour intensity developed at 432nm as a result of the reaction between 2-thiobarbituric acid and various sugars relative to that developed by equi- molar amounts of methyl-3,6-anhydro-~-galactose and carrageenan are shown in Table 111.March, 19741 WITH 2-THIOBARBITURIC ACID 181 TABLE I11 SPECIFICITY OF 2-THIOBARBITURIC ACID ASSAY FOR CARRAGEENAN CONTAINING 3,6-ANHYDRO-D-GALACTOSE Ratio r Sugar Fructose .. .. .. .. Ribose . . .. .. .. Fucose . . .. .. .. Mannose . . .. .. .. Rhamnose . . . . .. Xplose . . + . .. .. Arabinose .. .. .. Galactose .. .. .. Glucose . . .. .. .. A* 80.0 2.0 2.0 1-8 1.8 1.2 0.6 0.6 0.6 - Bt 197.0 5.0 5.0 4.0 4-0 2.5 1.4 1-4 1.4 absorbance (432nm)hsing lpmol of sugar absorbance (432nm) using lpmol of methyl-3,6-anhydro-~-galactose absorbance (432nm) using lpmol of sugar absorbance (432nm) using lpmol of carrageenan (repeating unit) * Ratio A = 100 x t Ratio B = 100 x The minimum theoretical relative molecular mass of the repeating carrabiose unit in carra- geenan when sodium is the micro-cation is 405 (calculated on the structures shown by Rees12) and this value was used in calculating the equivalent molar concentrations.Chondroitin sulphate and heparin at a concentration of 200 mg per 100 ml showed absorbances at 432 nm of 0-055 and 0.017, respectively. Determination of degraded carrageenan in blood and urine-Pre-treatments of blood and urine, as described in ( b ) above, required to reduce interference in the assay did not completely remove interfering substances ; blank samples containing no carrageenan showed absorbance values of 0.11 to 0-17 (urine) and 0.05 to 0.08 (ox and guinea-pig blood). However, after accounting for blank values, assays of carrageenan in blood (2 to 100 mg per 100 ml) and urine (1 to 40 mg per 100 ml) yielded graphs that indicated conformity to Beer’s law over the ranges of direct application and the equations in Table IV were derived from the average values obtained. TABLE IV EQUATIONS FOR COLOUR DEVELOPMENT BETWEEN 2-THIOBARBITURIC ACID AND DEGRADED L-CARRAGEENAN IN URINE AND BLOOD Degraded i-carvageenapz in- Urine .. .. .. y = 0.0403~ Control . . .. .. y = 0.0473~ Ox blood .. . . y = 0.0110~ + 0.046 y = absorbance a t 432 nm (corrected for blank values in blood and urine); and x = concentration of degraded L-carrageenan/mg per 100 ml. Blood and urine controls were aqueous solutions of degraded &-carrageenan, treated in a similar manner to plasma and charcoal-treated urine test samples.Control . . .. .. y = 0*0108X Reproducibility-In aqueous solution, the coefficient of variation of the absorbance at 432 nm (for a fifteen-sample series) was not more than 6.6 per cent. at degraded carrageenan concentrations of 1 to 2 mg per 100 ml, and not more than 5-5 per cent. at higher concen- trations. In blood, the coefficient of variation of the absorbance at 432 nm was not more than 6 per cent. at a degraded carrageenan concentration of 20 mg per 100 ml of blood (five-sample series). The reproducibility of the results for urine was less than that in aqueous solution or in blood because of the difficulty of removing all interfering substances from the samples. Coefficients of variation a t degraded carrageenan concentrations in the range from 3 to 45 mg per 100 ml of urine were 5 to 11 per cent.In a six-sample series containing eight to twelve different concentrations of degraded carrageenan, the correlation coefficients between the absorbance at 432 nm and concentration were not less than 0.994.182 ANDERSON AND BOWTLE : DETERMINATION OF IOTA-CARRAGEENAN [A?%a,!$si!, VOl. 99 RESORCINOL METHOD- While the results of Yaphe and Arsenault’ were, in general, confirmed for fructose and for 3,6-anhydro-~-galactose, it was found that the development of the measured absorbance peak at 555 to 558 nm was time dependent and that it occurred after formation of another peak, at 515 to 520 nm, which decreased as the size of the measured peak increased. Further, significant deviations from Beer’s law at 555 to 558 nm occurred at the upper concentration ranges for degraded iota-carrageenan, 16 to 96 mg per 100 ml, although these deviations could be decreased by adjusting the heating time for colour development from 10 to 15 minutes and increasing the 1,l-diethoxyethane concentration from 2-56 to 12-9 pmol per 100 ml of reagent.Further modifications to the 1 ,l-diethoxyethane concentration and heating time were required for carrageenan in urine and unacceptably high blank values could not be overcome when determining carrageenan in blood. Also, for fructose, 3,6-anhydro-~-galactose and carrageenan, a single concentration of 1,l-diethoxyethane did not yield maximum colour development at 555 to 558 nm over the entire range of concentrations investigated. Excess or insufficient 1,l-diethoxyethane caused distortion of the spectra and lowering of the absorb- ance peak.DISCUSSION The use of 2-thiobarbituric acid provides the basis for a method for the determination of 3,6-anhydro-~-galactose and polysaccharides that contain this sugar. Such determinations have previously involved the use of resorcinol reagents, which are believed to form coloured condensation products with 5-hydroxymethyl-2-furaldehyde or its derivative, laevulinic acid, resulting from hydrolysis of the polysaccharide and ring rearrangement of the liberated 3,6-an- hydro-D-galactose. We have found, however, that the resorcinol method is unsuitable for routine direct application in the determination of carrageenan containing 3,6-anhydro-~-galac- tose both in aqueous solution and in biological fluids because of spectral distortion effects that result from the varying 1,l-diethoxyethane requirements for optimal colour development of a variety of test substance concentrations and also because of high blank values.Recoveries of carrageenan from urine were varied (140 per cent. at 10 mg per 100 ml to 70 per cent. a t 120mg per l O O m l ) and the method was found to be virtually inapplicable to assays in blood samples. The proposed method, involving the use of 2-thiobarbituric acid, avoids the difficulties associated with the resorcinol method because measurements are made with reference to a single-peak spectrum and Beer’s law is obeyed over the entire ranges of direct application for both 3,6-anhydro-~-galactose and sulphated polysaccharides containing this sugar, in aqueous solution, blood and urine.The method shows high specificity for 3,6-anhydro-~-galactose, for carrageenan that contains this sugar and for fructose (Table 111). The low absorbances yielded by a number of mono- saccharides are comparable with those found for resorcinol,7 indicating a corresponding lack of interference in the 2-thiobarbituric acid method. In calculating the relative molecular mass of the carrabiose unit used for comparison of these sugars, the minimum theoretical value was used and thus the results given in Table I11 show the maximum interference in the assay that could be caused by these sugars. In addition, colour development in the Z-thio- barbituric acid method by the sulphated polysaccharides heparin and chondroitin sulphate is less than 0.5 per cent. of that developed by corresponding amounts of carrageenan con- taining 3,6-anhydro-~-galactose. Neither of these polysaccharides contains 3,6-anhydro- D-galactose but both might easily cause confusion in the determination of any one sulphated polysaccharide in biological fluids when other methods of assay are used.Fructose develops a strong colour with thiobarbituric acid and might be expected to cause interference, especially in blood and urine. However, when using the pre-treatments described, the interference due to normal levels of all substances is reduced to a value that is widely accepted as being unavoidable in a colorimetric assay of biological materials. In any experiment in which fructose may occur together with carrageenan, treatment of the sample by heating it with 4 N sodium hydroxide solution prior to assay with 2-thiobarbituric acid will destroy any fructose present without affecting the assay.Chloral hydrate has recently been reported13 as developing a colour when treated with thiobarbituric acid under mild, non-acidic conditions (pH 9.5). We have found, however,March, 19741 WITH 2-THIOBARBITURIC ACID 183 that this substance does not interfere in the assay of carrageenan with thiobarbituric acid. Methods that have been used for the determination of carrageenan, which involve the use of cationic dyes, for example toluidine blue, are less suited to the determination of small amounts as toluidine blue is a general reagent for macro-anions in acidic solution, which leads to low specificity and susceptibility to interference from other macro-anions, when such methods are applied to complex materials.Methods that involve the precipitation and isolation of the sulphated polysaccharide prior to infrared examination and determination with toluidine blue,14 apart from incorporating a positive identification step rendered necessary by the non-specificity of the test, are tedious, tend to be subject to substantial quantitative error and require relatively large sample volumes (20 ml of blood; 10 ml of urine) that are im- practical when the experiment calls for small laboratory animals, which may be required to survive the experiment. The need for a rapid, reliable method for the determination of carrageenan containing 3,6-anhydro-~-galactose in the biological fluids of large numbers of small animals has recently intensified, not only as a result of the unknown metabolism of carrageenans and recognition of their toxicity, but also because they find continued use in biological investigationsg~10 and in foodstuffs. The method described, involving the use of 2-thiobarbituric acid, is suitable for such investigations, which have hitherto been hindered by the lack of a suitable assay technique. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. REFERENCES MacIntosh, F. C., Biochem. J., 1941, 35, 776. Jaques, L. B., Monkhouse, F. C., and Stewart, M., J . Physiol. (Lond.), 1949, 109, 41. Scott, J. E., Meth. Biochem. Analysis, 1960, 8, 145. O'Neill, A. N., J . Amer. Chem. Soc., 1955, 77, 2837. Yaphe, W., Analyt. Chem., 1960, 10, 1327. Arsenault, G. P., and Yaphe, W., Analyt. Biochem., 1965, 13, 133. Yaphe, W., and Arsenault, G. P., Ibid., 1965, 13, 143. Watt, J., and Marcus, R., Gut, 1971, 12, 164. Anderson, W., and Soman, P. D., J . Pharm. Pharmac., 1967, 19, 520. Anderson, W., and Bowtle, W. J., Ibid., 1972, 24, 166P. Percheron, F., C. r. Hebd. Se'anc. Acad. Sci., Paris, 1962, 255, 2521. Rees, D. A., A h . Carbohyd. Chem., 1969, 24, 267. Kamat, S. S., Barve, V. P., and Mahal, H. S., Analyst, 1972, 97, 877. Beattie, I. A., Blakemore, W. R., Dewar, E. T., and Warwick, M. H., Fd Cosmet. Toxicol., 1970, Received July 6th, 1973 Accepted October 4th, 1973 8, 257.

ISSN:0003-2654    

DOI:10.1039/AN9749900178

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

184 Analyst, March, 1974, Vol. 99, $9. 184-189 Determination of Trace Amounts of Lead in Steel and Cast Iron by Atomic-absorption Spectrometry with the Use of Carbon Furnace Atomisation BY F. SHAW AND J. M. OTTAWAY (Department of Pure and Applied Chemistry, University of Strathclyde, Cathedral Street, Glasgow, G1 1XL) A method is described for the determination of 1 to 150 p.p.m. of lead in steel and cast iron involving the use of atomic-absorption spectrometry and carbon furnace atomisation. Samples are dissolved in nitric or perchloric acid and analysed directly without pre-concentration. THE determination of levels of lead greater than 0.01 per cent. in steels can be performed satisfactorily by atomic-absorption spectrometry using flame atomisation.192 However, at lower levels the method lacks sensitivity and a Study Group set up by the Chemical Analysis Committee of BISRA preferred a method based on solvent extraction and spectrophoto- metric determination with dithizone, and this method is now adopted as the British Standard Method (BS 1121) .3 Various atomic-absorption procedures have been developed for the determination of low levels of lead in steel and these procedures have been reviewed by Scholes2 and by Hofton and H ~ b b a r d .~ In all instances, complex solvent extraction pro- cedures have been found necessary and the time of analysis can be very long. The presence of small amounts of lead can cause hot rupture during the rolling and forging of stainless steels and can cause the formation of a graphite structure known as Widmanstatten graphite, which may lead to catastrophic failure of cast irons. There is therefore a need for a rapid method for the determination of lead in steels and cast irons in the range 0-0001 to 0.01 per cent.Recently, colleagues at the University of Strathclyde5 have developed a rapid method for determination of lead at these levels based on anodic stripping voltammetry. The great sensitivity of this technique makes possible the direct analysis of solutions of steels with interference only from high concentrations of copper and molybdenum. Owing to the small sample size required, carbon furnace and carbon filament atomisation provide a considerable improvement in absolute sensitivity over flame atomisation for all elements6 However, Fernandez and Manning' also demonstrated an improvement in the limit of detection in terms of concentration by a factor of 50 for the determination of lead by carbon furnace atomisation compared with flame atomisation.It seemed possible, therefore, that this technique might also offer a rapid method for the determination of lead in steel and cast iron, provided that the problems of the matrix could be overcome. Interferences have been reported7,S in the determination of lead by this technique but it has been founds that these are serious only when the solutions are prepared in chloride media. Provided that the lead solutions are prepared in oxy-anion media, e.g., nitric acid, there is no interference from large amounts of iron and other metals.s By using these conditions, we have developed a simple and rapid method for the determination of small amounts of lead in steel and cast iron.EXPERIMENTAL REAGENTS- Reagents of the highest available purity were used throughout. Stock lead solution (100 $.p.m. of lead)-Dissolve 0.16 g of analytical-reagent grade lead nitrate in water, transfer the solution to a 1-litre calibrated flask and dilute to the mark with water and sufficient AnalaR nitric acid to make the final solution M in nitric acid. Iron solution (10 000 p.9.m.) for interference studies-Dissolve 0.5 g of BCS 149/3 iron in 10 ml of 40 per cent. nitric acid, transfer the solution into a 50-ml calibrated flask and dilute to the mark with water. 0 SAC and the authors.SHAW AND OTTAWAY 185 APPARATUS- The instrument used for all measurements was a Perkin-Elmer 306 atomic-absorption spectrometer equipped with an HGA-70 heated graphite atomiser and a deuterium arc back- ground corrector and coupled to an Electronik 19 strip-chart recorder.A Perkin-Elmer Intensitron hollow-cathode lamp was used as the source, The design and operation of the HGA-70 has been described in detail el~ewhere.~g~ Samples are atomised in a graphite tube, 5-3 cm long and 1 cm in diameter, under an argon atmosphere. Samples were transferred to the centre of the tube by means of 50 or 20-4 Eppendorf micropipettes. The HGA-70 has variable time and temperature selectors for sequentially drying, charring and atomising the samples and, once set, this sequence of operations proceeds automatically. In a typical lead determination, the sample or standard is introduced into the centre of the tube and is then dried at 100 "C.Samples can then be charred at an intermediate temperature of 490 "C and are finally atomised at 2200 "C. Only the atomic-absorption signal obtained during the atomisation period is recorded, as shown in Fig. 1. Both the time of drying and the volume of sample introduced into the tube are varied according to the sample being analysed. PROCEDURE A: MILD STEELS AND CAST IRONS IN THE RANGE 0.0001 TO 0.0010 PER CENT. OF Preparation of calibration solutions-Dilute 10 ml of stock lead solution (100 p.p.m.) to 1 litre with water. This solution should be freshly prepared every day. Transfer 0, 1.0, 2.0, 3.0, 4.0 and 5.0 ml of this solution into 100-ml PTFE beakers each containing 0.5 g of BCS 149/3 iron and add 10 ml of 40 per cent.nitric acid. When the iron has dissolved, transfer the solutions into 50-ml calibrated flasks and dilute each solution to the mark with water. The solutions contain the equivalent of 0, 0.0002, 0.0004, 0.0006, 0.0008 and 0.0010 per cent. of lead in steel when 0.5 g of steel sample is used to prepare 50 ml of solution. (ii) Preparation of sample solutions-Weigh 0.5 g of sample into a 100-ml PTFE beaker and dissolve it in 10 ml of 40 per cent. nitric acid. Transfer the solution to a 50-ml calibrated flask and dilute to the mark with water. For the analysis of solutions, follow procedure E, below. LEAD- (i) PROCEDURE B: MILD STEELS AND CAST IRONS IN THE RANGE 0-0010 TO 0.010 PER CENT. OF Pre@aration of calibration solutions-Dilute 10 ml of stock lead solution (100 p.p.m,) to 100 ml with water.Transfer 0, 1.0, 2.0, 3-0, 4-0 and 5.0 ml of this solution into 100-ml PTFE beakers, each of which contains 0-5 g of BCS 149/3 iron, and add 10 ml of 40 per cent. nitric acid. When the iron has dissolved, transfer the solutions into 50-ml calibrated flasks and dilute to the mark with water. These solutions contain the equivalent of 0, 0-0020, 0-0040, 0.0060, 0.0080 and 0,0100 per cent. of lead in steel when 0-5 g of steel sample is used to prepare 50 ml of solution. Preparation of sample solutions-Proceed as in procedure A (ii) above. For the analysis of solutions, follow procedure E, below. LEAD- (i) Prepare this solution freshly every day. (ii) PROCEDURE c: MILD STEELS I N THE RANGE 0.0100 TO 0.0150 PER CENT.OF LEAD- (i) Preparation of calibration solutions-Transfer by microburette 0, 0.50, 0-60, 0-70 and 0.80 ml of the stock lead solution (100 p.p.m.) into 100-ml PTFE beakers, each of which contains 0.5 g of BCS 149/3 iron, and add 10 ml of 40 per cent. nitric acid. When the iron has dissolved, transfer the solutions into 50-ml calibrated flasks and dilute to the mark with water. These solutions, when diluted five-fold, contain the equivalent of 0, 0*0100, 0.0120, 0.0140, 0-0160 per cent. of lead in steel when 0.5 g of sample is used to prepare 250 ml of solution. (e) Preparation of sample solutions-Proceed as in procedure A (ii) above. Before injection of the sample, dilute each solution five-fold. For the analysis of solutions, follow procedure E, below.PROCEDURE D : STAINLESS STEELS IN THE RANGE 0-0010 TO 0-0100 PER CENT. OF LEAD- (i) Pre@aration of calibration solutions-Dilute 10 ml of the stock lead solution (100186 SHRW AND OTTAWAY: DETERMINATION OF TRACE [Analyst, Vol. 99 p.p.m.) to 100 in1 with water. Transfer 0, 1-0, 2.0, 3.0, 4.0 and 5-0 ml of this solution into 100-ml PTFE beakers, each of which contains 0-5 g of BCS 149/3 iron, and add 10 ml of 60 per cent. m/m perchloric acid. When the iron has dissolved, transfer the solutions into 50-ml calibrated flasks and dilute to the mark with water. These solutions contain the equivalent of 0, 0.0020, 0.0040, 0.0060, 0.0080 and 0.0100 per cent. of lead when 0-5 g of steel sample is used to prepare 50 rnl of solution. (ii) Prepayation of sample solutiofzs-Weigh 0.5 g of sample into a 100-ml PTFE beaker and dissolve it in 10 ml of 60 per cent.m/m perchloric acid. Transfer the solution into a 50-ml calibrated flask and dilute to the mark with water. For the analysis of solutions, follow procedure E, below. This solution should be freshly prepared each day. PROCEDURE E : OPERATION OF THE INSTRUMENT- The instrument is operated under the following conditions : Procedure A B, c D I A \ Wavelength/nm . . .. . . . . Lamp current/mA . . . . . . . . Spectral band widthlnm . . .. .. Drying temperature/"C . . . . . . Drying time/s . . .. .. .. Charring temperaturelac .' . .. .. Charring time/s . . .. .. .. Atomisation temperature/'C . . .. Atomisation voltsge/V . . . . .. Atomisation time/s .. .. .. .. Volume of sample solution/pl . . .. Scale expansion . . .. .. * . Argon flow-rate/l min-l (at 40 p.s.i.) . . 383.3 8 0.7 100 40 - - 2200 8 10 60 x 3 1.5 283.3 8 0.7 100 30 - - 2200 8 10 20 x l 1.5 283.3 8 0.7 100 40 490 30 2200 8 10 50 x3 1-5 Sequentially inject samples and standards into the graphite tube and record the atomic- Interpolate sample concentrations from a absorption signal during the atomisation step. calibration graph obtained from the standards. RESULTS AND DISCUSSION INTERFERENCES IN THE DETERMINATION OF LEAD- Studies718 on interferences in the determination of lead by atonlic-absorption spectro- metry using carbon furnace atomisation have indicated that elements such as sodium, iron, calcium and aluminium depress the lead signal when solutions are prepared in chloride media.No interference was found, however, when solutions were prepared in chloride-free media by using nitrate salts and nitric acid. This procedure evidently prevents the volatilisation of lead as a molecular chloride. Use of an oxy-anion medium leads to the formation of the relatively involatile oxides and recent evidencelo suggests that these oxides are efficiently reduced by the carbon from the graphite tube, liberat-ing metal atoms directly in the gaseous state. In the determination of lead in steel at levels down to 0.0001 per cent., a ratio of lo6 would exist between iron and lead concentrations. No interference from 10000 p.p.m. of iron was found on the signal of 0.01 p.p.m. of lead in nitrate media under the conditions described in procedure E.It would therefore be possible to analyse solutions of cast iron and steel by direct comparison with standard solutions that contain only lead in the appro- priate solvent. However, a smoke signal is given by the iron matrix after the atomic- absorption signal of lead, and although the effect of this signal is removed by the background corrector, it was decided, as a precautionary measure, to add the appropriate concentration of pure iron (BCS 149/3) to the calibration solutions to match that in the samples. DETERMINATION OF LEAD IN STEELS AND CAST IRONS- steels and cast irons. The above procedures were applied to the determination of lead in a range of standard Undissolved silica and carbon were allowed to settle to the bottomMarch, 19741 AMOUNTS OF LEAD I N STEEL AND CAST IRON 187 of the calibrated flask before withdrawing the appropriate aliquot for analysis, but the solution could be filtered if required.In our view, analysis at the levels described should be made as simple as possible so as to avoid possible sources of Contamination. The results are shown in Table I. Results obtained by anodic stripping voltainmetry5 are also given for comparison. TABLE I DETERMINATION OF LEAD IN STEELS AND CAST IRONS Lead, per cent. Sample D1 (cast iron) . . D2 (cast iron) . . D5 (cast iron) . . D6 (cast iron) . . D7 (cast iron) . . D8 (cast iron) . . D9 (cast iron) . . BCS 330 (mild steel) BCS 326 (mild steel) BCS 328 (mild steel) BCS 334 (stainless steel) BCS 335 (stainless steel) .. .. .. .. ... . .. .. .. .. .. Ccrtificate value* 0~00012 0.0028 0.0004 0.0022 0.0038 0.0018 0.0070 0.003 0-014 0.015 0-0011 0.0015 Results by procedure indicated A: 0.00013, 0.00010 0.00014, 0.00015 0.00015 B: 0.0031, 0.0029 0-0027, 0.0028 0.0029 A: 0.00035, 0*00037 0.00037, 0*00036 0.00036, 0-00033 B: 0.0024, 0.0025 0.0024, 0.0023 0.0024 B: 0.0039, 0.0041 0.0042, 0.0041 0-0040 B: 0.0018, 0.0020 0.0018, 0.0019 0.0017 B: 0.0070, 0.0077 0.0069, 0*0073 0,0075 B: 0.0025, 0.0026 0.0023, 0.0026 0.0028, 0.0026 C: 0.015, 0.014 0.014, 0.015 0-014, 0.015 C: 0.014, 0-015 0.016, 0.015 0-015, 0,015 D: 0.0010, 0.0010 0~0009, 0.0009 0~0010 D: 0*0015, 0.0014 0.0013, 0.0013 0.0013 Anodic stripping5 - 0.0022 0*0004 0.0024 0.0038 0.0017 0.0066 t o 0.008 0.0022 0.013 0.015 0*0010 0.0013 * The cast iron samples were provided by the British Cast Iron Research Association, Blantyre, Nr.Glasgow and the certificate values for these samples are the analytical results supplied by them which were obtained by a spectrophotometric method. We are grateful to Mr. J. Sneddon for providing these samples and results. The results obtained by atomic-absorption spectrometry are averages from three measurements on each solution. Typical results for sample BCS 326 and a 0.00014 per cent. lead standard are shown in Fig. 1. The results suggest that the method would be satisfactory for the determination of lead in steel and cast iron. A larger range of results was obtained for sample D9 and a similar range was obtained by anodic stripping voltammetry, probably indicating that this sample is inhomogeneous.Ten samples can be analysed in approxi- mately 1 hour, most of this time being taken up in dissolution of the sample; a single sample can be analysed in about 15 minutes.188 SHAW AND OTTAWAY: DETERMINATION OF TRACE [Analyst, VOl. 99 Fig. 1. Atomic-absorption signals for solutions prepared as in procedure A for (A) a standard solution containing the equivalent of 0.0001 per cent. of lead, i.e. 0.01 p.p.m. of lead, in 10 000 p.p.m. of iron (signal includes a small lead blank from BCS 149/3); (B) sample D1 (both A and B a t x 3 scale expansion); and (C) a standard solution containing 0.01 p.p.m. of lead and 10 000 p.p.m. of iron a t x 10 scale expansion showing a small residual smoke smoke signal at D The reproducibility of the method was tested in two ways (Table 11). The reproduci- bility of the instrument was tested by carrying out ten readings on the same sample solution.The reproducibility of the method as a whole was then tested at two concentration levels, by carrying out ten complete analyses of two standard steel samples. The results in Table I1 indicate that the main contribution to the standard deviation is from the instrument repro- ducibility, the relative standard deviation of sample D1 being greater than that of sample BCS 330 as a x 3 scale expansion was used for D1 and no scale expansion for BCS 330. At the concentration levels being determined, the precision is considered to be adequate. There appear to be small differences between the results on samples BCS 330 and D1 in Tables I and 11.However, calculations involving all of the results for these samples only increase the rela- tive standard deviations to 4.2 per cent. for BCS 330 and 13.6 per cent. for D1. The detection limit (20) and sensitivity (1 per cent. absorption) for the lowest concentration range, procedure A, were found to be 0.00004 and 0.000008 per cent. of lead, respectively. At this lowest concentration range, a blank was detected due to lead in the pure iron added to the standard solutions, and this blank was subtracted from the readings on the standard solutions. As mentioned above, if samples are atomised after only a drying step, smoke is given out during atomisation but only after the lead signal has been obtained. Without the background corrector, a large background absorption signal is obtained from the smoke butMarch, 19741 AMOUNTS OF LEAD I N STEEL AND CAST IRON 189 use of the background corrector effectively suppresses this signal.The small residual back- ground signal can be seen at x10 scale expansion in Fig. 1. Investigations designed to reduce the smoke signal by varying the charring temperature and time resulted only in loss of lead during the charring step at temperatures that were still ineffective in removing the smoke. For determinations on solutions in nitric acid, a charring step was therefore omitted. With perchloric acid, which was necessary for dissolving stainless steels, an explosive evolu- tion of smoke occurred during atomisation if no charring step was included. A charring temperature of 490 "C effectively removed most of the smoke from these solutions without a significant loss of lead.TABLE I1 REPRODUCIBILITY TESTS IN THE DETERMINATION OF LEAD Instrument Reproducibility of reproducibility, separate determinations, per cent. of lead per cent. of lead BCS 330 0.0027 0.0028 0.0028 0.0027 0.0027 0.0026 0.0027 0.0027 0.0026 0.0026 Mean . . . . .. .. . . 0.0027 Certificate value . . .. .. . . 0.003 Standard deviation . . .. .. 0-000075 Relative standard deviation, per cent. 2.8 95 per cent. confidence limits, per cent. of lead . . .. . . .. .. - BCS 330 0.0025 0.0026 0.0024 0.0025 0.0026 0.0026 0.0025 0.0026 0.0025 0.0024 0.0025 0.003 0.000082 3.3 f0~00019 D1 0. 000 14 0.000 14 0~00019 0.00014 0~00012 0.00014 0.00015 0.000 16 0.000 13 0*00014 0.00015 0~00012 0~00002 13-3 f 0.000045 our knowledge , no previous publications have described the application of carbon atomisation to the determination of trace elements in iron and steel.The determination To furnace of chromium in steel by use of a tantalum filament has been reported,ll but only at levels of chromium above 0-3 per cent. In the carbon furnace, lead appears to be released readily from the iron matrix and it would seem possible that other volatile elements could be determined by this technique. With less volatile elements, background correction would be essential and the release of the element from the iron matrix might be more difficult. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. REFERENCES Elwell, W. T., and Gidley, J. A. F., Analytica Chim. Ada, 1961, 24, 71. Scholes, P. H., AnaZyst, 1968, 93, 197. Postlethwaite, R. T., Kidman, L., Bagshawe, B., Bills, K. M., Harrison, T. S., and Watt Smith, J. A., J . Iron Steel Inst., 1970, 500. Hofton, M. E., and Hubbard, D. P., Analytica Chim. Acta, 1970, 52, 425. Metters, B., and Cooksey, B. G., Analyst, in the press. Kirkbright, G. F., Ibid., 1971, 96, 609. Fernandez, F. J., and Manning, D. C., Atom. Absorption Newsl., 1971, 10, 65. Shaw, F., and Ottaway, J. M., to be published. Manning, D. C., and Fernandez, F., Atom. Absorption Newsl., 1970, 9, 65. Campbell, W. C., and Ottaway, J. M., submitted for publication. Maruta, T., and Takeuchi, T., Analytica Chim. Ada, 1973, 66, 5. Received December 28th, 1973 Accepted January 17th, 1974

ISSN:0003-2654    

DOI:10.1039/AN9749900184

出版商:RSC    

年代:1974

数据来源: RSC

摘要:

190 Book Reviews [A?znlyst, VOl. 99 VOCABUL.4IRE DES AGENTS DE SURFACE, TERMS ET D~FINITIONS (VOKABULARIUhl VON TENSIDEN BEGRIFFE UND DEFINITIONEN ; JTOCARULARY OF SURFACE ACTIVE AGENTS, TERMS AND DEFINITIONS). (Trilingual.) 2nd Edition. Pp. xiv + 135. Paris: Comitk International des D&riv@s Tensio-Actifs (C.I.D.) Commission de Terminologie. 1972. Price 20F. The second edition of this work by the’ Terminology Commission of the C.I.D. is welcome, but further effort must still be devoted to this field. Readers will find this work very helpful; the indexing is good for the three different languages used in the definitions. One is left, however, with the feeling that a small percentage of the definitions have received insufficient thought, are too theoretical to be helpful to the practising analyst and one or two can be misleading to those not conversant with the detergent field.For example, soap would be better defined as from a mixture of fatty acids containing 8 to 24 carbon atoms; loss of surface-active characteristics is only one requirement for a biodegradable surface-active agent; biodegradability is also referred only to loss of surface activity; procedures used to measure degree of biodegradability may assess com- ponents that have lost their surface activity and different procedures give different degrees of biodegradation; saponification products from neutral fat can also include fatty alcohols and sterols. The text could also benefit by stating how chelating and sequestering agents differ from one another. G. F. LONGMAN ATLAS OF THERMOANXLYTICAL CURVES.Volume 2. (TG-, DTG-, DTA-CURVES MEASURED SIMULTANEOUSLY.) Edited by G. LTPTAY. Pp. 161 (loose-leaf). London, New York and Rlieine: Heyden & Son Ltd. 1973. Price L11.50; $31.66; DM94.50. This Atlas is the latest in a useful series. The layout is slightly different from that of the first volume in that small samples heated a t a slow rate were printed in the first volume on transparent sheets which could bc superimposed on results for larger samples heated quickly which were printed in black on white paper. In the present volume, both plots are printed on the same sheet of white paper. To make the best use of the Atlas, it is best to read the Preface which is included in Volume 1 b u t omitted from Volume 2. The results quoted without critical comment but with precision serve to illustrate the advan- tages and disadvantages of the combination of techniques employed.Thus to quote a few examples, the data for barium oxalate hemihydrate do not indicate that, as formed from the interaction of the soluble barium salt and oxalic acid, the precipitate may be found to have the formula BaC20,.H,C,04.2H,0 and not BaC,04.&H20 as used in the study quoted in the volume. Further- more, the Atlas fails to indicate the way in which the atmosphere plays a decisive part in the oxalate decompositions while other materials are relatively unaffected by the surrounding atmos- phere. This is recognised in some of the coals quoted, which are also reported heat-treated in nitrogen as well as static air.2\11 of the results are clearly presented and the notes are easy to understand. The comments made by the reviewer are only meant to indicate to possible users of the Atlas recognised limitations in the techniques and in a0 way to detract iroiii the advantage offered by these two volumes in providing typical TG, 13TG and DTA curves for some 125 different materials. It should also be noted that the list of references provided is not a complete list and, indeed, this point is made in the preface to Volume 1. As an indication of possible material for further volumes, it woulcl seem feasible to include repeats of some ol the materials already quoted using atmospheres other than static air and crucibles other than platinum. L). DOLLISIORE THE DETERNISATION OF SULPHUR-CONTAINNG GROUPS.Volume 1. THE ~LUALYSIS OF SULPH- Pp. viii + 149. In this short, yet surprisingly comprehensive monograph, a chapter is dedicated to each of the sulphur groiips named in the title. Curiously, isocyanates are inclutlcd, although they contain no sulphur. Each chapter has a similar format, beginning with a brief description of the occurrence OXIDES, SULPHONYL HALIDES, THIOCYXNATES, ISOTIIIOCYAXATES AND ISOCYANATES. By M. R. F. ASHWORTH. London and New I’ork: -\cademic Press. 1972. Price L3.20. A n Iiztevnntional Sevies of lkfonogvaphs, N o . 2.March, 19741 BOOK REVIEWS 191 and use of compounds containing the sulphur group in question, and followed by sections dealing with chemical and physical methods of determination (and, frequently, of detection) of the group.Much of the information concerning the analytical methods is presented in tabular form, and usually in chronological order, which frees the text from a great deal of unnecessary detail while retaining comprehensive coverage. The chemical methods include descriptions of the various decomposition methods, and gravi- metric, titrimetric, spectrophotometric and polarographic finishes. A number of the methods are specific for the particular functional group, but many are simply variations of general methods of sulphur determination. Usually only brief outlines of the various methods are given, but occasionally complete procedures are included. The physical methods are concerned mainly with nuclear magnetic resonance, ultraviolet and infrared spectroscopy and the various chromatographic techniques, and are generally dealt with in less detail than the chemical methods.The book is well produced, appears to be free from typographical errors, and contains an extensive author index as well as the subject index. It should be an essential reference text for all organic analysts. A. TOWNSHEND MASSENSPEKTRENSAMMLUNG VON L~SUKGSMITTELN, VERUNREINIGUNGEN, SAULENGELEGMATERIA- LIEN UND EINFACHEN ALIPHATISCHEN VERBINDUNGEN. By MARGOT SPITELLER and G. SPITELLER. Pp. xiv + 243. Vienna and New York: Springer-Verlag. 1973. Price DM58; $21.50. This is a useful compilation of the mass spectra of common solvents, gas-liquid chromato- graphic paclcings and simple compounds. It is clearly designed to aid those searching for spurious or inexplicable peaks in the display from a combined gas - liquid chromatograph - mass spectro- meter system.The information is tabulated under a variety of headings so that the whole makes a very useful laboratory manual. A brief discussion of the fragmentation patterns of the spectra introduces the compilation. D. BETTERIDGE DYNAMIC MASS SPECTROMETRY. Volume 3. Edited by D. PRICE. Pp. viii + 340. London, In the second volume of this series, the Editor stated that “dynamic mass spectrometry is intended to promote the growth of this technique by providing a medium for the publication of its current developments and applications,” and Volume 2 did indeed try to fulfil this aim. Volume 3 is rather a mixture. It is devoted to time-of-flight mass spectrometry, b u t it contains two excellent long review articles on the applications of inhomogeneous oscillatory electric fields in ion physics and on the application of dynamic mass spectrometers to problems in gas analysis.Both review articles are supported by extensive bibliographies containing nearly 500 references. Much of the remainder of the book is devoted to the proceedings of a European Symposium on Time-of-Flight Mass Spectrometry held 2 ycars ago, and is of primary interest to present and prospective users of time-of-flight mass spectrometers. It is hard to resist the conclusion that this series is in danger of falling between two stools. If its aim is to cover systematically the development of dynamic mass spectrometry, one would think that a deliberate and larger selection of review articles (and some research papers) would be appropriate.To mix these with unselected contributions to a symposium produces a whole which is neither comprehensive nor sufficiently typical. I t is to be hoped that future volumes will include more research papers on the applications of dynamic mass spectrometers in the life sciences and space research as well as the latest dcvelop- ments in related topics such as chemical ionisation, gas chromatography, data handling, surface studies and other selected topics. New York and Kheine: Heyden 8t Son Ltd. 1972. Price k8.75; $21.50; DM72. J. M. B. BAKKER ORGANIC REAGENTS IN METAL ANALYSIS. By K. BURGER. in Analytical Chemistry, Volume 54. Pp. 268. Braunschweig : Pergamon Press. 1973. Price j55.80.International Series of Monographs Oxford, New York, Toronto, Sydney and The main emphasis of the book is on the determination of trace amounts of metals (within the broadest interpretation of the word metals) in, e.g., high-purity materials, although the information, as presented, should enable the analyst to provide his own “tailor-made” procedures. I t may be reasoned that much of the information is already freely available elsewhere, but the initial approach on this occasion is somewhat unusual in that the book deals, in detail and expertly, with the complex chemical reactions involved, from a co-ordination chemistry viewpoint (Chapter 1).192 BOOK REVIEWS [Analyst, Vol. 99 In Chapter 2, established analytical procedures are reviewed in the light of the author’s personal experience.The two main headings in this chapter are “The Methods of Application of Selective Organic Reagents, ” and “Some Important Organic Metal Reagents,” the latter including phenanthroline and its related compounds, oximes, flavones, dithiocarbamates and arsonic acids. Chapter 3 has about the same number of pages as each of the other two chapters, and includes Summarising Tables (e.g., an alphabetical list of organic reagents with supporting details, and a similar list in which the metals appear first), References (496), Author Index and Subject Index. Dr. Burger is Professor of Inorganic and AnalyticaJ Chemistry at the L. Eovos University in Budapest, and this book is an English translation of his 1969 Hungarian publication, supple- mented by several recent references and published procedures.While the potential value of this monograph should not be underrated, current trends in, for example, instrumental methods for determining trace amounts of metals may mean that authoritative publications such as this are likely to have the greatest appeal to research workers in the more conventional fields of analysis. W. T. ELWELL PARAMAGNETIC LANTHANIDE SHIFT REAGENTS IN NMR SPECTROSCOPY : PRINCIPLES, METHODO- LOGY AND APPLICATIONS. By J. REUBEN. Progress in hruclear Magnetic Resonance Spectro- scopy, Volume 9, Part 1. Pp. viii + 70. Oxford, New York, Toronto, Sydney and Braun- schweig: Pergamon Press. 1973. Price fl2. Most failures to obtain the expected information arise when chemical shifts are so small that lines overlap and the spin - spin coupling pattern has complex second-order features.This has resulted in the continual progress to higher frequencies with instruments such as the expensive 220-MHz spectro- meters with superconducting magnets. In 1969, C. C. Hinkley realised that the addition of para- magnetic rare earth complexes (often called shift reagents) to a solution could usually increase chemical shifts, and the idea has proved so simple and practical that over 200 papers on organic applications appeared in the next 3 years. A card-index file on these has been essentially incor- porated into the main section of the book. Since the style is that of the less happy features of annual reports and the interest of individual papers relates to specific organic compounds rather than to the technique, the outcome is decidedly stodgy.A typical reagent is Eu(fod),, where (fod) stands for the anion of the enol form of 1,1,1,2,2,3,3- heptafluoro-7,7-dimethyloctane-4,6-dione. The mode of action appears to be to form complexes with the molecules of interest and the size and magnitude of the shift depend on the stability of the complex and the dominance of contact or pseudo-contact features. The stability question is covered in this text, but the rather difficult contact and pseudo-contact features, each of which can lead to shifts of either sign, are quoted rather than discussed. This is a pity as already, apparently, wrong deductions have been made by those who overlook the (3 cos2 19 - 1) angular term in the pseudo-contact shift or make other assumptions such as a ligand-independent g-factor anisotropy. Some mention of distance determination is made, but its reliability is not discussed. Also, it seems, the enhanced chemical shifts may make difficult quantitative analyses by nuclear magnetic resonance rather easier. To summarise, this book is valuable as being the chief review to date in English, but for anyone who hoped for a critical review and a clear explanation of the more theoretical features of lanthanide shift reagents, it is something of a disappointment. Nuclear magnetic resonance and its many abilities are by now well known. D. H. WHIFFEN

ISSN:0003-2654    

DOI:10.1039/AN9749900190

出版商:RSC    

年代:1974

数据来源: RSC