摘要:

1374 Analyst, November, 1983, V O ~ . 108, $9. 1374-1379 Comparison of Three Methods for the Determination of Urea in Compound Feed and Silage Michael O'Keeffe Analytical Services Laboratory, Agricultural Institute, Dunsinea Researcla Centve, Castleknock, County Dublin, Ireland and John Sherington Statistics Department, Agricultural Institute, 19, Sandymount Avenue, Dublin 4, Ireland Urea levels in compound feed were determined by three methods : the phenol - hypochlorite measurement of ammonium ions released by urease ; the p - dimethylaminobenzaldehyde (DMAB) colour reaction with urea; and the Conway microdiffusion measurement of ammonia released by urease. The phenol - hypochlorite method had comparable accuracy and precision to the official DMAB method and was an improvement on the microdiffusion method.The phenol - hypochlorite method, produced as a clinical chemistry kit, can be used for the determination of urea in water extracts of compound feed and of chopped, fresh silage. This method is simple, rapid, inexpensive and may be automated for the determination of urea used as supplementary nitrogen in compound feed and silage. Keywords : Urea determination ; compound feed; silage ; phenol - hypochlovite method ; water extract The ability of ruminants to convert non-protein nitrogen into protein has allowed the use of urea as a source of supplementary nitrogen with compound feeds112 and with poor quality hay3 or ~ i l a g e . ~ $ ~ The amount of urea that can be utilised as non-protein nitrogen in animal feed- stuffs is limited by factors such as the effect on palatability of the feed, the rapid production of ammonia in the rumen leading to nitrogen losses and/or toxicity and reduced animal per- formance.There is a requirement for good assay methods for urea in animal feedstuffs to ensure that supplementary urea is at the correct levels. Official methods of analysis for urea in animal feed include urease conversion of urea into ammonia with determination by distalla- tion into acid and titration with alkali and colorimetric determination of urea using @di- methylaminobenzaldehyde (DMAB) .6 In this laboratory a urease method,' based on a micro- diffusion method for urea in blood,s had been used successfully for a number of years. Other workers have determined urea in animal feedstuffs by the microdiffusion method4 and by electron-capture gas chr~matography.~ Because of the irregular demand for urea assays in feedstuffs received at this laboratory and the relatively complicated and labour-intensive nature of the microdiff usion method, we attempted to utilise a clinical chemistry kit method, based on the phenol - hypochlorite reaction with ammonium ions,1° as an alternative. In this work we compared the phenol- hypochlorite, DMAB and microdiffusion methods for the determination of urea in compound feeds, and the application of the phenol - hypochlorite method to the determination of urea in grass silage. The DMAB method was chosen as the reference method because of its official status,6y11 and because it differs from the other methods in not utilising urease but measuring urea directly via a urea - DMAB colour complex.Experimental Apparatus A Pye Unicam SP6-500 spectrophotometer with l-cm cells was used in the phenol - hypo- chlorite and DMAB methods; a Conway microburette and standard all-glass Conway micro- diffusion units were used in the microdiffusion method.* A mechanical shaker was used and all glassware, including the microdiffusion units, was acid-washed, cleaned with detergent and rinsed with distilled, de-ionised water.O'KEEFFE AND SHERINGTON 1375 Reagents throughout. All chemicals were of analytical-reagent grade and distilled, de-ionised water was used Phenol - hypochlorite method Mannheim, Cat. No, 124788, Urea Enzymatic Colorimetric Method). All reagents for this method were those supplied in the clinical chemistry kit (Boehringer Phosphate bufer (50 mmoll-l) - urease (10 U ml-l) solution.Urea standard solution (30 mg 1-l). Phenol (0.106 moll-l) - sodium nitroprusside (0.17 mmoll-l) solution. Sodium hypochlorite (11 mmol 1-l) - sodium hydroxide (0.125 M) solution. DMAB method All reagents for this method are as described for the AOAC method.6 Microdifusion method Hydrochloric acid, 0.02 M. Boric acid with indicator. Dissolve 10 g of boric acid in 700 ml of water and 200 ml of ethanol. Add 10 ml of pH indicator (0.33% m/V bromocresol green plus 0.67% m/V methyl red in ethanol) and add 0.01 M sodium hydroxide solution dropwise until the solution is pale red. Add 112 g of potassium carbonate to 100 ml of water. Prepare freshly for each assay a 2% m/V aqueous solution, adjusted to pH 7.0 with phosphate buffer, from type I11 urease (30OOUg-l), obtained from Sigma Chemicals Ltd.Dissolve 3.0 g of disodium hydrogen orthophosphate and 2.0 g of potassium dihydrogen orthophosphate in water and dilute to 100 ml. Dilute to 1 1 with water. Potassium carbonate solution, saturated. Urease solution. Phosphate bufer solzhon. Urea standard solution, 0.05y0 mlV. Silicone grease. Obtained from Edwards High Vacuum Ltd. Procedures Sample preparation Compound-feed samples were prepared that consisted of ground barley, a mineral - vitamin supplement and soybean meal with urea (AnalaR grade, crystalline) at levels of 0-30 g k g l (Table I). The constituents of each feed were mixed thoroughly using a catering-type food blender.Three samples of each feed were milled on a Wiley mill fitted with a No. 20 (850 pm) sieve. TABLE I COMPOSITION OF FEED PREPARED FOR UREA DETERMINATION Constituentlg kg-1 Mineral - vitamin Feed Ground barley Soybean meal supplement Urea A .. .. . . 820 150 30 0 B . . . . .. 820 145 30 5 c .. . . . . 820 140 30 10 D .. .. .. 820 130 30 20 E .. .. .. 820 120 30 30 Extraction of urea Weigh in duplicate 1.0 g of ground com- pound feed into a 30-ml (23 x 150 mm) stoppered test-tube, add 20 ml of water and shake thoroughly. Incubate in a water-bath at 50 "C for 10 min and then centrifuge at lOOOg. Urea is determined in the supernatant. Phenol - hypochlorite and microdiflmion methods.1376 O'KEEFFE AND SHERINGTON : COMPARISON OF THREE AnaZyst, VoZ. 108 Weigh in duplicate 0.5-1.0 g of either finely chopped (<lO-mm lengths) of fresh (wet) silage or dried (40 "C for 48 h), ground (1.0-mm sieve) silage into a 30-ml stoppered test-tube and extract in the same way as for the compound feed.Alternatively, soak 50 g of chopped, fresh silage in 200 ml of water overnight and determine the urea content of the resulting supernatant "silage juice." DMAB method. The extraction of urea from duplicate 1 .O-g samples of compound feed was as described for the AOAC method.6 Urea determination Dilute the extract supernatant with water to bring the urea concentrations within the range of the clinical chemistry kit (0-5 mg per 100 ml). Pipette 0.1 ml of phosphate buffer - urease solution into the reagent blank, standard and sample tubes (16 x 150 mm test-tubes), 0.2 ml of the urea standard solution into the standard tubes and 0.2 ml of the diluted sample extracts into the sample and sample blank tubes.Stopper the tubes, mix the contents and incubate in a water-bath at 37 "C for 10 min. Add 5 ml of phenol - sodium nitroprusside solution and 5 ml of sodium hypochlorite - sodium hydroxide solution to all of the tubes. Stopper, mix and incubate in a water-bath at 37 "C for 15 min. Measure the absorbances of standards (std. A ) , samples (sample A ) and sample blanks (sample blank A ) against the reagent blank at 550 nm. The mass of urea is given by the following equation : Phenol - hypochlorite method. 6 X (Asample - Asample blank) X dilution of sample extract Urea/g k g l = .~ &td. x mass of sample x 10 DMAB method.Urea was determined on extracts of compound feed as described for the Microdifum'on method. Dilute the extract supernatant with water to bring the urea con- Spread a layer of silicone grease on the outer wall of the Conway microdiffusion unit and Pipette 0.5 ml of Cover the AOAC method.6 centrations within the range of the microdiffusion assay system (0-50 mg per 100 ml). pipette 1.0 ml of boric acid with indicator into the central well of the unit. urease solution and 0.2 ml of sample extract into the outer chamber of the unit. unit with the lid and mix the contents in the outer chamber by carefully rotating the unit. TABLE I1 DETERMINATION OF UREA IN FEED USING THREE METHODS OF ANALYSIS Mean Standard Coefficient of Feed Method of analysis concentration*/g kg-l error/g kg-l variation, % A .. . . Phenol - hypochlorite 0.2 0.12 - DMAB 0.2 0.23 - Microdiff usion 0.5 0.38 - B . . .. D .. . I E .. . . Phenol - hypochlorite 4.5 DMAB 3.9 Microdiff usion 5.0 Phenol - hypochlorite 9.2 DMAB 8.5 Microdiff usion 9.5 Phenol - hypochlorite 17.4 DMAB 18.1 Microdiff usion 19.5 Phenol - hypochlorite 27.2 DMAB 27.8 Microdiff usion 28.0 0.12 4.4 0.17 7.3 0.44 15.1 0.44 8.2 0.32 6.5 0.56 10.2 0.36 3.6 0.22 2.1 0.46 4.1 0.62 3.9 0.43 2.7 0.75 4.6 * Mean of three samples of each feed analysed, in duplicate, on three different days.November, 1983 1377 Slide the lid back just suffici- ently to pipette 1.0 ml of potassium carbonate solution into the outer chamber, replace the lid, mix the contents and allow ammonia to diffuse into the central well for 90 min.Titrate the contents of the central well with 0.02 M hydrochloric acid to a permanent pale red colour, using the Conway microburette. Prepare the standards and reagent blanks in the same way, using 0.2 ml of urea standard solution and 0.2 ml of water, respectively. Prepare sample blanks using 0.2 ml of sample extracts but adding no urease to these units. The mass of urea is given by the following equation : METHODS FOR UREA IN COMPOUND FEED AND SILAGE Incubate the sample at an ambient temperature for 15 min. (sample titre - sample blank titre) x dilution of sample extract x 10 Urea/g kg-l = ~ (standard titre - blank titre) Results and Discussion Urea in Compound Feed The levels of urea determined in five compound feeds, by duplicate analyses of three sub- samples of each feed by three methods, are shown in Table 11.Analyses of the three sub- samples of each feed were carried out on different days. Mean urea levels, together with standard error (SE) and coefficients of variation (CV) are included. The urea levels determined in the feeds are less than the target levels of 5, 10, 20 and 30 g k g l of urea by all methods (Table 11). A possible explanation for these lower levels are losses during the milling of the compound feeds.12 Comparison of Methods A split-plot analysis of variance (Table 111) demonstrates a significant difference (significance, P < 0.01) in methods of analysis that is not related to the level of urea in the compound feed (method of analysis by level of urea interaction term not significant).The standard error of the difference between the methods, applied to the method means (Table 111), indicates that, in general, the results by the microdiffusion method are significantly different to those obtained by the other methods. The phenol - hypochlorite method gives results comparable to those obtained with the official DMAB method for urea in feed. This similarity of results obtained with the DMAB and phenol - hypochlorite methods is impressive considering that the urea extractions from feed for these methods are different, while urea determination by the phenol - hypochlorite and microdiffusion methods is on a common extract of feed. TABLE I11 VARIANCE ANALYSIS FOR DETERMINATION OF UREA IN FEED BY PHENOL - HYPOCHLORITE, DMAB AND MICRODIFFUSION METHODS The method means were as follows: phenol - hypochlorite, 11.70; DMAB, 11.68; and The standard error of the means = 0.229 and number of degrees freedom = 20.microdiffusion, 12.49gkg-l. Degrees of Source of variation freedom Mean square F-value Significance Urea level . . .. .. 4 2 190.44 1580 P <0.001 Residual . . * . . . 10 1.39 Method .. .. .. 2 6.29 8.04 P (0.01 Method x urea level . . .. 8 1.09 1.40 N.S.* Residual . . .. .. 20 0.78 Between duplicate . . * . 45 1.07 * Not significant. Reproducibility and Precision The coefficient of variation (CV) values (Table 11) are a measure of the day-to-day repro- ducibility of the analytical methods, as sampling variation is common for each method. The reproducibility is acceptable for all three methods with feed samples containing approximately1378 O’KEEFFE AND SHERINGTON : COMPARISON OF THREE Analyst, VoZ.108 20 and 30 g kg-l of urea (CV < 5%). However, for feeds containing approximately 5 and 10 g k g l of urea, the reproducibility is less satisfactory, particularly for the microdiffusion method (CV > loyo). The variance between duplicates is determined for each method (Table IV) and the phenol - hypochlorite method shows the lowest variance. Applying Bartlett’s test for homogeneity13 to the three variance values gives a variance ( X 2 ) of 3.05 (degrees of freedom = 2), which is not significant. The phenol - hypochlorite method, therefore, is at least as precise as the other methods . TABLE IV VARIANCE BETWEEN DUPLICATES FOR UREA DETERMINATION IN FEED BY PHENOL - RYPOCHLORITE, DMAB AND MICRODIFFUSION METHODS The number of degrees of freedom = 15.Method Variance Phenol - hypochlorite . . .. . . 0.587 DMAB .. .. .. .. . . 1.155 Microdiffusion . . .. .. . . 1.474 Urea in Silage Sample type Different sample types may be used for the determination of urea in grass silage using the phenol - hypochlorite method. The urea content determined in “silage juice,” a preparation used for determining ammonia nitrogen in silage, and on a water extract of fresh, chopped silage, the extraction methods used for compound feed, are compared in Table V for a number of silage samples containing urea at levels of up to 30 g kg-l. Levels of urea determined in the water extracts are significantly higher (P < 0.05) than in the “silage juice” samples, suggesting that soaking of silage in water overnight to produce “silage juice” does not extract all the urea from the sample.At the other extreme, urea determined in a water extract of dried, ground silage is generally lower than that determined in a water extract of fresh, chopped silage (Table VI). Mean values (n = 3) for urea, in silage containing urea in the region of 20-60 g k g l , are higher in two of the three silages for the extract from fresh silage than for the extract from dried, ground silage. Drying and/or grinding causes loss of urea in some silages. TABLE V UREA DETERMINATION ON SILAGE USING TWO EXTRACTION TECHNIQUES Number of degrees of freedom = 9, t = 2.56 and significance, P < 0.05.Urea concentration for each samplelg kg-1 1 2 3 4 5 6 7 8 9 10 “Silage juice” . . . . 4.6 0.0 2.3 26.7 0.0 1.3 10.5 0.0 0.0 0.0 Water extract . . . . 4.3 0.9 6.5 27.9 1.0 7.7 13.1 1.2 0.0 0.0 A r 7 Precision and recovery The precision of the method can be assessed from the replicated assays of the three silages (Table VI). Precision is good when urea is determined on a water extract of fresh, chopped silage, with CV values being <a%. The mean recovery of urea added at 10 g kg-l to silage samples was 10.15 g k g l , with a standard error of 0.427 g k g l (n = 6). Conclusions The phenol - hypochlorite clinical chemistry kit can be successfully applied to the determina- tion of urea on a water extract of compound feed. This method has comparable accuracy and precision to the official DMAB method and is better than the microdiffusion method.Carried out manually, the phenol - hypochlorite method takes less than half the time for either of theNovember, 1983 METHODS FOR UREA IN COMPOUND FEED AND SILAGE TABLE VI 1379 COMPARISON OF UREA DETERMINED ON EXTRACTS OF FRESH, CHOPPED SILAGE (FCS) AND OF DRIED, GROUND SILAGE (DGS) Mean urea Standard Coefficient of Sample Extract concentration*/g kg-l error/g kg-l variation, yo A .. .. .. FCS 54.4 1.10 3.5 DGS 47.5 0.27 1 .o B .. .. .. FCS 32.1 0.13 0.7 DGS 24.3 0.21 1.5 c .. .. .. FCS 23.7 0.14 1.1 DGS 24.0 1.11 8.0 * Mean of extracts from three samples of each silage. other methods. carried out on automated equipment. for the determination of urea on a water extract of fresh, chopped silage.For large numbers of samples, the urea determination by this method can be The phenol - hypochlorite method can be used, also, The authors thank Ms. N. McNeely for her technical assistance, Mr. J. P. Hopkins for his help with feed compounding, and Ms. M. Hennessy for preparing the manuscript. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. References Orskov, E. R., and Grubb, D. A., Anim. Feed Sci. Technol., 1977, 2, 307. Umunna, N. N., Klopfenstein, T. J., Hasimoghu, S., and Woods, W. R., Anim. Feed Sci. Technol., Umunna, N. N., J . Agric. Sci., 1982, 98, 343. Thomas, C., Wilson, R. F., Wilkins, R. J., and Wilkinson, J. M., J . Agric. Sci., 1975, 84, 353. Giardini, A., Lambertini, F., Gaspari, F., and Lo Bruno A., Anirn. Feed Sci. Technol., 1976, 1, 465. “Official Methods of Analysis of the Association of Official Analytical Chemists,” Twelfth Edition, Spillane, T. A., “Animal Production Research Report,” Agricultural Institute, Dublin, 1968, p. 134. Conway, E. J ., “Microdiffusion Analysis and Volumetric Error,” Fourth Edition, Crosby Lockwood, Arnold, J. P., Chem. Ind. (London), 1973, 15, 751. Fawcett, J. K., and Scott, J. E., J . Clin. Pathol., 1960, 13, 156. Agricutural Development and Advisory Service, “Technical Bulletin 27 : The Analysis of Agri- Potts, T. J., J . Assoc. OH. Anal. Chem., 1962, 45, 587; 1967, 50, 56. Bartlett, M. S., J . R. Statist. Soc., Suppl., 1937, 4, 137. 1982, 7, 375. Association of Official Analytical Chemists, Washington, DC, 1975, p. 132. London, 1957. cultural Materials,” HM Stationery Office, London, 1973. Received February 2nd, 1983 Accepted June 16th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801374

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1380 Analyst, November, 1983, Vol. 108, pp. 1380-1385 Determination of Kerosene, Tri butyl Phosphate, Di butyl Butylphosphonate, Di-2-ethyl hexylphos- phoric Acid and Trioctylphosphine Oxide in Phosphoric Acid Ching-Hui Kuo," Fu-Chung Chang and Yu-Chai Yeh Analytical Chemistry Centre, Institute of Nuclear Energy Research, P.O. Box 3-19, Lungtan, Taiwan, Republic of China Kerosene, tributyl phosphate (TBP), dibutyl butylphosphonate, di-Z-ethyl- hexylphosphoric acid and trioctylphosphine oxide in phosphoric acid were determined by gas chromatography. Toluene and TBP were chosen as internal standards. The organic contents in phosphoric acid were first extracted by carbon tetrachloride with an extraction efficiency of about 99%. The determination of low concentration organic constituents can be per- formed by an extraction - concentration method.The determination of three different peak patterns are discussed. Keywords ; Kerosene, tributyl phosphate, dibutyl butylphosphonate, di-2-ethyl- hexylphosphoric acid and trioctylphosphine oxide determination; carbon tetrachloride extraction ; gas - liquid chromatography ; $re-concentration The determination of trace amounts of kerosene, dibutyl butylphosphonate (DBBP) , di-2- ethylhexylphosphoric acid (HDEHP) and trioctylphosphine oxide (TOPO) in phosphoric acid is necessary in the process for uranium recovery from wet-process phosphoric acid. Alkyl esters of phosphoric acid have been separated by paper chromatographyl-3 and the esterifica- tion of alkyl phosphate using diazomethane has been Campbell5 determined organic extractants in re-processed reactor fuel with gas chromatographic measurements by employing 20y0 Apiezon N on Chromosorb W and a flame-ionisation detector.In that determination, HDEHP was measured at the detection limit of 0.1%. Grob and McCrea8 determined 12 phosphine oxides by means of a thermal conductivity detector and a column packed with 5% SE-30 on Porapak Q. In the uranium recovery process, organic constituents were separated from phosphoric acid by an oil - water separator; the residue of trace organic contents in phosphoric acid was removed by adsorption on activated charcoal. The efficiency of the separator and the organic constituents content in each of the separation steps and in the refined phosphoric acid were determined by gas chromatography.The high concentration of organic constituents in phosphoric acid can be determined directly by injection of the dilute carbon tetrachloride ~olution,~ but the accumulated injec- tions with phosphoric acid solution would result in the gradual deterioration and deformation of the packing material. This paper describes the determination of the organic content in phosphoric acid, at the micrograms per millilitre level, using a simple procedure of extraction and concentration, but without a tedious procedure such as a methylation or silylation. Experimental Instrumentation The conditions for gas - liquid chromatography (GLC) were as described in Table I. Reagents Kerosene (Union Chemical Works, Republic of China, 99.6y0, sp, gr., 0.775), HDEHP (Union Carbide, 95.27%, determined by the potential methodlo), TOPO (General Mills, 97%), toluene (Osaka, Japan, 97y0, general-purpose reagent), TBP (E.Merck, Darmstadt, FRG, 99yo), DBBP (ICN Pharmaceuticals Inc., Plainview, NY, 99%) and carbon tetrachloride (Union Chemical Works, Republic of China) were used. * To whom correspondence should be addressed.KUO, CHANG AND YEH 1381 TABLE I CONDITIONS FOR GAS - LIQUID CHROMATOGRAPHY Condition Description Gas chromatograph . . .. . . Varian, Model 3700 Detector . . .. .. . . . . 1. Flame-ionisation detector (FID) Integrator. . . . .. .. . . Varian, Model CDS-111 Recorder . . . . .. .. . . Varian, Model 9176 Glass column . . .. .. . . 10 f t x 0.25 in o.d., 2 mm i.d., 5% Dexsil300 on 80-100 mesh Chromosorb WAW/DMCS.Pre-conditioned for at least 16 h at 330 "C Carrier gas .. .. ,. . . Helium Flow-rate . . . . .. . . . . 30 ml min-l with an auto-flow controller Hydrogen flow-rate for FID . . . . 30mlmin-l Air flow-rate for FID .. . . 300 ml min-l Hydrogen flow-rate for FPD . . . . 140 ml min-l Air flow-rate for FPD . . .. . . 1. 80 ml min-l Determination of kerosene- 2. Dual flame-photometric detector (FPD) with phosphorus filter 2. 170 ml min-l Injector temperature . . .. . . 160 "C Column temperature . . . . . . Set at 50 "C for 3 min, programmed to rise to 150 OC at Determination of TBP, DBBP, HDEHP and TOPO- Injector temperature . . .. . . 250 "C Detector temperature . . . . 340 "C Column temperature . . Detector temperature .. .. 180°C 20 "C min-1 . . . . Set at 180 "C for 3 min, programmed to rise to 320 "C at 20 "C min-l Procedure To analyse the samples, 50 ml of phosphoric acid solution were transferred from the uranium recovery process into a 250-ml stoppered Erlenmeyer flask and mixed immediately for 5min with an equal volume of carbon tetrachloride, which contained 100pgml-1 of toluene and 100 pg ml-l of TBP.Two layers formed in the flask after the mixing procedure. Phosphoric acid on the upper layer prevents the evaporation of carbon tetrachloride. The organic constituents remain at a constant level in the carbon tetrachloride layer for several days. A 5-p1 volume of the bottom layer (carbon tetrachloride) was injected, with a 10-p1 Hamilton microsyringe, into the gas chromatograph. The GLC conditions were then set to those for the determination of kerosene. After completing each batch of samples, the con- ditions were then set to those for the determination of the rest of the constituents in the bottom layer. If the concentration of determinands is below the detection limit (kerosene, 10 p.p.m.; TBP, 10 p.p.m.; DBBP, 10 p.p.m. ; HDEHP, 200 p.p.m. ; and TOPO, 10 p.p.m.), the carbon tetrachloride layer was placed in a 50-ml flask and the solution was concentrated using a Vigeaux distillation column. The minimum detectable amountsll of organic constituents are listed in Table 11. TABLE I1 MINIMUM DETECTABLE AMOUNTS OF ORGANIC CONSTITUENTS Organic constituent Minimum detectable amountlg Kerosene . . .. 5 x 10-8 TBP .. .. ,. 2 x 10-8 DBBP . . .. .. 2 x 10-8 HDEHP .. .. 6 x lo-' TOPO .. .. .. 3 x 10-8 Calculation Toluene was chosen as an internal standard for the determination of kerosene and tributyl phosphate was used as an internal standard for the determination of DBBP, HDEHP and1382 A KUO et al. : DETERMINATION OF KEROSINE, TBP, Analyst, VoZ. 108 TABLE I11 EXTRACTION EFFICIENCY OF ORGANIC CONSTITUENTS IN 28% PHOSPHORIC ACID EXTRACTED WITH AN EQUAL VOLUME OF CARBON TETRACHLORIDE Constituent found in CC1, layer, p.p.m. A I \ Extraction HDEHP TOPO Kerosene 1 190 16 365 2 2.1* 0.1* <5 Extraction efficiency, % . . . . 99 99 > 99 * The solution had been concentrated before flame-ionisation detection. TOPO, height, H , and concentration, C, as is expressed by equation (1). The concentration of constituents can be calculated from the relationship of peak The internal standard, I, represents either toluene or TBP.K , is a constant of organic constituent X. The concentration of each constituent can be determined from equation (2) by the use of a calibration graph or by means of an HP-97 calculator with a curve-fitting program. B J 0 4 8 12 16 Retention time/min Fig. 1. Chromatograms of kerosene and toluene in carbon tetrachloride determ- ined by flame-ionisation detection at lo-'* a.u.f.s. A, Kerosene (775 pg ml-l) ; B, toluene (100 pg ml-1) ; and C, carbon tetrachloride.November, 1983 DBBP, HDEHP AND TOPO IN PHOSPHORIC ACID Results and Discussion Extraction With Carbon Tetrachloride 1383 Carbon tetrachloride is a good solvent for gas chromatographic analysis because of its chemical stability and high purity.The pure organic constituents (kerosene, TBP, DBBP, HDEHP and TOPO) can be thoroughly mixed with carbon tetrachloride, but are less soluble when mixed with phosphoric acid. Under vigorous agitation in the uranium recovery process, hundreds of parts per million of kerosene, tens of parts per million of DBBP, thousands of parts per million of HDEHP and tens of parts per million of TOPO were found in the 28% phosphoric acid phase. On standing, the less dense organic content will float to the upper layer. Therefore, the results do not represent the bulk solution when the upper or the lower part of the solution only is analysed. The extraction efficiencies were better than 99% in 28% phosphoric acid and are listed in Table 111. The extraction efficiencies were indirectly calculated from two consecutive extractions of organic constituents in the carbon tetrachloride phase, because the direct injection of phosphoric acid solution results in column deteriorati~n.~ The extraction efficiencies were influenced by the concentration of phosphoric acid.Kerosene, for example, was recovered at 99 and 89740 in solutions of 28 and 85% phosphoric acid, respectively. The lower recovery was due to the higher viscosity of S5(30 phosphoric acid. Determination of Kerosene Kerosene is a mixture of hydrocarbons with the number of carbons ranging from 9 to 14, as the chromatogram in Fig. 1 shows, which makes kerosene difficult to determine. How- ever, only one of the peaks was chosen for calculation, as the composition or ratio of hydro- carbons before or after extraction is the same in each sample of kerosene.The determination was carried out by using equation (2) with an internal standard (100 pg ml-l of toluene). 1 I D C 5 0 4 8 12 16 Retention time/min Chromatograms of TBP, HDEHP and TOPO determined by flame-ionisation detection a t 2 x lo-'* a.u.f.s. Solutions were (a) concentrated and (b) dilute in carbon tetrachloride. A, TBP (10 pg ml-l); B, HDEHP (197 pg ml-l) ; C, TOPO (32 pg ml-l) ; and D, tetrachloromethane plus kerosene. Fig. 2. I I I I 0 2 4 6 Retention time/min Fig. 3. Chromatogram of DBBP and TBP in carbon tetrachloride determined by flame-ionisation detection at 4 x 10-10 a.u.f.s. A, DBBP (1000 pg ml-l); B, TBP (1 000 pg ml-l) ; and C, tetra- chloromethane.1384 Analyst, VoZ.108 The area under the peaks of kerosene, above the dashed line in Fig. 1, was integrated by an integrator. The graph of peak-area ratio (AkerosenelAtoluene) veYsZts concentration of kerosene is rectilinear over the range 10-1 000 pg ml-l. The calculation of peak height is a convenient method for the determination of low concentrations of kerosene. The peak at a retention time of 9.8 min was chosen for the peak-height calculation because it showed the highest response. The graph of peak-height ratio (kerosene to toluene) ueyszts concentration of kerosene was also rectilinear in the same range. The relative standard deviation for 290 pg ml-l of kerosene with seven determinations was within 2%. KUO et aZ. : DETERMINATION OF KEROSINE, TBP, Determination of TBP, DBBP and TOPO The low concentration of alkyl esters in phosphoric acid can be determined with the extrac- tion - concentration procedure followed by flame-ionisation detection.The amounts of organic constituents were unchanged after the concentration procedure, as is shown in Fig. 2 (e.g., TBP, HDEHP and TOPO). The relative standard deviation of four experiments was within 3%. The calibration graphs of TBP, DBBP and TOPO were rectilinear in the concentration range 10-1 000 pg ml-l. The samples contained no TBP and were determined using equation (2) with 100 pg ml--l of TBP as an internal standard. Kerosene may cause significant interference in the determination of TBP and DBBP owing to peak overlapping. The problem can be easily solved by the use of a flame-photo- metric detector.Kerosene did not show interference in the determination of TBP and DBBP, because the flame-photometric detector is more sensitive to phosphorus than to hydrocarbons. The DBBP peak with the similar response of TBP is shown in Fig. 3. Determination of HDEHP The peak height of HDEHP increased as the concentration increased, but no peak was found at the same retention time on the chromatogram obtained with flame-photometric detection, which indicated that the response of HDEHP is due to the fragment of hydrocarbon that contains no phosphorus. Fig. 4 shows the concave upward calibration graph of HDEHP with an ex- ponential power of 1.43 and with 80 pg ml-1 of TBP as an internal standard. The peak-area ratio ueysuus concentration of HDEHP was calculated by a curve-fitting program with an HP-97 calculator.The square-root graph of response veysus concentration of HDEHP is rectilinear. The chromatogram in Fig. 2 was obtained with a flame-ionisation detector. The values of the intercept, a, and the slope, k , are listed in Table IV. 4.00 3.00 m 1 p 2.00 q I1 P 1 .oo 2.00 1.50 3 I r 1.00 ; 5 I1 0.50 0 2000 4000 6000 8000 10000 HDE HP concent ration/pg m I - ' internal standard, TBP (80 pg ml-l). Fig. 4. Calibration graphs of HDEHP with an Because HDEHP is near its boiling point, thermally labile, and the association of dimeric HDEHP is stronger than in monocarboxylic acid,12 the fragment that contained no phos- phorus might be decomposed on the column. Theoretically, the square-root graph shows a linear relationship if the response is due only to the contribution of one fragment from one dimeric HDEHP, as shown in equation (3).November, 1983 DBBP, HDEHP AND TOPO IN PHOSPHORIC ACID 1385 CC14 column BHDEHP + (HDEHP), -+ fragment .. . . ’ * (3) The response is proportional to the concentration of dimeric HDEHP, i.e., (HDEHP),, which in turn equilibrates with the concentration of monomeric HDEHP. Then R = KC&,,,, or The straight line in the square-root graph did not pass through the origin. This deviation from the theoretical graph may be attributed to the HDEHP partially retained in the column. Further experimentation is needed before a final judgement can be made on this point. = K‘CHDEHp, where R = AnDEHp/ATBp and K is a constant. TABLE IV INTERCEPT, a, AND SLOPE, K, OF THE SQUARE-ROOT GRAPH OF THE HDEHP CALIBRATION‘ GRAPH Experiment No.* CTBP/mg 1-l at kt/l mg-1 Y2t 1 80 0.22 1.78 x 10-4 0.99 2 50 0.32 2.77 x 10-4 1.00 3 50 0.32 3.05 x 10-4 1.00 * 1 and 2 were performed with a used column; 3 was performed with a newly pre- t The values of a, k and y2 were obtained using an HP-97 calculator with a least- pared column.square fitting program; y2 is the correlation coefficient. Conclusion The organic contents in phosphoric acid were determined by the procedure of extraction - concentration in the carbon tetrachloride phase. Three different types of peak pattern can be accurately calculated with an internal standard in the following ways. Multi-peaks, such as kerosene, can be determined from the peak height of the highest response.The calibration graph should be re-calibrated if a new batch of kerosene is used. Normal separated peaks such as TBP, DBBP and TOPO, can be easily calculated from the peak height using a recti- linear calibration graph. Non-stoicheiometric peaks such as HDEHP, can be measured from the peak area, either from the concave calibration graph with a curve-fitting program or from the graph of square root of response versus concentration. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. References Nelson, A. K., and Toy, A. D. F., Inorg. Chem., 1963, 2, 775. Moule, H. A., and Greenfield, S., J . Chromatogr., 1963, 11, 77. Zangen, M., Marcus, Y., and Bergmann, E. D., Separ. Sci., 1968, 3, 1. Hardy, C. J., J . Chromatogr., 1964, 13, 372. Campbell, M. H., Anal. Chem., 1966, 38, 237. Horton, A. D., J . Chromatogr. Sci., 1972, 10, 125. Kuo, C. H., Shih, J. S., and Yeh, Y . C., Analyst, 1982, 107, 1190. Grob, R. L., and McCrea, G. L., Anal. Lett., 1967, 1, 53; Anal. Abstr., 1969, 16, 737. Kuo, C. H., Shih, J. S., Yeh, Y. C., and Wu, S. C., J . Chin. Chem. Soc. (Taipei, ROC), 1981, 28, 89. Schimitt, J. M., and Blake, C. A., Jr., USAEC Report ORNL-3548, 1964. McNair, H. M., and Bonelli, E. J., “Basic Gas Chromatography,” Fifth Edition, Varian, Palo Alto, Peppard, D. F., Ferraro, J. R., and Mason, G. W., J . Inorg. Nucl. Chem., 1958, 7, 231. CA, 1969. Received April l l t h , 1983 Accepted June 28th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801380

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1386 Analyst, November, 1983, Vol. 108, $9. 1386-1391 Increase in the Sensitivity of the Fluorescent Reaction of the Complexing of Aluminium with Morin Using Surfactant Agents Julio Medina Escriche, Miguel De La Guardia Cirugeda" and Felix Hernandez Hernandez Analytical Chemistry, University College of Castellon, Valencia University, Castellon de la Plana, Spain The effects of surfactants on fluorescence analysis were studied. The addition of non-ionic surfactants (ethylene oxide - propylene oxide condensates) to a metal complex solution causes a remarkable enhancement of fluorescence, by which means the sensitivity of the fluorimetric determination of aluminium is increased ten-fold over conventional methods. The optimum conditions in which the increase in fluorescence intensity is produced were studied and are as follows: 3% surfactant, pH 3.8 in acetic acid - acetate buffer at 25 "C; and the intensity of fluorescence is measured at 495 nm and excited at 430 nm.Using a morin concentration of 0.005~0 in the solution under analysis, the calibration graph is linear up to 35 p.p.b. (35 parts in lo9) of aluminium. The relative standard deviation for the analysis of ten replicates of a solution containing 2 p.p.b. of aluminium is 3% ; when it contains 10 p.p.b. the relative standard deviation is 2%. The detection limit of the method is 0.2 p.p.b., using an excitation slit of 10 nm and an emission slit of 5 nm. From the study of interfering ions it was deduced that the presence of surfactants gives a higher selectivity than a conventional method.Keywords : Aluminium determination ; fEuoYescence analysis ; surfactant agents ; morin ; increased sensitivity The increase in sensitivity of reactions in which coloured species are formed by the addition of surfactants is an area of research that has been recently developed1v2 and there are many instances in which the sensitivity and selectivity of these reactions have been improved by the addition of surfactants, improvements that have been explained by the formation of mixed species and/or formation of micelles. This explanation could be extended to reactions forming fluorescent complexes ; however, in the literature only the following have been described : aluminium - L~mogallion,~ gallium - L~mogallion,~~~ aluminium, gallium, indium - Lumogallion6 and zinc - quinolin-8-01-5- sulphonic acid,' all with increased fluorescence intensity due to the addition of non-ionic and cationic surfactants.Aluminium is, in this area, one of the most studied elements. Ishibashi and Kina3 found that the addition of a non-ionic surfactant (of the nonylphenoxy- polyethyleneoxyethanol type) to the aluminium - Lumogallion complex caused a six-fold enhancement in fluorescence above the conventional method proposed by Nishikawa and co- workers.8~9 Pilipenko et al.6 obtained a ten-fold increase in sensitivity over the same system, by the addition of a cationic surfactant (of the polyoxyethylenated amine type). The object of this work was the study of the action of surfactants on the fluorescence of the aluminium - morin (3,5,7,2',4'-pentahydroxyflavone) complex in order to improve its analyti- cal characteristics.This system has been chosen because morin is one of the most used reagents for qualitative and quantitative analyses of aluminium and it can be more easily acquired than other reagents, such as Lumogallion, that have been proposed in the recent literature. Experimental Apparatus and Reagents Fluorescence intensity measurements were made on a Perkin-Elmer 3000 spectrofluorimeter ; the corrected excitation and emission spectra were recorded on a Jobin-Yvon JY-CS3. Spain. * Department of Analytical Chemistry, Faculty of Sciences, Valencia University, Burjasot, Valencia,ESCRICHE, CIRUGEDA AND HERNANDEZ 1387 Temperature checks were carried out using a Selecta Termotronic S-389 thermostat, which measures temperature to &0.5 "C.The pH was measured to pH *O.Ol with a Crison Digit 74 pH meter. The 10 p.p.m. stock solution of aluminium was prepared by dissolving 0.1758g of AlK(S04),.12H,0 (Merck analytical-reagent grade) in water, adding 1 ml of 1 + 1 sulphuric acid and diluting to 11. The morin solution was prepared daily by dissolving 0.1 g (Merck analytical-reagent grade) in 100 ml of ethanol solution containing 9% methanol and 5% water. The surfactant agents used were Genapol PF-20 and PF-10 (Hoechst) and Tergitol XD (Union Carbide) with a propylene oxide - ethylene oxide ratio of 1.6,4.0 and 1.0, respectively. Distilled, de-ionised water was used. General Procedure An aliquot of the aluminium solution was transferred into a 100-ml beaker and 5-ml of morin solution were added; the pH was adjusted to different values using hydrochloric acid, sodium hydroxide solution and various buffers.An aqueous solution of various surfactants at different concentrations was then added and the solution was diluted to 100 ml; the fluorescence intensity was measured at different temperatures. Results and Discussion At first, the experimental conditions given by Willlo for the fluorimetric determination of aluminium with morin were reproduced and the effects of many different surfactants on fluorescence intensity (Ip) were observed. It was found that cationic surfactants such as cetyltrimethylammonium bromide (CTAB) (a quaternary ammonium salt) and non-ionic surf act ants (polyoxyethylenat ed non ylphenols, polyox yethylenat ed fatty alcohols, fatty carboxylic acid esters and alkanoamides) did not increase the I , of the complex, but decreased it greatly.Only in some instances was an initial light enhancement observed for high con- centrations of surfactant but this was followed by a sudden decline of the fluorescence and an increase of the respective blanks. Finally, it was found that the addition of Genapol PF-20 (non-ionic surfactant, ethylene oxide - propylene oxide condensate) caused a remarkable ten-fold enhancement of fluorescence, analogous to those obtained by Ishibashi and Kina3 and Pilipenko et aZ.6 for the aluminium - Lumogallion system. Figs. 1 and 2 show excitation and emission spectra of the aluminium - morin complex in the presence and absence of 3% of Genapol.The addition of surfactant causes a hyperchromic but not an isochromic shift, which means that the interaction between surfactant and ground and 0.8 350 400 450 500 550 600 Excitation wavelength/nrn Fig. 1. Excitation spectra of lA, aluminium - morin - Genapol; 2A, aluminium - morin; 1B and 2B are corrected spectra. Conditions as follows : aluminium, 5 p.p.b. ; morin, 0.005% ; Genapol PF-20, 3%.1388 ESCRICHE ef al. : INCREASE IN SENSITIVITY OF FLUORESCENT Analyst, VoE. 108 r 0.8 4d .- v) Q) 4- .- p) 0.6 0 8 0.4 0 LL - 0.2 0 28 I I I 475 500 525 550 575 600 Emission wavelengthhm Fig. 2. Emission spectra of IA, aluminium - morin - Genapol; 2A, aluminium - morin; 1B and 2B are cor- rected spectra. Conditions: aluminium, 5p.p.b. ; morin, 0.005~0 ; Genapol PF-20, 3% ; Aexc., 430 nm.excited states of the complex must have been very small because it could not be detected spectrophotomet rically . l1 In both instances, the maximum fluorescence was obtained at 495 nm, corresponding to a maximum excitation of 430 nm. Effect of pH The effect of pH on the aluminium - morin - Genapol system was studied over a pH range of 1-10, using hydrochloric acid and sodium hydroxide solutions for pH adjustment, and com- paring the I , values with the corresponding blank, The maximum difference between the fluorescence of the system and the blank was obtained at a pH between 3.5 and 4.0. At higher pH, both are analogous (Fig. 3). The variation graph of the I , of the aluminium - morin complex is also shown in Fig. 3; the optimum pH corresponds to a value of 3.0, which agrees with that in the literature.1° Using an acetic acid - acetate buffer solution over the 3.5-4.0 pH range, the variation of the fluorescence was studied and an optimum pH value of 3.8, with a maximum variation of fluorescence of 2%, was found. 70 60 > *.' .- 50 8 40 2 30 E +- .- C is' 20 10 1 2 3 4 5 6 7 8 9 10 PH Fig.3. Effect of pII on the aluminium - morin - Genapol system. 1, Aluminium - morin - Genapol; 2, morin - Genapol; and 3, aluminium - morin. Conditions : aluinin- ium, 5 p.p.b.; morin, 0.005y0; Genapol, 0.5%.November, 1983 REACTION OF A1 WITH MORIN USING SURFACTANTS 1389 Effect of Surfactant Concentration and Study of the Development of Fluorescence Over a Period of Time Eight series of solutions with a fixed concentration of morin (0.005~0) and aluminium (5 p.p.b.) (5 parts in lo9) and variable concentrations of surfactant were prepared. The measurements were made at pH 3.8 and 25 "C and it was observed that when the surfactant concentration increased the I , also increased until it reached 3%; from this value onwards a decrease in intensity was observed.The experimental results show that the maximum I , was obtained after 1.5 h for concentrations similar to or higher than 0.5% and remained stable for at least 5 h. When the surfactant concentration was smaller than 0.5%, the I , became unstable after 1.5 h. Thus, the optimum surfactant concentration was 3% ; for this value there was a maximum difference between the intensity of fluorescence of the complex and that of the blank (Fig.4). The influence of the concentration of Genapol PF-20 on the I , was studied. 0 1 2 3 4 Surfactant concentration, YO Fig. 4. Influence of surfactant concentration for a A, 5 p.p.b. aluminium - morin - measurement period of 2 h. surfactant; and B, morin - surfactant. Effect of Temperature The effect of tempera- ture was studied between 15 and 40 "C and it was found that the optimum temperature for fluorescence development was 25 "C (Fig. 5 ) . The I , of the system was very sensitive to temperature variations. 15 20 25 30 35 40 Temperatu re/*C Fig. 5. Effect of temperature. A, 5 p.p.b. aluminium - morin - surfactant; and B, morin - surfactant.1390 Analyst, VoZ. 108 Order of Reagent Addition The effect of the order of reagent addition was also studied and it was found that the fluores- cence development and maximum IF did not depend on this.The order of addition chosen was as follows. An aliquot of the aluminium solution was transferred into a 100-ml beaker and 5ml of morin solution were added. The pH was adjusted to 3.8 with acetic acid- acetate buffer solution and then 20ml of the 15% Genapol PIT-20 solution were added, diluting to 100 ml. The fluorescence intensity was measured after 2 h at 25 "C using an excitation wavelength of 430 nm and an emission wavelength of 495 nm. Analytical Characteristics Range of applicability The range of concentrations in which the recommended procedure can be applied was studied and it was found that the calibration graph was linear up to 35 p.p.b.of aluminium. The following equations corresponding to the calibration graphs between (a) 0-10, (b) 0-50 and (c) 0-100 p.p.b. of aluminium with concentration increases of 1,5 and 10 p.p.b., respectively, were obtained : ESCRICHE et aZ. : INCREASE IN SENSITIVITY OF FLUORESCENT (a) I F = 9 . 2 1 ~ + 12.3 Y = 0.999 Y = 0.998 Y = 0.998 (b) IF = 1.87~ + 5.05 (c) I, = 0 . 9 4 ~ + 2.15 where c is the gradient and Y is the correlation coefficient. Precision The standard deviation, s, for the analysis of ten replicates of a sample containing 2 p.p.b. of aluminium was equivalent to 0.006 p.p.b. (relative standard deviation, Sr = 3%). With an aluminium content of 10 p.p,b. the relative standard deviation was 0.2%. Detection limit This was estimated for the k = 3 ( k is the numerical factor chosen according to the confi- dence level required) level from the sensitivity of the calibration graph in its linear portion and was 0.2 p.p.b.for aluminium. This value is of the same order as those obtained by Ishibashi and Kina (0.5 ~ . p . b ) ~ and Pilipenko et al. (0.15 p.p,b.)6 for the aluminium - Lumo- gallion complex treated with surfactants. It is appreciably lower than those obtained by Katyal and Prakash (1 and 5 p.p.b.)12 and Golovina et al. (5 p.p.b.)lS for the aluminium - morin system and the Nisikawa et al. value (4 ~ . p . b . ) ~ for the aluminium - Lumogallion system in the absence of surfactants. Other data in the literature for these same systems in the absence of surfactants (0.25 p.p.b.)1° and (0.05 p.p.b.)14 are abnormally low and they have been questioned by Pilipenko et aLs Interferences Study The effect of 17 ions on the fluorescence of the aluminium - morin - Genapol system was studied for 2 p.p.b.of aluminium. The tolerance in the I , values was equal to the standard deviation for the method. In most instances, the presence of Genapol PF-20 gives a higher selectivity except for the ions SiO,2-, Pb2+ and Zn2+. The interferences produced by Cr3+, Mg2+, NH4+ and PO:- were eliminated (the interference of PO," is one of the most important for the aluminium - morin system in absence of surfactant) (Table I). It was proved that one of these interferences, Pb2+, was the result of the stabilisation of this system by Genapol PF-20, which is at present being studied. Increase in Fluorescence of the Aluminium - Morin Complex by the Use of Other Ethylene Oxide - Propylene Oxide Condensates In order to discover whether the increase in fluorescence for the aluminium - morin system by the addition of Genapol PF-20 is accidental or whether the mechanism depends on the nature of the surfactant compound, the fluorescence intensity was measured under the optimum conditions previously chosen, and in the presence of variable concentrations of Genapol PF-10 and Tergitol XD, both being ethylene oxide - propylene oxide condensates.Both surfactants gave a sensitivity increase of the same order as Genapol PF-20, but theNovember, 1983 REACTION OF A1 WITH MORIN USING SURFACTANTS 1391 TABLE I EFFECT OF DIVERSE IONS Limiting concentration, p .p.b.Limiting concentration, p.p.b. Aluminium - Ion morin* SO,2- . . . . >loo0 ~ 0 ~ 3 - .. 3 c1- * . . . NO,- .. .. . . >loo0 F- . . .. 5 Bea+ . . . . Cae+ . . . . >loo0 co2+ . . . . >loo0 - __ - 1 Aluminium - morin - Genapolt >10000 > 10000 > 10 000 > 10000 100 10 20 5 000 > 10000 Ion Cr3+ . . .. cuz+ . . .. Fe3+ . . .. Mga+ . . .. NH,+ . . .. Ni2+ . . .. Pb2+ . . .. Zn2+ . . .. r Aluminium - morin* 30 20 100 200 500 > 1000 1000 > 1 000 1 Aluminium - morin - Genapolt >10000 100 100 > 10 000 > 10000 >10000 60 20 * Data published by Will10 for 2 p.p.b. of aluminium. t Experimental data obtained under conditions analogous to those of Will.l0 maximum enhancement was obtained for surfactant concentrations of 0.5-1 yo. At higher concentrations, the fluorescence suddenly decreased, which did not occur with Genapol PF-20.The maximum fluorescence intensity in the presence of Genapol PF-10 was obtained for a time between 30 min and 2 h and after 4 h in the presence of Tergitol XD. Thus, ethylene oxide - propylene oxide condensates could be used to increase the fluores- cence intensity of the aluminium - morin complex when their optimum concentration has been studied and their correct measurement time has been determined. Conclusions A ten-fold sensitivity increase in the fluorimetric determination of aluminium using morin was obtained by the addition of surfactant agents (ethylene oxide - propylene oxide conden- sates). The optimum conditions of reaction correspond to a pH of 3.8 in the presence of 3% of Genapol PF-20 at 25 “C; the fluorescence intensity reached a maximum value after 1.5 h and remained stable for at least 5 h.No shift was observed in the excitation and emission wavelengths of the aluminium- morin - Genapol system, which means that the interaction between surfactant and the ground and excited states of the complex seems to have been weak. The detection limit was reduced from 5 or 1 to 0.2 p.p.b. and some of the most notable inter- ferences (pog3-, Mg2+, Cr3+, NH,+) were also eliminated. Other ethylene oxide - propylene oxide condensates provoked a sensitivity enhancement of the same order, only the optimum surfactant concentration and the fluorescence development time being modified. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. References Hinze, W. L., in Mittal, K. L., Editor, “Solution Chemistry of Surfactants,” Plenum Press, New Ueno, K., “MTP International Review of Science. Physical Chemistry, 1, Volume 13, Analytical Ishibashi, N., and Kina, K., Anal. Lett., 1972, 5, 637. Kina, K., and Ishibashi, N., Microchem. J . , 1974, 19, 26. Kina, K., Hirokata, K., and Ishibashi, N., Bunseki Kagaku, 1977, 26, 246. Pilipenko, A. T., Volkova, A. T., Psienko, G. N., and Denisenko, V. P., Ukr. Khirn. Zh., 1980, 46, Kina, K., Tamura, K., and Ishibashi, N., Bunseki Kagaku, 1974, 23, 1406. Nishikawa, Y., Hiraki, K., Morishige, K., and Shigematsu, T., Bunseki Kagaku, 1967, 16, 692. Nishikawa, Y., Hiraki, K., Morishige, K., and Nagano, N., Bunseki Kagaku, 1968, 17, 1092. Will, F., Anal. Chem., 1961, 33, 1360. Winefordner, J. D., “Spectrochemical Methods of Analysis,” John Wiley, New York, 1971, pp. 423- Katyal, M., and Prakash, S., Talanta, 1977, 24, 367. Golovina, A. P., Alimarin, I. P., Kuznetsov, D. I., and Filyugina, A. D., Zh. Anal. Khim., 1966, 21, Hydes, D. J., and Liss, P. S., Analyst, 1976, 101, 922. York, 1979, Volume 1, pp. 79-127. Chemistry, Part 2, Organic Reagents,” Butterworths, London, 1973, pp. 43-69. 200. 425. 163. Received February 7th, 1983 Accepted May 5th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801386

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1392 Analyst, November, 1983, Vol. 108, $9. 1392-1395 Extraction and Spectrophotometric Determination of Uranium in Ores Jose Aznarez, Francisco Palacios and Juan Carlos Vidal Department of Analytical Chemistry, Faculty of Sciences, University of Zaragoza, Zaragoza, Spain An extraction - spectrophotometric method is proposed for the determina- tion of trace amounts of uranium in ores, based on its extraction with tri- octylphosphine oxide in toluene and development of colour with glyoxal bis(2-hydroxyanil) (GBH) or 1-(2-pyridylazo)naphth-2-01 (PAN) in NN- dimethylformamide in the organic extraction phase without back-extraction. The maximum absorbance with GBH as reagent occurs a t 600 nm with a molar absorptivity of 1.48 (f 0.01) x lo4 1 mol-l cm-l and with PAN as reagent a t 555 nm with a molar absorptivity of 2.61 (f 0.02) x lo4 1 mol-l cm-1. Beer's law is obeyed over the ranges 0.6-10.5 and 0.3-6.0 pg ml-l of uranium(V1) (corresponding to 20-350 and 10-200 pg of uraniuni in the sample) a t 600 and 555 nm, with GBH and PAN, respectively.The proposed method has been applied successfully to the analysis of standard and synthetic uranium ores with uranium contents of up to 0.15%. Keywords : Uranium determination ; ove analysis ; spectvopkotometvy ; glyoxal bis(2-hydroxyanil), 4-( 2-pyvidylazo)resorcinol and 1-( 2-pyridy1azo)naphth- 2-01 reagents Solvent extraction is often used for pre-concentration and separation in determinations of elements, owing to the insufficient sensitivity and selectivity of most spectrophotometric reagents.lS2 The determination is subsequently carried out after removal of the organic solvent by evaporation and calcination or by back-extraction into the aqueous phase by means of suitable masking agents and pH buffer solutions.3 The direct measurement of the absorbance in the organic extract is sometimes possible if the reagent used achieves the sensitivity and selectivity required, as happens with extrac- tion - spectrophotometric reagents,4 ternary complex formation5 or ion-pair association with bulky organic dyestuffs.6 However, a high absorbance of the reagent blank often leads to difficulties in these spect rophot ome t ric determinations.This paper describes a method based on the extraction of a colourless ion-pair complex or covalent, partially ionic compound into a non-polar solvent.Once the phases have been separated, the organic extract is mixed with a suitable spectrophotometric reagent dissolved in a polar, highly solvating solvent, such as NN-dimethylformamide, acetonitrile or dioxane, which is miscible with the extraction solvent. A high dielectric constant of the solvent mixture favours both the rupture of the ion-pair associate or the covalent, partially ionic compound and the inner complex formation with the spectrophotometric reagent. The proposed method has been applied to the determination of uranium in geochemical samples. Uranium at the microgram level has been extracted with tributyl phosphate' (TBP) or trioctylphosphine oxide (TOP0)8-10 in toluene and its spectrophotometric determina- tion was carried out with glyoxal bis(2-hydroxyanil) (GBH) ,4-(2-pyridylazo)resorcinol (PAR) or 1-(2-pyridylazo)naphth-2-01 (PAN) in NN-dimethylformamide (DMF) solution.Experimental Apparatus used. used for pH determinations. and 100-ml separating funnels. A Pye Unicam SP8-100 automatic recording spectrophotometer with 1-cm silica cells was An Orion Ion-analyzer microprocessor/901 with glass and saturated calomel electrodes was Other apparatus consisted of a Haake thermostatic bath, a Kotermann mechanical shakerAZNAREZ, PALACIOS AND VIDAL 1393 Reagents All chemicals were of analytical-reagent grade. Uranium(VI) stock solution, 1000 yg ml-l. nitrate in doubly distilled water and diluting to 1000 ml in a calibrated flask. Uranium( VI) standard solations. solution with doubly distilled water. Stock solutions of other ions, 10-2 M.salts in 0.1 M nitric acid. Tributyl phosphate (TBP) solution in toluene, 10% V/V. Trioctylphosphine oxide (TOPO) solution in toluene, 1 yo m/V. Propylamine solution in DMF, 1% VlV. Pyridine solution in DMF, 10% V/V. tert-Butylamine solution in DMF, 1 yo V/V. Glyoxal bis(2-hydroxyanil) (GBH) solution in DMF, 2% m/V. 4-(2-Pyridylazo)resor~inol (PAR) solution in DMF, 0.02% m/V. 1-(2-PyridyZazo)naphth-2-01 (PAN) solution in DMF, 0.1 yo m/V. Prepared by dissolving 2.1100 g of uranyl Prepared freshly by appropriate dilution of the stock Prepared by dissolving appropriate amounts of suitable Procedure Dissolution of uranium ore Weigh in a platinum crucible an appropriate amount of 200-mesh uranium ore (0.1-1.0 g, depending on the uranium content of the sample).Add 5 ml of concentrated nitric acid and 5 ml of 48% hydrofluoric acid and evaporate to dryness on a water-bath. Add a further 5 ml of concentrated nitric acid and 5 ml of hydrofluoric acid and evaporate to dryness on a hot-plate. Cool and dissolve the residue in 10 ml of 5 M nitric acid, then dilute to 25 ml with distilled water in a calibrated flask. If necessary, filter off any residue through Albet 242 filter-paper. Extraction procedure Pipette an aliquot of the sample solution (containing 10-250 pg of uranium) into a separat- ing funnel. Add 1 ml of 1.5% m/V sodium fluoride solution. Extract with 10 ml of TOPO solution in toluene by mechanical shaking for 5 min and allow the phases to separate. Wash the organic phase with 10 ml of 2 M nitric acid solution.Discard the aqueous phase. Spectrophotometric procedure Pipette 3 ml of the extracted solution, 3 ml of the spectrophotometric reagent solution and 1 ml of propylamine solution into a flask. 3 "C for 5 min in a thermostatic bath, then cool and dilute with DMF in a 10-ml calibrated flask. Measure the absorbance at 600 nm (with GBH as spectrophotometric reagent) or at 555 nm (with PAN as reagent) within 30min after dilution against a reagent blank as reference, prepared by the same procedure but not containing uranium. Prepare a calibration graph by taking independent portions of uranium(V1) standard solutions, extracting them from 2 M nitric acid solution and applying the above spectrophoto- metric procedure.Heat at 80 Results and Discussion Spectral Characteristics Preliminary tests were made to study the formation of the uranium(V1) complexes with GBH, PAN and PAR in DMF as solvent, without the extraction process, taking advantage of the solubility of uranyl nitrate in DMF. The spectra obtained were not modified by addition of TBP or TOPO solution, showing that there was no masking effect over uranium(V1) in the spectrophotometric reaction in the solvent mixture. However, when the test was carried out with the extracted solution, there was no formation of the uranium(V1) - reagent complex and therefore no development of colour. The addition of an organic base, such as propylamine, tert-butylamine or pyridine, was necessary. The cause seems to be the simultaneous extraction of nitric acid by TBP or TOPO solution.Kojima et a1.l0 have shown that the distribution coefficient of the uranium(V1) -TOP0 extraction passes through a maximum at about 0.5 M nitric acid. The decrease in the distribu-1394 Analyst, VoZ. 108 tion coefficient at high acidity was caused by the fact that nitric acid was extracted with TOPO rather than the uranium(V1) - TOPO compound as the concentration of nitric acid increased. The uranium(V1) - TOPO compound seems to be U0,(N0,)2(TOPO)2. The uranium(V1) - GBH complex exhibits a maximum at 600 nm when measured against a similar reagent blank, with a molar absorptivity of 1.48 x lo4 1 mol-1 cm-1. The absorbance of the reagent blank was 0.005 -+ 0.002 for ten replicate determinations at 600 nm against DMF as reference.The uranium(V1) - PAN complex exhibits a maximum at 555 nm against a reagent blank, with a molar absorptivity of 2.61 x lo4 1 mol-l cm-l. The absorbance of the reagent blank was 0.05 Ifr 0.01 at 555 nm for ten replicate determinations against DMF as reference. The maximum absorption of the uranium(V1) - PAR complex appeared at 545 nm against the reagent blank, with a molar absorptivity of 3.9 x lo4 1 mol-l cm-l, but the absorbance of the reagent blank against solvent at the same wavelength was high, 0.08 f 0.02 for ten deter- minations, Propylamine, tert-butylamine and pyridine in DMF solution at several concentrations were used as organic bases for colour development. The temperature and time of warming and the stability of the measured absorbance were also studied.The best results were obtained by heating at 80 & 3 "C for 5 min with propylamine or tert- butylamine solutions as bases, The absorbance maximum of the solution remained constant for 30 min when the concentration of the base was less than 0.06 M in the final measured solution with GBH and PAN; however, with PAR as reagent the absorbance stability was inadequate. Extraction Characteristics The extraction of 150 g of uranium(V1) by TBP solution in toluene was 98.0 & 1.5% com- plete for the range 0.1-0.4 M nitric acid and 3.5 M ammonium nitrate. The aqueous to organic volume ratio was 2 : 1. The extraction of 250 pg of uranium(V1) by TOPO solution in toluene was 98.5 + 1.1% complete (ten determinations) in the range 1 4 M nitric acid, with a distribu- tion coefficient of logD = 3.9 in 2 M nitric acid.With TBP solutions in toluene at concentrations higher than 20% V / V , the development of the colour was not complete. AZNAREZ et al. : EXTRACTION AND SPECTROPHOTOMETRIC Calibration Graph, Sensitivity and Precision The sensitivity of the determination expressed in terms of molar absorptivity was 1.48 (f 0.01) x lo4 1 mol-l cm-l at 600 nm for GBH as reagent and 2.61 (& 0.02) x lo4 1 mol-l cm-l with PAN as reagent. Beer's law was obeyed over the ranges 0.6-10.5 and 0.3-6.0 pg ml-1 of uranium(V1) (corresponding to 20-350 and 10-2OOpg of uranium in the sample) at 600 and 555 nm with GBH and PAN, respectively. The precision for ten replicate determina- TABLE I EFFECT OF FOREIGN IONS ON THE DETERMINATION OF 50 pg OF URANIUM(VI) WITH TOPO EXTRACTION Foreign ion Ca, Sr, Ba, Mg .. .. .. .. c1-, so,z-, Pop . . .. .. Zn, Mn(II), SiO,, A1 . . .. .. La, Fe(III), Cr(III), B(II1) . . .. l7- r - .. .. * . Cu(II), Ni(II), Cb(I1) . . .. .. -PI_ i n .. .. Ti(IV), Cd(III),'Ce(I< ' . . .. Zr . . .. .. .. .. Tolerance limit*/mg per 50 pg U(V1) with GBH or PAN as reagent Masking agent agent agent f A > Without masking With masking 125 95 75 50 25 10 F- (15 g 1-l NaF) 0.1 6 F- (15 g 1-1 NaF) 0.1 2.5 * The tolerance limits given correspond to the concentration level at which the interference causes an error in the uranium determination of more than f 2%.November, 1983 DETERMINATION OF URANIUM IN ORES 1396; tions of 100 pg of uranium(V1) standard solution was 0.70 and 0.75% (as standard deviation) with GBH and PAN, respectively.Interference Studies The tolerance limits for various foreign ions in the determination of 50 pg of uranium(V1) are shown in Table I. The following cations were not extracted by TBP in toluene from 0.1 M nitric acid or by TOPO in toluene from 2 M nitric acid: Al(III), Fe(III), Cr(III), La(III), Ca(II), Sr(II), Ba(II), Mg(II), Zn(I1) and Mn(II), even in presence of 0.2 M chloride, 0.1 M sulphate and 0.1 M phos- phate. Therefore, their tolerance limits were very high, as shown in Table I. Cu(II), Co(II), Ti(1V) Ce(IV), Ce(III), Th(1V) and Zr(1V) were extracted partially and Ce(IV), Th(1V) and Zr(1V) present serious interferences in the determination of uranium(V1) with GBH or PAN. Fluoride ions interfere with the uranium extraction process with TBP solution.This inter- ference can be decreased by addition of boric acid solution. The tolerance limit of fluoride ions with TOPO extraction was far higher, probably owing to the acidity (2 M nitric acid) used in the extraction process. This advantage has been used for elimination of interferences due to Ti(IV), Ce(IV), Th(1V) and Zr(1V) by addition of sodium fluoride solution in the extraction process. It is worth noting that the interferences were the same for both GBH and PAN reagents, in spite of their different molecular constitutions. Determination of Uranium in Natural Samples synthetic samples. logical Sciences (IGS 37) to contain 0.148% of uranium, was used as a reference. samples were prepared by thorough mixing of IGS 37 and calcium carbonate powder.values, as illustrated in Table 11. The proposed method has been applied to the determination of uranium in natural and A Rio Algom, Canada, uranium ore, certified by the Institute of Geo- Synthetic The results obtained by following the proposed procedure agreed well with the expected TABLE I1 RESULTS OF THE DETERMINATION OF URANIUM IN DIFFERENT SAMPLES U found,* % 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. r I Sample U expected, yo With GBH With PAN IGS 37t . . . . 0.148: 0.145 0.146 B§ .. .. . . 0.105 0.103 0.105 C$ .. .. . . 0.093 0.090 0.095 * Each value is the average of five separate determinations. t Uranium ore from Rio Algom, Canada. $ Certified value, standard deviation 0.006% (44 determinations). 5 Synthetic samples: IGS 37 + calcium carbonate. A§ . . .. . . 0.125 0.123 0.122 References Marczenko, Z., “Spectrophotometric Determination of Elements,” Ellis Horwood, Chichester, 1976. Rajamoorthi, K., Mohan, S. V., and Balasubramanian, G. R., Analyst, 1981, 106, 641. Budesinsky, B. W., Macrochem. J., 1977, 22, 50. Pkrez-Bustamante, J. A., and Delgado, F. P., Analyst, 1971, 96, 407. Idriss, K. A., Seleim, M. M., Abu-Bakr, M. S., and Saleh, M. S., Analyst, 1982, 107, 12. Koch, S., and Ackermann, G., 2. Chem., 1980, 20, 449. Kolank, Z., and Petrish, G., B e y . Bunsenges. Phys. Ckem., 1979, 83, 1110. Shigetomi, Y., Kohma, T., and Kamba, H., Talanta, 1981, 27, 1079. Tsurumi, C., Furuya, K., and Kamada, H., Analyst, 1981, 106, 944. Kojima, T., Shigetomi, Y . , Kamba, H., Iwashiro, H., Sakamoto, T., and Doi, A., Analyst, 1982, Received November 29th, 1982 Accepted June 13th, 1983 107, 519.

ISSN:0003-2654    

DOI:10.1039/AN9830801392

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1396 Analyst, November, 1983, Vol. 108, pp. 1396-1401 Ste pw ise Co m pl exomet r ic Deter m i nation of Calcium and Magnesium in the Presence of a High Manganese and Iron Content Using Potassium Hexacyanoferrate(l1) as a Masking Agent Samarendra Dasgupta and Birendra C. Sinha Analytical Chemistry Division, Central Glass and Ceramic Research Institute, Calcutta-700032, India and N. S. Rawat Department of Chemistry, Fuel and Mineral Engineering, Indian School of Mines, Dhanbad-826004, India A critical study has been made on the masking of manganese and iron by their precipitation as Fe,[Fe(CN),] and Mn,[Fe(CN),J with K4[Fe(CN),] in the presence of ascorbic acid and potassium chloride for the complexometric titration of calcium plus magnesium with EDTA a t pH 10. The optimum acid concentration and temperature for the selective and quantitative precipi- tation of Mn (I I) and Fe( I I) liexacyanoferrates (I I), which are granular and non- adsorbant metallochromic indicators, are found to be 1-2.5 N hydrochloric acid and 25-50 O C , respectively.In a solution with an acidity of lower than 1 N, the hesacyanoferrates(I1) of Mn(I1) and Fe(I1) coprecipitate calcium and magnesium hexacyanoferrates(I1). At 70 O C , the amount of coprecipitation increases. Up to 08.75 and 19.60 mg of manganese and iron, respectively, can be successfully inaslced in coiiiplesonietric titration. For the titration of calcium alone at pH 12, the interference of manganese and iron has been overcome by osidising Mn(I1) - TEA to Mn(II1) - TEA, which is stable against EDTA titration with air bubbling.Iron forms a quantitative Fe - TEA complex almost instantaneously at pH 12. A simple procedure has been devised for the titration of Ca + Mg with EDTA after masking man- ganese and iron with K,[Fe(CS),], a non-toxic reagent. For calcium, TEA alone is used for masking both manganese and iron. Keywords : Calcium and magnesium determination ; complexowetry ; man- ganese and iron interference ; potassium hexacyano ferrate (11) ; selective precipitation In a previous paper the results of a critical study on the quantitative masking of manganese with potassium cyanide for the stepwise complexometric titration of calcium, magnesium and manganese with EDTA, have been rep0rted.l However, the method has the disadvantages of using potassium cyanide, a toxic reagent, and only tolerating iron up to 5 mg per 200 ml in the titrating solution.With increasing iron concentration, the end-point of the titration is seriously affected owing to the intense yellow colour of the hexacyanoferrate( 11) complex. The addition of a reducing agent such as hydroxylamine or ascorbic acid reduces not only the Fe(II1) to the Fe(I1) cyanide complex but also the Mn(II1) to the Mn(I1) cyanide complex, which is co-titrated with calcium and magnesium. Triethanolamine (TEA)2p3 can mask large amounts of Fe(II1) but only up to 3 mg of Mn. With increasing amounts of manganese, the Mn(II1) - TEA complex, formed by aerial oxidation at pH 10, interferes by imparting a green colour to the solution and then slowly hydrolyses to give a manganese hydroxide precipitate that seriously affects the EDTA titration of calcium and magnesium. The use of o-phenan- throline4 as a masking agent for many cations, including manganese and iron, is uneconomical and unsatisfactory.Thus no satisfactory method for the masking of iron and manganese when they are present together in significant amounts in the complexometric titration of calcium and magnesium has been described in the literature. In this study, liexacyanoferrates( 11), well known precipitants for many metal^,^^^ which have never been utilised for masking by precipitation in EDTA titrimetry, have been used for precipitating iron and manganese as Fe(I1) and Mn(I1) hexacyanoferrates(I1) so that aDASGUPTA, SINHA AND RAWAT 1397 direct titration of calcium and magnesium is possible.The optimum conditions of acid con- centration and temperature for precipitation of Fe,[Fe(CN) 6] and Mn,[Fe(CN),] with K,- [Fe(CN),] have been found to be 1-2.5 N hydrochloric acid and 30 + 5 "C, respectively, where calcium and magnesium hexacyanoferrates(I1) ,' Ca(NH,), [Fe(CN),], -log(solubility product) = 7.4; Mg,[K,Fe(CN),], -log(solubility product) = 8.3, do not coprecipitate. The extent of toleration of manganese and iron has been found to be 68.75 mg of manganese (-25 ml of 0.05 M manganese) and 19.6 mg of iron (=7 ml of 0.05 M iron) for the direct titration of com- bined calcium and magnesium (Ca + Mg) with EDTA at pH 10. The titration of calcium alone at pH 12 is hardly affected because manganese is converted by aerial oxidation to a stable Mn(II1) - TEA complex and iron, probably to colourless Fe(I1) - TEA, which are inert to EDTA titration at such a high pH.Based on the above results, a simple, rapid and accurate method has been devised for the complexometric determination of calcium and magnesium in the presence of large amounts of manganese and iron, which are often present in slags. Experimental Reagents All reagents used were of AnalaR or general-reagent grade unless otherwise specified. Standard calcium chloride solution, 0.5 M. Dissolve 5.0 g of dry calcium carbonate in dilute hydrochloric acid, boil to expel the carbon dioxide and dilute to 1 1 in a calibrated flask after cooling. EDTA solution, 0.05 M. Standardise against standard calcium chloride solution ; use a dilute standard of ca.0.025 M for a low calcium and magnesium content. Manganese chloride solution, 0.05 M. Dissolve 9.895 g of MnC1,.4H20 in water, acidify with a few millilitres of dilute hydrochloric acid and dilute to 1 1. Magnesium chloride solution, 0.05 M. Dissolve 1.22 g of magnesium ribbon in dilute hydrochloric acid with heating and dilute to 1 1 in a calibrated flask after cooling. Iron(III) chloride solution, 0.05 M. Dissolve 1.40 g of iron wire in dilute hydrochloric acid and oxidise the iron with a few millilitres of nitric acid. Mixed indicator. Thoroughly mix 0.08 g of naphthol green, 0.05 g of o-cresolphthalein complexone and 20 g of ammonium chloride in an agate mortar. Calcein indicator. Mix thoroughly 0.2 g of calcein and 20 g of potassium chloride in an agate mortar.Ammonia solution, 4 and 2 N. Thymolphthalein. Titan yellow, 0.1% in absolute ethanol. Triethanolamine (TEA), 30% V/V in water. Hydrochloric acid, 6 N. Ammonia - ammonium chloride bufer solution, pH 10. Dissolve 67.5 g of ammonium chloride in 250 ml of water, add 570 ml of liquid ammonia and dilute to 1 1. The solution is finally checked for pH. Ascorbic acid, solid. Potassium hexacyanoferrate(II) K, [Fe(CN) .3H,O, solid. Potassium hydroxide solution, 2 and 5 N. Dissolve 0.1 g of the indicator in 100 ml of 30% TEA. Preparation of Sample Solutions Moisten a dried (105-1 10 "C) and weighed (0.5 g) sample with water in a platinum basin and treat with 10 ml of hydrofluoric acid and 1 ml of sulphuric acid (18 N). Heat the mixture on a sand-bath until fumes of sulphur trioxide are evolved. Repeat this treatment with a further 10 ml of hydrofluoric acid (after cooling) and evaporate the solution to dryness.Fuse the residue with 2-3 g of potassium hydrogen sulphate, cool and dissolve in 5% hydrochloric acid. Dilute the solution to 250 ml in a calibrated flask. Determination of Calcium Pipette a 25-ml aliquot or more of the test solution into a 500-ml conical flask and dilute to 150 ml. Add 2 ml of thymolphthalein. Add slowly 20 ml of 30% TEA solution followed by the dropwise addition of 0.1 N potassium hydroxide solution until the solution turns blue or green. Then add slowly 15 ml of 5 N potassium hydroxide solution, with swirling of the1398 Analyst, VoZ. 108 solution. Bubble air through it for 10 min and titrate with standard EDTA in the presence of 0.2 g of calcein indicator.The end-point is indicated by a colour change to red with the disappearance of the green fluorescence. The titre obtained is a measure of the calcium content. DASGUPTA et a,?. : STEPWISE COMPLEXOMETRY OF Ca Determination of Calcium and Magnesium Combined (Ca + Mg) Transfer quantitatively an aliquot of 25 ml or more of the test solution, containing not more than 68.75 mg of manganese and 19.6 mg of iron, into a 500-ml conical flask. Drop a small piece of universal indicator paper, pH 1-10, into the solution. Neutralise the solution by the dropwise addition of 4 N' ammonia solution. Acidify with 18 ml of 6 N' hydrochloric acid and dilute with water to approximately 100 ml.Add 4 g of potassium chloride, 1 g of ascorbic acid and dissolve. Swirl the solution after adding 2 g of K,[Fe(CN),] until the hexacyano- ferrate(I1) dissolves. Keep the solution for a few minutes in order for complete precipitation to occur. Neutralise the solution with 4 N' ammonia solution in the presence of a fresh piece of indicator paper. Add 10 ml of 30% TEA solution followed by 20 ml of buffer solution of pH 10 (ammonia - ammonium chloride) and dilute to about 200 ml with water. Add 0.3- 0.5 g of the mixed indicator and titrate with standard EDTA, the end-point being indicated by a sharp colour change from pink to green. The difference between the first (for calcium) and second (for Ca + Mg) titres corresponds to magnesium. Results and Discussion From the literatures it can be seen that Mn(I1) can be quantitatively precipitated in a solu- tion as Mn,[Fe(CN),], -log(solubility product) = 12.10, or KsMn, [Fe(CN),], -log(solubility product) = 63.55, by the addition of K,[Fe(CN),].However, it is not known whether calcium or magnesium, when present along with manganese, would contaminate the precipi- tate because calcium or magnesium also produce complex hexacyanoferrates( 11) such as Ca(NH,), [ Fe(CN),], -log(solubility product) = 7.4, and Mg, [ K,Fe( CN),] , - log(solubi1ity product) = 8.3. From preliminary experiments, it has been found that while titrating calcium or magnesium with EDTA at pH 10 in the presence of Mn(I1) hexacyanoferrate(II), which is precipitated by K,[Fe(CN),] at the same pH, the results for the determination of calcium or magnesium are low probably owing to coprecipitation. As the literature does not provide any information regarding optimum conditions for the selective and quantitative precipitation of Mn(I1) hexacyanoferrate in the presence of calcium and magnesium for the complexometric titration I 1 .o - f 8 2mol O L I I I I I I I I 2.5 2.0 1.5 1 N 0 2 4 6 8 10 PH Hydrochloric acid concentration Fig.1. Effect of hydrochloric acid concentration and tempera- ture on the selective precipitation of Mn(I1) and Fe(I1) hexa- cyanoferrate(I1) indicated by EDTA titration of a known amount of added Mg at pH 10. Lines show the effect (similar results) a t A, temperatures of 25, 35 and 50 "C; B, a t 70 "C; and C, a t 35 "C for the selective precipitation of Fe(I1) hexacyano- ferrate(I1).The broken line represents the theoretical value.November, 1983 AND Mg IN THE PRESENCE OF HIGH Mn AND Fe CONTENT 1399 of the two metals (Ca, Mg) , a critical study of the effect of acid concentration and temperature on the selective precipitation of Mn(I1) in the presence of magnesium has been carried out by titrating a known amount of magnesium (4.65 ml of 0.05 M Mg solution) with EDTA after precipitating out manganese (27.5 mg) as Mn(I1) hexacyanoferrate(I1) at different acid strengths and temperatures. - E 3 4.85 I- 2 2 4.0 LCa 'c 3.0 - 5 >" 2.0 0 5 10 15 20 25 30 35 40 Volume of 0.05 M Mn/Fe/ml Fig. 2. Effect of concentrations of Mn and Fe precipitated as Mn(I1) and Fe(I1) hexacyanoferrate(I1) at 35 f 5 "C and 1 N HC1 on the EDTA titration of a known amount of added Mg at pH 10.A and B show, respec- tively, limits of Mn and Fe concentrations admissible. The broken line represents the theoretical value. The results (Fig, 1, A) show that the titre values for magnesium equal the theoretical value when manganese is precipitated as Mn,[Fe(CN),] at 25, 35 and 50 "C in 1-2.5 N hydrochloric acid, indicating the absence of any coprecipitation of magnesium or selective and quantitative precipitation of Mn(I1) with K,[Fe(CN),]. However, at low acid concentrations of pH 1-10, low results for magnesium support the coprecipitation of magnesium as hexacyanoferrate(I1) along with Mn( 11) hexacyanoferrate( 11). When the temperature of precipitation is raised to 70 "C (Fig. 1, B) determined magnesium values are slightly below the theoretical value at acid strengths of 1-2.5 N, while the same values at pH 1-10 are much lower, indicating a higher order of co-precipitation.Another interesting observation made at this temperature (70 "C) is that the solution develops a green colour that gradually increases with decreasing acid concentration. 4.50 @ 0 5 10 15 Time/min Fig. 3. Effect of time on the quanti- tative oxidation of Mn(TEA)2+ to Mn(TEA)S+ with air bubbling indicated by EDTA titration of a known amount of added Ca at ca. pH 12. A, B, C repre- sent such effects on Mn in amounts of 27.5, 55.0 and 110 mg, respectively. The broken line represents the theoretical value.1400 Analyst, VoZ. 108 The same study, in the presence of combined calcium and magnesium (Ca + Mg), yielded the same spread of results.Thus the study revealed that the best temperature range and acid concentration for the selective and quantitative precipitation of Mn(I1) hexacyanoferrate(I1) complex and for the complexometric titration of calcium or magnesium or both combined at pH 10 are, respectively, 25-50 "C and 1-2.5 N hydrochloric acid. The precipitation of iron (14 mg) as Fe,[Fe(CN),] in the presence of magnesium (4.85 ml of 0.05 M Mg solution) has been similarly studied at 35 "C in different concentrations of hydrochloric acid. During precipitation, sufficient ascorbic acid and potassium chloride are added to reduce iron to the divalent state and to increase the stability of Fe(I1) hexacyanoferrate(I1) by forming a complex of the typeg K - M - [Fe(CN),], having a low free energy (AG) value.The results of the study (Fig. 1, C) indicate the same range of acid concentration, LE., 1-2.5 N hydrochloric acid, as that of manganese for selective and quantitative precipitation of Fe(I1) for complexo- metric titration of calcium and magnesium at pH 10. The precipitates of Mn(I1) and Fe(I1) hexacyanoferrates( II), being white and granular, provide an advantageous background for a sharp end-point and do not adsorb any metallochromic indicator. DASGUPTA et al. : STEPWISE COMPLEXOMETRY OF Ca TABLE I DETERMINATION OF CALCIUM AND MAGNESIUM IN SYNTHETIC SOLUTIONS CONTAINING DIFFERENT AMOUNTS OF IRON AND MAGNESIUM Fe takenlmg Mn takenlmg Ca takenlmg Ca found/mg Mg takenlmg Mg found/mg 14.0 27.5 1.16 1.20 1.46 1.40 14.0 27.5 9.30 9.25 11.75 11.82 14.0 27.5 18.60 18.75 17.58 17.65 19.6 68.75 1.16 1.14 1.46 1.40 19.6 68.75 18.60 18.50 17.58 17.48 Fig.2 (A and B) shows the limits of manganese (68.75 mg = 25 nil of 0.05 M Mn solution) and iron (19.6 mg = 7 ml of 0.05 M Fe solution), which do not affect the accuracy of EDTA titration of Ca + Mg. For titration of calcium alone at pH 12, manganese and iron have been quantitatively masked with TEA and by bubbling air through the solution. In conformity with Nitangle,lo it has been found that quantitative masking by manganese at pH 12 takes place by oxidising the Mn(I1) - TEA complex to Mn(II1) - TEA, which is stable against EDTA titration. TABLE I1 DETERMINATION OF CaO AND MgO IN SLAGS CONTAINING A HIGH MANGANESE AN'D IRON CONTENT Sample slag* (steel making) Jy-30/80 SiO, 37.78% Al,O, 2.82 % SiO, 48.99% Al,O, 2.04% SiO, 48.15% Al,O, 2.49% SiO, 49.03% Al,O, 1.44% SiO, 43.01 % Al,O, 1.89% Jy-33/80 Jy-22/80 J y-20/80 Jy-26/80 Found, yo Mean, oh - & r- CaO MgO CaO MgO CaO ::!: %] 3.25 2.88 3.24 3.25 6.95 6.90 0.45 6.97 0.41 6.99 7.02 0.38 9.00 0.20 9.10 0.3,) 9.12 0.25 9.16 9.25 0.25 ;:;:} Trace 7.33 Trace 7.35 7.35 3.48 3.61 !:::} 3.52 3.23 3.52 3.48 3.15 Certified valuest - MgO Fe,O, MnO 2.95 23.89 7.64 0.42 21.02 5.90 0.25 23.93 8.03 Trace 20.62 7.35 3.25 13.82 5.94 * Slag from the Steel Authority of India. t CaO and MgO values determined by EDTA after separation of iron by hexamine and manganese in the filtrate by H,S.November, 1983 AND Mg IN THE PRESENCE OF HIGH Mn AND Fe CONTENT 1401 The effect of time on the quantitative oxidation of Mn(I1) -TEA to Mn(II1) -TEA by bubbling air through the solution is shown in Fig.3. The experiment was carried out by titrating directly a known amount of calcium (4.65 ml of 0.05 M Ca solution) in the presence of manganese with EDTA at pH 12 after adding TEA and bubbling air through the solution for different intervals of time. The results indicate that the solution bubbled for 5 min gives correct values for calcium in the presence of manganese (A, 27.5 mg; B, 55.0 mg) while with higher amounts of manganese (1 10.0 mg) , the time required for quantitative oxidation is 10 min (C). Whereas the masking of manganese with TEA requires air bubbling, that of iron does not. Correct determinations of calcium are always obtained whether the solution is bubbled or not, probably owing to the formation of colourless Fe(I1) - TEA in a highly alkaline medium.ll Based on the above observations a simple, rapid and accurate complexometric method for the determination of calcium and magnesium in the presence of a high iron and manganese content by direct titration with EDTA has been devised.Table I shows results for the determina- tion of calcium and magnesium in synthetic solution containing a high iron and manganese content and Table I1 shows those for slags rich in iron. The results are in good agreement with the certified values. The authors are grateful to Dr. S. Kumar, Director of the Institute, for his permission to publish the paper. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. References Sinha, B. C., and Dasgupta, S., Talanta, 1978, 25, 693. Pribil, R., Chem. Listy, 1953, 47, 1333. Pribil, R., Korbl, J., Kysil, B., and Vobora, J., Chem. Listy, 1958, 52, 243. Kpoanica, M., and Pribil, R., Collect. Czech. Chem. Commun., 1960, 25, 2230. Cheng, K. L., Anal. Chem., 1955, 27, 1594. West, T. S., and Sykes, A. S., “Analytical Applications of Diaminoethanetetraacetic Acid,” Second Lurie, J ., “Handbook of Analytical Chemistry,” translated from Russian by N. Bobrov, Mir, Moscow, Bellomo, A., Marco, D. D., and Casale, A., TaZaPzta, 1972, 19, 1236. Bellomo, A., Talanta, 1970, 17, 1109. Nitangle, E. R., Jr., Anal. Chem., 1959, 31, 146. Jorgensen, C. K., “Inorganic Complexes,” Academic Press, London and New York, 1963, p. 119. Edition, BDH Chemicals Ltd., Poole, Dorset, p. 49. 1975. Received February 15th, 1983 Accepted May 4th, 1983

ISSN:0003-2654    

DOI:10.1039/AN9830801396

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1402 Analyst, November, 1983, Vol. 108, pp. 1402-1408 Spectrophotometric Determination of Vanadium by Oxidation of Pyrogallol Red Julio Medina Escriche, A. Sevillano Cabeza, Miguel de la Guardia Cirugeda" and F. Bosch Reig Analytical Chemistry, University College of Castellon, Valencia Univevsity, Castellon de la Plana, Spain A spectrophotometric method of vanadium determination is described. It is based on the oxidation of Pyrogallol Red (PGR) and vanadium is deter- mined by the decrease in absorbance of its characteristic band a t 490 nm and a t pH 4. This absorbance decrease is proportional to the concentration of vanadium(V). At a pH of 4, an ionic strength of 0.1 M, a temperature of 25 "C and a wavelength of 490 nm, there is a linear relationship between the absorbance of PGR (6 x 10-5 M), a t a fixed time, and the concentration of vanadium(V) over the range 0-1.83 p.p.m.The limit of detection of vanadium is found to be 0.05 p.p.m. In the presence of potassium bromate, the determination is possible a t the parts per billion level. This paper describes studies of the selectivity of the method with respect to possible interference from 20 important species contained in ferrous and non-ferrous alloys, which have been classified according to their possible mechanism of interference. The precision and accuracy of the method a t times of 5 and 10 min are also described. Keywords : Vanadium determination ; Pyrogallol Red oxidation ; spectrophoto- metry 4,5,6-Trihydroxy-3-oxo-9-(phenyl-o-sulphonic acid)xanthene, Pyrogallol Red (PGR) , has been widely used in analytical chemistry as a metallochromic indicator for complexometric titrations and as a spectrophotometrical reagent .l In the literature, only one complex, vanadium (IV) - PGR, a violet complex, with the stoicheiometry 1 : 2 has been described (at pH 4.4 with A,,,.at 540 nm). The Beer - Lambert law is obeyed over the range 0.2-8.0 p.p.m. of vanadium (IV) and the absorbance value remains constant even up to 24 h.2 In contrast, the possibility of simultaneous determinations of W and Mo, W and V and V and Sn with PGR by differential spectroscopy has been indicated and the determination of trace amounts of lead4s5 and iodide,6 by means of their catalytic effect on the oxidation of PGR by persulphate and hydrogen peroxide, respectively, has also been described.Experimental Reagents All reagents used were of analytical-reagent grade unless otherwise specified. V'anadiztwz(V) stock solzttion, M. A 1.232-g mass of sodium vanadate (NaVO,) was dissolved in de-ionised water (by warming) and then diluted to 1 1. The solution was standard- ised with iron( 11) ethylenediammonium sulphate (general purpose reagent grade) volumetric standard. The working solution was prepared by the appropriate dilution of the stock solution. Bzt$er solzttions. 2.2 M acetic acid - 0.5 M sodium acetate buffer of pH 4, 0.2 M acetic acid - 0.5 M sodium acetate buffer of pH 5 and 0.4 M potassium dihydrogen orthophosphate - 0.05 M sodium hydroxide buffer of pH 6, were used. Pyrogallol Red, and 8 x M solutions. Masses of PGR (Merck Chemicals) of 0.1000 and 0.0800 g were dissolved in 250 ml of methanol.Solutions are stable for at least a month. Apparatus All the spectroscopic measurements were made on a Pye Unicam SP 8-100 spectrophoto- meter using 1-cm cells. A Crison-501 pH meter, equipped with a Metrohm EA-121 glass- Spain. * Department of Analytical Chemistry, Faculty of Sciences, Valencia University, Burjasot, Valencia,ESCRICHE, CABEZA, CIRUGEDA AND REIG 1403 calomel electrode system, was used for measuring the pH of the solutions. The pH should be measured to an accuracy of & 0.01 pH unit. A Frigedor Selecta-398 refrigerator unit for baths and a Thermotronic Selecta-389 immersion thermostat capable of maintaining the temperature at 0.05 "C, were also used. Results and Discussion General Procedure Into a series of 25-ml calibrated flasks, hydrochloric acid or sodium hydroxide solution or 5 ml of the appropriate buffer solution were added to obtain solutions of different acidities.The 10-4 M vanadium(V) solution was then added and the solution was diluted to ca. 20 ml with de-ionised water. This solution was shaken gently while 1 or 2 ml of or 8 x 10-4 M PGR were added, respectively. The chronometer was turned on when the last drop had been added and the solution was diluted to the mark with de-ionised water. As the decomposition process of the characteristic band of PGR is quicker than the process of appearance of a new band, the decrease in absorption was followed by measuring the maximum wavelength of PGR at the corresponding pH, against water as a reference blank, at times of 1.5 and 2 min and then at l-min intervals for up to 20 min. Influence of pH and Calibration Graphs of the Vanadium(V) - PGR System This study was performed over a pH range of 1-7 using hydrochloric acid and sodium hydroxide.The effect of acidity variation of the medium on the decomposition rate of 4 x 1 0 - 5 ~ PGR in the presence of 0.20p.p.m. vanadium(V) gave the following results: at pH 1,2 and 3, a first quick stage between 90 and 180 s was followed by a lower stage; at pHs 4,5 and 6 the process was more uniform, the rate of the initial stage being almost equal to the rate between 180 and 1080 s ; at pH 7 the process was quicker than the former ones and this phenomenon may be caused by the combined action of vanadium(V) and the instability of the reagent (Fig.1 and Table I). Solutions of a higher pH than 7 have not been tested because of the reagent instability. In order to prove the possible analytical application of the vanadium (V) - PGR system, the regression between the absorbance values of PGR 4 x M solutions at a fixed time and 0.85 0.80 0.75 0.70 n 5 0.65 a 0.60 0.55 0.50 al m n 200 400 600 800 1000 Time/s Fig. 1. Variation of PGR absorbance with time at different pH values. A, pH = 1.20, A = 466 nm; B, pH = 6.85, A = 540 nm; C, pH = 2.15, A = 466 nm; D, pH = 6.30, A = 520 nm; E, pH = 3.08, A = 466nm; F, pH = 5.29, A = 510nm; and G, pH = 4.08, A = 490 nm. Conditions as follows : p.p.m. ; and temperature, 25 "C. PGR, 4 x 1 0 - 5 ~ ; v ( v ) , 0.201404 ESCRICHE et al.: SPECTROPHOTOMETRY OF Analyst, Vol. 108 TABLE I VARIATION OF DECOMPOSITION RATE OF PGR WITH PH IN THE PRESENCE OF VANADIUM(V) Conditions were as follows: PGR, 4 x M ; vanadium(V), 0.20 p.p.m.; and temperature, 25 "C. Reaction rate/A s-l* - -2.14 -0.13 - 10.71 -0.37 - 8.81 -2.56 - 4.29 - 3.05 -9.05 -7.83 -7.62 - 6.49 - 14.29 - 10.90 v, x 10-5 v x 10-5 PH 1.20 2.15 3.08 4.08 5.29 6.30 6.85 Wavelengthlnm 466 466 466 490 510 520 540 * A = Absorbance units. different concentrations of vanadium(V) (c,) up to 1.63 p.p.m. was studied in the pH range for which the process was most uniform. This study was performed at pH 4, 5 and 6 in acetic acid - sodium acetate and potassium dihydrogen orthophosphate - sodium hydroxide buffer solutions, with an ionic strength ( I ) of 0.1 M and temperature 25 "C.At pH 4.02, a graph of absorbance (measured at the absorption maximum of PGR, 490 nm) against cv in the range 0-1.53 p.p.m. was linear with a correlation coefficient (Y) that varied from -0.999 to -0.998 and the slope (S) varied between -0.120 and -0.165, for times between 3 and 20 min. At pH 5.10, there is a linear correlation between absorbance (measured at Amax. 510 nm) veysus cv plotted over the range 0.05 to -1.43 p.p.m. for times longer than 12 min with Y between -0.997 and -0.995 and S between -0.018 and -0.046 for times between 12 and 20 min. At 0.20 p.p.m. of vanadium(V) the absorption spectra of PGR was modified and the Amax. moves from 510 to 520 nm, but non-linearity occurs at this wavelength. At pH 6.14, the calibration graph, at Amax, 535 nm, is linear over the range 0-0.81 p.p.m.of vanadium(V) with a value of Y that varies from -0.994 to -0.967 and a value of S between -0.095 and -0.245, for times between 5 and 20 min. From the results, a pH of 4 was chosen as the optimum working pH. However, instead of working at the initial PGR concentration of 4 x 10-5 M (which provided an absorbance in an intermediate range of minimum photometric error) we operated at its upper limit of 6 x M, which increased the linearity range from 1.53 up to 1.83 p.p.m. of vanadium(V) ; an enhance- ment of sensitivity was also achieved, because the slope of the calibration graph increased by approximately 20% (Table 11). As S increases and Y decreases with time (Table 11), 5 or 10 min were chosen as the most suitable measuring times.TABLE I1 CALIBRATION GRAPHS Conditions were as follows: pH, 4; I , 0.1 M ; temperature, 25 "C; and Amax., 490 nm. Time/ min 1.5 3.0 5.0 10.0 16.0 20.0 f 0-1.53 p.p.m. V(V) - 4 x 10-5 M PGR x = -0.101~ + 0.531 x = -0.120~ + 0.531 x = -0.134~ + 0.531 x = -0.151~ + 0.531 x = -0.160~ + 0.529 x = -0.165~ + 0.527 Calibration graph 0-1.83 p.p.m. V(V) - Y 6 x M PGR -0.9986 x = -0.121~ + 0.798 -0.9988 x = -0.146~ + 0.799 -0.9986 k = -0.162~ + 0.799 -0.9984 x = -0.178~ + 0.796 -0.9980 x = -0.185~ + 0.792 -0.9976 x = -0.189~ + 0.788 Y - 0.999 4 - 0.999 1 - 0.999 3 -0.9990 -0.9988 - 0.9982November, 1983 VANADIUM BY OXIDATION OF PYROGALLOL RED 1405 Limit of Detection 0.02 p.p.m. of vanadium(V) for 11 independent solutions of 4 x deviation (s) of 1.14 x For these times and a numerical factor K = 2, the theoretical limit of detection (c,) is M PGR with a standard M PGR, cL is 0.05 p.p.m.with s = 4.08 x This system was studied in the presence of potassium bromate, proving that for the conditions described above, it is possible to carry out the determination of vanadium(V) at the p.p.b. level, because of the existence of linear regression of A (PGR, 6 x lop5 M) veYszGs cv over the range 0-14.26 p.p.b. of vanadium(V) in the presence of 8.8 x M of potassium bromate, with I = -0.9995 and c, of the order of 0.4 p.p.b. of vanadium(V), at a measuring time of 5 min. p.p.m.; for 6 x p.p.m. Influence of Temperature The study of the influence of temperature on the decomposition of PGR in the presence of vanadium(V) at pH 4.0 was performed at 15,25,30,35 and 40 "C.The rate constant ( K ) and the order of reaction (n) with respect to vanadium(V) were calculated by the differential method and determining the initial rate of reaction ( Vo) (Table 111). TABLE I11 DEPENDENCE OF RATE CONSTANT AND REACTION ORDER WITH TEMPERATURE pH, 4; and I, 0.1 M. Conditions were as follows: PGR, 6.3 x M ; vanadium(V), 1.02-1.83 p.p.m.; TemperaturelK . . . . 288 298 303 308 313 K x 10-3/~-~ . . . . 1.19 1.29 1.34 1.39 1.42 n .. .. .. . . 0.96 1.01 0.98 0.96 0.97 In order to calculate the activation energy (E) and the frequency factor ( A ) , the Arrhenius equation was applied; the plot of 1nK veIszGs 1/T is a straight line (Fig. 2); 1nK = -692.68 x 1/T - 4.373, with Y = 0.99999 when E = 1.376 kcal mol-l and A = 0.013 s-l.From this study we can conclude that at the temperatures studied, the Arrhenius equation was followed, except at 40 "C. This is because of the decomposition of the reagent and the small influence of temperature on the decomposition rate of PGR in the presence of vanadium- (V). Therefore 25 "C was chosen as the working temperature. -6.65 -6.60 -6.70 -6.75 1 , I , I 3.2 3.3 3.4 3.5 Temperature x 103/K Fig. 2. Arrhenius representation. Conditions as follows: PGR, 6.3 x M ; V(V), 1.02-1.83p.p.m.; pH, 4; I, 0.1 M ; and temperature, 288, 298, 303, 308 and 313 K. Interferents The influence of 20 different species in ferrous and non-ferrous alloys on the decomposition1406 ESCRICHE et al. : SPECTROPHOTOMETRY OF Analyst, Vol.108 of PGR in the presence of vanadium(V) was studied and classified according to the possible process taking place. The results are shown in Table IV. The processes observed in the presence of manganese(VII), chromium(V1) and lead( 11) are particularly interesting because these elements provoked an acceleration in the decomposition of PGR in the presence of vanadium(V). However, in the presence of 0.20,0.81 or 1.22 p.p.m. of vanadium(V) there is a linear relation- ship between the absorbance (490 nm) and chromium(V1) concentration over the range 0.02- 0.80 p.p.m. for times between 1.5 and 20 min and for manganese(VI1) in the range 0.03- 1.10 p.p.m. for times between 1.5 and 15 min. Therefore it is possible to determine an element in the presence of another by using the decomposition of the reagent.TABLE IV CLASSIFICATION OF INTERFERENTS Conditions were as follows: PGR, 4 x 1 0 - 5 ~ ; V(V), 0.20 p.p.m.; pH, 4; Amax., 490 nm; temperature, 25 "C; and time 5 min. Maximum tolerance, f2%. Species As(V) (Na2HAs0,.7H20) . . Fe(II1) [Fe(N0,),.9H20] . . Cr(II1) [Cr(N0,),.9H20] . . Zr(1V) (ZrOCl2.8H2O) . . W (VI) ( Na2W0,.2H20) Mo(V1) [(NH,),Mo7O2,.4H2O] Sn(1V) (SnC1,) . . .. Ti(1V) (TiOSO,) . . .. Pb(I1) [Pb(NO,),] . . .. Mn(VI1) (KMnO,) . . . . Cr(V1) (K,Cr,O,) . . . . B (Na,B,O,. 10H20) . . Sb(V) (SbCl,) . . .. I , .. Egi) ( ~ g A r ) 3 . 9 H , o ] . . Co(I1) [Co(N0,),.6H20] . . Ni(I1) [Ni(NO3),.6H2O] . . Cu(I1) (CuSO4.5H,O) . . Mn(I1) (MnSO,.H,O) . . P (Na,HPO,) .. .. .. .. .. .. .. . . .. . . .. .. .. . I .. .. .... .. .. .. .. .. * . .. .. .. .. .. .. .. .. . . . . .. .. .. . - .. .. .. .. Ratio of V(V) species Interfering process 1 : 37500 1 : 7500 1 : 1250-4500 1 : 30 1:25 1: 10 1:5 1 : 3.5 1: 1 1: 1 1 : 0.5 1 : 0.25 500 1 : O . l 1: 1500 1 : 500 1: 10 Complex formation with PGR Possible complex, non- !Decomposition of PGR optimum pH r 1 : 5-1 500 1:27500 1 : 15500 }NO interference Precision and Accuracy A study of the precision was performed with 11 independent solutions of various concentra- tions of vanadium(V) and a fixed concentration of PGR. The results are shown in Table V. TABLE V PRECISION DATA FOR THE METHOD The following conditions were used: pH, 4; I, 0.1 M; Amax., 490 nm; temperature, 25 "C; and time, 1-5 and 2-10 min. PGR (6 x PGR (4 x 10-5~) A r ~r Mean value found Standard deviation, Mean value True concentra- tion of V(V), p.p.m.0.20 0.41 0.51 0.61 0.81 1.02 1.43 1.83 of V(V), p.p.m. p.p.m. of V(V), p.p.m. p.p.m. -7 - e - 7 - 7 21 x2 S1 s2 X1 x2 $1 $2 0.15 0.17 0.01 0.01 0.181 0.191 0.008 0.008 0.35 0.389 0.01 0.009 0.500 0.510 0.009 0.009 0.57 0.61 0.01 0.01 0.81 0.84 0.01 O.O€ 1.02 1.05 0.01 0.01 1.444 1.463 0.008 0.005 1.400 1.400 0.008 0.008 1.788 1.80 0.009 0.01November, 1983 VANADIUM BY OXIDATION OF PYROGALLOL RED 1407 The study of the accuracy7-10 was performed over the range 0.20-1.83 or 1.43 p.p.m. of vanadium(V) with 6 x The homogeneity of the variances of the analysed samples was confirmed by application of Bartlett's test. The linear regression of the values obtained for each analysis of each sample and the corresponding real values were obtained.The statistical t-test was applied to the study of the slope and the intercept of the straight lines was obtained. From this study we can affirm that the method proposed does not present a constant-type error (a slope equal to unity) and it does not need a blank correction (an intercept equal to zero) when performed under the following conditions: (1) at a time of 5 min, (a) over the range of 0.20-1.43 p.p.m. of vanadium(V) and 4 x M PGR and (b) over the range of 0.61-1.83 p.p.m. of vanadium(V) and 6 x M PGR; (2) at time of 10 min, in the range 0.20-1.83 p.p.m. of vanadium(V) and 6 x M PGR. M or 4 x M, PGR, respectively, at times of 5 and 10 min. Recommended Procedure Samples containing between 1.25 and 45.75 pg of vanadium(V) were placed in 25-ml cali- brated flasks, 5 ml of 2.2 M acetic acid - sodium acetate -0.5 M buffer solution were added and diluted to 20 ml with de-ionised water.This solution was shaken gently while 2 ml of 8 x lo-* M PGR were added. The chronometer was turned on when the last drop had fallen and the solution was diluted to the mark with de-ionised water. The absorbance was measured at 490 nm at a temperature of 25 "C against water as a reference and at a time of 10 min. The corresponding vanadium concentration was calculated from the equation of the calibration graph. Description of the Phenomenon Solutions of PGR between 2 x and 8 x 1 0 - 5 ~ , in the presence of vanadium(V) of concentrations between 0.05 and 1.83 p.p.m., suffered a decomposition process that decreased the absorbance of the wide band that is present at 490 nm, until its complete disappearance and a new band at 390 nm was obtained (Fig.3), which proved that the final intensity of this second band was proportional to the initial concentration of PGR. The disappearance rate of the band at 490 nm and the appearance of the 390 nm one were dependent on the concentra- tion of the vanadium (V) present. M, in the presence of vanadium- (V) in the range 0.604 p.p.m., the spectra of PGR suffered a bathochromic shift of the band at However, in PGR solutions between 4 x and 8 x 1 .o 7 h 26 min 0.8 8 2 2 2 % 0.6 0.4 0.2 1 .o 350 400 450 500 Wavelengthlnm 550 600 Fig. 3. Vatiation of PGR absorbance with time in the presence of V(V). Conditions as follows: PGR, 8 X loe5 M ; V(V), 0.41 p.p.m.; pH, 4; I , 0.1 M ; and temperature, 25 "C.1408 ESCRICHE, CABEZA, CIRUGEDA AND REIG 400 450 500 Wavelengthhm 550 600 Fig.4. Variation of PGR absorbance spectra with time alone and in the presence of different amounts of V(V) and V(1V). Conditions as follows: A, V(V) - PGR, 2 x M : 4 x M ; B, V(IV) - PGR, 2 x M: 4 x M ; times, (1) 3 min, (2) 2 h and (3) 24 h ; pH, 4; I , 0.1 M ; and temperature, 25 “C. 490 to 540 nm, which was unstable with time, with the appearance of a new band at 390 nm. This process is analogous to the one that occurred in the V(1V) - PGR system (Fig. 4), which is also unstable with time. The decomposition process of PGR by vanadium(V) seems to be one of oxidation, because its spectrum coincides with the one observed in the treatment of PGR with small amounts of persulphate or hydrogen peroxide at 50 “C. This reaction appears to correspond to a cyclic process, because it has been proved that, with time, small amounts of vanadium(V) are able to oxidise very large amounts of PGR. This result is a contradiction to that of Mushran et aL2 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. References Antonovich, V. P., and Suvorova, E. N., Fiz. Khim. Metody Anal., 1978, 3, 9. Mushran, S. P., Prakash, O., and Awasthi, J. N., Microchem. J . , 1969, 14, 29. Prange, Th., Lechner-Knoblauch, U., and Umland, F., Fresenius 2. Anal. Chem., 1981, 306, 201. Jasinskiene, E., and Kalesnikaite, S., Liet. TSR Aukst. Mokyklu Mosklo Darb., Chem. Chem. Technol., Anderson, R. G., and Brown, B. C . , Talanta, 1981, 28, 368. Jasinskiene, E., and Umbraziunaite, O., Zh. Anal. Khim., 1973, 28, 2025; Chem. Abstr., 1974, 80, Mandel, J., and Linnig, F. J., Anal. Chem., 1957, 29, 743. Commissariat & 1’Energie Atomique, “Statistique AppliquCe 1’Explotation de Mesures,” Masson, De la Guardia, M., Salvador, A., and Berenguer, V., An. Quim., 1981, 77, 129. De la Guardia, M., Salvador, A., and Berenguer, V., paper presented at “5” Encontro Anual da Received February 7th, 1983 Accepted May 121h, 1983 1969, 11, 51; Zh. Anal. Khim., 1970, 25, 87. 66402r. Paris, 1978. Sociedade Portuguesa de Quimica,” 1982.

ISSN:0003-2654    

DOI:10.1039/AN9830801402

出版商:RSC    

年代:1983

数据来源: RSC

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Analyst, November, 1983 SHORT PAPER 1409 A Simple Versatile Hydride-generation Configuration for Inductively Coupled Plasmas Robert C. Hutton and Brian Preston Technical and Analytical Services, Tioxide UK Limited, Central Laboratories, Stockton-on-Tees, Cleveland, TS18 2NQ Keywords : Hydvide-generation configuration ; inductively coupled plasma The inductively coupled plasma (ICP) is now reaching wider acceptance amongst analytical chemists. The versatility of the source and its ability to perform multi-element analysis on a wide variety of sample types from nanograms per millilitre to percentage levels make it a particularly powerful analytical technique. The formation of volatile hydrides is recognised as an attractive method of improving sensitivity for certain elements that are difficult to excite prior to analysis by atomic- absorption or -fluorescence spectrometry.Several workers have also used this to advantage in conjunction with ICP systems. Thompson and co-worker~l-~ have described a continuous flow system employing sodium tetrahydroborate(II1) reduction, for the determination of As, Ge, Hg, Sb, Se, Te and Bi in a variety of matrices including soils, sediments, herbage and geochemical samples. Simpler discrete sampling systems have also been described. Broekaert and Leis6 compared a discrete and continuous flow hydride system for the deter- mination of arsenic and reported a superior detection limit using the former system. This was used to determine arsenic in waste water and steel. Pickford' reported a very simple syringe hydride technique whereby the hydride gas was generated within a disposable syringe and then injected directly into the nebuliser of the ICP.Despite the advantages in sensitivity afforded by these systems, each suffers from some drawbacks. The continuous flow systems all require some modification to the sampling system, resulting in down time during conversion from hydride into conventional liquid sampling and vice versa. The latter system, whilst not requiring any modification to the conventional system, may not be easily automated and, in our experience, resetting of the analytical wavelength over long analysis runs may be a time-consuming task. This allows both sensitive hydride or conventional solution analysis to be performed with no down-time. In this paper, a simple modification to the nebuliser assembly is described.Experimental A Radyne R50-P plasma generator, rated at a maximum forward power of 5 kW but operating at about 3 kW forward power, was used in conjunction with a de-mountable Greenfield-type torch. The nitrogen coolant gas flow-rate was 18lmin-l and the argon plasma gas flow-rate was 7 lmin-l. The sample injector gas flow-rate was 0.8 lmin-l, which afforded compromise sensitivity for all the elements of interest. Analytical observa- tions were made on an area located 10 mm above the load coil. The nebuliser consisted of a V-groove type based on that described by Walcott and Sobel.* The emission measurements were performed on a Spex 1704 l-m focal length mono- chromator with 20 pm slit width and 2 mm slit height. Two 2 in diameter lenses were used to focus a 1 : 1 inverted plasma image directly on to the slits of the spectrometer.An EM1 9558QB photomultiplier tube operating at 1.3 kV and a Bentham 210E current amplifier were used as the detection system, reading directly on to a chart recorder. The hydride system, illustrated schematically in Fig. 1, consisted of three Schuco mini- pumps in conjunction with a Newton Mk IV autosampler.1410 SHORT PAPER Analyst, Vol. 108 Nebuliser Fl NaBH4 Acid wash 4 ml min-' * Sample w Drain Autosam pier Schematic flow diagram of hydride and/or liquid sampling system for ICP. Fig. 1. Reagents All solutions were prepared from analytical-reagent grade reagents. Analyte solutions for As, Bi, Sb, Se and Te were prepared in 30% V/V hydrochloric acid.Analyte solutions for Sn were prepared in 5% V/V hydrochloric acid. The reductant solution used was 2% m/V sodium tetrahydroborate(II1) maintained in 0.1 M sodium hydroxide solution. The wash solution was 2% V/V hydrochloric acid. Results and Discussion The initial criterion when designing this system was to produce a hydride device that could be used without the need to dismantle the nebuliser - spray chamber assembly. Initial experience with a configuration that connected directly to the plasma injector tube suggested that frequent dismantling led to variations in plasma conditions and also to torch damage. The obvious approach therefore was to pass the hydride gas through the normal liquid sample orifice of the nebuliser. This is similar to the approach adopted by McKinnon and Giessg who modified a commercial GMK-type nebuliser to generate the hydride within the spray chamber.We have found, however, that with our system, this configuration did not allow a sufficiently rapid diffusion of hydride gas into the spray chamber and resulted in tailing signals with poor sensitivity. Liquid sample Carrier "I I Hydride sample Fig. 2. Schematic diagram of nebuliser configura- tion for hydride and/or liquid sampling.November, 1983 SHORT PAPER TABLE I 141 1 DETECTION LIMITS (28) OBTAINED USING THE HYDRIDE SYSTEM AND INSTRUMENTAL CONDITIONS DESCRIBED IN THE TEXT Detection limit/ Element Wavelength/nm ng ml-l As . . .. . . 228.81 0.5 Bi . . .. . . 306.77 0.4 Sb .. .. . . 231.15 2 Se .. .. .. 196.03 1 Sn . , .. . . 286.33 4 Te . . .. . . 238.58 5 Relative standard deviation, % 2.4 2.3 2.3 7.1 2.4 2.8 A second approach was adopted in which a secondary introduction device was used, con- sisting of wider bore tubing. The orifice was positioned directly in front of the nebuliser gas jet, in the position previously occupied by the aerosol impactor. This is illustrated in Fig. 2. With this configuration, sharper signals resulted and acceptable detection limits, as illus- trated in Table I, were achieved. The advantages of the system are that it is primarily a permanent configuration that allows a rapid switch over from hydride to normal liquid sample introduction in seconds via the three-way tap, as illustrated in Fig. 1, with no dismantling and hence no down-time.No extra gas flows are required to transport the hydride gas into the spray chamber and, when required, additional channels could be added to incorporate interference suppressants such as EDTA, should the application so require. Typical calibration graphs are illustrated in Fig. 3 for arsenic, showing both hydride and conventional nebulised sample introduction. Extended dynamic range for such elements allows determinations to be made up to 10000 pg ml-l with rapid switch over. It is envisaged that the modified configuration discussed here, would be applicable to most ICP nebuliser assemblies. These compare favourably with previous va1ues.l~~~~ The system could be easily automated and this is one area being actively pursued. 0.01 0.1 1 10 100 1000 10000 Log(concentration/pg mt-I) Fig. 3. Calibration graphs for arsenic on ICP using (A) hydride and (B) conventional liquid sampling. The authors thank the Directors of Tioxide UK Limited for permission to publish this work. 1. 2. 3. 4. 5. 6. 7. 8. 9. References Thompson, M., Pahlavanpour, B., Walton, S. J., and Kirkbright, G. F., Analyst, 1978, 103, 568. Thompson, M., Pahlavanpour, B., Walton, S. J., and Kirkbright, G. F., Analyst, 1978, 103, 705. Pahlavanpour, B., Thompson, M., and Thorne, L., Analyst, 1980, 105, 756. Pahlavanpour, B., Thompson, M., and Thorne, L., Analyst, 1981, 106, 467. Thompson, M., and Pahlavanpour, B., Anal. Chim. Acta, 1979, 109, 251. Broekaert, J. A. C., and Leis, F., Fresenius 2. Anal. Chem., 1980, 300, 22. Pickford, C. J., Analyst, 1981, 106, 464. Wolcott, J . F., and Sobel, C. B., Appl. Spectrosc., 1978, 32, 591. McKinnon, P. J., and Giess, K. C., ICP I n f . Newsl., 1982, 8, 24. Received Mawh 29th, 1983 Accepted June 27th, 1083

ISSN:0003-2654    

DOI:10.1039/AN9830801409

出版商:RSC    

年代:1983

数据来源: RSC

摘要:

1412 Book Reviews Analyst, November, 1983 EXPERIMENTAL METHODS IN PHOTOCHEMISTRY AND PHOTOPHYSICS. PARTS 1 AND 2. By J . F. RABEK. PriceL89.95 (Parts ISBN 0 471 90029 X (Part 1); 0 471 90030 3 (Part 2); 0 471 10090 0 (set of both Pp. xx + 592 (Part 1); xx + 505 (Part 2). 1 and 2). Wiley-Interscience. 1982. Pa*)* The dust cover of the book describes the aims of the work as “Giving an up-to-date survey of most of the available methods and commercially available equipment applied in the study of photochemical and photophysical reactions. It presents the most important information, prin- ciples and applications of different methods which can be directly employed in everyday work.” It is therefore against these objectives that the reviewer has assessed the two parts. The work is a mammoth task, in total 30 chapters in 1100 pages, with some 2100 references and a further biblio- graphy of 700 documents.The first 16 chapters are concerned primarily with the optics and physics of instrumentation] e.g., radiometric units, polarisation components and photodetectors. The remaining chapters deal with specific applications, e.g., luminescence-lifetime spectroscopy, flash-kinetic spectroscopy, actinometry and light ageing of materials. The short final chapter on hazards in photochemical research was especially useful. The book is profusely illustrated, although it must be said that much of the material is readily a.vailable in manufacturers literature. The errors that the reviewer spotted were very few indeed. Certain sections would have benefited from being fuller, e.g., 10 pages are devoted to diffraction gratings and grating monochromators, whereas some 40 pages are devoted to optomechanical components, such as optical benches and vibration isolation equipment.I found it slightly frustrating to have the references to both parts at the back of Part 2, resulting in constant cross-checking between the two volumes. The references given are, however, very comprehensive and are one of the major strengths of the book. Having given such an exhaustive treatment on the equipment available and on the techniques to be used in photochemistry and photophysics, I would like to have seen a chapter on possible errors of measurement, but perhaps that shows the bias of the reviewer as a physicist. In conclusion, I believe the book lives up to the objectives set on the dust cover and the two parts will prove an invaluable reference work to any in the fields of photochemistry or photophysics. Unfortunately, their price of ,689.95 will preclude their purchase by many potential users.The text is lucid and easy to understand. Nevertheless, it is most useful to have all the material collated in one place. D. IRISH TRACE ELEMENT ANALYTICAL CHEMISTRY IN MEDICINE AND BIOLOGY. VOLUME 2. PRO- CEEDINGS OF THE SECOND INTERNATIONAL WORKSHOP, NEUHERBERG, FEDERAL REPUBLIC OF GERMANY, APRIL 1982. Pp. xvi + 1189. Walter de Gruyter. 1983. Price DM280. ISBN 3 11 00861 6. Edited by PETER BRATTER and PETER SCHRAMEL. This expensive but wieldy volume is a record of lectures, papers and posters presented at a recent workshop on trace elements.I t is divided into five main sections: Nutritional Require- ments, Metabolic and Biochemical Effects, Subclinical and Chronic Effects, Diagnosis of Trace Element Supply, Analytical Requirements and Potentialities. The book is well produced apart from the occasional and annoying manual alterations to the camera-ready copy. Discussions associated with the main lectures and after individual sessions have been reduced to a list of topics and a list of contributors-as such they have no scientific value and should have either been reported in full or, better still, omitted. I question the value of including papers (p. 1129) that have already appeared elsewhere: these should also have been omitted. In order to facilitate rapid publication the Editors have not extensively edited the 92 papers contained in this volume.Consequently, some do not match up to the standards usually applied to scientific papers, in as much that some papers present preliminary or inconclusive data or announce the intention to pursue a particular line of research. There are also one or two papers that seem unrelated to the main topic ; for example, the paper dealing with time-resolved fluorimetric analyses for enzymesBOOK REVIEWS 1413 (p. 1143) is very interesting as a general technique but its relevance to trace element analysis is not clarified. This book does, however, bring together a vast body of information on analytical methods for trace element analysis, e.g., proton-induced X-ray emission (p.235) , neutron-activation analysis (p. 483), atomic-absorption spectroscopy (p. 667), energy-dispersive X-ray fluorescence (p. 72 1) , secondary ion mass spectrometry (p. 849), back-scattering spectrometry (p. 1001) and GLC and HPLC of chelates (p. 1109). Amongst the plenary lectures, Hambidge (p. 3) provides an account of trace element require- ments in neonates with particular emphasis on Zn and Cu. Nordberg’s paper (p. 291) on the sub-clinical and chronic effects of various trace metals is a useful summary of the consequences of exposure to As, Be, Cd, Cr, Pb, Hg and Ni. Diagnosis of trace metal deficiency by methods other than measurement of metal concentrations in biological fluids or tissues is covered in a paper by Kirchgessner, Keichlmayer-Lais and Roth (p.41 7 ) . In particular, the possibility of assessing deficiency by measuring the concentrations of storage proteins (e.g., Fe and ferritin) or determining the activity of metalloenzymes (e.g., Mn and superoxide dismutase or arginase) is reviewed critically. This book, like other proceedings of conferences and symposia, may be treated more as a published record of events for delegates rather than a comprehensive text. However, it does form a useful starting point for anyone wishing to gain an overview of current trends and develop- ments in trace element analysis. L. J. KRICKA REVIEW QUESTIONS IN ANALYTICAL TOXICOLOGY. By JACK E. WALLACE, CLIFFORD B. WALBERG, NORMAN A. WADE, RICHARD F. SHAW, ALPHONSE POKLIS, JOSEPH E. MANNO, BARBARA R. MANNO, ROBERT H. CRAVEY and YALE H.CAPLAN. Pp. vi + 184.90 Biomedical Publications (distributed by John Wiley). 1982. Price L14. ISBN 0 931890 098. This small loose-bound book contains over 1000 questions and answers on forensic toxicology. The questions are of the multiple-choice type and cover the fields of pharmacology, analytical chemistry, therapeutic monitoring, clinical toxicology, forensic toxicology and industrial toxi- cology. They are designed to show the areas of knowledge required by the practitioner, but by their nature do not search any topic in depth. The book is aimed at the requirements for the student in the USA and a small number of questions would not be relevant to the British student. A few of the questions are ambiguous and a number of the answers are not acceptable.A statement in the beginning of the book indicates that a few errors may have crept in. Some senior forensic toxicologists when shown this book tended to wonder about its usefulness, but it was noticed that they spent a considerable time reading it and looking up the answers. I recommend this book to the student who may wish to check the type of detailed knowledge required and the fields covered and to the expert who may wish to test his opinion against that of the authors. HAMILTON SMITH This is so, but the number is small. TRACE ELEMENT SPECIATION IN SURFACE WATERS AND ITS ECOLOGICAL IMPLICATIONS. Edited Pp. xii + by GARY G. LEPPARD. 320. Plenum. 1983. Price $45. ISBN 0 306 41269 1. NATO Conference Series, Series I : Ecology, Volume 6 . Trace elements can exist in waters in a great variety of physico-chemical forms. It is now widely recognised that an understanding of the behaviour and effects of such elements requires a know- ledge not merely of their total concentrations, but also of their distribution between the different forms or “species.” In particular, the toxicity of trace elements to aquatic organisms may be markedly influenced by the speciation of the elements.Despite the importance of the topic, and the considerable research effort that has been expended on it, few texts devoted solely to trace element speciation have appeared and the present volume is, therefore, of special interest. It contains papers presented at a NATO Advanced Research Workshop Programme entitled “Trace Element Speciation in Surface Waters and its Ecological Implications” held in Nervi (Genoa), Italy, 2-4 November, 1981.The Workshop was organised in three parts: (1) Analytical Approaches to the Problem of Trace Element Speciation; (2) Trace1414 BOOK REVIEWS Analyst, Vol. 108 Element Species and General Aspects of their Interactions with Aquatic Life ; and (3) New Perspec- tives and Future Actions. The written papers are presented under these headings [five each in parts (1) and (3) and six in part (2)], together with an introductory synopsis of the Workshop’s discussions and recommendations. The discussions of individual papers are also reproduced, and the whole is comprehensively indexed. Part (1) contains a general review of the current position of speciation studies, emphasising the analytical and experimental approaches, together with a number of papers dealing with particular aspects in greater detail.These include physical separation techniques, voltammetry and gas and liquid chromatography (in conjunction with atomic-absorption spectrometry) for the deter- mination of organometallic species. Part (2) contains a number of papers dealing with laboratory and field studies of the effects of trace metals on organisms and ecosystems (though these give little detail of the concerted applica- tion of chemical speciation analysis and biological techniques) and reviews of the biological responses of organisms to trace metals, of the influence of speciation on the biological effects of trace elements and of the biological control of trace element equilibria, The papers in part (3) are more disparate and, in some instances, appear to have no more justification for appearing under the general heading “New Perspectives and Future Actions” than some of those in parts (1) and (2).They include papers on the application of voltammetry and neutron-activation analysis, a review of trace element interactions with particulate matter and a discussion of the approaches to monitoring the environmental effects of pollutants. This last chapter will be of particular interest to those with responsibility for the production and implementation of measures to protect aquatic environments. In summary, this book contains much that will be of interest to analysts, aquatic chemists and biologists concerned with the effects of trace elements in water.Such deficiencies as it possesses are those often found in collections of presented papers, e.g., a degree of overlap and certain weaknesses in continuity, but it incorporates much valuable material not gathered together else- where. The reader familiar with the status of trace element speciation in water some 10-15 years ago will be left with the impression of much done-but of far more still to do. Given the operational nature of most analytical approaches to trace element speciation, it is particularly pleasing that the Workshops brought together chemists and biologists and endorsed (among other topics) research to develop speciation schemes that relate directly to bioavailability. D. T. E. HUNT THERMAL ANALYSIS.-PROCEEDINGS OF THE SEVENTH INTERNATIONAL CONFERENCE ON THERMAL Pp.xxxii + 792 (Volume Price A40 (Volume 1 ) ; A40 (Volume ANALYSIS, VOLUMES 1 AND 2. 1); xxxii + 739 (Volume 2). 2). Edited by BERNARD MILLER. Wiley - Heyden. 1982. ISBN 0 471 26243 9; 0 471 26244 7 (Volume 1 ) ; 0 471 26245 5 (Volume 2). It was the original intention for the two volumes under review to greet delegates on their arrival a t the Seventh International Conference on Thermal Analysis, in Kingston, Ontario, in order to inform them of the content of the technical sessions. In the event, they were not avail- able until some time after the Conference. The contents follow the customary format for conference proceedings, namely, extended abstracts in camera-ready form. This, inevitably, results in a range of quality of the printed material, from the superb to the acceptable.Nevertheless, all abstracts are perfectly legible and remarkably free from errors-a tribute both to the authors and to the Editor, the latter also having had the unenviable tasks of collating the abstracts, preparing the list of contents and compiling an author index, all of which he has done magnificently. Readers who did not attend the conference will, perhaps, assume that all the abstracts contained in the two volumes formed the basis of papers presented at the conference. Such, however, was not the case and in the Proceedings of subsequent ICTA Conferences there would, in the present reviewer’s opinion, be some merit in indicating which of the abstracts were not expanded into presented papers.The papers are presented in five sections, each including a Plenary Lecture: Theory and Instru- mentation (I), Inorganic Chemistry, Metallurgy, Earth.Science, Ceramics (11) , Organic Chemistry, Biological and Medical Sciences (III), Polymer Science (IV) and Applied Science and Industrial Applications (V). In addition to the abstracts, three Award Papers are reproduced in full, namely: DuPont-ICTA (P. K. Gallagher), Netzsch-GEFTA (R. C. Mackenzie) and Mettler-NATAS (JenNovember, 1983 BOOK REVIEWS 1415 Chiu). It would be discriminatory, if not invidious, to select for comment any of the 200-plus papers. Sufficient to say that they represent the enormous diversity of disciplines that now successfully use thermal methods and possession of these volumes is essential for anyone in the field who wishes to remain up to date with its rapid expansion.One (small) criticism: it is a pity that the Editor missed several instances of non-recommended nomenclature, particularly when the recommendations originate from ICTA ! C. J. KEATTCH CHROMATOGRAPHY OF ALKALOIDS. PART A: THIN-LAYER CHROMATOGRAPHY. By A. BAERHEIM SVENDSEN and R. VERPOORTE. Journal of Chromatography Library, Volume 23A. Pp. xvi + 534. Elsevier. 1983. Price $104.25 (USA and Canada); Dfl245 (Rest of World). ISBN 0 444 42145 9 (Volume 23A); 0 44 41616 1 (Series). This book is the definitive work on thin-layer chromatography of alkaloids and, in my opinion, will probably remain so for many years to come. This volume (Part A) is the first of two, with Part B being given over to gas chromatography and high-performance liquid chromatography.In the preface the authors state that thin-layer chromatography has been applied to this area of analysis more than any other technique. This is undoubtedly true as i t is a technique of relatively long standing, but that does not mean that it is now the most widely used. Perhaps a more detailed comparison of the chromatographic techniques to be covered in Parts A and B could have been included here. For example, the ability of thin-layer chromatography to screen many samples simultaneously or the accuracy of quantification of high-performance liquid chromato- graphy could be emphasised. This volume only covers the literature up until the beginning of 1979 and the methodology in terms of instrumental techniques has changed dramatically since then.The book is divided into two parts, a general part and a special part. In the former the materials and techniques of thin-layer chromatography are outlined and the experienced analyst will find little new here, although i t will prove useful to novices in the field. The second part is divided into seven sections covering different structurally based alkaloids and it is here that the reader is struck by the amazing amount of data provided. In all instances solvent systems, detection methods and quantification are discussed with many data on solvent systems compositions and RF values being quoted in tables. The main classification of alkaloids is based on structural differences with the areas sub-divided into chapters covering smaller groups.The main groups are : pyrrolidine, pyrrolizidine, pyridine, piperidine and quinolizidine ; tropane ; quinoline ; phenyl- ethylamine and isoquinoline ; indole ; steroidal alkaloids ; and miscellaneous alkaloids including xanthine, diterpene and imidazole alkaloids. In all instances the intending analyst will not be lacking experimental detail. The style of presentation makes for easy reference but the layout of the text, and indeed the style of printing, is not aesthetically pleasing. In some of the tables subscript numerals have become over-printed with the following line but this does not lead to ambiguity. In conclusion, this volume will provide an excellent reference for those working in this area of analysis. Because of the enormous amount of work published on the chromatographic analysis of alkaloids it is inevitable that it must be divided into more than one volume, but a division on the basis of alkaloid type rather than chromatographic method may have been more useful to the analyst.This would have allowed a critical appraisal of all the techniques available for a specific analysis. Part 2 of this work is awaited with interest; it is hoped it will contain more up-to-date references of the instrumental techniques. R. MACRAE SYNTHESIS AND APPLICATIONS OF ISOTOPICALLY LABELED COMPOUNDS. PROCEEDINGS OF AN INTERNATIONAL SYMPOSIUM, KANSAS CITY, MO, U.S.A., 6-11 JUNE 1982. Edited by WILLIAM P. DUNCAN and ALEXANDER B. SYSAN. Pp. xxviii + 508. Elsevier. 1983. Price $110.75 (USA and Canada); Dfl1260 (Rest of World).ISBN 0 444 42152 1. It is rare to find a collection of papers representing the proceedings of a symposium that combine to form a generally useful reference volume for those not fortunate enough to have been able to attend the actual conference. This publication is something of an exception, as it presents an extremely useful overview of the “state of the art” in respect of the synthesis and uses of both stable and radioactive isotopes. Divided into 16 sections, there are, amongst the total of 108 contributions, papers of interest to chemists of all persuasions, although it has to be said that there is a strong biochemical bias.1416 BOOK REVIEWS Analyst, Vol. 108 Subjects covered include pharmacological and both in vivo and in vitro medical applications, environmental and industrial waste research and the synthesis, separation and purification of labelled compounds.Of particular interest to the analytical chemist are papers on advances in radio-HPLC and the increasing use being made of an expanding range of both stable and radioactive isotopes as probes for nuclear magnetic resonance and mass spectrometric studies. However, it would be unfair to pick out any particular contribution for special mention as the general quality of the papers is so high. Overall, whilst not a publication for individual purchase, it should certainly find a place on the library shelf of any organisation concerned with the use of isotopes. IAN C. DOWNING RECENT DEVELOPMENTS IN MASS SPECTROMETRY IN BIOCHEMISTRY, MEDICINE, AND ENVIRON- SPECTROMETRY IN BIOCHEMISTRY, MEDICINE AND ENVIRONMENTAL RESEARCH, VENICE, JUNE 18-19, 1981.Analytical Chemistry Symposia Series, Volume 12. Pp. x + 345. 1983. Price $80.75 (USA and Canada); Dfl190 (Rest of World). MENTAL RESEARCH, 8. PROCEEDINGS OF THE 8TH INTERNATIONAL SYMPOSIUM ON MASS Edited by ALBERTO FRIGERIO. ISBN 0 444 42055 X. Reviewing Volume 8 in a long-running series of publications led me to look back a t Volume 1. There are fewer papers in Volume 8, but the mixture remains much the same with seven papers devoted to the analysis of endogenous compounds, six papers on xenobiotic substances, two on respiratory gas analysis, one on “environmental” studies and two on advances in methodology. A change from Volume 1 is the inclusion of five Plenary lectures and also posters.A negative change is the dropping of a subject index. Although these proceedings have appeared 2 years after the conference, the papers cover some unusual topics. Thus Roboz’s paper on some applications in microbiology covers some diagnostic techniques for microbial infections in immunosuppressed patients. Two papers on 8-carbolines and one each on catecholamine metabolites, octopamine and tuberculostearic acid illustrate the use of mass spectro- metry of endogenous compounds as a diagnostic tool. A cluster of papers on drug analysis includes one on the detection of tranquillisers in meat production a t the p.p.b. level in tissue. An increasing interest in folk medicine for new pharma- ceutical products is reflected by a paper on the metabolism of harringitonine, obtained from a Chinese tree. Mass spectral techniques are covered by early FAB work, whilst a short paper by Gupta and Joshi presents the EI spectra of a large number of sulphur-containing drugs. The sole “environmental” paper looked a t the metabolites formed by interaction of deoxy- ribonucleosides and benzo[a]pyrene. Most papers seem of sufficient standard to be published in scientific journals, containing full experimental detail, results and conclusions. The various Plenary lectures also follow this pattern and here perhaps one would like to see a more general review of the area of interest. The book is short of environmental research papers; only one poster has an environmental slant (the inter- action of chlorine with hydrocarbons under solar radiation). However, these criticisms apart, the book does contain an interesting series of papers, biased towards biochemical research, and should appeal to those people working in this area who want a broad overview of fashionable topics in this field. However, the price ($80) will probably deter all but institutional libraries. Why cannot such a series as this be produced in a soft-covered version for the more impecunious amongst us ? As with most conference proceedings, the papers vary in content and interest. N. J . HASKINS

ISSN:0003-2654    

DOI:10.1039/AN9830801412

出版商:RSC    

年代:1983

数据来源: RSC