摘要:

Analyst, June, 1973, Vol. 98, pp. 443-449 443 The Determination of Tin and Antimony in Lead Alloy for Cable Sheathing by Atomic-absorption Spectroscopy BY TERESA M. QUARRELL, R. J. W. POWELL AND H. J. CLULEY (The General Electric Company Limited, Central Research Laboratories, Hirst Research Centre, Wembley, Middlesex, HA 9 7PP) A method has been evolved for the rapid determination of tin and antimony at levels of about 0.4 and about 0.2 per cent., respectively, in lead alloy used for sheathing electric cables. The sample is dissolved in a mixture of fluoroboric acid and hydrogen peroxide and the determination is completed by atomic-absorption spectro- scopy with the use of an air - acetylene flame for antimony and a nitrous oxide - acetylene flame for tin. The method of dissolving the sample avoids the precipitation reactions that are likely to arise from lead, antimony or tin if conventional acid dissolution processes are used and hence permits a direct and rapid analysis by the atomic-absorption technique.Calibration for antimony must be effected with a solution containing the dissolution mixture and, in calibration for tin, lead must additionally be present. THREE alloys of lead, in addition to unalloyed lead, are commonly used as sheathing materials for electric cables. One such alloy, which was the subject of this investigation, is alloy E, in which the alloying elements are tin and antimony at the levels of 0.4 and 0.2 per cent., respectively. Table I gives the composition specified for alloy E.l TABLE I COMPOSITION OF ALLOY E AS SPECIFIED IN B.S.801: 1953 Element Antimony .. .. Tin . . .. . . Tellurium . . .. Silver . . .. .. Copper .. .. .. Bismuth .. .. Zinc . . .. .. Other elements (total) Lead . . . . .. Content, per cent. M i n e u r n .. ,. 0.15 0.26 .. .. 0.35 0.46 .. .. - 0.006 .. .. - 0.006 .. .. - 0.06 .. .. - 0.06 .. .. - 0.002 .. ,. I 0.01 .. . . Remainder Remainder For controlling the composition of alloy E, the determination of the alloying elements tin and antimony is of particular concern. Published methods for these determinations2J are commonly based on titrimetric methods, with the use of iodine and bromate as the titrants for tin and antimony, respectively. However, the determination of these elements by atomic-absorption spectroscopy appeared to offer a more convenient and rapid means of controlling the composition of the alloy, and the evolution of such a procedure is described in this paper.EXPERIMENTAL The steps involved in developing the proposed method were as follows: choicc of flames; dissolution of samples ; and study of interferences. Of particular importance in the choice of flames was the necessity to ensure that adequate sensitivity could be achieved for the determination of tin; antimony, which can be measured with higher sensitivity than tin by flame-absorption methods, was not expected to cause difficulties. The choice of a dissolution procedure for lead-alloy samples was also of importance, @ SAC and the authors.444 [Analyst, Vol. 98 as lead, tin and antimony tend to give rise to precipitation reactions in the presence of the acids that are commonly used for the dissolution of these metals. Clearly, the ideal dissolu- tion procedure should be capable of dissolving and retaining in solution all the constituents of the alloy.The investigation of these aspects of the proposed method and of possible interferences is described in the following sections. CHOICE OF FLAMES- The flame generally used for the determination of antimony is the air - acetylene flame,4g6 which gives adequate sensitivity for antimony but poor sensitivity for tin. The use of both air - hydrogen6 and nitrous oxide - acetylene' flames for determining tin has been reported. The optimum conditions were established for each flame and the signal to noise ratio on a standard solution containing 40 pg ml-l of tin was measured in each instance.(This concentration of tin corresponds to 1 g of lead alloy containing 0.4 per cent. of tin in 100 ml of solution.) TABLE I1 EFFECT OF TYPE OF FLAME ON THE SIGNAL TO NOISE RATIO FOR TIN QUARRELL et al.: DETERMINATION OF TIN AND ANTIMONY IN The results are given in Table 11. Oxidant Fuel Signal to F1 ame flow-rate/l min-1 flow-rate/l min-1 noise ratio Comments Air - hydrogen . . .. 5.0 7-0 11.3 - Air - acetylene . . . . 5.0 2.1 4.6 - Nitrous oxide - acetylene . . 6-0 4.8 10 Smoky flame Nitrous oxide - acetylene , . 5.0 4.3 13.2 Satisfactory flame The hydrogen flow-rate of 7.0 1 min-l was of necessity measured with a flow meter of higher capacity than that fitted on the instrument. A conversion factor relating the two flow meters was obtained, and when applied it gave the figure of 7.0 1 min-1 quoted in Table 11.The nitrous oxide - acetylene flame conditions that gave the maximum sensitivity resulted in a very sooty flame, which tended to cause blocking of the burner. The signal to noise ratio for a non-luminous nitrous oxide - acetylene flame, with wliicli it is far easier to work, was also measured and is included in Table 11. The loss in sensitivity incurred by using the less luminous flame W;LS not great, so these conditions were used when working with the nitrous oxide - acetylene flame. During the development of the method, a modified design of the burner head, with grooves parallel to the slot, was obtained. This burner head reduced still further the frequency with which the burner had to be cleaned of soot, but did not enable the acetylene flow-rate, and hence the sensitivity, to be increased without the incidence of scrious sooting.As the best signal to noise. ratio w;ts obtained with an air - hydrogen flame, a study of the interferences that occurred with this flame was undertaken. A scrious decrease in the instrumental response was observed wlien the flame was used in the determination of tin in a solution containing hydrochloric and nitric acids (see the following section). Different solutions of alloys prepared by using these acids were examined with the use of both an air- hydrogen and a nitrous oxide- acetylene flame. The results obtained are given in Table 111. DETERMINATION Solution number 1 2 3 4 5 6 7 TABLE I11 OF TIN I N ALLOY SOLUTIONS WITH THE USE OF DIFFERENT FLAMES Tin foundlpg ml-l r A > Nominal tin* Air - hydrogen Nitrous contentlpg ml-1 flame oxide - acetylene flame 41 40 b l 41 41 40 40 38.5 35 50 28.6 29.6 27.6 31.6 39 37.5 61.6 41.6 43-0 37.6 39 * Concentrations in solutions caIculated from the stated composition of the lead-alloy samples used in their preparation.June, 19731 LEAD ALLOY FOR CABLE SHEATHING BY ATOMIC-ABSORPTION SPECTROSCOPY 445 It can be seen that the results obtained with the air- hydrogen flame were always lower than those obtained with the nitrous oxide - acetylene flame, in some instances seriously so.The use of the air - hydrogen flame was therefore discontinued and all further investigations on the determination of tin were carried out with the nitrous oxide - acetylene flame. The effect of using an aperture in order to select radiation passing through the core of the flame was also examined.A rectangular aperture, 5 x 3 mm, was inserted in the attenuator carriage of the instrument, i.e., about 90 mm from the centre of the burner on the monochromator side. It was found that the use of this aperture combined with a wider slit improved the signal to noise ratio by a factor of two when measured on a standard solution containing 40 pg ml-1 of tin and 1 per cent. m/V of lead. DISSOLUTION OF SAMPLES- The first method examined for dissolving the sample was based on the first step of the British Standard procedure.2 Samples of alloy E were treated with a mixture of hydrogen peroxide and glacial acetic acid, which dissolved the lead and left a residue that contained mainly tin and antimony.This residue was removed by filtration, dissolved in 1 + 1 nitric acid - hydrochloric acid and the solution obtained was used for the de'termination of tin and antimony. Two samples of alloy E, and also a mixture of lead, tin and antimony metals, were examined by this method and the results are given in Table IV. As the results for the alloys were low, the tin and antimony contents of the filtrates were also determined and the results are also given in Table IV. TABLE IV EXAMINATION AFTER TREATMENT OF ALLOY E WITH ACETIC ACID - HYDROGEN PEROXIDE Nominal content Found in residue Found in filtrate Total +---\ & * Tin, Antimony, Tin, Antimony, Tin, Antimony, -ny, Sample per cent.per cent. per cent. per cent. per cent. per cent. per cent. per cent. A 0.4 1 0.2 1 0.325 0.175 0.073 0.023 0.398 0.198 B 0.40 0.20 0.345 0.185 0.060 0.010 0.406 0.195 Mixture of lead, tin and anti- mony metals 0-40 0.23 0.395 0.215 0.005 0.003 0.400 0-218 The method proved to be unsatisfactory, for the following reasons. (a) The residue that remains after treating the alloy with the cold acetic acid - hydrogen peroxide mixture is difficult to filter; the residue could be coagulated by boiling, but this treatment caused some dissolution of the tin and antimony (see Table IV). (b) An X-ray diffraction examination of the residue given by alloy E after treatment with the acetic acid - hydrogen peroxide mixture showed that it consisted of an antimony - tin intermetallic compound, which indicates that the insolubility of tin and antimony in a mixture of acetic acid and hydrogen peroxide is likely to depend on the relative amounts of the two elements present.Evidence of such an effect was provided by examining an alloy that contained tin and cadmium but no antimony; this alloy was found to dissolve completely in the acetic acid - hydrogen peroxide mixture. Overall, the evidence obtained showed that no reliance could be placed on all of the tin and antimony being present in the insoluble fraction after the dissolution with acetic acid - hydrogen peroxide. The consequent necessity for separate determinations of the two elements in the soluble and insoluble fractions to be made led to the abandonment of this approach.A further attempt was then made to adapt the dissolution step of the British Standard method2 so as to permit the use of atomic-absorption spectroscopy. The British Standard methods for determining tin and antimony both start with the treatment of the sample with an acetic acid - hydrogen peroxide mixture; hydrochloric acid is then added in order to dissolve the tin and antimony, the resultant precipitate of lead chloride is filtered off446 QUARRELL et d.: DETERMINATION OF TIN AND ANTIMONY I N [An&!yd, VOl. 98 and the tin and antimony are determined on the filtrate. The amounts of reagents used in this British Standard method give a solution that is too dilute for the determination of tin by atomic-absorption spectroscopy. A series of experiments was therefore carried out in order to assess the effect of using a smaller final volume.The results obtained from these experiments (Table V) indicate a loss of tin, which is probably caused by the retention of tin by the lead chloride precipitate. TABLE V RESULTS OBTAINED WITH THE MODIFIED BRITISH STANDARD METHOD OF DISSOLUTION Nominal content Found in solution Tin, I m o n y, Tin, Antimony, - Sample per cent. per cent. per cent. per ccnt. A 0.4 1 0.21 0.400, 0.378 0.206 B 0.40 0.80 0.358, 0.348 0.192 In view of the difficulties experienced with the selective dissolution procedure discussed above, a search was made for a single-stage procedure that is capable of dissolving and retaining in solution all of the constituents of the lead alloy. As the fluoroborates of tin and lead were known to be soluble, e.g., from their use in plating solutions, the use of fluoro- boric acid appeared to be worthy of a trial.It was found that l-g amounts of alloy E could readily be dissolved with 5 ml of 42 per cent. m/m fluoroboric acid provided that 4 ml of 100-volume hydrogen peroxide were also added as oxidising agent. This treatment completely dissolved the alloy in a few minutes and the solution obtained could be diluted with water to 100 ml without the formation of a precipitate. The same procedure was adopted later for dissolving pure lead to give a lead solution for addition to calibration standards in order to simulate alloy sample solutions, STUDY OF INTERFERENCES- Following the evolution of the method of dissolution with fluoroboric acid - hydrogen peroxide, it was necessary to establish whether the presence of the dissolution mixture and also of lead had any effect on the determination of tin and antimony by the flame-absorption technique.In the experiments that were carried out in order to investigate such effects, the flame systems used were those previously chosen, vix., air - acetylene for antimony and nitrous oxide - acetylene for tin. It was found that additions of hydrogen peroxide or fluoroboric acid to solutions that contain tin enhance the instrumental response to this element, although the effect of both additives together is similar to that of either additive alone; the additional presence of lead causes a further enhancement. The results of these experiments are given in Table VI.TABLE VI EFFECT OF MATRIX AND SOLVENT ON THE RESPONSE OF THE INSTRUMENT TO TIN Sample Instrument reading 40 p.p.m. of tin as fluoroborate in water . . .. .. .. .. .. 30 40 p.p.m. of tin + 4 per cent. of H202 . . . . . . . . . . . . .. 40 43 40 p.p.m. of tin + 5 per cent. of HBF, .. .. .. .. .. . . 39 40 p.p.m. of tin + 5 per cent. of HBF, + 4 per cent. of H20, . . .. .. 38 40 p.p.m. of tin + 5 per cent. of HBF, + 4 per cent. of H,02 + 1 per cent. of Pb. . Additions of antimony a t a level equivalent to 0.2 per cent. in lead alloy to a solution containing all the other constituents did not further affect the response of the instrument to tin. A corresponding set of experiments was carried out on a solution of antimony, and in this instance additions of hydrogen peroxide and fluoroboric acid increased the instru- mental response by about 8 per cent.Additions of lead and tin to solutions containing fluoroboric acid and hydrogen peroxide did not further affect the instrumental response to antimony . These results showed that for the determination of antimony, the calibration solutions should contain fluoroboric acid and hydrogen peroxide, while for determination of tin, the calibration solutions should contain lead in addition to the mixture used for dissolution.June, 19731 LEAD ALLOY FOR CABLE SHEATHING BY ATOMIC-ABSORPTION SPECTROSCOPY 447 METHOD APPARATUS- oxide attachment and an SP93 air compressor. determining individual elements are given in Table VII. A Pye-Unicam SP90 atomic-absorption spectrophotometer was used viTith an SP94 nitrous The experimental conditions used when Parameter Wavelength .. Slit width .. Burner . . .. Observation height Oxidant . . .. Oxidant flow-rate Fuel . . .. Fuel flow-rate . . Coarse gain . . Lamp current . . Damping. . . . Aperture . . TABLE VII INSTRUMENTAL CONDITIONS Antimony Tin . . .. 217.6 nm 286.3 nm * . . . Air - acetylene, 10-cm slot Nitrous oxide - acetylene, 5-cm slot .. .. 1.4 cm 1.0 cm .. .. Air Nitrous oxide .. .. 5 1 min-l (36 p.s.i.) 5 1 min-l (36 p.s.i.) .. .. Acetylene Acetylene . . . . 1.6 1 min-l (10 p.s.i.) 4.2 1 min-l (10 p.s.i.) .. .. 7 4 .. .. 2 or 3* 2 or 3* .. .. 15 mA 8 mA .. .. Not used Used 0.1 mm 0.4 mm .. .. * Position 2 gives a meter reading; position 3 gives a recorder reading. REAGENTS- Hydrogen peroxide, 100 volume-AnalaR grade.Fhoroboric acid, 42 per cent. m/m HBF,-Laboratory-reagent grade. Standard antimony sohtion-Dissolve 274 mg of AnalaR grade antimony potassium tartrate in water and dilute to 100ml. 1 ml of solution = 100 pg of antimony. Standard tin sohtion-To 50 mg of AnalaR grade metallic tin in a platinum vessel add 2 ml of 40 per cent. m/m analytical-reagent grade hydrofluoric acid. Add 100-volume hydro- gen peroxide dropwise until the tin has dissolved; care must be taken at this stage because if the peroxide is added too fast a precipitate of tin oxide is formed. When all of the tin has dissolved, add 2 g of AnalaR grade boric acid and 20 ml of water and heat the mixture gently until a clear solution is obtained. Transfer the solution into a 500-ml calibrated flask (@ass is satisfactory for the short period of contact involved), make up to the mark with water, mix and transfer it into a clean plastic bottle.Standard lead solution-Mix 65 ml of fluoroboric acid and 50 ml of 100-volume hydrogen peroxide in a plastic beaker. Add 12.5 g of pure AnalaR grade lead, piece by piece, and when all of the lead has dissolved transfer the solution into a 250-ml calibrated flask. Make up to the mark with water, mix and transfer the solution into a plastic bottle. CALIBRATION- Transfer 0, 2.5, 5.0 and 7 6 m l volumes of standard antimony solution into four separate 25-ml calibrated flasks. To each flask add 1.25 ml of fluoroboric acid and 1 ml of 100-volume hydrogen peroxide, make up to the mark with water, mix and transfer the solution into a plastic bottle.Transfer 0, 7.5, 1.0 and 12.5-ml volumes of standard tin solution into four separate 25-ml calibrated flasks. To each flask add 5 ml of standard lead solution, make up to the mark with water, mix and transfer the solution into a plastic bottle. With the instrument conditions as given in Table VII, aspirate each of the appropriate solutions into the flame and measure the absorption. Prepare calibration graphs of absorption against the amount of antimony or tin. ANALYSIS OF SAMPLES- If necessary, cut the sample into small pieces. Weigh 1.OOg of sample into a clean plastic beaker, add 5 ml of fluoroboric acid and then add 4ml of 100-volume hydrogen 1 ml of solution = 100 pg of tin. 1 ml of solution = 50 mg of lead.448 [Analyst, Vol.98 peroxide very slowly. When dissolution is complete, transfer the solution into a 100-ml cal- ibrated flask, dilute to the mark with water, mix and transfer the solution into a clean plastic bottle. With the instrumental conditions as given in Table VII, measure the absorption that can be attributed to tin and antimony and by use of the calibration graphs deduce the tin and antimony contents of the sample. RESULTS Three experiments were carried out in order to check the validity of the method. The precision of measurement was examined by taking ten replicate readings from a single solution that contained tin and antimony at levels equivalent to 0.2 per cent. of antimony and 0.4 per cent. of tin in lead alloy. The results are given in Table VIII.TABLE VIII STANDARD DEVIATIONS FOR REPLICATE MEASUREMENTS ON ONE SOLUTION QUARRELL et al.: DETERMINATION OF TIN AND ANTIMONY IN Element Standard deviation, per cent. (10 determinations) Tin (0.4 per cent.) . . .. Antimony (0.2 per cent.) .. 0.018 0.022 The over-all reproducibility was checked by applying the method to pairs of samples taken from adjacent regions on each of two lengths of cable sheath. The results obtained are given in Table IX. TABLE IX DETERMINATION OF TIN AND ANTIMONY IN ADJACENT SAMPLES OF CABLE SHEATH Sample Sample portion Antimony, per cent. Tin, per cent. Sheath A 1 0.21 0.38 2 0.21 0.39 Sheath B 1 0-22 0.40 2 0.21 0-41 The method was checked €or bias by taking the mass of independently analysed white metal (B.C.S. 177/1) that is required to give amounts of antimony and tin similar to those in alloy E, and adding sufficient pure lead to give a total mass of 1 g.The mixture was then treated as a sample. The results are given in Table X. TABLE X DETERMINATION OF ANTIMONY AND TIN IN B.C.S. 177/1 DILUTED WITH LEAD METAL Element Calculated content, per cent. Amount found, per cent. Antimony . . .. Tin . . . . * . 0.24 0.46 0-23 0.45 CONCLUSION The method evolved is simple and direct and hence is appropriate for use in the control of alloy composition. A particular advantage of the method is that complete dissolution of the sample is effected in a single step. The chemical properties of lead, tin and antimony are such that one or another of them will give rise to precipitation reactions in the presence of any of the acids that are commonly used for dissolution of these metals. The use of the fluoroboric acid - hydrogen peroxide mixture for dissolution overcomes this problem and permits full advantage to be taken of the virtue of many flame methods, that is, the ability to effect determinations directly on a sample solution without the need for chemical separations to be carried out. The method has been shown to give an accuracy and precision that are acceptable for the routine determination of alloy composition.It should be noted that the use of a dissolution mixture containing fluoroboric acid for the analysis of a lead-base alloy by atomic-absorption spectroscopy has also found favour elsewhere : after the work described in this paper had been completed, a method was described by Gouin, Holt and Millers for the determination of tin and antimony in type metal by atomic-absorption spectroscopy. These authors used a mixture of fluoroboric and nitricJune, 19731 LEAD ALLOY FOR CABLE SHEATHING BY ATOMIC-ABSORPTION SPECTROSCOPY 449 acids for dissolution of the sample, with subsequent addition of tartaric acid to ensure the retention of antimony in solution. The amounts of antimony (3 to 17 per cent.) and tin (3 to 7 per cent.) that were determined by these authors were much greater than those of concern to us in alloy E. REFERENCES 1. 2. British Standard Method 3908, Part 10, 1967; Part 11, 1968. 3. 4. 5 . 6. 7. 8. British Standard B.S. 801 : 1953. GonzAIez Lbpez, A., and Arribas Jimeno, S., Infcidn Quim. Analdt. P w a A$. Ind., 1968, 22, 123. Hwang, J . Y., and Sandonato, L. M., Analyt. Chew., 1970, 42, 744. Slavin, S., and Sattur, T. W., Atom. Absorption Newsl., 196% 7, 99. Juliano, P. O., and Harrison, W. W., Analyt. Chem., 1970, 42, 84. Manning, D. C., Atom. Absorption Newsl., 1965, 4, 267. Gouin, J. V., Holt, J. L., and Miller, R. E., Analyt. Chem., 1972, 44, 1042. Received November 30th, 1972 Accepted February 2nd, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800443

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

450 Analyst, June, 1973, Vol. 98, pp. 450-451 Replacement of Platinum Vessels with a Pressure Device for Acid Dissolution in the Rapid Analysis of Glass by Atomic-absorption Spectroscopy BY Y. HENDEL ( I M I Institute for Research and Development, P.O. Box 313, Haifa 31000, Israel) The rapid analysis of glass is made possible by replacing the crucibles in which time-consuming fusion is carried out by a device for quantitative acid dissolution under pressure and subsequent atomic-absorption spectroscopic determinations of the elements. The sample is decomposed by hydrofluoric acid at 105 "C in a decom- position vessel consisting of a crucible-shaped stainless-steel container fitted with a removable PTFE crucible and a stainless-steel screw-cap with a PTFE disc inserted in the metal body.Subsequent addition of boric acid forms the analysis matrix of fluoroboric acid - boric acid for the atomic-absorption determinations of silica, alumina, iron, titanium, magnesium, calcium, sodium and potassium. This procedure obviates the use of platinum vessels, prevents losses of constituents due to alloying, reduction and volatilisation, does not introduce extraneous cations, and is reliable, simple and rapid to perform. THE conventionally used chemical methods for the determination of major and minor con- stituents of glass are based on its fusion with suitable fluxes in platinum crucibles. Appro- priate mixtures of acids (hydrofluoric acid plus sulphuric or perchloric acid) are also used for constituents other than silica. The subsequent determinations are carried out by gravimetry, spectrophotometry or atomic-absorption spectroscopy.Platinum crucibles conventionally used to date in the step involving decomposition of glass by fusion may present serious analytical as well as financial disadvantages. The initial investment involved in the acquisition of platinum ware, especially if the latter is needed for simultaneous batch work on many series, may be prohibitive. In addition, the use of platinum ware may account for sample contamination and cause losses of some of the constituents by reduction and formation of alloys or by volatilisation. All fusion techniques require lengthy manipulations and the introduction of excessive amounts of alkalis over the mass of sample taken, frequently to avoid difficulties that occur during the decomposition stage.Thus, besides precluding the direct determination of the alkali metals present in the sample from a single decomposition, excessive amounts of extraneous cations derived from the fusion mixtures may cause subsequent chemical inter- ferences and undesirable instrumental or spectral effects, or both, especially when atomic- absorption spectrophotometry is used in the determination of the individual elements. The common practice of effecting decomposition by using mixtures of acids suffers from two major disadvantages. One is that the time-consuming removal of hydrofluoric acid by evaporation is required in conventional acid-decomposition procedures. The second major disadvantage is that under these conditions silica cannot be determined. For an over-all simplification of the procedure for glass analysis, a modified method has been successfully applied.This method was earlier reported by Bernasl for the acid decomposition under pressure and comprehensive analysis of silicates. A subsequent paper2 describes the chemical analysis of Apollo 14 lunar samples by the same methodl with con- firmatory conclusions concerning the satisfactory precision and accuracy of the results obtained. The modified method for the analysis of glass obviates the use of platinum vessels, prevents losses of constituents, in particular losses caused by volatilisation, does not introduce extraneous cations and is simple to perform. The procedure consists in the acid decomposition @ SAC and the author.HENDEL 451 under pressure, in a specially designed decomposition vessel," of a 100 to 150-mg sample ground to 100 mesh.This vessel consists of a crucible-shaped stainless-steel container fitted with a removable PTFE crucible, which is closed by hand-tightening a stainless-steel screw cap with an inserted PTFE disc on to the metal body. A PTFE pouring spout, which facili- tates the quantitative transfer of the solution of the decomposed sample, is snapped on to the periphery of the rim of the crucible. Decomposition is effected with 4ml of 48 per cent. hydrofluoric acid in the presence of about 0-3 ml of aqua regia and by placing the vessel into a drying oven at 105 "C for 30 minutes. On cooling the vessel to ambient temperature, 3.0 g of boric acid that had been previously dissolved in hot water are added to the sample solution, thus forming the fluoroboric acid - boric acid matrix.The solution is then trans- ferred into a 100-ml calibrated flask for accurate volume adjustment. The contents should then be transferred within 2 hours into a plastic storage bottle. Appropriate dilutions are made whenever necessary. For the determination of each element, identical concentrations of fluoroboric acid - boric acid matrix are used in the sample and standards. The determinations are then carried out by atomic-absorption measurements with air - acetylene and nitrous oxide - acetylene flames. The determinations of silicon, iron and titanium are carried out by direct comparison with single-component standards in the matrix.To take account of any possible inter- element effects in the determinations of aluminium, magnesium, calcium, sodium and potas- sium, the sample and standard solutions contain, in addition to the matrix, high concen- trations of either sodium or potassium ions. It was earlier established that during the residence time of the sample solution in the calibrated glass flask, no analytically significant contamination 0ccurred.l Furthermore, the fluoroboric acid - boric acid matrix is known to ensure the stability in solution of both samples and standards for at least several weeks. Results for the determination of eight constituents in a single sample can be reported within 5 to 7 hours, depending on the type of instrument used, while the actual operation time needed is 4 hours, as compared with about 15 hours required by the conventional methods used to date.A comparison of the results for standard sample No. 93 [borosilicate glass, National Bureau of Standards (N.B.S.)] and standard glass No. 1 (standard soda - lime - magnesia - silica glass, Department of Glass Technology, University of Sheffield) by the ra.pid method of acid decomposition under pressure with their respective certified values is shown in Table I. TABLE I COMPARISON OF RESULTS FOR STANDARD SAMPLES BY THE RAPID METHOD OF ACID DECOMPOSITION UNDER PRESSURE WITH CERTIFIED VALUES N.B.S. 7 Certified Constituent values SiO, 80.6 A1203 1.94 Fez03 0.076 TiO, 0.027 0.026 E?: Not detected Na,O 4-16 K,O 0.16 standard sample No. 93 Rapid method of acid decomposition under pressure 1.89 0.078 0.029 0.023 Not determined 4.22 0.14 h \ 80.1 Standard glass No. 1 r \ A Certified Rapid method of acid values decomposition under pressure 71-74 72.8 1.55 1.34 0.15 0.16 0.05 0.05 3.56 3.3 8-49 8.3 13.25 13.1 0.80 0-7 The permission of the management of IMI Institute for Research and Development, Haifa, to publish this paper is gratefully acknowledged. REFERENCES 1. 2. Bernas, B., .4naZyt. Chern., 1968, 40, 1682. Schnetzler, C. C., and Nava, D. F., Earth PZavzet. Sci. Lett., 1971, 11, 345. Received November lst, 1972 Accepted February 9th, 1973 * Uni-Seal Decomposition Vessels, Ltd., P.O. Box 9463, Haifa 31094, Israel.

ISSN:0003-2654    

DOI:10.1039/AN9739800450

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

452 AnaZyst, June, 1973, Vol. 98,PP. 452-455 Thermometric Assay of Some Sulphonamides of Pharmaceutical Importance BY L. S. BARK AND J. K. GRIME (Department of Chemistry and Applied Chemistry, University of Salford, Salford, M5 4 WT) The thermometric determination of several sulphonamides used in pharmaceutical preparations is described. The sulphonamide is dissolved in the minimum amount of dilute sodium hydroxide solution and the pH adjusted to 8.9 with thymolphthalein as indicator. The solution is then made up to 10 cm3 with an appropriate buffer solution (pH 8.0 or 9.18). In these controlled alkaline conditions, the sulphonamide is titrated directly with silver nitrate solution, the equivalence point being determined thermo- metrically. The effects of several matrix ingredients in common use in pharmaceutical preparations have been determined. The time of the titration is approximately 1 minute and the accuracy is within &2 per cent.THE proven bactericidal properties of compounds containing the sulphonamido group have ensured the continued, widespread use of sulphonamides as medicaments. These compounds are used either singly or in combinations with related sulphonamides. The methods of the British Pharmacopoeia1 for determining sulphonamides involve either a potentiometric titration with sodium nitrite solution or, for some selected sulphonamides, a non-aqueous (dimethylformamide) acid - base titration with a solution of lithium methoxide in toluene - methanol. Several workers have suggested the use of silver nitrate for the gravimetric293 or titri- metric4-9 determination of various sulphonamides.Only two thermometric methods have been proposed : the heat of neutralisation of some of these bases with sulphuric acid has been used for their determination,lO while Schafer and Wildell made use of the heat of oxidation of some sulphonamides with sodium hypo- chlorite. In some dosage forms, the sulphonamides may be mixed with magnesium stearate, lactose and starch; hence thermometric titrimetry with a strong acid or a strong oxidising agent has obvious limitations in such instances. The titration of these sulphonamides with silver ions in controlled alkaline conditions obviates these difficulties6 and thus affords the opportunity for a rapid thermometric method involving the dosage forms to be used.EXPERIMENTAL APPARATUS- Details of the apparatus have been previously described.12913 The titrant was delivered to the sample by a constant-speed peristaltic pump. The reaction vessel was thermally insulated in a suitable manner and the temperature changes were recorded as the imbalance voltage from a Wheatstone bridge containing a 10 000-!2 thermistor as one of its arms. The thermistor acted as the temperature sensor. The titrant and the sample were both initially a t room temperature. REAGENTS- drug manufacturers- S.uZ~~out.amides-Samples of the following sulphonamides were used as supplied by the Sulphathiazole [2-(4-aminobenzenesulphonamido) thiazole] . Sulphadiazine [2- (4-aminobenzenesulphonamido)pyrimidine]. Sulphamerazine [Z- (4-aminobenzenesulphonamido)-4-methylpyrimidine]. Sulphadimidine [2- (4-aminobenzenesulphonamido) -4,6-dimethylpyrimidine]. Sulphafurazole [5- (4-aminobenzenesulphonamido)-3,4-dimethylisoxazole]. Sulphamethizole [2-(4-aminobenzenesulphonamido) -5-methyl-l,3,4-thiadiazole]. @ SAC and the authors.BARK AND GRIME 453 Succinylsulphathiazole { 2- [a- (3-car box ypropionamido) benzenesulphonamido] thiazole Sulphapyridine 12- (4-aminobenzenesulphonamido) p yridine] .Bufer solution l-This solution, at pH 9.18, was a 0.1 M aqueous solution of sodium Bufer solution 2-This solution, at pH 8.0, was a 0.1 M solution of boric acid, adjusted Silver nitrate solution-A 0-30 M aqueous solution of silver nitrate was made up and monohydrate }. tetraborate (borax). to pH 8.0 with 0.1 M sodium hydroxide solution. standardised against sodium chloride solution by Mohr’s method.METHOD- Dissolve a known amount of the sulphonamide (between 10 and 70 mg) in the polythene vesseP2 in the minimum volume of 0.1 M aqueous sodium hydroxide solution (2 to 5 cm3). Adjust the pH to 8.9 (with thymolphthalein as indicator) by dropwise addition of 0.1 M nitric acid. Adjust the volume to 10 cm3 with the appropriate buffer solution. Place the titration vessel in the block of insulation12 and allow the mixture to stand at room temperature for 3 to 5 minutes so as to allow thermal equilibrium to be attained. The amount of sulphonamide present can then be calculated from the enthalpogram. Titrate the sulphonamides against the standardised silver nitrate solution. D I s c u s s I o N Although the sulphonamides are soluble in either dilute mineral acids or dilute alkali solutions, the silver salts are precipitated only in neutral or slightly alkaline conditions. The reaction must therefore be carried out in the latter conditions. The alkalinity must, TABLE I SOME TYPICAL RESULTS ON PURE SULPHONAMIDES Results are for (a) the minimum, and (b) the maximum amount of sulphonamide taken Compound Sulphathiazole .. .. Sulphaf urazole .. Sulphadiazine . . .. Sulphamethizole . . Sulphadimidine .. Sulphamerazine . . Succinylsulphathiazole Sulphapyridine . . .. .. .. .. .. .. .. .. .. PH 8.0 9.18 8.0 9.18 8.0 9.18 8.0 9-18 8.0 9.18 8.0 9.18 8.0 9-18 Amount takenlmg (a) 24.4 (b) 58.4 (a) 22.4 (b) 63.4 (b) 54.1 (a) 30.8 (b) 83.9 ( a ) 21.7 (a) 16.6 (b) 56.1 (b) 61.6 (a) 27.0 (b) 52.8 ( b ) 57.1 (a) 25.5 (b) 51-7 (b) 42.5 (b) 70.3 (a) 28.6 (b) 31.1 (b) 52.6 (a) 34.9 ( b ) 45.7 (a) 29.2 (a) 21.2 (a) 26.3 (a) 7.9 (a) 30.0 Amount found/mg 24.6 56.3 22.2 63.0 33.9 54.2 30-5 84.0 21.3 45.6 16.8 56.5 29.2 62.0 30.7 56.0 20.8 57.2 26.6 52.0 26.7 42.6 7.9 70.0 29.6 30.9 29.6 52.5 8.0 Compound insoluble 9.18 (a) 39.0 40.8 (b) 38-1 40.0454 BARK AND GRIME: THERMOMETRIC ASSAY OF SOME [Ana&d, VOl.98 however, be controlled so that the formation and precipitation of hydroxy compounds of silver are avoided. If any titrant is consumed by such processes, erroneous results are obtained. From the results given in Table I it can be seen that of the two buffers used, that at pH 9.18 gave the optimum results over a larger range of amounts of compounds and is thus recommended for all compounds except sulphamethizole.The consistently high results obtained with sulphapyridine are probably caused by the formation of the silver salt of the amido group and also some silver - pyridine complex. The upper limit for the amount of the various compounds taken is a direct result of the geometry of the apparatus. Above this limit, the bulk of the precipitate causes poor heat transfer throughout the reaction mixture. The resultant curvature of the enthalpogram at the end-point makes extrapolation necessary, with a concomitant loss in accuracy. Thus the optimum range recommended is between 2-5 x mol of sulphonamide in the 10 cm3 of solution, i.e., a 2.5 x loy3 to 2.5 x and 2.5 x M solution.Detailed results for the determination of sulphathiazole are given in Table 11. TABLE I1 DETAILED RESULTS FOR THE DETERMINATION OF SULPHATHIAZOLE Amount taken/mg Amount found/mg 22.4 22.2 29.8 30.3 30.6 31.0 38.4 38.6 38.5 38.2 40.1 39.8 50.4 50.4 55.3 55.0 61.2 61-5 63.4 63.0 pH of all solutions = 9.18. Error, per cent. - 0.90 + 1.6 + 1.3 + 0.5 - 0.8 - 0.75 0.00 - 0.54 + 0-49 - 0.64 The results obtained for the sulphonamides in admixture with some of the usual excipients, vix., lactose, magnesium stearate and starch, indicate that the method has potential use for the determination of single sulphonamides in the dosage forms (Table 111). As the dosage form is usually a tablet containing about 500 mg of sulphonamide and 100 mg of excipient, it is necessary to crush the tablet and to use a nominal 50-mg sample.The finely powdered sample is stirred with the sodium hydroxide solution for approximately 3 to 5 minutes in the reaction cell, during which time the sulphonamide dissolves. The pH of the solution is adjusted as previously described. When thermal equilibrium has been achieved, the solution is titrated. Compound Sulphadimidine TABLE I11 EFFECT OF EXCIPIENTS Excipient Amount takenlmg Amount found/mg Lactose (30 mg) 30.5 30.7 Lactose (60 mg) 30-8 31.0 Starch (30 mg) 35-1 35-3 Starch (60 mg) 32.9 33-45 Magnesium stearate (30 mg) 31.2 31.0 Magnesium stearate (60 mg) 25.0 25.3 pH of all solutions = 9.18. The over-all time taken for the determination of duplicates from one tablet is approxi- mately 10 minutes, excluding crushing and weighing.The actual time taken for each titration is approximately 1 minute. In practice, we have found this method to have several advantages over those given in the British Pharmacopoeia, which recommends dead-stop titrations with sodium nitrite solution for all the sulphonamides listed here, except for sulphafurazole, which is titrated with lithium methoxide solution. The lithium methoxide method requires that the titrantJune, 19731 SULPHONAMIDES OF PHARMACEUTICAL IMPORTANCE 455 be protected against carbon dioxide contamination, and it is always necessary to titrate a blank sample. The use of sodium nitrite necessitates frequent re-standardisation with sulphanilic acid. While it is necessary to re-standardise the silver nitrate solution used’in the method des- cribed here, the frequency of re-standardisation is low.The electrodes used in the dead-stop titration need to be cleaned frequently, and in practice we have found that the platinum coils require more prolonged washing between titrations so as to ensure cleadiness than does the thermistor used in the proposed method. We thank Boots Pure Drug Co., Ciba-Geigy Ltd. and May and Baker Ltd. for the gifts of the sulphonamides used in this work. One of us (J.K.G.) thanks the Science Research Council for the award of a Studentship. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. REFERENCES “The British Pharmacopoeia 1968,” The Pharmaceutical Press, London, 1968, pp. 951,960 and 1234. Stainier, C., and Lapikre, C., Analytica Chim. Ada, 1947, 1, 178. De Reeder, P. L., Ibid., 1954, 10, 413. Perelman, Ya., and Kozlova, V. I., Farmatsiya, Mosk., 1947, 10, 22; Chem. Abstr., 1947, 41, 7666. Marques Leal, A., and Silipe, M. A. R., J o m . Farm. (Lisbon), 1949, 8, 85; Chem. Abstr., 1951, 45, Kum-Tatt, L., Analyst, 1957, 82, 185. Blazek, J., and Stefskal, Z., &lkd Farm., 1956, 5, 27; Chem. Abstr., 1957, 50, 16569g. Marcarovici, C. G., and Ceausescu, D., Anal. Acad. Rep. Popularii Rom., Sect. Mat. Fiz.-Chem., Stolte, H., Pharm. Ztg, 1960, 105, 780. Dolique, R., and Mas, P., Trav. SOC. Pharm. Montpellier, 1952, 12, 75. Schafer, H., and Wilde, E., Z. analyt. Chern., 1950, 130, 396. Bark, L. S., and Bate, P., Analyst, 1971, 96, 881. 4885e. Mem. No. 33, 1949, 51. t , Ibid., 1972, 97, 783. -- Received January 3rd, 1973 Accepted February 163A, 1973

ISSN:0003-2654    

DOI:10.1039/AN9739800452

出版商:RSC    

年代:1973

数据来源: RSC

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456 Analyst, June, 1973, Vol. 98, $$. 456457 Analytical Methods Committee REPORT PREPARED BY THE FISH PRODUCTS SUB-COMMITTEE Nitrogen Contents of Raw Fish THE Analytical Methods Committee has received the following Report from its Fish Products Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The Fish Products Sub-committee has recommended nitrogen factors for use in the analysis of food products containing cod1 and coal fish (saithe).2 Both recommendations were based on the results of determinations of the nitrogen contents of the whole fish. These TABLE I NITROGEN CONTENTS OF RAW FISH SPECIES Common name Anchovy .. .. .. Brill . . .. .. Catfish (rockfish) . . + . Cod .. .. .. Crab .... .. King . . .. .. Norwegian .. .. Crayfish . . .. .. Dab - . .. .. Dogfish . . .. . . Eel . . .. . . Flounder (fluke) . . .. Haddock .. .. .. Hake .. .. .. Halibut . . .. . . Herring . . . . .. Lemon sole . . . . Ling . . .. .. Lobster . . .. .. Mackerel . . .. .. Pilchard . . .. . . Plaice . . .. . . Pollack (lythe). .. .. Porbeagle . . . . . . Prawn (deep water) . . Redfish . . .. . . Saithe (coal fish, coley) . . Salmon Atlantic .. . . Sockeye .. . . Chinook .. . . Pink . . .. .. Sardine . . .. .. Shark (basking) . . .. Skate (ray, roker) .. Shrimp .. .. .. Trout . . .. .. Tuna .. .. .. Whiting . . .. .. Whiting (blue) . . .. (Greenland, black, mock) Witch . . .. .. Wrasse . . .. .. . . .. . . .. .. . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... .. .. .. .. .. .. .. .. .. .. .. .. . . .. . . .. .. .. .. .. Systematic name3 Engraulis encrasicholus Scophthalmus rhombus . . Gadus morhua . . .. Anarhichas sp. .. . . Cancer pagurus , . .. - - Astacus fluviatilis . . Limanda limanda . . Squalus acanthias . . Platichthys flesus . . Melanogrammus aeglejinus Hippoglossus hippoglossus Reinhardtius hippoglossoides Microstomus kitt .. Molva molva . . .. Scomber scombrus . . Savdina pilchardus . . Pleuronectes platessa . . Pollachius pollachius . . Lamna nasus . . . . Crangon sp., Pandalus sp. Sebastes sp. . . . . Pollachius virens . . Anguilla sp. . . .. Merluccius sp. . . . . Clupea harengus . . .. Homarus sp. .. .. Salmo salar . . . . Oncorhynchus nerka . . Oncovhynchus tschawytscha Oncorhynchus gorbuscha small Sardina pilchardus Salache Maxima ..Craxgon sp., Pandalus sp. Salmo trutta . . . . Raja sp. . . . . . . .. .. .. .. .. .. . . .. . . . . .. . . .. . . .. .. . . . . . . . . .. .. .. . . .. .. .. .. . . .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. . . .. . . .. .. .. .. .. . . . . . . . . . . .. . . . . . . .. .. . . .. .. . . .. .. .. .. .. .. .. .. .. .. .. .. . . .. .. .. . . .. .. .. .. . . .. .. .. . . .. .. .. .. .. .. .. .. .. .. .. Thunnus sp., Neothunnus sp., Euthynnus sp.. . Merlangius merlangus . . .. .. .. Micromesistius poutassou . . .. .. Glyptocephalus cynoglossus . . .. .. Labrus sp. .. .. .. .. .. Range of nitrogen contents,* per cent. 2.45 3.17 2-58 to 3.14 2-21 to 3.20 2.4 1.10 to 2.36 2.14 to 3.43 3.86 2-05 to 3-04 2.02 to 3.24 1.86 to 3.41 2.69 to 2.77 2.33 to 3.25 2.64 to 2.98 2.78 to 3.27 1.98 2.56 to 3.41 2.63 to 2.94 2-63 to 3-56 - 2.70 2.57 to 3-66 2.45 to 3.20 2.51 to 3.02 3.06 to 3-46 3.68 to 4-32 2.38 to 2.86 2.69 to 3.17 2-51 t o 3.46 3.60 2.83 to 3.50 3.06 3.20 3.07 2-43 2.92 to 3-87 1.68 to 3.78 2.80 to 3.67 3.84 3.04 to 3.18 2-22 to 2.55 2.33 to 2-52 3.08 to 3.15 * Where a range is not given the figure is the average result of a number of determinations.@ SAC.ANALYTICAL METHODS COMMITTEE 457 determinations were carried out for the Sub-committee on fish that had been landed over a period of at least 1 year. It had originally been the intention to carry out similar investi- gations on all the more important fish species that are used for manufacturing purposes, but, during the work on coal fish, considerable difficulty was experienced in obtaining sufficient fish on which to base a recommendation.The Sub-committee was of the opinion that this difficulty would increase for the less frequently used species and would thereby make the collection of sufficient information an extremely long process. In consequence, it was decided not to proceed with this aspect of the work. It is realised, however, that some analysts still require, from time to time, information on fish species other than those already dealt with by the Sub-committee. Some information on the nitrogen contents of raw fish species was known to be contained in the literature and some members of the Sub-committee had access to other, unpublished, information. In the belief that it will be of value to analysts who are required to examine fish products, this information has been collected and is contained in Table I.The Sub-committee has not, however, attempted to draw any conclusions from these figures, nor does it make any specific recommendations. It is emphasised that the figures are not the results of analyses carried out at the request of the Sub-committee and, for the most part, the absolute reliability of the information cannot be attested. For this reason, no attempt has been made to give mean values for the different species or to derive an average factor for all fish or groups of similar fish. The Sub-committee thanks, for their help and communications, The Ministry of Agri- culture, Fisheries and Food, Torry Research Station and The Official Norwegian Quality Control Institute for Canned Fish Products, Stavanger. REFERENCES 1. 2. 3. Analytical Methods Committee, Analyst, 1966, 91, 540. - , Ibid., 1971, 96, 744. Waterman, J. J., “Fish Names in the Common Market,’’ Torry Advis. Note. No. 66, 1972.

ISSN:0003-2654    

DOI:10.1039/AN9739800456

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

458 Analyst, June, 1973, Vol. 98, pp. 458460 Analytical Methods Committee REPORT PREPARED BY THE METALLIC IMPURITIES IN ORGANIC MATTER SUB-COMMITTEE The Determination of Small Amounts of Zinc in Organic Matter by Atomic-absorption Spectroscopy THE Analytical Methods Committee has received the following Report from its Metallic Impurities in Organic Matter Sub-committee. The Report has been approved by the Analytical Methods Committee and its publication has been authorised by the Council. REPORT The constitution of the Metallic Impurities in Organic Matter Sub-committee responsible for the preparation of this Report was: Dr. L. E. Coles (Chairman), Mr. W. Cassidy, Dr. J. C. Gage, Dr. R. A. Hoodless, Miss E. M. Johnson, Mr. D. A. Lambie, Dr. H. Liebmann, Dr. R. F. Milton, Mr.W. L. Sheppard, Mr. G. B. Thackray and Mr. C. A. Watson, with Mr. P. W. Shallis as Secretary. In 1967, the Sub-committee recommended a procedure involving the use of dithizone for the determination of small amounts of zinc in organic matter.l This method is still considered to be satisfactory, but advances in instrumentation and technique have, in the opinion of members of the Sub-committee, made atomic-absorption spectroscopy equally satisfactory for the determination of zinc and, in general, it is more convenient and rapid in application. This Report gives details of conditions that have been found to be satisfactory and the Sub-committee recommends that either the dithizone procedure1 or atomic-absorption spectroscopy should be used for the determination of zinc in organic matter; the method selected will depend on the material to be analysed. GENERAL CONSIDERATIONS- Atomic-absorption measurements of zinc solutions are normally carried out at 213-8 nm.In this region of the electromagnetic spectrum, energy is maintained by using wider slits and a higher voltage compensates for reduced photomultiplier sensitivity. The products of incomplete combustion also absorb light to a greater extent in this region than at longer wavelengths. Monochromators of good resolving power are therefore necessary so as to ensure minimum interference when zinc is to be determined in solutions containing more than an equal amount of copper. Compounds that yield elemental sulphur on burning also interfere at this wavelength and due care should be taken when separations with ammonium pyrrolidine dithiocarbamate (APDC) are effected. SAMPLE PREPARATION- The determination of zinc in organic materials by atomic-absorption spectroscopy is not materially affected by the use of different acids.It is, however, advisable to use the same acid composition and concentration for standards and blanks as are used for the samples. In general, the acid concentration should not exceed about 2 N in the aspirated solution, although with “high solids” burners the use of considerably higher acid concentrations may be satisfactory. Dry or wet ashing is suitable for the destruction of organic matter before the deter- mination of zinc. For certain types of liquid samples, e.g., ready-to-drink beverages, and for semi-solid foodstuffs, alternative satisfactory procedures are described.Copper has absorbance lines in the vicinity of 213-8nm. @ SAC.ANALYTICAL METHODS COMMITTEE 459 DRY ASHING- If the organic matter can be readily dry ashed below 500 "C it is still necessary to check the recovery of zinc, which may not be complete.2 Porcelain crucibles should not be used, as zinc can be extracted from the glaze.3 It is sometimes advantageous to mix approximately 0.2 g of calcium carbonate with the sample before ashing. This mixing results in an aerated mass that does not fuse into the material of the container and dissolution in acids is facilitated. The residue from a dry-ashing procedure is best dissolved in a mixture of hydrochloric acid and water (1 + 1 V/V). If the zinc in the sample is not completely dissolved in this mixture, a 2 + 1 + 3 V/V mixture of hydrochloric acid, nitric acid and water can be used.WET ASHING- Any of the usual techniques4 can be used, but the easiest method of digesting many organic materials is with sulphuric acid and dropwise addition of 50 per cent. hydrogen per~xide.~ The use of glassware that has been etched with boiling solutions of strong alkalis should be avoided, as zinc can be leached from the glass during the oxidation process, For both wet and dry ashing, sample masses and final volumes can be chosen so as to give the optimum sensitivity required. READY-TO-DRINK BEVERAGES- These beverages can be aspirated without prior destruction of the organic matter. A suitable dilution with water should be prepared so as to minimise the effect of the presence of soluble solids in the drink.Soluble solids are troublesome in the aspirated sample only at concentrations above about 3 per cent. SEMI-SOLID FOODSTUFFS- A rapid method for foodstuffs is based on that described by Simpson and Blay.6 To 10 g of the homogenised sample are added 40 ml of water and 10 ml of concentrated hydro- chloric acid. The mixture is heated to boiling and then simmered gently for not more than 5 minutes. The solution is then cooled, transferred to a 100-ml calibrated flask, diluted to volume and mixed, Sufficient solution (normally 10 to 20ml) for the analysis is removed and filtered. It is essential not to prolong the boiling, as charring might occur that could hold back trace amounts of the metal at the filtration stage.Similarly, a higher acid concentration can also increase charring and for this reason the mixture recommended here is less concen- trated than that used by Simpson and Blay.6 OILS, FATS AND FATTY FOODS- These materials may be difficult and sometimes impossible to wet oxidise to give an aqueous solution. At zinc contents below 0.1 p.p.m., contamination from reagents and vessels used to prepare aqueous solutions can be greater than the actual zinc contents. It is then simpler to aspirate solutions of the fatty matter in an organic solvent directly into the flame. When this direct aspiration is used, care must be taken that the spraying characteristics of the reference sample are identical with those of the unknown. Oils and fats from different sources having different physical properties (e.g., density and viscosity) will give different background responses and also modify the atom-producing capacity of the flame.It is, therefore, preferable to use the maximum possible dilution of the fatty matter in an appro- priate solvent. When dilution causes too great a loss in sensitivity it is possible to aspirate a 50 per cent. m/m solution of fatty matter in the solvent, but the aspirating air must be pre- heated and solutions should be incubated to the same temperature (30 to 40 "C). Fats can then be aspirated without precipitation in the nebuliser and all oils will tend towards common spray- ing characteristics at the higher temperature. A calibration graph is prepared by supplement- ing a similar metal-free oil with an organozinc compound, such as zinc oleate or naphthenate.Pentyl acetate (metal free) is a good general solvent for this type of work. Suitable adjustments to the fuel flow will be necessary to compensate for the burning capacity of the fat and solvent. It may be necessary to separate fatty matter from formula- tions, e.g., from carbohydrates by solvent extraction, and from the aqueous phase by stirring at 80 "C for fat - water emulsions such as margarines.460 ANALYTICAL METHODS COMMITTEE THE USE OF AMMONIUM PYRROLIDINE DITHIOCARBAMATE- This reagent, which was introduced by Malissa and Schoffmann,' can be used for the extraction of zinc from a wide range of aqueous solutions into an-organic solvent suitable for direct atomic-absorption spectrophotometry.8 Extraction of the zinc into an organic phase for atomic-absorption spectrophotometry offers several advantages : the concentration of the metal in the organic phase can be 100 times that in the aqueous phase, enabling smaller amounts to be determined; the atomic-absorption signal for zinc in an organic solvent is considerably enhanced in comparison with that obtained from a similar concentration in aqueous solution; and the zinc is separated from the high concentration of salts, which inevitably arises when certain organic materials are wet digested, ashed or diluted.The sensitivity of zinc determination by atomic absorption varies with the equipment being used, but in organic solvents such as 4-methylpentan-2-one it is usually between 0.01 and 0.1 p.p.m., and a linear calibration graph is normally obtained up to at least 10 p.p.m., so that if the zinc is extracted into 10 ml of solvent the method can be used for amounts of zinc from between 0.1 and 1 pg to between 10 and 100 pg, according to the equipment available.The zinc - APDC complex can readily be extracted from aqueous solution within the range frorn strongly acidic (5 N) to a pH of 10 into polar organic solvents such as chloroform, 4-methylpentan-2-one and heptan-2-one. Chloroform is useful if very high concentration factors are required, but leads to flame instability and attack on the nebuliser with some equipment when sprayed directly. For most purposes 4-methylpentan-%one or heptan-2-one is more satisfactory, the latter having a lower solubility in acidic aqueous solution.Owing to the solubility of the solvents in acidic aqueous solutions, the solutions should be saturated with the solvent before extraction of the zinc - APDC complex, which is formed immediately on addition of the APDC. For amounts of zinc below 100 pg two extractions with 4 ml of solvent, each after the addition of 1 ml of 1 per cent. aqueous APDC, will remove all the detectable zinc from 100 ml of solution; the two extracts are then combined, diluted to 10 ml in a calibrated flask and sprayed into the atomic-absorption spectrophotometer. The calibration graph must be prepared by extraction of standard amounts of zinc under conditions similar to those used for the samples, as the sensitivity may vary according to the solvent composition.Extraction of zinc with APDC can be applied directly to the aqueous solutions obtained from the above general methods of sample preparation provided that they are diluted, when necessary, so that the acidity is not greater than 5 N. OPERATING CONDITIONS- The optimum operating conditions recommended by the instrument manufacturer should be used. The zero should be set by using an appropriate blank, and standard solutions for the calibration should be prepared so as to have the same degree of acidity as the samples. The instrument should be set up with a zinc hollow-cathode lamp operated at the recom- mended current, the monochromator a t 213-8nm and with the slit width adjusted to give an acceptable signal to noise ratio. Neon-filled zinc cathode lamps should be used; the use of brass cathode lamps or argon-filled lamps should be avoided. 1. 2. 3. 4. 5. 6. 7. 8. REFERENCES Analytical Methods Committee, Analyst, 1967, 92, 324. Gorsuch, T. T., Ibid., 1959, 84, 135. Zeitlin, H., Frodyma, M. M., and Ikeda, G., Analyt. Chem., 1958, 30, 1284. Analytical Methods Committee, Analyst, 1960, 85, 643. -, Ibid., 1967, 92, 403. Simpson, G. R., and Blay, R. A., Fd Trade Rev., 1966, August, 35. Malissa, H., and Schoffmann, E., Microchirn. Acta, 1955, 187. Watson, C. A., Monograph 74, Hopkin & Williams Ltd., Chadwell Heath, Essex, 1969.

ISSN:0003-2654    

DOI:10.1039/AN9739800458

出版商:RSC    

年代:1973

数据来源: RSC

摘要:

Analyst, June, 19731 Book Reviews 461 NEUERE METHODEN ZUR ANALYSE VON TENSIDEN. By H. KONIG. Pp. viii + 239. Berlin, Heidelberg and New York : Springer-Verlag. The book consists essentially of two chapters, one on methods for the separation and identi- fication of surfactants (177 pages) and the other on methods for their quantitative determination (49 pages). After an introduction, the first chapter comprises a section on the separation of types of surfactant (by ion exchange) followed by four sections on the separation and four on the identi- fication of anionics, amphoterics, non-ionics and cationics. One third of each section, on average, is a literature survey covering both old and new methods, while half comprises infrared and nuclear magnetic resonance spectra and thin-layer chromatography diagrams for numerous commercial products.The chapter on quantitative analysis is a combination of a literature survey, which refers indiscriminately to both good and bad analytical methods, and brief accounts of the author’s own experiments, which, so far as I have studied them, fall largely into the latter category. Widely discrepant results by different methods are quoted without any suggestion as to the correct figures or the reasons for error, and serve only to warn the reader not to follow the author’s unenlightened approach to his subject. The section on phosphate esters (3% pages) displays such unfamiliarity with ion-exchange procedures as applied to surfactants as to cast serious doubts on the usefulness of the review of the technique in the previous sections.On reviewing the heterogeneous mixture, I find it difficult to imagine who will benefit froin the book. The literature surveys are not very extensive (total references, 180) ; the infrared spectra are on a small scale, each 103 x 35 mm, and better treatments of the subject are available else- where, and the thin-layer chromatograms of single commercial substances do not appear to be of great practical use. This leaves the nuclear magnetic resonance spectra (fifty-six in number, each 126 x 60 mm) and a few lists of commercial products and their R, values in thin-layer chromatography as the principal parts of any potential value. Konig’s book may be of use to someone who desires a compact collection of infrared spectra, or a glimpse at the possibilities of nuclear magnetic resonance spectroscopy for analysing surfac- tants. I t may also be appreciated by an analyst who is new to the subject and who desires a review of the types of product that are commercially available. To other potential reaclers, the work has little to offer.197 1. Price DM58 ; $17.70 (approx.) . There is a list of contents but no index. W. U. SMITH RTUDE ANALYTIQUE D E DERIVBS FLUORES : APPLICATIONS A L’ANALYSE PHARMACEUTIQUE. By M. HANOCQ. Pp. 241. Brussels: Editions Arscia S.A.; Paris: Librairie Maloine S.A. 1972. Price Belg.F490. The applicability of several standard methods of isolation and determination of fluorine to the analysis of organofluorine compounds, certain pharmaceutical products and blood and urine is described, in French, in this volume.After a brief general introduction on the significance of fluorine in therapeutics, dentistry and toxicology, there follow two chapters on the determination of fluoride by the alizarin fluorine blue method and by the fluoride-selective electrode and one on the separation of fluorine by microdiff usion. Each chapter is a self-contained technical report comprising an introduction, a detailed experimental section and conclusions. They are supported by a comprehensive bibliography, which covers the published literature up to 1969. The experi- mental section mostly confirms earlier studies by other authors; the amount of new information is limited and concerns mainly the use of dimethyl sulphoxide to enhance the sensitivity of the alizarin fluorine blue method and the use of the fluoride-selective electrode in mixed aqueous - organic solvents.A short chapter is devoted to the analysis of a range of organofluorine compounds of medical interest and the final chapter gives details of methods for the determination of fluorine in samples of pharmaceutical significance. The book concludes with two summaries, one in French and the other in English; the translation into English would scarcely do justice to a good 0-level student and the reviewer found the French easier to follow. Although bound in soft covers, the book is excellently produced on good quality paper, but its content is such that it is difficult to judge for whom it is intended; research workers will find the bibliography useful and the book may be of limited use as a laboratory manual.J . K. FOREMAN462 BOOK REVIEWS [Analyst, Vol. 98 AUSGEWAHLTE METHODEN DER WASSERUNTERSUCHUNG. Band 1. CHEMISCHE, PHYSIKALISCH- FUR WASSERWIRTSCHAFT, Berlin, with assistance from the FORSCHUNGSINSTITUTES FUR MIKROBIOLOGIE UND HYGIENE, Bad Elster. Loose-leaf. Pp. xvi + 250. Jena: VEB Gustav Fischer Verlag. 1971. Price DM35.50. This book, prepared by an East German team, covers the chemical and physical analysis of natural fresh waters and waste waters, and is a worthy addition to the growing collection of books on the subject. The “Elektrochemische” in the title presumably refers to methods, such as con- ductivity, which are not yet available, otherwise its inclusion seems pointless. The methods recommended are all of the so-called “traditional” type, usually requiring a titrimetric or colori- metric finish.Atomic-absorption and gas-chromatographic methods are not included, neither is the electrode method for dissolved oxygen. The organic section covers only phenols and anionic surfactants. Within the above limitations, this seems to be a sound and well prepared book, especially as the methods were subjected to collaborative testing and modified when necessary. An examina- tion of selected parts of the book yielded no surprises; the salicylic acid method for nitrate and the boiling permanganate method for low C.O.D. values deserve attention in this country. The B.O.D. test is defined unequivocally as a test for organic matter, and nitrification is regarded as an interference.In the section on the C.O.D. test, chloride interference is said to occur by oxidation to chlorine, which can be corrected for; this is surely wrong when samples contain ammonia, as they usually do. The use of mercury(I1) sulphate for eliminating chloride interference is men- tioned, however. There is a particularly good introduction to the section on cyanide. The book is well produced in loose-leaf form with a ring binder. The style is concise, lucid and explicit, with very few long sentences, and should pose few problems even to those who, like this reviewer, have only a modest knowledge of German. H. A. C. MONTGOMERY LITHIUM-DRIFTED GERMANIUM DETECTORS, THEIR FABRICATION AND USE. AN ANNOTATED BIBLIOGRAPHY. Compiled by INA CALLOWAY BROWNRIDGE.Pp. xiv + 210. New York, Washington and London: IFI/Plenum. 1972. Price $23. Lithium-drifted germanium detectors are used increasingly for gamma-ray spectrometry They operate by using an electric field to sweep out charge carriers produced by the interaction of gamma-rays with the detector; the total amount of charge collected is proportional to the energy dissipated in the intrinsic region. They provide very high resolution by comparison with sodium iodide - scintillator detection systems, and are now used extensively for activation analysis. This bibliography lists 790 entries from the international literature, covering articles published up to May, 1971. Many of the references refer to the fabrication of detectors and the associated electronics covering items such as material selection, encapsulation, mounting, charge collection, efficiency measurements, cryostat design and the design or optimisation of various types of spectro- meter.The references to applications appear to be less extensive, but the subject index lists activation analysis (26 entries), biological applications (9), criminology (1), fall-out (3), fission- product analysis (lo), fuel elements (8) and space applications (7). Overall, a very useful combination of references is provided, particularly for those involved in detector fabrication (74) and system design. For those interested in using germanium detectors for analytical work, the subject index is a little disappointing and requires close examination to locate references of interest-for example, the entry a ‘computer analysis” refers to only three papers on computer methods for analysing spectra, but many more can be found via “peak fitting” or “spectrum analysis.” INTRODUCTION TO MOLECULAR PHOTOCHEMISTRY.By C . H. J. WELLS. Pp. xii + 146. London: This book is intended to provide undergraduates with an introduction to photochemistry. It is written clearly and has an abundance of well drawn figures that complement the text. Great emphasis is placed on the definition and explanation of the basic terms used by photochemists. Some of the principles of electronic spectroscopy are also described. In addition, there is a chapter on the kinetics of photochemical processes and two chapters, corn prising nearly one third of the book, on photochemical reactions. Inevitably, many interesting fields are excluded by the terms of reference, but students faced with a new course on photochemistry will find this book very useful.CHEMISCHE, PHYSIKALISCHE UND ELEKTROCHEMISCHE METHODEN. Edited by the INSTITUT R. K. WEBSTER Chapman and Hall. 1972. Price L1.70. D. BETTERIDGEJune, 19731 BOOK REVIEWS 463 QUANTITATIVE MEASUREMENTS AND CHEMICAL EQUILIBRIA. By ERNEST H. SWIFT and ELIOT A. BUTLER. Pp. xiv + 719. San Francisco: W. €3. Freeman and Co. 1972. Price $14.50. A more appropriate title to this book would be “An Introduction to Quantitative Inorganic Analysis,” but one can understand any attempt to avoid producing yet another book having this title. The book aims to provide an intensive training in certain of the fundamental techniques of quantitative chemical measurements.Much of it is devoted to a rather elementary treatment of gravimetric and titrimetric analysis, the latter occupying almost half of the book. Despite the great impact of complexometry over the past 25 years, this method receives scant treatment. It does, however, include the Ringbom curve, an item often omitted when presenting this topic. Forty-eight pages cover laboratory equipment and operations and feature, with appropriate diagrams, how to hold a glass stopper while pouring liquid from a reagent bottle and how to insert a glass tube into a stopper. Optical and electrical methods, again treated a t an elementary level, occupy the final 63 pages. As in so many American books, there is a profusion of numerical problems and questions.Detailed experimental procedures are given throughout, each being followed by an elaborate system of notes. There is little to fault in the treatment of the subject matter as such. In fact, it is dealt with in a most thorough manner and conforms to high educationaI standards. What is far more difficult is to justify the scope of the book, particularly if one has in mind U.K. analytical chemistry courses. At the lower end it assumes virtually no chemical background on the part of the student, and at the other end it stops short of giving a balanced course a t a reasonable level. One novel feature of the book is the inclusion of mass titrations carried out with a polythene wash-bottle and a top-pan balance. W. J. WILLIAMS PMR SPECTROSCOPY IN MEDICINAL AND BIOLOGICAL CHEMISTRY.By A. F. CASY. Pp. xvi + 425. Dr. Casy has set out to write a book that assumes a familiarity with nuclear magnetic resonance theory, which many of his potential readers will not possess. It is a pity that he does not provide more background theory to support the many applications discussed. On the few occasions when some theory is presented, it is quite inadequate. For example, in the section on aromatic ring current effects (p. 93), a clear qualitative picture of the origin of these effects does not emerge from the text. The book contains a clear detailed discussion of the analytical aspects of nuclear magnetic resonance and a useful chapter on the nuclear magnetic resonance spectral features of nitrogen- containing compounds.Dr. Casy discusses many interesting examples of the application of nuclear magnetic resonance techniques to the study of compounds of pharmacological and biological interest and, although little attempt has been made to assess the papers critically, the book will serve as a useful reference source. An appendix on solvent and hydrogen-bonding effects contains many useful practical hints. I t is unlikely that many scientists will buy their own copy of this book but, because of its reference value, laboratories interested in this type of work will need to purchase a copy. London and New York: Academic Press. 1971. Price ,57-30; $23. J. FEENEY ANALYTICAL CHEMISTRY : KEY TO PROGRESS ON NATIONAL PROBLEMS. Proceedings of the 24th Annual Summev Symposium on Analytical Chemistry, held at the National Bureau of Stan- dards, Gaithersburg, Maryland, June 1.6-18, 1971.Edited by W. WAYNE MEINKE and JOHN K. TAYLOR. National Bureau of Standards Special Publication 351. Pp. x + 470. Washing- ton: U.S. Department of Commerce. 1972. Price $3.60. This book is a record of six papers delivered by invitation in order to direct attention to analytical problems in important areas of current everyday interest. Unusually, the volume is prefaced by the complete re-publication of a paper presented in 1933 by Dr. G. E. F. Lundell and subsequently published the same year in I n d . Engng Chew., Analyt. Edn, entitled “The Chemical Analysis of Things as They Are.” This paper deals with basic points relating to such matters as sampling and accuracy and is still quoted today.The chapters that follow relate basically to the American scene and are devoted in turn to the consideration of analytical problems in biochemical research and clinical chemistry, agricultural science, air pollution control, water pollution control, oceanography and in solid-state research and electronics. A panel discussion concludes each chapter; each covers a wide range of individual topics. “Problems in Agricultural464 BOOK REVIEWS [Analyst, Vol. 98 Science,’’ for example, includes fumigation, nutrition and amino-acid analyses, fats and fatty acids, fibrous compounds, seed and plant constituents, meat quality and the composition of meat and dairy products, the sensory characteristics of food, veterinary chemicals, mycotoxins, plant growth regulators, pesticides, nitrosamines and pollutants.While it is not possible to treat all of the problems that arise in these areas in depth, the areas discussed clearly relate to a wide field of stimulus for analytical research. This is also true for other chapters, especially perhaps that on biomedical research and clinical chemistry, which is illustrated with both diagrams and cartoons. The text throughout is supported by references to the original literature. A compre- hensive index adds to the value of the book and helps to draw together common analytical interest from a very wide variety of sources, H. EGAN THE ANALYTICAL CHEMISTRY OF SULFUR AND ITS COMPOUNDS. Part 11. Edited by J. H. KARCH- MER. Volume 29 in Chemical Analysis: A Series of Monographs on Analytical Chemistry and its Applications. Pp.xviii + 835. New York, London, Sydney and Toronto: Wiley- Interscience. 1972. Price k21.25. This volume deals with the analytical chemistry of sulphides, disulphides and polysulphides, thiophenes, sulphur analogues of carbonyls, carboxylic and carbonic acids and quadrivalent and sexavalent sulphur compounds. In conjunction with the first volume, the most commonly encountered sulphur compounds are covered. In each of the chapters there is a general pattern and in covering the analytically significant properties, most techniques have been dealt with. For each group of compounds there is a relatively large number of pertinent references, so that the whole can probably become a source book for the analytical chemistry of sulphur.Although there is excellent coverage, it is inevitable that some specialists may feel dis- appointed that a particular chapter has not been devoted to their particular speciality. However, by judicious use of the excellent index they will, I am sure, be able to find enough of relevance to interest them. This is a well written book and the authors of the various chapters, and the editor, have filled a gap in analytical chemistry. L. S. BARK THE DETERMINATION OF HYDROXYL GROUPS. By STIG VEIBEL. A n International Series of Monographs, hTo. 1. Pp. xviii + 159. London and New York: Academic Press. 1972. Price jtj3.50; $10.50. The term “Determination” in the title of this text goes beyond the normal use of the word. This text includes methods for the detection of the hydroxyl group and methods for characterising hydroxy-compounds as well as methods for measuring the hydroxyl group. Twenty-four pages are devoted to detection methods, thirty-nine to characterisation and eighty pages to measurement. The chemical methods are described completely in the text, and they are compared and evalu- ated. The instrumental methods for dealing with the hydroxyl group are only lightly treated. This is not detrimental to the text as someone who is interested in wet methods is rarely also interested in instrumental methods. The text includes not only the common, well accepted methods but also some of the less common methods. The book is authoritative and well joined together to present a unified picture of the subject area. It is obvious from the text that Dr. Veibel is well versed in the material of which he speaks. This book should interest both students and practitioners in the field of organic chemistry and organic analysis. S. SIGGIA

ISSN:0003-2654    

DOI:10.1039/AN9739800461

出版商:RSC    

年代:1973

数据来源: RSC