摘要:

ANALYST, MAY 1991, VOL. 116 52 1 Separation of Trace Amounts of Silver by Volatilization Prior to Its Determination in Copper Tailings and a Copper Ore by Atomic Absorption Spectrometry Barbara Roianska Department of Analytical Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland The volatilization of Ag from samples of complex composition by using various additives was investigated and the optimum conditions were established, viz., additive, Florisil-CaO ( 5 + 1-10 + 1 m/m); additive : sample mass ratio, 2; heating time, 2 h at 1200°C; and air flow-rate, 0.17 I min-1. The accuracy and precision of the method for the determination of Ag by flame atomic absorption spectrometry after separation by volatilization from copper tailings and a copper ore were found to be good.Keywords: Volatilization technique; additive; copper tailings; silver determination; atomic absorption spectrometry The determination of the small amounts of Ag present in copper ores and tailings by flame atomic absorption spec- trometry (AAS) requires dissolution of the samples, followed by separation and concentration of the Ag. Because of the complex composition of the samples, both processes tend to be time consuming. Dissolution under pressure in a PTFE bomb with a mixture of HF and HN03, and separation by solvent extraction are most frequently used.l.2 Volatilization from solid samples appears to be an attractive separation method for trace elements. The procedure is simple and enables the losses of analyte and contamination from the reagents to be minimized.Methods for the separation of trace elements by volatilization have been reviewed by T01g3 and Bachmann.4 A volatilization technique was mainly used to separate Se, As, Cd, Zn, TI and Pb, in a stream of oxygen or hydrogen, from relatively non-volatile matrices.5-9 Recently, Zhuikov and co-workedOJ1 studied the volatility of elements in oxygen and hydrogen streams at 1000-1200 "C, their interaction with Si02 and absorption of the elements on various high-temperature oxide filters in an air or oxygen stream. These workers proposed a method for the separation and concentration of Pt, Ir and Au from geological samples prior to their determination by neutron activation and X-ray fluorescence. 1",11 In order to increase the yield of analyte volatilization from a sample of complex composition, the addition of suitable substances to the heated sample is often required.The choice of the optimum additives depends on the elements to be volatilized and the composition of the sample. In previous papers, MgO was used in the thermal evolution of Se (Se02) from dust and slags produced by the copper industry;12 alumina, a Florisil-CaO mixture or MgO was used for pyrolytic separation of mercury from industrial samples. 13,14 Zhuikov and co-workersI0311 examined several additives and achieved increased yields of Pt (Pt02) and Ir (Ir03) by 1 2 sublimation in the presence of Nb205, Ti02 and metallic Nb. The recovery of Ag was not investigated. The application of volatilization to the separation of trace amounts of Ag has not been reported previously.This work is a continuation of our earlier investigations into the separation of trace elements from industrial samples of complex composi- tion by volatilization. The experimental arrangement is based on apparatus described by Geilmanns and Heinrichs and Keltsch.9 Experimental Apparatus The typical apparatus used for separation by volatilization is shown in Fig. 1. A quartz tube (16 mm i.d.) was connected by a ground joint to a quartz water-cooled condenser. A resistance-type electric furnace was used. The temperature in the sample heating zone can reach 1200-1300°C and was measured with a 10% Rh-Pt : Pt thermocouple. Air purified by passage through molecular sieves was used as a carrier gas. The flow-rate was regulated by a needle valve and controlled by a flow meter.The sample was placed in an alundum boat. A Pye Unicam SP-90 series 2 atomic absorption spectrometer and a Thermo Jarrell-Ash S11 atomic absorption spectrometer were also used. Reagents All the chemicals used were of analytical-reagent grade. Stock solution of Ag, 1 mg ml-1. Prepared by dissolving 1.575 g of AgN03 in water to which 1 ml of concentrated HN03 had been added and diluting to 1 1 with water. Alumina (Merck, 1077); specific surface area, 131 m2 g-1. Alumina, obtained from the Department of Solid State Technology, Warsaw University of Technology; specific surface area, 190 m2 g-1. 5 7 ____) Fig. 1 inlet; 6, air outlet; 7, water inlet; and 8, water outlet Experimental arrangement for the volatilization of Ag: 1, electric furnace; 2 alundum boat; 3.quartz tube; 4, Teflon foil; 5, air522 ANALYST, MAY 1991, VOL. 116 FLorisil (magnesium silicate), 60-100 mesh (Fluka). Calcium oxide (Reachim). Procedure A weighed portion of the finely ground sample (about 50 mg) was mixed with the appropriate additives and placed in the alundum boat in the quartz tube and heated for 2 h at 1200 “C in an air stream at a flow-rate of 0.17 1 min-1. After cooling the tube and withdrawing it from the furnace, concentrated HN03 was transferred by pipette into the condenser through the ‘gas inlet’ until the finger was completely immersed. After 3 h, the acidic solution was transferred into a quartz beaker, the condenser rinsed with a small amount of concentrated HCI and the solution evaporated to dryness.After cooling, the walls of the beaker were rinsed with 1.5 or 4 ml of 1 mol dm-3 HCI and the beaker was covered and gently heated. The solution was transferred into a 2 or 5 ml calibrated flask and diluted to the mark with 1 mol dm-3 HCI. Silver was measured by AAS with standards prepared in 1 mol dm-3 HCl. Results Preliminary experiments were carried out with copper tailings ‘C’, which is relatively rich in Ag. The determined amounts of Ag were compared with results obtained after an extractive separation. The blanks from the additives were below the limit of detection. By using the simple experimental arrangement described here, the volatilized Ag was collected not only on the cooled finger surface but also on the surface of the tube condenser.The geometrical parameters of the furnace and the condenser can be optimized but at this stage of the investigation the sole aim was to determine the conditions for quantitative volatil- ization. It was found that the efficiency of the volatilization of Ag after heating a sample containing no additives was low (see Table 1). Because losses of Ag at temperatures higher than 600°C in the presence of an ashing aid, viz., Mg(N03)2, have been reported previously, the addition of Mg(N03)2 was examined. The recovery of Ag after heating 50 mg of the sample mixed with 50 mg of Mg(N03)2 at 1200°C for 1 h was 40%. For comparison, after the additon of a fused oxidizing agent, viz. , KN03, under the same conditions, the volatilization yield was only 5%. In further experiments, the effect of the addition of some refractory compounds such as metal oxides and magnesium silicate, which are known13.14 to prevent melting of industrial copper samples, was studied (see Table 1).Table 1 Influence of the addition of high-temperature oxides and Florisil on the yield of Ag by volatilization. Heating time, 1 h; air stream flow-rate, 0.17 1 min-1; sample: copper tailings ‘C’, 50 mg Additive : sample ratio Temperature/ Yield of Ag Additive (m/m> “C (Yo) None None None Florisil Florisil Alumina (Merck) Alumina CaO Florisil-CaO (4 + 1) FlorisiI-La2O3 (4 + 1) Si02-CaO (4 + 1) La203 - - - 1:l 1:l 2 : 1 2: 1 1:2 1:2 2: 1 2 : 1 2: 1 500 1OOO 1200 500 1100 1100 1100 1 loo 1100 1100 1100 1100 S 8 10 8 so 66 79 46 25 84 83 80 In order to increase the recovery of Ag, the influence of the addition of substances widely used as carriers in spectrography was examined.Alkali metal and ammonium halides, CaC03 and CaC204 (substances decomposed with the evolution of gas), separately or mixed with oxides or graphite in various mass ratios, were tested, but they were found to be less efficient than Florisil-CaO, alumina or silica. The optimum volatilization conditions were therefore established by using oxides and Florisil mixtures as additives. The dependence of the recovery of Ag on the additive to sample mass ratio is shown in Fig. 2. The best volatilization yield was obtained at a ratio of 2 for all the additives. At a ratio of 3, a decrease in the recovery was observed, particularly at shorter heating times.A more detailed examination of the influence of various ratios of components at a constant additive to sample mass ratio is shown in Fig. 3. The mean results for mixtures of Florisil-CaO ( 5 + 1-10 + 1 m/m) were significantly higher than those obtained with other component ratios, and complete recovery was attained. The combinations of CaO and SO2 were not effective. 100 80 - 8 3 60 - + F 40 K 20 0 1 2 3 Additive : sample mass ratio Fig. 2 Dependence of the recovery of Ag on the additive : sample mass ratio. Sample, copper tailings ‘C’; temperature, 1200 “C; and air flow-rate, 0.17 1 min-’. Additive: A, Florisil-CaO (5 + l), heating time, 2.5 h; B, Florisil-CaO (5 + l), heating time, 1 h; C, CaO, heating time, 1 h and D Florisil, heating time, 1 h 4- I 100 50 Florisil or SiOz mass (%) 0 0 50 CaO mass (%) 100 Fig.3 Dependence of the recovery of Ag on the mass ratio of the additive components. Sample, copper tailings ‘C’; additive : sample mass ratio, 2; temperature, 1200°C; and air flow-rate, 0.17 1 min-l. Additive: A, Florisil-CaO, heating time, 2.5 h; B, SiOZ-CaO, heating time, 2.5 h ; and C, Florisil-CaO, heating time, 1 hANALYST, MAY 1991, VOL. 116 100 E 80 2 Y- $ 60 > 8 40 523 - - - . The use of CaC03 instead of CaO did not change the yield after heating for 1, 2 and 2.5 h, while the use of lanthanum oxide was less efficient. Heating at 1200 "C for 2-2.5 h allows a volatilization yield of 96% to be obtained with Si02 and Florisil (Fig. 4). With the addition of CaO and A1203, only a 90% yield can be achieved. By using the chosen mixture of additives, the dependence of the recovery of Ag on the heating temperature (Fig.5 ) and the gas flow-rate (Fig. 6) was investigated. 70 ' ' I J 1 2 Heating time/h Fig. 4 Dependence of the recovery of Ag on heating time. Sample. copper tailings 'C', SO mg; additive:sample mass ratio = 2; temperature, 1200°C; and air flow-rate 0.17 1 min-I. Additive: A , Florisil-CaO ( 5 + 1); B, SiO,; and C, AI2O3 20 ' I I 1 1 I 700 800 900 1000 1100 1200 TemperaturePC Fig. 5 Influence of heating temperature on the recovery of A . Sample, copper tailings 'C', SO mg; additive, Florisil-CaO ( 5 t 17; additive : sample mass ratio = 2; and heating time, 2 h LT 60 ' I I I _. 0.10 0.15 0.20 0.25 Flow-rate/l min- Fig. 6 Influence of air flow-rate on the recovery of Ag.Sample, copper tailings 'C', 50 mg; additive : sample mass ratio = 2; additive. Florid-CaO (5 + 1); temperature 1200°C; and heating time, 1 h Under the optimum conditions, viz., additive, Florisil-CaO ( 5 + 1-10 + 1 d m ) ; additive:sample mass ratio, 2; heating time, 2 h; heating temperature, 1200°C; and air flow-rate, 0.17 1 min-1, Ag was volatilized and determined in other copper tailings and a standard reference material, copper-zinc ore (RUS-1) (Table 2). Discussion Copper ores and flotation tailings are examples of materials with a complex composition. Sulphides of Fe, Cu and Zn, and minerals such as quartz and plagioclase usually occur in copper ores. Tailings contain considerable amounts of Si02 (24- 70%), CaO (7-21%), A1203 (3-8%), MgO (3-10%), Fe (6-7%), organic C (1-2%), Pb, Zn, Na and Mn [n X (n = 1-9)] and trace amounts of Ni, Co, Mo, Sb, Sn, As, Cd and Ag.Volatilization of Ag from samples of complex composition also appears to be a complex process, and several partial processes have to be taken into consideration: (1) thermal decomposition of Ag compounds; (2) evaporation or sublima- tion of Ag or Ag compounds; (3) transport of Ag vapour or vapours of volatile Ag compounds across a sample bed to the surface; and (4) transport of Ag vapour from the surface. Solids added to the heated sample (additives) could essentially influence the above processes as follows. (1-2%0), CU (0.05-0.3%), K (2.7-3.1%), S (0.5-3.1%), C Thermal Decomposition of Ag Compounds According to the data for pure substances,'s Ag2S04 is among the most stable compounds of Ag.It can be formed from Ag2S during heating in air at 450"C, and decomposed at 80&1000 "C: Ag2S04 + 2Ag + SO3 + f02 The decomposition of AgN03 occurs at 600-800 "C, Ag2C03 at 700-800 "C, and dissociation of Ag20 to Ag at 400 "C. The decomposition reactions of solids, viz., temperature and rates of decomposition and also the mechanism of the reactions, can be affected by the presence of other solids. Reports in the literature also include examples of the decomposition of Ag compounds catalysed by a solid product (e.g., Ag20 by Ag) or by a solid additive.16 The reaction mechanism could be changed by the formation of a new phase. The presence of a gaseous reactant product decreases the reaction rate. Reduc- tion of the pressure of SO3 by formation of the stable compound CaS04 could accelerate the decomposition of Ag2S04. However, it is difficult to explain the increase in the evaporation yield in the presence of A1203, as A12(S04)3 i s not thermally stable.Evaporation or Sublimation of Ag or Ag Compounds By considering the data for pure substances under vacuum at 1200 "C, and because of the relatively high vapour pressure of Ag (0.2 mmHg17) and AgCl (40 mmHglX), it can be expected ~ Table 2 Results of the determination of Ag in copper tailings and a copper-zinc ore (RUS-1) Literature X Certified Sample x* (Yo) n RSDT values$ (YO) value for Ag ( Y ) Tailings 'C' 5.50 x 10-3 6 2.0 5.59 x 10-3 - Tai I ings 'B' 2 . 4 6 ~ 10-3 4 2.3 2.4 x 10-3 - RUS-1 2 . 7 6 ~ 10-3 4 2.2 2.82 x 10-3 2.7 f 0.2 x 10-3 * Mean value of Ag found.t RSD = Relative standard deviation. $ Results of flame AAS determination after separation of Ag by solvent extraction.'524 ANALYST, MAY 1991, VOL. 116 that the thermal evolution of trace amounts of Ag should not be limited by evaporation. The vapour pressure, however, over the complex solid system is different and cannot easily be calculated. The rate of evaporation depends strongly on the surface area and on the melting point of the sample matrix. We have observed an increase in the volatilization yields in the presence of additives that prevent melting. The heated samples contain sulphides, sulphates and carbonates that are easily melted and low melting point silicates (the liquid phase can be seen from relatively low temperatures owing to the eutectic point19 of the FeO-Si02 system).The addition of MgO is very effective in preventing the samples from melting; unfortunately, MgO is also the most effective collector of Ag at llOO"C.11 Magnesium silicate was found to be a suitable additive for both the copper tailings and the high pyrites sample (RUS-1). The mixtures (or rather solid solutions) of Fe and Mg silicates melt at a temperature higher than 1200°C. Among alumina-metal oxide binary systems, only A1203- Cu20 has a eutectic point below 1200 "C.20 When heated in an air stream with additives, the samples of copper tailings form a complex system of oxides, silicates and spinels and do not melt at 1200°C. The compounds formed depend on the ratio of the components, hence the system is difficult to describe. The addition of alkali or alkaline earth metal chlorides, assuming conversion of Ag compounds into AgCl, was not effective.Transport of Ag Vapour or Vapours of Volatile Ag Compounds Across a Sample Bed to the Surface Diffusion processes and the reaction of Ag vapour with the matrix and with additives are essential for the transport of Ag through the sample bed. According to Zhuikov et al.," Ag vapour can be absorbed by CaO in a stream of air at 1000-1100 "C, but the process is reversible at higher tempera- tures. This might explain the decrease in the volatilization yield with an additive to sample ratio of >2 with a short heating time (Fig. 2). The complex composition of the samples makes the system so complicated that it is difficult to state which process limits the volatilization of Ag.The choice of additives has to be determined by experiment. The additive suitable for copper tailings 'C', however, was also effective for the other copper tailings and the copper-zinc ore. The investigation of the volatilization of Ag is also important from the point of view of losses of Ag during the preliminary ignition of the samples, which is often part of the routine analysis of ores and other geological materials containing organic carbon. Fishkova and Kurskij21 explained the poor recovery of Ag, after ignition and aqua regia (HC1-HNO3, 3 + 1) dissolution of trace amounts of Ag spiked on silica, by formation of sparingly soluble compounds. On the basis of the results presented here, it is suspected that Ag can be lost by volatilization because the volatilization yields from matrices rich in silica are relatively high.Conclusion The proposed method for the separation of Ag prior to its determination by AAS is simple and useful for a short series of samples. Good agreement with the results obtained after extractive separation and with certified values demonstrated that the accuracy of the proposed method was good. This work was supported by research programme CPBP- 01.18. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 References Skorko-Trybulowa, Z., Boguszewska, Z., and Roianska, B., Mikrochim. Acta, Part I , 1979, 151. Lachowicz, E., Analyst, 1987, 112, 1623. Tolg, G., Talanta, 2972, 19, 1489. Bachmann, K., Talanta, 1982, 29, 1. Geilmann, W., Fresenius Z. Anal. Chem., 1958, 160,410. Gielmann, W., and Neeb, K. H., Fresenius 2. Anal. Chem., 1959, 165,251. Tolg, G., Meyer, A., Hofer, Ch., and Knapp, G., Fresenius Z. Anal. Chem., 1981,305, 1. Tolg, G., Kaiser, G., and Han, H. B., Anal. Chim. Acta, 1981, 129, 9. Heinrichs, M., and Keltsch, M., Anal. Chem., 1982, 54, 1211. Zhuikov, B. L., Popeko, G. S., and Hyong, F. T., Zh. Anal. Khim., 1986,41, 1653. Zhuikov, B. L., Popeko, G. S., and Ortega, H. D., J. Radioanal. Nucl. Chem. Lett., 1987, 117, 11. Roianska, B., and Roiowski, J., Mikrochim. Acta, Part 11, 1984, 481. Roianska, B., and Lachowicz, E., Anal. Chim. Acta, 1985,175, 211. Roianska, B., and Domanska, M., Anal. Chim. Acta, 1986, 187, 317. Duval, C., Inorganic Thermogravimetric Analysis, Elsevier, Amsterdam, 1963. Comprehensive Chemical Kinetics. vol. 22, Reactions in the Solid State, eds. Bamford, C . H., and Tipper, C. F. H., Elsevier, Amsterdam, 1980. Niesmiejanow, A. N., Zh. Phys. Khim., 1959,33,342. Computer Aided Data Book of Vapour Pressure, ed. Ohe, S . , Data Book Publishing, Tokyo, Japan, 1976. Muan, A., in High Temperature Oxides, ed. Alper, A. M., Academic Press, London, 1970, part 1, ch. 7. Ryshkewitch, E., Oxide Ceramics, Academic Press, London, 1960. Fishkova, N. L., and Kurskij, A. H., Zavod. Lab., 1989,55(8), 34. Paper 01044066 Received October 1 st, 1990 Accepted November 22nd, 1990

ISSN:0003-2654    

DOI:10.1039/AN9911600521

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST, MAY 1991, VOL. 116 525 Determination of Trace Amounts of Copper, Nickel and Zinc in Palladium Compounds by Solvent Extraction Flame Atomic Absorption Spectrometry Sijka A. Popova, Stefanka P. Bratinova and Christina R. lvanova Central Research Laboratory, Higher Institute of Chemical Technology, I 156 Sofia, Bulgaria A method is described for the determination of trace amounts of Cu, Ni and Zn in diamminedichloropalladium and diamminedinitropalladium by flame atomic absorption spectrometry after an extraction procedure using ammonium pyrrolidin-I-yldithioformate [ammonium pyrrolidinedithiocarbamate (APDC)] as complexing agent and isobutyl methyl ketone (IBMK) as extractant. Another extraction system, NH4SCN-IBMK, was used for the preliminary removal of Pd which also forms extractable complexes with APDC.Optimum conditions for the selective separation of Pd and for the simultaneous extraction of Cu-, Ni- and Zn-PDC complexes into IBMK were determined. The sensitivity and precision of the proposed method are sufficient for quality control requirements. Keywords: Copper, nickel and zinc determination; solvent extraction flame atomic absorption spectrometry; diamminedichloropalladium; diamminedinitropalladium; ammonium pyrrolidin-7-yldithioformate Diamminedichloropalladium [ Pd(NH3)2C12] and diamminedi- nitropalladium [Pd(NH3)2(N02)2] are used as raw materials in the production of microelectronic systems; hence they have to conform to a high degree of purity necessitating exacting quality control requirements. The content of impurities such as Cu, Ni and Zn in these materials needs to be be controlled and should not exceed 0.001-0.0001Y0.There are no methods described in the literature for the atomic absorption spec- trometric determination of Cu, Ni and Zn in the Pd compounds studied here. Hence there is a need for an accurate method for the determination of Cu, Ni and Zn in Pd(NH3)2C12 and Pd(NH3)2(N02)2 with high sensitivity and selectivity. This problem has been solved by using solvent extraction prior to flame atomic absorption analysis. An extraction system extensively used and preferred in atomic absorption analysis is a combination of ammonium pyrrolidin- 1-yldithioformate [ammonium pyrrolidinedithiocarbamate (APDC)] as complexing agent and isobutyl methyl ketone (IBMK) as extractant. The main problem in applying the APDC-IBMK extraction procedure to the determination of Cu, Ni and Zn in Pd compounds is the co-extraction of Pd.1 This necessitates its prior removal from the system; precipitation is not recom- mended for this purpose, because of the large amount of Pd involved and the possibility of coprecipitation of Cu, Ni and Zn.It has been recommended that the separation of Pd be carried out by extraction of its rhodanide (sulphocyanide) complex into IBMK.2.3 Extraction of 99.9% of the Pd into the organic phase from 3-6 mol dm-3 HC1 can be achieved with a single extraction procedure.2 In order to develop a suitable method it is necessary to examine the conditions under which the extraction of Cu, Ni and Zn together with Pd as their rhodanide complexes can be avoided, and to optimize the conditions for the solvent extraction pre-concentration of Cu, Ni and Zn with the use of APDC-IBMK and their subsequent determination by flame atomic absorption spectrometry.Experimental Sample Preparation A 1.000 g sample of Pd(NH3)2C12 or Pd(NH3)2(N02)2, previously dried at 105 "C, was dissolved in 10 ml of 1 mol dm-3 HCI by heating at about 90 "C for 1 h. After cooling to room temperature, the solution was diluted to 50 ml with de-ionized water. Reagents All reagents were of analytical-reagent grade, and de-ionized, doubly distilled water was used throughout. Ammonium thiocyanate solution, 20% . Previously purified by extraction with APDC-IBMK. Ammonium pyrrolidin-1-yldithioformate solution, 1 YO.A 1.00 g amount of the reagent was dissolved in 50 ml of water containing 1 ml of 25% ammonia solution and the solution was diluted to 100 ml. The residue was filtered. The solution was prepared daily, Sodium hydroxide solution, 25% (metal-free). Sodium hydroxide pellets (250 g) were dissolved in 1 1 of water and the solution was transferred into a separating funnel. A 1 ml volume of APDC solution was added and the mixture extracted with 20 ml of IBMK. The addition of APDC and extraction was repeated until the extracts were colourless. The solution was stored in a polyethene bottle. Isobutyl methyl ketone (Merck). Standard solutions of Cu, Ni and Zn, 1 mg ml-1 each (BDH). Working standard solutions of Cu, Ni and Zn were prepared daily by appropriate dilution of the stock standard solutions.Instrumentation A Perkin-Elmer Model 3030B atomic absorption spec- trometer equipped with hollow cathode lamps for Cu, Ni and Zn as light sources was used. The absorption signals were measured under the conditions shown in Table 1. A pH-meter (Radiometer) was also used. Results and Discussion Conditions for the Separation of Pd As has been reported previously,2 virtually complete extrac- tion of Pd as its rhodanide complex can be achieved over a wide range of acidity (3-6 mol dm-3 HCl). It is known, however, that Cu, Ni and Zn also form stable rhodanide complexes.4 This necessitates optimization of the conditions for the selective extraction of Pd into IBMK. The Ni-rhodanide complex is not extracted into IBMK and remains entirely in the aqueous phase under the optimum conditions for the extraction of Pd as its rhodanide complex (Fig.1, curve 1). In addition, the Cu- and Zn-rhodanide complexes are not co-extracted with the Pd-rhodanide com-526 ANALYST, MAY 1991, VOL. 116 100 80 s - 60 0 1 .- ta 40 20 E ta Table 1 Optimum conditions for the determination of Cu, Ni and Zn in the aqueous and organic phases -: 2 - - - - Acetylene flow-rate/ Aspiration rate/ 1 rnin-1 ml min-1 Linear Air range of Wave- Slit- Lamp flow-rate/ Aqueous IBMK Aqueous IBMK calibration Metal lengthhm width/nm current/mA 1 min- solution solution solution solution graph/mg 1-' c u 328.1 0.7 15 18.4 4.0 2.6 6 5 0.1-4.0 Ni 232.0 0.2 25 18.4 4.0 2.6 6 5 0.5-6.0 Zn 213.8 0.7 6 18.4 4.0 2.6 6 5 0.1-2.0 - 3 - 1 00 80 - s 60 0 .- +I g 40 CI 20 0 w I x'x\x 1.0 2.0 3.0 4.0 5.0 6.0 [HCll/mol dm-3 Fig.1 Effect of hydrochloric acid concentration on the percentage extraction of 1, Ni-; 2, Cu-; and 3, Zn- rhodanide complexes into IMBK: CuII, 3.10 X 10-5 rnol; N P , 6.10 x 10-5 rnol drn-3; Zn", 7.65 x rnol drn-3; aqueous phase, 20 ml; organic phase, 5 rnl; and NH4SCN, 0.4 rnol dm-3 plex from a strongly acidic medium (6 rnol dm-3 HCl) (Fig. 1, curves 2 and 3). Hence, extraction of the Pd-rhodanide complex should be carried out from 6 mol dm-3 HCI in order to remove Pd selectively, thus allowing the subsequent determination of Cu, Ni and Zn by flame atomic absorption spectrometry. It was established that two extractions for 1 min each in the presence of at least a 5-fold molar excess of the reagent (NH4SCN) with respect to Pd was sufficient for the complete removal of Pd into IBMK.Determination of Cu and Ni The medium, after separation of Pd, is strongly acidic (6 rnol dm-3 HCI). Extraction of Cu-, Ni- and Zn-PDC complexes into IBMK under these conditions has not been fully described in the literature.5-8 However, it has been shown9 that these metals form complexes with APDC over a wide pH range (1-14). Reducing the acidity of the solutions to be analysed from 6 rnol dm-3 to a pH >1 causes additional difficulties, because of the need to introduce large amounts of NaOH, which might lead to contamination. Hence, the possibility of carrying out the extraction procedure from strongly acidic media was investigated. It has been reportedlo that 90% extraction can be achieved from 6 mol dm-3 HCI media.Our investigations, however, do not entirely support these data (Fig. 2). Complete extraction of Cu can in fact be obtained in the range 1-6 rnol dm-3 HC1. However, in acidic media >3 mol dm-3, the total extraction of Ni into IBMK as its APDC complex is not possible. The extraction procedure must therefore be carried out at HCI concentrations of up to 3 mol dm-3 in order to obtain the simultaneous extraction of Cu and Ni. Unfortunately, under these conditions Zn remains O t - PH 8.0 6.0 4.0 2.0 2.0 4.0 6.0 [HCl]/mol dm-3 Fig. 2 Effect of ( a ) pH; and (b) hydrochloric acid concentration on the percentage extraction of 1, Cu-; 2, Ni-; and 3, Zn-PDC complexes into IBMK: Cull, 1.55 x 10-5 mol dm-3; Ni", 3.05 X 10-5 rnol dm-3; Zn", 3.88 x lo-" rnol aqueous phase, 40 ml; organic phase, 5 ml; and APDC.3.00 x rnol drn-3 entirely in the aqueous phase and hence its determination together with Cu and Ni in the organic phase is not possible. It was found that the ratio of the volume of the aqueous phase to the volume of the organic phase (Va : V,) in the range from 2 : 1 to 10 : 1 has no effect on the extent of extraction of Ni and Cu under the optimum conditions for the acidity where the extraction is nearly 100%. Hence, the acidity of the aqueous phase can be decreased by a 2-fold dilution with water. Total extraction of Cu and Ni as their APDC complexes into lBMK is achieved by using a 10-fold molar excess of the reagent for Cu and a 60-fold molar excess for Ni (Fig. 3). A large excess of the chelating agent is required to allow for decomposition of the reagent in strongly acidic media.6 A single extraction procedure for a period of 10 s is sufficient because the rate at which the metal chelates are formed and extracted increases as the acidity of the aqueous phase is increased.7 If the absorption signals for Cu and Ni are measured less than 30 min after the extraction procedure, then separation of the organic layer from the aqueous layer only is required.However, if the absorption signals are measured after more than 30 min it is necessary for the organic phase to be washed with water in order to remove the remaining acid and so prevent it from decomposing the Cu- and Ni-PDC complexes ,6 which would reduce the absorption signals. Hence, it was established that it is possible to determine Cu and Ni simultaneously in Pd(NH3)2C12 and Pd(NH&(N02)2 by employing extraction with APDC-IBMK in 3 rnol dm-3 HCl media after preliminary extraction of Pd into IBMK as its rhodanide complex.As mentioned above, under these condi- tions Zn remains in the aqueous phase. For the simultaneous determination of Zn, Cu and Ni, the extraction should be carried out at pH 2. Particular attention has to be paid to the blank; therefore, the base used forANALYST, MAY 1991, VOL. 116 527 Table 2 Determination of Cu, Ni and Zn in Pd(NH3)2C12 and Pd(NH3)2(N02)2 Compound Method Cucontent (YO) RSD* (%) Nicontent (YO) RSD* (YO) Zncontent Determination of Cu and Ni in strongly acidic media (3 mol dm-3 HC1)- Pd(NH3)2C12 Calibration graph (2.63 f 0.04) x 10-4 5.2 (5.25 4 0.04) x 3.6 - Standard additions (2.68 t 0.04) x 4.8 (5.32 t 0.04) x 4.8 - Pd(NH3)2(N02)2 Calibration graph (2.72 k 0.05) x lo--' 6.2 (7.20 4 0.03) X lo--' 2.5 - Standard additions (2.67 t 0.05) x 7.2 (7.25 t 0.04) x 10F4 3.9 - Determination of Cu, Ni and Zn at p H 2.0- Yo) RSD*(%) Pd(NH3)2C12 Calibration graph (2.75 k 0.05) x 10-4 7.1 (5.20 t 0.04) x 10-4 4.2 (3.61 k 0.04) x 10-4 5.1 Standard additions (2.70 t 0.05) x 10-4 6.8 (5.27 4 0.04) X 10-4 4.8 (3.67 * 0.04) X 10-4 4.7 Pd(NH3)2(NO& Calibration graph (2.67 4 0.04) x 10-4 5.3 (7.14 t 0.04) x 10-4 3.7 (4.72 k 0.04) x 3.9 Standard additions (2.63 4 0.04) x 10-4 5.5 (7.19 k 0.04) X 10-4 5.5 (4.80 f 0.04) X 5.2 * RSD = relative standard deviation.100 x-x-x--x t l / ** Y D Table 3 Recovery of Cu, Ni and Zn added to Pd(NH3)2C12 and Pd(NH3)2(N02)2 by flame atomic absorption spectrometry using the APDC-IBMK extraction system 0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 APDC/10-6 rnol Fig.3 Effect of the amount of APDC on the extraction of 1, Cu; and 2, Ni into IBMK: Cu", 1.55 x 10-5 mol dm-3; NiII, 3.05 x 10-5 rnol dm-3; HCl, 3 mol dm-3; aqueous phase, 40 ml; organic phase, 5 ml adjusting the pH must have been purified previously. As is shown in Fig. 2 the most suitable pH range is 2.0-2.5. At lower pH values the extraction of Zn is decreased considerably, whereas at higher values serious problems arise with the blank even when purified NaOH is used. At pH 2.0-2.5, a period of 10 s is not sufficient for the extraction procedure; a shaking time of 60 s is required.Because the extent of APDC decomposition decreases under these conditions, the mini- mum amount of the chelating agent required for quantitative extraction is much smaller; however, it is recommended that the procedure be carried out using the same amount of APDC as required for the procedure in strongly acidic media, viz., 3.00 X 10-3 rnol dm-3. Absorption signals measured for Cu, Ni and Zn in the organic phase are stable for more than 24 h, hence washing of the organic phase is not necessary. The following procedures were used for the determination of Cu, Ni and Zn in Pd(NH3)2C12 and Pd(NH3)2(N02)2. Separation of Pd An aliquot of Pd(NH3)2C12 or Pd(NH3)2(N02)2 solution was placed in a 100 ml separating funnel. A 10.3 ml volume of concentrated HCI plus 3 ml of a 20% solution of NH4SCN were added and the mixture was diluted to 20 ml with water.Then, 5 ml of IBMK were added and the mixture was extracted for 1 min. After the two phases had separated, the organic layer was discarded. The procedure was repeated with another 5 ml aliquot of IBMK and the organic layer was again discarded. Atomic Absorption Spectrometric Determination of Cu and Ni The aqueous phase from above was transferred into another separating funnel, and 10 ml of water plus 1 ml of a 1% solution of APDC were added. The mixture was shaken Recovery Expected/ Element Found/pg Added/pg yg M* Yo * c u 2.7 10 12.7 12.4 97.6 Ni 5.2 10 15.2 15.1 99.3 Zn 3.6 1 0 13.6 13.3 97.8 * Mean of five determinations. vigorously for about 10 s and allowed to stand for 10 min after which 5 ml of IBMK were added.The mixture was shaken for 30 s and, after the two phases had separated, the aqueous layer was discarded. The organic phase was collected in 5 ml calibrated tubes and diluted to the mark with pure IBMK. The organic layer was aspirated directly into the flame and the absorption signals for Cu and Ni were measured with background correction under the conditions given in Table 1. Atomic Absorption Spectrometric Determination of Cu, Ni and Zn The aqueous phase remaining after the separation of Pd was transferred into 50 ml beakers. An 18 ml volume of 25% NaOH was added and the pH adjusted to 2.0-2.5. One millilitre of a 1% solution of APDC was added and the mixture was transferred quantitatively into another 100 ml separating funnel and diluted to 50 ml with water.A 5 ml aliquot of IBMK was added and the mixture was shaken for 30 s. The aqueous phase was discarded and the organic layer collected in 5 ml calibrated tubes and diluted to the mark with pure IBMK. The organic phase was injected directly into the flame and the absorption signals for Cu, Ni and Zn were measured with the background correction under the con- ditions given in Table 1. Standard solutions for calibration graphs were prepared each time by the same extraction procedure, extracting the appropriate volumes of Cu, Ni and Zn solutions each with a concentration of 10 mg 1-1. The determination of Cu, Ni and Zn in Pd(NH3)2C12 and Pd(NH3)2(N02)2 was carried out by using the calibration graph and standard additions pro- cedures.The results are shown in Table 2. As can be seen, the results obtained using the standard additions method corre- spond to those obtained using the calibration graph method. In addition, similar results for Cu and Ni were obtained with the two procedures. Hence, the proposed method is accurate and free from interferences. Recoveries of Cu, Ni and Zn from the two Pd compounds were studied by carrying out standard additions of these metals to Pd(NH3)2C12 and Pd(NH3)2(N02)2 during the dissolution procedure. The results obtained for the recovery study are shown in Table 3.528 ANALYST, MAY 1991, VOL. 116 In conclusion, a reproducible and highly sensitive method for the determination of Cu, Ni and Zn by extraction with APDC-IBMK followed by flame atomic absorption spec- trometry has been developed. The method was applied to the determination of these elements in Pd(NH3)2C12 and Pd(NH3)2(N02)2- References 1 Sychra, V., Slevin, P. J . , Matousek, J., and Bek, F., Anal. Chim. Acta, 1970, 52, 259. 2 Teruo, I . , Bunseki Kagaku, 1966, 15, 109. 3 Popova, S. A., and Bratinova, S. P., J. Anal. At. Spectrom., 1990, 5,35. 4 Marczenko, Z., Photometric Determination of Elements, Mir, Moscow, 1971. 5 Dellien, I . , and Persson, L., Talanta, 1979, 26, 1101. 6 Takada, T., Talanta, 1982, 29, 799. 7 Murakami, M., and Takada, T., Talanta, 1985,32,513. 8 Murakami, M., and Takada, T., Talanta, 1990, 37, 229. 9 Watson, C. A . , Ammonium Pyrrolidinedithiocarbarnate, Mono- graph 74, Hopkin and Williams, 1974. Brook, R. R., Hoashi, M., Wilson, S. M., and Zhang R., Anal. Chim. Acta, 1989, 217, 165. 10 Paper 0102924F Received June 28th, 1990 Accepted January 3rd, 1991

ISSN:0003-2654    

DOI:10.1039/AN9911600525

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST, MAY 1991, VOL. 116 Study of the Conversion of Asparagine and Glutamine of Into Diaminopropionic and Diaminobutyric Acids Using [Bis(trifluoroacetoxy)iodo]benzene Prior to Amino Acid Determination Dominique Fouques and Jacques Landry Laboratoire de Chimie Biologique, INRA, INA-PG, F78850 Thiverval-Grignon, France 529 Proteins The treatment of several proteins with [bis(trifluoroacetoxy)iodo]benzene (BTI) was examined as a possible way to determine separately their asparagine and glutamine content, through the quantification of their corresponding 2,3-diaminopropionic and 2,4-diaminobutyric acids. The diamino acid peaks were resolved between those of phenylalanine and lysine after a modification of the chromatographic conditions required for phenylthiocarbamylamino acid analysis.Rate studies performed on three proteins with BTI in the presence of dimethylformamide at 60 "C showed a maximum conversion of amides into diamino acids ranging from 50 to 83% after 4 h of contact, thereby making the direct quantification of amides in protein through the evaluation of diamino acids unsuitable; a fast (30 min) and virtually complete disappearance of glutamine; and a slower (2 h) and only partial (65 f 6%) disappearance of asparagine. Keywords: Protein; glutamine and asparagine; [bis(tri f1uoroacetoxy)iodolbenzene; phen yl isothioc yanate; high -perf0 rmance liquid chroma tog rap h y Protein hydrolysis, as routinely performed with 6 rnol dm-3 HCI for the determination of the amino acid composition of the protein, converts asparagine (asn) and glutamine (gln) into aspartic (asp) and glutamic (glu) acids.These amides are generally included in the sums 'asx' (asp + asn) or 'glx' (glu + gln). They can be separately assayed only from modified samples. Proposed modifications involve the esterification, ie., reduction, of the free carboxylic acids1 or the conversion of amides into amines by a Hofmann degradation reaction using [bis(trifluoroacetoxy)iodo]benzene (BTI).2 In the latter situation, asn and gln are recovered, after hydrolysis of the polypeptide, as diaminopropionic acid (DAPA) and diamino- butyric acid (DABA), respectively. From the foregoing, the quantification of asn and gln in proteins can be performed either from the differences in asx and glx between untreated and BTI treated samples, or from the DAPA and DABA produced.The first alternative was developed by Soby and Johnson2 who reported determinations of asn and gln consis- tent with sequence data. The second method was described by Vendrell and Aviles3 who observed an incomplete conversion of amides into DAPA and DABA but did not provide any quantitative data on yield. In the present study, the use of BTI and the quantification of the resulting diamino acids, DAPA and DABA, through their phenylthiocarbamyl (ptc) derivatives were further investi- gated with the aim of establishing appropriate conditions for the determination of the asn and gln content of polypeptides. Experimental Materials Horse heart cytochrome c, bovine pancreatic ribonuclease A, bovine pancreatic a-chymotrypsinogen A and oxidized bovine insulin (B chain) were obtained from Sigma.Hen egg-white lysozyme, trifluoroacetic acid (TFA), butyl acetate and BTI [sold as 'iodosobenzene bis( trifluoroacetate)'] were purchased from Merck. Dimethylformamide (DMF), DAPA and DABA were of analytical-reagent grade. Phenyl isothio- cyanate (PITC) and triethylamine (TEA) were supplied by Pierce. Sodium acetate and high-performance liquid chroma- tography (HPLC) grade acetonitrile were obtained from Merck. Nova-Pak (C18, 5 ym, 15 x 0.39 cm i.d.) and Pico-Tag (Clx, 4 pm, 15 x 0.39 cm i.d.) analytical columns were from Waters Associates. BTI Treatment The polypeptide (50 or 100 pg) dissolved in 60 p1 of 0.01 mol dm-3 TFA was mixed in an Eppendorf microtube with 60 yl of a freshly prepared BTI solution (0.08 mol dm-3) in aceto- nitrile or DMF and heated in a water-bath at 35 or 60 "C for between 30 min and 16 h.Samples with DMF were first evaporated under reduced pressure in a SpeedVac concen- trator, redissolved in 200 p1 of water and extracted three times with an equal volume of butyl acetate. Samples with aceto- nitrile were directly extracted three times with 200 1.11 of diethyl ether. The resulting aqueous phases were then evaporated to dryness before acid hydrolysis and amino acid determination were carried out. Amino Acid Determination Acid hydrolysis was performed with 6 mol dm-3 HCl for 24 h at 110 "C. Amino acids were determined by reversed-phase HPLC after derivatization with PITC.4 Chromatography was carried out using a Waters Associates system consisting of two pumps (M510), a gradient former (M680) and an absorbance detector operating at 254 nm.The ptc-amino acids were separated on a Nova-Pak coupled with a Pico-Tag columns Table 1 Programme used for ptc-amino acid separation and column washing Flow-ratel Timelmin ml min-l A* (YO) Bt (Yo) Curve No.$ 0.00 1 .o 90 2.25 1.0 90 5.25 1 .o 82 24.00 1 .o 52 24.50 1.5 0 29.50 1.5 0 30.50 1.5 90 36.00 1.5 90 36.50 1.0 90 38.00 Next injection 10 10 18 48 100 100 10 10 10 - 6 5 6 6 6 6 6 6 * Solvent A: 0.14 mol dm-3 sodium acetate containing 0.5 ml1-1 of triethylamine and adjusted to pH 6.4 with orthophosphoric acid. t Solvent B: acetonitrile-solvent A (3 + 2). $ Pre-programmed curve profiles, linear (6) or convex (5).530 ANALYST, MAY 1991, VOL. 116 maintained at 40 "C in a .water-bath. The elution and regeneration programme is given in Table 1. A Pierce amino acid standard H, to which were added equimolar amounts of methionine sulphone, cysteic acid, DAPA, DABA and norleucine , was used as a reference sample. Results and Discussion Separation of Rc-DAPA and Ptc-DABA The ptc-DAPA and ptc-DABA were co-eluted between ptc-phe and ptc-lys under the chromatographic conditions described by Bidlingmeyer et ~ 7 1 . ~ The resolution between ptc-DAPA and ptc-DABA was improved by decreasing the slope of the elution gradient. However, a fall in the slope that was too marked led to an overlapping of the ptc-phe and ptc-DAPA peaks. The optimum separation between ptc-phe, ptc-DAPA and ptc-DABA was achieved with the chromato- graphic conditions reported in Table 1; the results are shown in Fig.1. A procedure allowing DAPA and DABA to be quantified together with 19 other amino acids including cysteic acid and methionine sulphone, at the picomolar level and within a relatively short analysis time (24 min), was designed. Any pre-column method of derivatization would be suitable for DAPA and DABA provided that adequate chromatographic conditions, such as those described for dansyl derivatives,3 could be found for separating the resultant derivatives. On the other hand, the close resemblance of DAPA, DABA and lysine, which differ only by the number of methylene groups present in their side chains, caused them to be co-eluted in the classical ion-exchange procedure of amino acid determination as noted by Soby and Johnson.* I P 0.1 91 + 0.05 0 DABA DAPAI ,K Retention time - Fig.1 Separation of ptc-amino acids, including DAPA and DABA. A standard sample containing 500 pmol of each amino acid was injected. Norleucine (Nle) was used as the internal standard. Cya, cysteic acid; MSO?, methionine sulphone; and the one-letter code is used for other amino acids. Retention times (in minutes) are as follows: Cya, 3.38; D, 3.48; E, 3.66; S, 6.33; G, 6.71; H, 6.99; R, 7.77; 17.66; I , 18.25; L, 18.67; Nle. 19.46; F, 20.67; DAPA, 20.93; DABA, 21.25; and K, 23.01 T, 8.33; A , 8.68; P, 9.15; MS02,9.79; Y, 13.07; V, 14.57; M, 15.56; C, BTI Treatment Four proteins were treated with BTI for 4 h in the presence of acetonitrile or DMF, at 35 or 60 "C. Bis(trifluoroacetoxy)iodo- benzene has been used in the presence of acetonitrile to convert amides of small molecules into amines under mild conditions (at room temperature for 2-5 h)6 and it has also been employed in the presence of DMF at 35 "C for small peptides,7.8 and at 60 "C for proteins.2 As shown in Table 2, the best conversion occurred in the presence of DMF at 60 "C; at this temperature, the solvent had a stronger effect on asparagine than glutamine. In addition, the conversion was not affected when the concentration of BTI was vaned from 0.016 to 0.8 mol dm-3 (data not shown).Acetonitrile made the extraction procedure simple and induced no interference in the chromatogram. Dimethylformamide caused the presence of additional peaks, the magnitudes of which were related to the concentration of BTI used, and impeded the quantification of DAPA and DABA when a high concen- tration of BTI (0.8 mol dm-3) was used. Kinetics of Conversion of Asparagine and Glutamine Fig.2 depicts the effects of treatment with BTI on three proteins left in contact with the reagent for between 30 min and 16 h. The effects were assessed through the decrease of asx and glx, and the appearance of DAPA and DABA. The kinetic curves were normalized by expressing the data as the ratio of the experimental value to that predicted from the amino acid sequence. Hence, the ratio for asx or glx must decrease from 1 to a value corresponding to the ratio of asp (or glu) to asx (or glx) calculated from the sequence data for the complete disappearance of asn and gln.Similarly, the ratio for DAPA and DABA must increase from 0 to 1 corresponding to the complete conversion of asn and gln. The kinetics for the conversion of individual amino acids displayed the same profile regardless of the proteins being studied (Fig. 2). The following information could be obtained from the graphs (Fig. 2). (i) The maximum disappearance of glx was reached after about 30 min and that of asx after 2 h. This corresponded to a near complete conversion for gln and partial conversion for asn when the ratios were compared with those anticipated from the sequence data; (ii) the appearance of DAPA and DABA was progressive, reaching a plateau after 4 h, however, the levels of appearance were lower than those expected from the disappearance of asn and gln. This discrepancy cannot be ascribed to any interference involving the derivatization with PITC as no significant differences were observed between untreated and BTI-treated proteins regard- ing stable amino acids other than lysine. Lysine, as shown in Fig.2, displayed the same behaviour as DAPA and DABA, although its quantification should be independent of the rate of amide degradation. From the foregoing, BTI was assumed to react with the diamino acids present in the polypeptide or formed during the Table 2 Influence of BTI reaction conditions on the production of diamino acids CH3CN DMF DMF: 35 "C 60 "C 35 "C 60°C CH3CN" Cytochrome c DAPAT DABA Lysozyme DAPA DABA Ribonuclease A DAPA DABA a-Chymotrypsinogen DAPA DABA 1.7$ 2.9 3.0 1 .o 2.0 1.6 , 1.7$ 3.05 4.8$ 0.7 0.9 1.2 - 3.3 - - 4.5 - - 5.7$ - - 5.6 - 3.2$ 1.1 2.2 1.1 5 .O 1.7 1.1 1.2 5.6§ 1.7 5.1 1.1 7.0$ 1.2 6.0 1.1 * Ratio of the value after reaction in DMF, at 60 "C and after reaction in CH,CN, at 60 "C.t DAPA and DABA values were determined based on their ratios to alanine in the hydrolysates and expressed in moles per mole of protein. $ Mean of two experiments. § Mean of three experiments.ANALYST, MAY 1991, VOL. 116 53 1 I (a) I , . . Dl L 0) p 0.8 0 01 3 m m v) 4- - - 0.4 .- E 01 Q X 0 .- 0 0 4- m n 0.8 0.4 2 4 6 8 1 6 Timelh Fig. 2 Time course of asx and glx decrease, and DAPA and DABA increase in BTI treated proteins. ( a ) insulin B; (6) cytochrome c; and (c) ribonuclease A. 0, (asx)tr,,t,~/(aSx),, uence; 0, (glx),,,,,,,/(glx)- \equence; 0, DAPN(asn),eguence; ., DAhW(gln),,,u,,c,; and A, (lyS)treate,l(lyS)yquence.[O] and [O] Correspond to expected values for the complete disappearance of asn and gln. respectively. Sequence data arc from references 9-1 1 treatment, to yield intermediate compounds which were unaffected by acid and were gradually converted back into their initial state i.e., that of a diamino acid. On the other hand, BTI caused the complete disappearance of free gln and asn after 30 min and 2 h of contact, re- spectively, however, neither DAPA nor DABA was detected. From Fig. 2, it was deduced that a maximum yield of about 50% for DAPA, 75% for DABA and 85% for lysine after a protein contact time of at least 4 h with BTI could be obtained. The value for the yield of DABA exhibited some variations from one protein to another; the same was probably true for the yield of DAPA.This made the evaluation of these diamino acids unsuitable for assaying asn and gln in proteins. Such an assay can be performed only by estimating the disappearance of asn and gln resulting from the use of BTT, as proposed by Soby and Johnson.2 However, contrary to the results obtained by those workers2 the disappearance of asn was found, in the present study, to be incomplete, averaging about 65%. Additional information on the rate of amide disappearance for four proteins treated with BTI for 4 h in the presence of DMF at 60 "C (as described by Soby and Johnson2) is given in Table 3. The results are expressed in two ways. The first relies on the sequence data for the asx (or glx) content in an untreated sample, which minimizes the effect of experimental errors.The second took into consideration experimental values only, which gives a truer picture of the variability of the assay for proteins of unknown sequence. Both methods of Table 3 Disappearance of asn and gln for four proteins treated with BTI for 4 h (all values in %) Cyto- Ribo- Par- chrome nuclease a-Chymo- Mean k 67 k 2 d a s n t 70 66 65 67 dgin 90 97 89 91 92 + 4 L n $ 60 56 70 62 62 + 6 fig,,, I10 90 96 99 98 + 8 ameter Insulin B C A trypsinogen SD* * SD = standard deviation. -t d,,, = 100[(asx)s - ( a ~ x ) ~ ] / ( a s n ) ~ , S = sequence9-12 and T = $ a,,, = 100[(asx)NT - ( a ~ x ) ~ ] / ( a s n ) ~ , NT = no BTI treatment. BTI treatment. expression led to close values for the rates of amide disappearance, in agreement with the mean values deduced from Fig.2, and confirmed the degradation to be virtually exhaustive for gln and partial for asn. On the other hand the standard deviation was higher when only experimental values were taken into account, suggesting some fluctuations in the determination of asp and glu when using the PITC derivatiza- tion. It is known that the yields of ptc-asp and ptc-glu are sometimes variable owing to the presence of material extrac- ted from the glass tube during acid hydrolysis, which perturbs the derivatization. 13 Conclusion The results presented here afford a further insight into the use of BTI for the determination of asn and gln in proteins. In this way a direct assay through the evaluation of DAPA and DABA cannot be exploited as the conversion into these diamino acids is incomplete and variable from one protein to another.Therefore, an indirect assay based upon the estima- tion of degraded amides, as proposed by Soby and Johnson,* is required. The disappearance, probably complete for gln irrespective of the protein being studied, is partial for asn, varying in narrow limits from one protein to another. Thus, the determination of asn implies not only an accurate assessment of its disappearance rate and its variability from one protein to another but also a precise quantification of asp. These observations are being investigated further. 1 2 3 4 5 6 7 8 9 10 11 12 13 References Wilcox. P. E . , in Methodsin Enzymology, ed., Hirs, C. H. W . , Academic Press, New York, 1967, vol. 11, p. 63. Soby, L. M., and Johnson, P., Anal. Biochem., 1981, 113, 149. Vendrell, J., and Aviles. F. X., J. Chromatogr., 1986,358,401. Bidlingmeyer, B. A., Cohen, S . A., and Tarvin, T. L., J . Chromatogr.. 1984, 336. 93. Legris-Delaporte, S.. and Landry, J., J . Cereal Sci., 1987, 6, 119. Radhakrishna, A. S., Parham, M. E . , Riggs, R. M., and Loudon. G. M., J . Org. Chem., 1979, 44, 1746. Parham, M. E., and Loudon, G. M., Biochem. Biophys. Res. Commun., 1978, 80, 1 . Parham, M. E., and Loudon, G. M., Biochem. Biophys. Res. Commun., 1978, 80, 7. Ryle, A. P., Sanger. F., Smith, L. F., and Kitai, R., Biochem. J., 1955, 60, 541. Margoliash. E.. Smith, E. L.. Kreil. G., and Tuppy. H., Nature (London), 1961, 192, 1125. Smyth. D. G., Stein. W. H., and Moore, S . , J. Biol. Chem., 1963. 238, 227. Hartley, B. S., and Kaufmann, D. L., Biochem. J . , 1966. 101, 229. Mora, R., Berndt, K. D.. Tsai, H.. and Mercdith. S . C., Anal. Riochem., 1988, 172, 368. Paper Of05302C Received November 26th, 1990 Accepted January 23rd, i 991

ISSN:0003-2654    

DOI:10.1039/AN9911600529

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST, MAY 1991, VOL. 116 533 Analytical Applications of Oxocarbons Part 3.* Specific Spectrophotometric Determination of Oxalic Acid by Dissociation of the Zirconium( iv)-Chloranilate Complex Anne-Marie Dona and Jean-Franqois Vercheret Unite de Recherche Associee 500 du C. N. R.S., Faculte des Sciences, B. P. I 18, 76134 Mont-Saint-Aignan, France Oxalic acid can be determined spectrophotometrically, as it dissociates the chloranilate complex of zirconium(iv) at pH 2. The decrease in the absorbance at 335 nm is proportional t o the amount of oxalic acid present. Optimum conditions for the method are described. The sensitivity of the method is high, allowing the determination of 0.035 ppm of oxalic acid. Because of the very high stabilities of the zirconium(iv) complexes of chloranilate or oxalate, few compounds interfere, particularly hydroxy acids.D-Glucose and alditols did not interfere, which could be useful in studies on solutions of biological interest. Keywords: Oxalate determination; chloranilate; zirconium(iv); spectrophotometry In recent years, there has been an increasing interest in the determination of oxalic acid in biological and non-biological materials.1 Current methods are based on prior separation by solvent extraction, precipitation or chromatography; oxalate is then determined by amperometry2 or spectrophotometry.3 In order to develop less time-consuming procedures , more specific methods have been investigated, based on elec- trogenerated chemiluminescence4 or enzymic techniques, using either oxalate decarboxylase5 or immobilized oxalate oxidase.6.7 Few methods are based on spectrophotometry. Although oxalate and its complexes are colourless, absorbance varia- tions can be produced when oxalate reacts with a metal ion, dissociating the coloured complex initially present.Such a method has been developed, for example, by using the uranium-4-(2-pyridylazo)resorcinol (PAR) complex.8 The absorbance decreased linearly with the oxalate concentration in the range 0-3 ppm, but the method was subject to numerous interferences. In order to increase the selectivity of the procedure, Salinas et al. 3 combined separation and spectro- photometry by extracting a mixed vanadate-mandelohydrox- amate4xalate complex into toluene, with the assistance of a phase-transfer reagent (a quaternary ammonium salt).The method allowed the determination of oxalate in urine and blood serum. We attempted to resolve the problem of specificity in another way, by using a metal ion which would form oxalate complexes with particularly high stabilities compared with other interfering biological species. In this respect, it was con2idered that carbohydrates would be likely interferents in biological samples. Zirconium(1v) was chosen because the corresponding stability constants9 appeared to fulfil these conditions, thus avoiding the necessity of extracting oxalate prior to the absorbance measurements. Chloranilate (the ion of 2,5-dichloro-3,6-dihydroxy-l,4-benzoquinone) was chosen 0 L -I Chloranilic acid (H&) Chloranilate ion (C2-1 * For Part 2 of this series, see reference 22.t To whom correspondence should be addressed. as the coloured complex-forming agent, because it belongs10 to the oxocarbon*I series. This ensured that it had a high solubility in water and that its complex with zirconium(1v) was highly coloured.12.13 Finally, the zirconium(Iv)-chloranilate complex was less stable than the zirconium(Iv)-oxalate complex and could be dissociated within a suitable pH range. Experimental All chemicals were of analytical-reagent grade. Stock solutions of known concentrations of chloranilic acid (Fluka, puriss, 2.5 x 10-3 mol dm-3), zirconyl chloride octahydrate (Fluka, puriss, 0.1 mol dm-3) and oxalic acid (1 g 1-1) were prepared by exact weighing and dilution in purified (Millipore) water. Solutions of the zirconium(rv)-chloranilate complex were prepared by mixing, in the following order, chloranilic acid, hydrochloric acid (1 x 10-3 mol), zirconyl chloride and water.The typical concentration of the complex was 1.67 X 10-4 or 1.67 x 10-5 mol dm-3 depending on whether 1 mm or 1 cm cells were used. The volume of the solution (pH = 2) was 100 cm3. The solutions were used after allowing them to stand at room temperature for 24 h. For the determination of oxalate and interference studies, oxalic acid was added either in solid form or in solution with a micropipette (V,,, = 1 cm3). Absorbance measurements were made immediately on a Kontron Uvikon 860 spectropho- tometer equipped with 1 mm or 1 cm quartz cells, at ambient temperature. The pH values were measured with a Metrohm 632 pH meter and a combined glass electrode.Principle of the Method for the Determination of Oxalate The method is based on the competitive complexation of zirconium(1v) by chloranilate and oxalate. Chloranilic acid (H2C) is known’2,*3 to give a bright magenta solution with a low concentration of zirconium(1v) even in a strongly acidic solution. In the complex(es), the ligand possesses an aromatic structure14 in which the charges are shared by the oxygen atoms. Accordingly, an intense ultraviolet band is found at 335 nm. On the other hand, oxalic acid also forms stable complexes with zirconium(1v)Y in acidic media, with the formula Zr(Ox),(2,-4)- (n = 1-4). If the concentration and pH are adjusted so that the oxalate complex(es) is(are) more stable than the chloranilate complex(es) , the over-all reaction can be displaced to favour the formation of the oxalate species according to the following equation: ZrC, + nOx Zr(Ox), + mC534 ANALYST, MAY 1991, VOL.116 where ZrC, and Zr(Ox), are the chloranilate and oxalate complexes, respectively (charges are omitted for simplicity). Fig. 1 shows schematically the reactions involved in the process. The spectrum of the zirconium(iv)-chloranilate complex is related to that of the free chloranilate ion, C2-. However, at pH 2, where the main uncomplexed species is the hydrogenochloranilate ion, HC- , a large absorbance differ- ence is observed at 335 nm. Hence, the dissociation of the zirconium(iv)-chloranilate complex could be monitored as a function of the concentration of oxalic acid, as shown in Fig.2. Results and Discussion Optimum Conditions for the Formation of the Zirconium(rv)-Chloranilate Complex All initial experiments were carried out with [H2C] = 5 x 10-4 rnol dm-3, which is the optimum concentration when using 1 mm cells. The effect of pH on the formation of the zirconium(Iv)-choranilate complex was studied. Maximum complex formation was obtained at a pH of 2.10. At higher pH values, progressive dissociation of the zirconium(lv)-chlor- anilate complex occurred with the release of C2-. After 2 h at pH >8, no complex could be detected; the spectrum was that of the C*- ion alone. Experiments were carried out to study the reversibility of this dissociation reaction. When the dissociated complex was subjected to an acidic medium (pH = 2), complexation was no longer possible, as the spectra indicated the presence of the free HC- ion.Hence, zircon- ium(rv) had been irreversibly transformed, in basic medium, into a species that was unable to react with chloranilic acid at any pH value. It has been reported15 that zirconium(rv) polymerizes in aqueous solution to a tetrameric hydroxide ,I6 Chloranilic acid Zirconium(iv)-chloranilate complex(es) Addition of oxalate F t - Zirconium(iv)-oxalate complex(es) Oxalic acid Zirconium(1v) Fig. 1 Principle of the competitive method for the determination of oxalic acid 1 .oo 8 ra 2 0.50 2 A ' 0 250 325 400 7Jnm Fig. 2 Variation of the spectrum of a solution of the zirconium(1v)- chloranilate complex as a function of oxalic acid concentration.[H2C] = 5 x 10-5 rnol dm-3; q = [ZrlV]/[H,C] = 0.33; pH = 2.09; and I = 1 cm. The spectra correspond, in the order shown by the arrow, to the concentrations of oxalic acid given in Fig. 4, curve 3 [Zr4(0H)8(H20) which is known17.18 to have a low tendency to undergo complexation. Hence, it was necessary to develop a procedure in which the zirconyl solution would not reach a pH >2. Therefore, the various reagents must be added in the following order: chloranilic acid, hydrochloric acid and zirconium(rv), and then water to make the solution up to the final volume. It was found that the maximum absorbance was not reached immediately at pH 2. The formation of the complex was slow and the reaction rate increased with the molar ratio q ( q = [ZrtV]/[H2C]). Formation of the complex was compIete after 5 h for a value of q greater than 0.15.Stoichiometry of the Zirconium( IvjChloranilate Complex The stoichiometry of the complex was determined by the molar ratio method at a pH of about 2, at which the complex had maximum stability. The results were not very reprodu- cible, because of the slow reaction rate. Care was taken to record the spectra after identical reaction times (24 h) for all the solutions with different values of q . At pH ~ 0 . 3 3 , the absorbance increased as a function of q , but the plot was not linear. However, if the points correspond- ing to q <0.1 were ignored, a satisfactory linear plot was obtained, giving a break for q = 0.33 (Fig. 3). The initial sharp increase in the absorbance for q <O.l might be due to the transient formation of a species containing a larger proportion of chloranilate, possibly with a stoichiometry of 1 : 4 , as zirconium(1v) is known to form octa-coordinated complexes.9 Nevertheless, the main species characterized under the conditions used here was the 1 : 3 zirconium(iv)-chloranilate complex.Attempts were made to verify this stoichiometry by using the molar ratio method in more acidic media (1 or 2 rnol dm-3 HCI). Unfortunately, the extent of complex formation decreased when the acid concentration was increased, yielding curves instead of linear segments. Tenta- tive determinations of the breaks on such plots gave values for q of 0.40-0.45, which could also be accounted for by a 1 : 2 stoichiometry for the complex. These results are in contrast to those of Thamer and Voigt12 which were obtained in very acidic media (2 rnol dm-3 HCIO4), and indicated both a 1 : 1 and a 1 : 2 complex.However, our findings in acidic media show that the low stability of the complex does not allow the precise determination of its composition. On the other hand, Varga and Veatch'g found that a 1 : 1 and a 1 : 3 complex were formed between hafnium(rv) and chloranilic acid in 3 rnol dm-3 HC104. Because zirconium and hafnium are elements with very similar properties,g it was surprising that complexes of different stoichiometries, viz., 1 : 2 or 1 : 3, should be formed under analogous conditions. The results presented here, however, support the formation of 0.990 0.770 al C 5 0.550 2 z 0.330 I 0.110 1 + / +/+ I I I I I I I I I I I 1 I I I I I I 0 0.05 0.15 0.25 0.35 0.45 4 Fig.3 Absorbance of a solution of the zirconium(iv)-chloranilate complex versus the molar ratio q. [H,C = 5 X lov4 rnol dm-3; q = [Zr1V]/[H2C]; pH = 2.0; I = 1 mm; and 1 = 335 nmANALYST, MAY 1991, VOL. 116 535 a zirconium(1v) complex with a 1 : 3 stoichiometry, as was found for hafnium(1v). 19 It was suggested that chloro complexes of zirconium(1v) could have been formed in this work, thus explaining the differences between our results and those obtained using the non-complexing acid HC104. Hence two complementary experiments were performed. In the first, the molar ratio method was used with 1 rnol dm-3 HClO4; this gave a curve similar to that obtained with 1 rnol dm-3 HCI. In the second, chloride ions, up to a concentration of 0.1 rnol dm-3, were added to a solution of the zirconium(iv)-chloranilate complex ([H2C] = 5 X 10-4 rnol dm-3, q = 0.33, pH = 2); no change in the absorption spectrum of the complex was observed, It was therefore concluded that the formation of chloro complexes was negligible under the experimental conditions used here.Determination of Oxalic Acid Taking into account the above results, the following condi- tions were chosen: [H2C] = 5 x 10-4 rnol dm-3; q = 0.33; pH = 2; path length (I) = 1 mm; and h = 335 nm. Experiments were carried out in which the decrease in the absorbance was monitored as a function of the oxalic acid concentration. The method was very sensitive. For example, a decrease in the absorbance of 0.117 was found for the addition of 0.2 cm3 of a solution of oxalic acid (1 g 1 - 1 ) to 100 cm3 of a solution of the complex (concentration of oxalic acid = 2 x 10-3 g 1 - 1 ) .The sensitivity was defined as the slope of the initial portion of the plot of absorbance versus oxalic acid concentration. It was found that the sensitivity was enhanced by using a lower concentration of the coloured complex, because less oxalic acid was necessary for its dissociation. A second series of measurements were made in which the concentrations of zirconium(1v) and chloranilic acid were reduced by a factor of 10, i . e . , [HZC] = 5 X 10-5 rnol dm-3; q = 0.33; and I = 1 cm. As expected, the sensitivity (S) increased ten times. For [H2C] = 5 X rnol dm-3, q = 0.33 and f = 1 mm, S = 58.5 1 g-1. For [H2C] = 5 x 10-5 rnol dm-1, q = 0.33 and 1 = 1 cm, S = 590 1 g-1.Detection Limit Under the standard conditions (pH = 2), the initial absor- bance of a solution of the zirconium(iv)-chloranilate complex containing no oxalic acid, obtained from six replicate determi- nations, was 0.89 ir 0.02, for 1 = 1 cm. This corresponded to an apparent molar absorptivity ( E ) of 17800 dm3 mol-1 cm-1 (calculated for one chloranilate moiety). Hence, the detection limit was defined as the oxalate concentration corresponding + + 0.850 I- i * 8 + % n a 0.750 0.650 0.550 1; + 1 + + * 3 1.0 3.0 5.0 7.0 9.0 Acid concentration/mg I-’ Fig. 4 Absorbance of a solution of the zirconium(~v)-chloranilate complex versus the concentration of organic acids. I, D-Gluconic acid; 2, oL-tartaric acid; and 3, oxalic acid.[H2C] = 5 X mol dm-3; q = [ZrIv]/[H2C] = 0.33; pH = 2.09; 1 =1 cm; and A = 335 nm to an absorbance value of 0.87, i.e., 0.035 mg 1-1 or 0.035 ppm. This detection limit is much lower than those reported for earlier methods, viz., 0.5 ppm3 and 0.4 ppm.8 This probably resulted from the very high absorptivity of the zirconium( rv)-chloranilate complex. Interferences Examination of the literature on the spectrophotometric determination of oxalate showed that many metal ions interfere. As oxalate can complex with nearly all metal cations, it is obvious that their tolerance limits will be very low in any method. Only the alkali metal ions (Na+, K+ and NH4+) can be tolerated in appreciable amounts (100 pprn). Alkaline earth metal ions such as Mg2+ and Ba2+ interfere slightly, but Ca2+ precipitates either chloranilate20 or oxalate and should be removed if present.The study of the interference of anions is more interesting. Oxo-ions (Mo042-, W042-, VO2+ and U022+) form col- oured complexes21-24 with chloranilate and hence interfere seriously. Dichromate would oxidize oxalate. Highly com- plexing agents such as ethylenediaminetetraacetic acid (EDTA) should, of course, be avoided. Of the inorganic anions, only fluoride9 can be expected to complex with zirconium(1v). Because the determination of oxalate is generally required for biological studies, the possible interference of biomol- ecules, such as carbohydrates, polyols and hydroxy acids, was examined. Chloride and sulphate ions, which are reported9 to form stable complexes with zirconium(iv), were also tested.A concentration that did not cause more than a 1% change in the absorbance was taken as the tolerance limit. The presence of 20 g 1-1 of D-glucitol, 20 g 1-1 of D-mannitol, 20 g 1-1 of xylitol, 7 g 1-1 of D-glucose, 5 g 1-1 of chloride and 0.01 g 1-1 of sulphate did not interfere with the determination of oxalate. On the other hand, 5 X 10-3 g 1-1 of D-gluconic acid caused a 7% decrease in the absorbance, whereas 5 X 10-3 g I-’ of DL-tartaric acid caused a decrease of 20% (Fig. 4). This showed that these acids formed fairly stable complexes with zirconium(1v). In order to confirm this, the corresponding sensitivities ( S ) were calculated under identical conditions: [H2C] = 5 x 10-5 rnol dm-3; q = 0.33; pH = 2; and f = 1 cm.Values of S of 620, 78 and 15 1 g-1 were found for oxalic, DL-tartaric and D-gluconic acid, respectively. This gave a relative order of stability of the three complexes which was in agreement with that obtained by an ion-exchange method.9 These results show that the stabilities of the complexes of zirconium(1v) decrease as the distance between the carboxyl groups of the hydroxy acids increases. The absence of one (gluconic acid) or two carboxyl groups (polyols) makes the complexes even less stable. The low stabilities of the polyol complexes suggest that the hydroxyl groups play little part in the chelation of zirconium(1v). Conclusion The method described here for the determination of oxalate compares favourably with a procedure recently reported by Salinas et af.3 It is essentially simpler, because the extraction step is avoided. The principle is slightly different, as no ternary complex is formed between zirconium(Iv), chlor- anilate and oxalate. The technique is based instead on ‘bleaching’ of a solution of a coloured complex consecutive to the formation of the more stable oxalate complex. However, the limitations are almost the same, and the list of interfering species is analogous, including those metal ions which can complex with chloranilic acid at pH 2, and the complexing agents of zirconium(1v). It appears, nevertheless, that the proposed method is potentially more sensitive (detection limit 0.035 ppm as opposed to 0.5 ppm), and possesses a higher536 ANALYST, MAY 1991, VOL. 116 specificity if organic interferents are considered.It is particul- arly significant that carbohydrates and polyols were found not to interfere, and that hydroxy acids interfered only slightly. This might prove useful in studies of solutions of biological interest. As with the related method based on bleaching of the uranium-PAR complex,* this might also be useful in the area of water resource research. The authors thank E. Leconte for technical assistance with part of the experimental work. References Hodgkinson, A., Oxalic Acid in Biology and Medicine, Academic Press, New York, 1977. Fogg, A. G., Alonso, R. M., andFernandez-Arciniega, M. A,, Analyst, 1986, 111, 249. Salinas, F., Martinez-Vidal, J. L., and Gonzalez-Murcia, V., Analyst, 1989, 114, 1685. Rubinstein, I . , Martin, C. R., and Bard, A. J., Anal. Chem., 1983, 55, 1580. Knowles, C. F., and Hodgkinson, A., Analyst, 1972,97,474. Nabi Rahni, M. A., Guilbault, G. G., and de Olivera, N. G., Anal. Chem., 1986,58,523. Almuaibed, A. M., and Townshend, A., Anal. Chim. Acta, 1989, 218, 1. Neas, R. E., and Guyon, J. C., Anal. Chem., 1972, 44, 799. 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Ryabchikov, D. I., Marov, I. N., Ermakov, A. N., and Belyaeva, V. K., J. Inorg. Nucl. Chem., 1964, 26, 965. Poirier, J. M., and Verchere, J. F., Talanta, 1979, 26, 341. West, R., and Powell, D. L., J. Am. Chem. SOC., 1963,85,2577. Thamer, B. J., and Voigt, A. F., J. Am. Chem. SOC., 1951,73, 3197. Hahn, R. B . , and Johnson, J. L., Anal. Chem., 1957,29,902. Andersen, E. K., Acta Cryst., 1967, 22, 196. Zielen, A. J . , and Connick, R. E., J. Am. Chem. SOC., 1956,78, 5785. Mak, T. C. W., Can. J. Chem., 1968,46, 3491. Connick, R. E., and McVey, W. H., J. Am. Chem. SOC., 1949, 71, 3182. Devia, D. H., and Sykes, A. G., Znorg. Chem., 1981,20, 910. Varga, L. P., and Veatch, F. C., Anal. Chem., 1967,39, 1101. Tyner, E. H., Anal. Chem., 1948,20, 76. Lee, W. F., Shastri, N. K., and Amis, E. S., Talanta, 1964, 11, 685. Poirier, J. M., and Verchere, J. F., Talanta, 1979, 26, 349. Poirier, J. M., and Verchere, J. F., J. Inorg. Nucl. Chem., 1980, 42, 1514. Marone, C. B., and Bianchi, G., An. Quim., 1973, 69, 205. NOTE-References 10 and 22 are to Parts 1 and 2 of this series. Paper 0/05144F Received November 16th, 1990 Accepted January 3rd, 1991

ISSN:0003-2654    

DOI:10.1039/AN9911600533

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST, MAY 1991, VOL. 116 537 Conductimetric Determination of Some Metal Ions Using Salicylaldoxime as the Reagent Mitali Sarkar Department of Chemistry, University of Kalyani, Kalyani 74 1235, Nadia, India A simple and sensitive conductimetric method for the determination of copper(li), nickel(ii), zinc(ii), lead(ii), palladium(ii), iron(ii1) and aluminium(lli) using salicylaldoxime in an ethanol-water mixture is described. The effect of solvent on the shape of the titration curve is studied; and statistical treatment of the experimental data indicates the method is both precise and accurate. Keywords : Con d u ctim e tric determination; sa lic ylaldoxim e; e th a n oi-wa te r mixture; me ta l ion As the conductance of a solution relates to the total ionic content, it can be used to follow reactions that result in a change in this quantity.Conductimetry was first developed as an electrochemical method for studying solutions. As the technique was devel- oped it was used for the analysis of solutions, melts and solids and pure liquids. Conductimetry is one of the most successful yet simple analytical techniques; it can be used for the determination of the titration end-point in neutralization and in precipitation and complex forming reactions in both aqueous and non-aqueous media.'+ In the work described in this paper, a conductimetric study of the interaction of some metal ions with salicylaldoxime in an ethanol-water (2 + 1) mixture has been carried out. Experimental All chemicals used were of analytical-reagent grade. Doubly distilled water with a conductivity of 1.58 X 10-4 S m-1 was used to prepare 1 x 10-2 mol dm-3 stock solutions of aqueous metal chlorides, which were standardized using ethylenedi- aminetetraacetic acid (EDTA) and metallochromic indica- tors .7 Apparatus A YSI Model 32M conductance meter (Yellow Springs Instrument Co., Yellow Springs, OH, USA) was used.The measurement range was 1.0-200.0 pS with a maximum error of k 0.2%. The YSI Model 3417 cell was also used with a conductivity cell constant, Kcell, of 100 m-1. Procedure A 10.0 ml aliquot of 1 x 10-3 mol dm-3 aqueous metal chloride was transferred into a beaker containing 20.0 ml of ethanol. The conductivity cell was immersed in the beaker and 1 x 10-2 mol dm-3 ligand solution was added from a microburette.The conductance was measured subsequent to each addition of ligand solution and after thorough stirring. A graph of conductivity versus titre was constructed and the end-poin t determined . Results and Discussion Conductimetric titrations were carried out in order to deter- mine the metal-ion concentration. The metal to ligand mole ratio, i.e., the composition of the chelate formed, can be determined from the shape of the titration curve. By changing the media of the titration, three different examples are described: (i) aqueous metal solution titrated with ethanolic ligand solution; (ii) ethanolic metal solution titrated with ethanolic ligand solution; and (iii) metal solution titrated with the ligand, both in an ethanol-water (2 + 1) mixture. The ligand concentration in each example was about ten times that of the metal solution in order to minimize the dilution effect on the conductivity throughout the titration.A dilution correction* was also made using the following equation, assuming that the conductivity is a linear function of dilution: where h is the corresponding electrolytic conductivity, V1 is the initial volume and V2 is the volume of added ligand (correc = corrected and obs = observed). The experiments were carried out in potassium chloride of an ionic strength of 0.1 mol dm-3 in order to suppress the effect of the migration of electroactive ions. Fig. 1 represents the CuII system and Fig. 2, the Fe"1 system. The wide curvature (Fig. 1 line A) around the end point, when the aqueous CuII solution is titrated with the ethanolic ligand solution, can be explained with respect to the formation of a precipitated chelate in the aqueous medium.However, the accuracy of the conductivity value in this region depends on the speed of precipitation, composition and solubility of the precipitate. An ethanolic CuII solution was titrated with an ethanolic solution of the ligand (Fig. 1 line B) and a small curvature around the end point was noticed. This is probably a consequence of most of the metal salts studied being insoluble in ethanol. The use of example (iii) was discussed to overcome 0 2 4 6 8 Volume of added titrantlml Fig. 1 Conductimetric titration of copper(I1) with salicylaldoxime solution. A , aqueous metal solution versus ethanolic ligand solution; B, ethanolic metal solution versus ethanolic ligand solution; and C, metal versus ligand, both in ethanol-water mixture538 80 c 60 r n t 0 > r -..: 40 .- c. a -a O 0 20 I 1 - - - - ANALYST, MAY 1991, VOL. 116 0 2 4 6 Volume of added titranuml 8 Fig. 2 Conductimetric titration of iron(ii1) with salicylaldoxime solution in ethanol-water mixture. A , 1 X 10-3 mol dm-3 metal versus 1 X lo-* rnol dm-3 ligand; and B, 1 x rnol dm-3 metal versus 1 x 10-l rnol dm-3 ligand the problem of solubility of the chelate and the metal ion, in this example an ethanol-water (2 + 1) mixture is used both for the ligand solution and for the titration medium. Fig. 1 line C shows the titration curve for a 1 x 10-3 mol dm-3 copper(1r) chloride solution with a 1 X 10-2 rnol dm-3 ligand solution in an ethanol-water (2 + 1) mixture, The conductivity increases initially, reaches a maximum and then decreases.The increase in the conductivity before the inflection point is the result of each Cut1 ion being replaced by two protons. The protons remain solvated and their interac- tion with the solvent depends on the ratio of ethanol to water used.9 The observed maximum conductivity value corre- sponds to a Cu"-ligand mole ratio of 1 : 2. The reaction can be represented as follows: CH=NOH a O H - cu2+ + 2c1- + 2 0 4 OH I 2H+ (solvated) + 2CI- + OIH After the equivalence point it is expected that the conductivity should either remain constant (added ligand remains undisso- ciated) or increase slightly (partial dissociation, if any, of the added ligand). CH=NOH + H+ (solvated) OH 0- However, the titration curve indicates that after the equiv- alence point the conductivity of the solution decreases.One assumption is that the protons available in the medium interact with the added ligand solution. A .CH=NOH The pH of the solution was measured before and after the end-point. An increase of pH by 0.32 justifies the above Table 1 Results of conductimetric titrations of metal ions with the ligand in an ethanol-water (2 + 1) mixture Masslg Metal-ligand Metal Taken Found Recovery (%) mole ratio 0.290 0.292 100.6 0.416 0.418 100.5 0.832 0.836 100.5 1.040 1.045 100.5 0.937 0.931 99.3 0.775 0.771 99.5 0.821 0.818 99.6 0.574 0.571 99.5 0.769 0.772 100.4 0.976 0.988 100.2 0.812 0.808 99.5 0.921 0.915 99.3 0.815 0.811 99.5 0.926 0.921 99.5 Copper( 11) 0.124 0.126 100.8 1 :2 Zinc( 11) 0.621 0.618 99.5 1 :2 Cadmium( 11) 0.449 0.447 99.4 1:2 Lead( 11) 0.697 0.702 100.7 1 : 2 Iron(i1) 0.722 0.720 99.7 1 :2 Iron(IIi)* 0.724 0.721 99.6 1:1 * 1 X rnol dm-3 FelI1 solution titrated with 1 x 10-1 mol dm-3 ligand solution in an ethanol-water (2 + 1) mixture.Table 2 Linear regression analysis of copper( u) Mass of copper(il)/g Taken Found 0.124 0.126 0.290 0.292 0.416 0.418 0.832 0.836 1.040 1.046 Shift Regression or intercept coefficient or of the or slope of Recovery regression regression (%) line line 100.8 100.6 0.0335 1 .OO46 100.5 100.5 100.5 assumption. Furthermore, when 1 x 10-2 rnol dm-3 of HCI in the ethanol-water (2+ 1) mixture was titrated with 1 x 10-2 rnol dm-3 of ligand solution a continuous decrease in the conductivity was observed, again, confirming the above assumption.Similar titration curves were observed for the titration of N P , Zn", Pb", Pd" and All11 with the ligand in the ethanol water (2 + 1) mixture. The observed maximum in the conductivity corresponds with a metal to ligand mole ratio of 1 : 2 in each instance. Interesting behaviour is observed for the titration of Fell' with the ligand: when 1 X 10-3 rnol dm-3 of iron(rr1) chloride is titrated with 1 X 10-2 rnol dm-3 ligand (L) solution in the ethanol-water (2 + 1) mixture (Fig. 2 line A) the conductivity decreases throughout the titration. Before the end-point, the highly mobile Fe"' ions are replaced by the solvated protons and the FeL2+ ions and the conductivity decreases rapidly.(The Fe"' ion has a greater mobility than the H+ ion in the ethanol-water mixture, this is evident because the molar conductivity of iron(rI1) chloride is greater than that of HCI over the same titrant concentration range. After the end-point the decrease in conductivity is smaller. The change in conductivity in this region is attributed to the replacement of H+ (solvated) by the [H-L]+ ions. Fe3+ + 3C1- + 2L --+ 2H+ (solvated) + 3C1- + (Feb)+ 2H+ (solvated) + 3C1- + FeL2+ -+2[H-L]+ + 3C1- + (FeL2)+ The two rectilinear curves before and after the inflection point meet at the end-point, the mole ratio here corresponds to a 1 : 2 complex for the Felt1 chelates.ANALYST, MAY 1991, VOL. 116 539 The change in the shape of the titration curve is of interest, as the Fell1 ion concentration is increased ten-fold when titrating against 0.1 mol dm-3 ligand solution (Fig.2 line B). The conductivity first increases and then decreases after the end-point. At this relatively high concentration, FeCI3 may initially be ionized incompletely. FeCI3 FeCI2+ + C1- Evidence supporting this dissociation can be found in the literature. 1 0 - 1 1 When the ligand is added in an ethanol-water (2+ 1) mixture, the H+ (solvated) ions replace the FeC12+ ions and the conductivity increases rapidly. FeCI2+ + CI- + L + [FeC12L] + C1- + H+ (solvated) After the end-point the H+ ion (solvated) is replaced by the slower moving [H-L]+ ion, therefore, the conductivity de- creases. The mole ratio for the Fe"' chelate in this instance is found to be 1 : 1 from the curve at the end-point.In such an instance the vacant metal site in the metal chelate might perhaps be filled by a solvent molecule, however, no direct proof for this is available. No such variation in the shape of the titration curve and hence the composition of the metal chelate was found for the Cull system by varying either the metal ion or ligand concentration. The data obtained from the conductimetric titration is summarized in Table 1. The data show that reproducible results are obtained with a good recovery. In order to establish whether the proposed method exhibits any fixed or proportional bias, a simple linear regression" of the metal concentration was calculated (dependent variable) and the corresponding true concentration (independent vari- able) was obtained using a programmable calculator.A Student's t-test (at a 95% confidence level) was applied to the slope and the intercept of the regression line. The data for the Cull system are given in Table 2. Statistical analysis of the data shows that the calculated slope and intercept do not differ significantly from the ideal value of unity and zero, respect- ively. Hence, it can be concluded that there are no systematic differences between the determined and true concentrations over a wide range. Similar calculations were carried out for other metals. Conclusion The proposed method is simple and has several advantages over other methods. A buffer is not necessary, in contrast to the conductimetric titration of metal ions with EDTA in buffered media.7 End-point detection is simple as no back- ground conductivity of the buffer affects the experimental value.13 Trace amounts of metal ions as low as 0.4 mg dm-3 can be determined by this method, even in the presence of interferent salts such as KCI and KN03 which might be present at concentrations in excess of ten-fold over the metal ion being determined.1 2 3 4 5 6 7 8 9 10 11 12 13 References Lopatin, B. A., Conductimetry and Oscillometry , Academy of Sciences of the USSR, 1971, ch. 1, p. 3 . Vydra. F., and Karlik, M., Chem. Listy.. 1957,50, 1749, 1754. Kolthoff, I . M., and Elving, P. J . , Treatise on Analytical Chemistry. Interscience. New York, 1963, Part I. Vol. 4, p. 2618. Foster, J. N.. Hanson, 0. C., Hon, J. F., and Muirhead. T. S., Pasovskaya, G. P., Zh. Anal. Khim., 1957, 12, 523. Hall, J. L., Gibson. J . A , , Jr., Wilkinson. P. R., and Philips. H. O., Anal. Chem.. 1954, 26, 1484. Vogel, A. I . , A Textbook of Quantitative Inorganic Analysis, English Language Book Society, 3rd edn., 1961. ch IV. Lingane, J. J., Electroanalytical Chemistry, Interscience, New York, 2nd ed., 1958, ch. 9, p. 188. Dneprov, G. F . , Uch. Zap. Leningord. Gos. Univ. im. A. A. Zhdanova, Ser Khim. Nuuk, 1953, (13). 56, Chem. Abstr., 1956, 50,5373c. Dawson, L. R . , and Belcher. R. L., Trans. Ky. Acad. Sci., 1951, 13, 129. El Aggan, A. M., Bradley, D. C., and Wardlaw, W.. J . Chem. Soc., 1958, 2092. Miller, J . C.. and Miller, J . N.. Statistics for Analytical Chemistry. Ellis Horwood, Chichester, 1984, ch. 1, p. 90. West, T. S . . Complexometry With EDTA and Related Reagents, 3rd edn, BDH Chemicals. 1969, p. 83. NASA, 1969, CR-1425, 189. Paper 0f03007D Received July 4th, 1990 Accepted November l l t h , 1990

ISSN:0003-2654    

DOI:10.1039/AN9911600537

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST. MAY 1991, VOL. 116 541 Extraction and Determination of Manganese(i1) in Environmental and Pharmaceutical Samples N. M. Sundaramurthi and Vijay M. Shinde" Analytical Laboratory, The lnstitute of Science, 15 Madame Carna Road, Bombay 400 032, India A method is proposed for the extraction of manganese(i1) from salicylate media by using Aliquat 336 dissolved in xylene as an extractant. The optimum conditions were determined from a critical study of pH, salicylate concentration, Aliquat 336 concentration, diluent and period of equilibration (shaking time). The method permits the separation of manganese from binary mixtures containing commonly associated metal ions. Manganese is determined either by spectrophotometry with 4-(2-pyridylazo)resorcinol or by atomic absorption spectrometry.The method is applicable to the extraction and determination of manganese in environmental and pharmaceutical samples. Keywords: Manganese(i1) extraction and separation; salicylate solution; liquid ion exchanger; pharmaceutical and environmental samples A large number of industries discharge metal-containing effluents into air and water resources without adequate treatment. Contamination of the environment by manganese is currently an area of concern. Although manganese is an essential micro-nutrient, it is a respiratory irritant and a systemic poison when inhaled (as oxides) in excessive amounts. Manganese compounds are known to catalyse the oxidation of sulphur dioxide to sulphur trioxide.1 In view of this, the determination of manganese is desirable. The proposed method fulfils this requirement.Few solvent extraction methods are known for manganese. Amines of high relative molecular mass2-6 have been used for the extraction of manganese(i1) from hydrochloric acid and thiocyanate solutions. Extraction of bromo complexes of manganese(1i) with Alamine 3362 and tributyl phosphate7 and of iodo complexes with Alamine 3362 and trioctylamine (TOA)8 have also been reported. Similarly, methyltrioctylam- monium chloride,g tributyl phosphate,'" bis(2-ethylhexyl) hydrogen phosphate ,11 long-chain alkylamines12 and Aliquat 33613 have been used for the solvent extraction of man- ganese(i1). However, existing methods suffer from several drawbacks, such as a longer extraction time,2,7,g temperature c ~ n t r o l , ~ .~ , ~ emulsification problems5.7.13 and incomplete extraction.3.6 Liquid ion exchangers such as Aliquat 336 and TOA have been used in this laboratory for the extraction of titanium(iv), zirconium(1v) and hafnium(rv) from salicylate ~olution.1~ An extension of this work has shown that it is possible to extract managanese from salicylate solution into Aliquat 336 dissolved in xylene. After stripping from the organic phase, manganese is determined by spectropho- tometry with 4-(2-pyridyazo)resorcinol (PAR). The method is simple, rapid and selective and affords separation of man- ganese from associated metal ions such as cobalt(ii), cop- per(ii), mercury(ii), iron(rIi), vanadium(v), chromium(vi) and tungsten(v1) in binary mixtures, and permits the determina- tion of manganese in alloys, pharmaceutical samples and environmental samples.Experimental Apparatus and Reagents Absorbance measurements were carried out on a Unicam SP 500 spectrophotometer with 1 cm silica cells and on a Varian Techtron AA6 atomic absorption spectrometer, and the pH was measured by a Control Dynamics digital pH meter equipped with a combined glass electrode. * To whom correspondence should be addressed. The stock solution of manganese(I1) was prepared by dissolving 1.1 g of MnS04-4H20 in 250 ml of distilled water containing 2 ml of concentrated sulphuric acid. The solution was standardized by titrimetry with ethylenediaminetetra- acetic acid15 and the metal content was found to be 1.068 mg ml-l. The solution was diluted further as required. Aliquat 336 (methyltrioctylammonium chloride) (Fluka, Buchs, Switzerland) was used without further purification. Solutions of Aliquat 336 (3% d v ) in xylene were shaken with an equal amount of 1 mol dm-3 sodium salicylate solution before use.A buffer solution of pH 10.0 was prepared from ammonium chloride (7 g) and concentrated ammonia solution (57 ml in 1 litre of water). 4-(2-Pyridylazo)resorcinol was used as a 0.1% aqueous solution for the determination of manganese. All the other chemicals used were of analytical-reagent grade, unless indicated otherwise. General Extraction Procedure for Manganese(x1) To an aliquot of a solution containing 8 pg of manganese, enough sodium salicylate was added to give a salicylate concentration of 0.05 mol dm-3 in a total volume of 25 ml.The pH of the solution was adjusted to 5.0 by the addition of sodium hydroxide solution and hydrochloric acid or by the addition of 6 ml of acetic acid-sodium acetate buffer solution of pH 5.0, then the mixture was shaken for 10 s in a separating funnel with 5 ml of 3% m/v Aliquat 336 solution. After the two phases had separated, the manganese was stripped from the organic phase with two 4 ml portions of 0.01 mol dm-3 sulphuric acid. The combined aqueous phases were shaken with 5 ml of xylene to remove the dissolved amine and analysed for manganese either by atomic absorption spec- trometry (AAS) or by spectrophotometry after adding 10 ml of buffer solution of pH 10 and 0.5 ml of 0.1% PAR solution.16 Results and Discussion Extraction Conditions The extraction of manganese(I1) was attempted at different pH values (3.2-11 .O), sodium salicylate concentrations (0.0125-0.25 mol dm-3) and Aliquat 336 concentrations (0.125-5%), all with xylene as the diluent.Metal ion recovery was calculated either by spectrophotometry or by AAS. It was found that 5 ml of 3% Aliquat 336 in xylene extracts microgram amounts of manganese (0.1-100 pg) quantitatively from 0.05 mol dm-3 sodium salicylate at pH 4.0-8.0 (Fig. 1).542 Milligram amounts of manganese (1-3 mg) were extracted with 5 ml of 5% Aliquat 336 in xylene from 0.05 mol dm-3 sodium salicylate at pH 4.0-8.0. The optimum extraction conditions are reported in Table 1. Effect of Diluent The effect of various diluents on the extraction of manganese by the proposed method was investigated.Of the solvents examined, such as benzene, toluene, xylene, hexane, chloro- form, carbon tetrachloride and nitrobenzene, the extraction was quantitative with xylene, toluene and hexane; however, xylene was preferred for subsequent work because it afforded clear separation of the two phases. Period of Extraction The extraction was very rapid. The period of shaking was varied from 5 to 60 s. The recoveries of metal ions at 5 , 7 and 9 s were 61.2, 86.2 and 98.2%, respectively. The extraction was quantitative at 10 s. However, it was found that prolonged shaking had no adverse effect on the extraction of the metal ion. Table 1 Optimum extraction conditions for manganese(i1) [Salicylate]/ Extraction [Mn] mol dm-3 [Aliquat 3361 period/s pH 0.1-100 pg 0.04-0.25 5 ml of a 3% 10 4.e8.0 1.0-3 mg 0.044.25 5 ml of a 5% 10 4.0-8.0 m/v solution m/v solution Table 2 Effect of foreign ions on the extraction of 8 pg of manganese( 11) Tolerance limit*/pg 400 320 160 120 80 64 40 24 8 Foreign ion Nitrite, iodide, tartrate, thiocyanate, nitrate Chloride, thiosulphate Phosphate.fluoride Ag', Pt", Ba" Mg", AI"', Ti", Vv, Sb"'. Uv' Cr"', 0sv"', Ce'" Ca",As"*, Mo"', Pd",Te", Wv', Hg", Bi"', thiourea. oxalate, citrate. sulphatc, cyanide Zr", Cd", Hf", Au"' Fell', Th" * The tolerance limit amount is thc average of triplicate analyses. ANALYST, MAY 1991, VOL. 116 Nature of the Extracted Species The log-log plot of distribution ratio versus salicylate concen- tration (at fixed pH and Aliquat 336 concentration) or distribution ratio versus Aliquat 336 concentration (at fixed pH and salicylate concentration) yielded a molar ratio of 1 : 2 with respect to both extractant and salicylate.Hence, the extracted species was thought to be an ion-associate of probable composition [(R4N+)2Mn(OC6H4COO)22-]. The anionic nature of the manganese-salicylate complex was confirmed by its adsorption on a column of Dowex 1-X8 anion-exchange resin. Effect of Foreign Ions Various amounts of foreign ions were added to a solution containing a fixed amount of manganese(ii), and the recom- mended procedure was followed for the extraction and determination of manganese ions. The tolerance limit was set at the amount of foreign ion required to cause a +2% error in the recovery of manganese. The results are reported in Table 2.Cobalt(Ii), nickel(I1) and copper(i1) (80 yg of each) were eliminated by prior washing with 1 mol dm-3 ammonia solution. Interference from zinc(ri) and lead(r1) was elimi- nated by selective masking with thiocyanate and thiosulphate, respectively. Separation and Determination of Manganese(i1) in Binary Mixtures Separation of manganese(I1) from binary mixtures containing titanium(iv), iron(ri1) and aluminium(m) was possible by selective stripping. Manganese was stripped into 0.01 mol dm-3 nitric acid. whereas titanium, iron and 100 h 8 2 80 E v -0 0 &. 60 5 E a *O c ," 40 c 3 4 6 8 10 12 Extraction of manganese as a function of pH. Mn" = 8 pg; PH Fig. 1 [sodium salicylate] = 0.05 rnol dm-3; and [Aliquat 3361 = 3% m/v Table 3 Separation of manganese(i1) from binary mixtures Manganese Added ion Composition of Mn(8)-Ni(25) Mn(8)-Cr( 16) Mn( 8)-Fe (8) Mn(8)-Hg(24) Mn(8)-Co( 16) Mn(8)-Cu(8) Mn(8)-Ti( 100) Mn( 8)-V( 100) Mn( 8)-Al(8) Mn(8)-W( 50) Mn( 8)-B i( 80) synthetic mixture" rec Amount :overedt/pg 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 8.0 Standard Relative Amount dcviation/pg standard deviation (YO) rccovcrcdl/pg 0.087 1.09 24.8 0.055 0.69 16.0 0.064 0.79 8.0 0.089 1.12 23.9 0.055 0.69 15.9 0.034 0.43 8.0 0.040 0.50 99.6 0.045 0.56 99.8 0.071 0.89 8.0 0.065 0.82 49.6 0.089 1.12 79.5 Standard Relative 0.109 0.44 0.141 0.88 0.109 1.37 0.155 0.65 0.167 1.05 0.087 1.09 0.179 0.18 0.224 0.22 0.130 1.58 0.155 0.31 0.178 0.22 deviatiodpg standard deviation (%) * Values in parentheses are the amounts of each metal ion in micrograms.t Mean of six determinations.ANALYST, MAY 1991, VOL. 116 543 Table 4 Determination of manganese in alloys and pharmaceutical samples Recovery of Mn by Certified proposed Sample value method* A 1 1 0 ~ ~ - High manganese steel (BCS-CRM 494)t 13.55 Yo 13.45% 13% Mnsteel (SS290/2)$ 12.5% 12.4% Monel alloy 400 (BCS-CRM 363) 1.03% 1 .02 Yo Pharmaceutical samples- Supradyn tablet Theragran-M tablet (Roche, India) 500 488 Pg (Sarabhai. India) 689 705 pg * Average of six determinations. I' BCS-CRM = British Chemical Standard, Certified Reference Material. 3 SS = Primary spectroscopic standard. Relative Standard standard deviation deviation (Yo) 0.022% 0.17 0.109% 0.88 0.014% 1.35 0.547 pg 0.11 0.894 pg 0.13 Table 5 Determination of manganese in environmental samples Recovery of Mn Amount of Mn by proposed found by Sample method" AASi Airborne particulate samples- Tilak Nagar 0.33 pg m-3 0.33 pg m-3 Khar 1 0.25 pg mp3 0.25 pg m-3 Khar I1 0.23 pg m-3 0.23 pg m-3 Parel 0.28 pg m-3 0.28 pg m-3 Water samples (Patalganga river water, Maharashtra)- Khopoli bridge 248 pg dm--? 250 pg dm-3 Rasayani 140 pg dm-' 142 pg dm-3 * Average of six determinations; manganese determined by spec- -t Manganese determined by atomic absorption spectrometry prior trophotometry after extraction.to extraction. aluminium were stripped with 2 rnol dm-3 sulphuric acid, 1 mol dm-3 hydrochloric acid and 2 mol dm-3 hydrochloric acid, respectively. Titanium, iron and aluminium were sub- sequently determined by spectrophotometry with hydrogen peroxide, 1' 1 , 10-phenanthroline'7 and Xylenol Orange, 18 respectively.Mercury(I1) and bismuth(ii1) exhibited co-extrac- tion and were separated after first stripping manganese into 0.01 rnol dm-3 nitric acid and then stripping mercury and bismuth into 1 mol dm-3 sulphuric acid. The stripped ions were determined by spectrophotometry with diphenylcarb- azide'g and Xylenol Orange,I7 respectively. Nickel(ii), cobalt(1i) and copper(ii) also co-extracted with manganese(I1). They were, however, stripped into 1 mol dm-3 ammonia solution and determined by spectrophotometryl7.2() before manganese was stripped and determined as described under General Extraction Procedure for Manganese(i1). The extraction of manganese with the recommended procedure facilitated its separation from chromium(vi), vanadium(v) and tungsten(v1) in binary mixtures as they were not extracted and remained completely in the aqueous phase.The aqueous solution containing chromium, vanadium and tungsten was evaporated to dryness, and the residue treated with perchloric acid to decompose salicylate and finally taken up in water. Chromium, vanadium and tungsten were then determined by spectrophotometry.17 The results of the separation are reported in Table 3. The recoveries of added ions were 299.2%. Application to the Analysis of Alloys, Pharmaceutical and Environmental Samples The proposed method was applied to the separation and determination of manganese in various alloys, namely, high manganese steel, 13% manganese steel and monel alloy 400. A 0.1 g amount of each of the alloys was dissolved in 4 ml of Concentrated nitric acid, and the solution diluted to 50 ml with water.An aliquot of the solution (0.5 ml of Mn steel and 1 ml of monel alloy solutions) was analysed for manganese by the proposed method. The results are in good agreement with the certificate values (Table 4). Two different multi-vitamin tablet preparations, namely Supradyn and Theragran-M, were also analysed by the proposed method. The tablets (one of each) were dissolved in 10 ml of 70% perchloric acid, the solution was evaporated to dryness, digested with 5 ml of 0.1 rnol dm-3 HCI, then filtered and the filtrate made up to volume (10 ml). An aliquot (1 ml) of the solution was used for analysis. The results are reported in Table 4. Water samples were collected from the Patalganga river (Maharashtra), sampled at Khopoli bridge and Rasayani, as there are many industries around these areas.Each sample (1 1) was concentrated and adjusted to 25 ml, and an aliquot (2 ml) of this solution was extracted by the proposed method. The results of the analysis are presented in Table 5 . Filter-paper strips containing adsorbed manganese particu- lates from polluted air samples were collected from different suburban areas of Bombay such as Tilak Nagar, Khar and Parel and were supplied by the Air Pollution Monitoring Research Laboratory, Municipal Corporation of Greater Bombay, Khar. The samples were analysed by the proposed method by digesting filter-paper strips (area, 8 cmz) with 15 ml of 25% nitric acid for about 15 min.After filtration, the entire solutions were used for the extraction and determination of manganese as described under General Extraction Procedure for Manganese(1i). The results obtained by the proposed method were confirmed by AAS prior to extraction and were found to be in good agreement (Table 5 ) . The detection limit for manganese was 0.1-100 pg in 25 ml. The authors thank the University Grants Commission, New Delhi, for financing the project and awarding a fellowship to one of them (N.M.S.). References Toxic Metals-Pollution Control and Worker Protection, ed. Marshall, S., Noyes Data Corporation, NJ, 1976, pp. 184-189. Florence. T. M.. and Farrar, Y . J., Aust. J . Chem., 1969. 22, 473. McClellen. B. E . , and Benson. V. M., Anal. Cliem., 1964, 36, 1985.Prabil. R., and Adam. J . . Talanta. 1973, 20. 49. Classen, V. P., de Jong, G. J . , and Brinkman, U. A. Th., Freaenius Z . Anal. Chem.. 1977, 287, 138.544 ANALYST, MAY 1991, VOL. 116 6 7 8 9 10 11 12 13 14 Sato, T., J. Chem. Tech. Biotechnol., 1979, 29, 39. Morris, D. F. C., Short, E. L., and Slater, D. N., J. Inorg. Nucl. Chem., 1964,26, 627. Imata, R., Niigata-ken Kogai Kenkyusho Kenkyu Hokoku, 1980,5,69. March, J. G., Microchem. J., 1985,32, 338. Agget, J., Evans, D. J., and Hancock, R., J. Inorg. Nucl. Chem. , 1968,38,2529. Islam, F., and Biswas, R. K., J. Bangladesh Acad. Sci., 1981,5, 61. de Jong, G. J., Kok, W. T., and Brinkman, U. A. Th., J. Chromatogr., 1977, 135, 249. Gogia, S. K., Singh, 0. V., and Tandon, S. N., Indian J. Chem. Sect. A , 1983, 22, 965. Sundaramurthi, N. M., and Shinde, V. M., Analyst, 1989,114, 201. 15 16 17 Vogel, A. I., A Textbook of Quantitative Inorganic Analysis, Longman, London, 3rd edn., 1962, p. 453. Photometric and Fluorometric Methods of Analysis, ed. Snell, F. D., Wiley, New York, 1978, p. 1028. Marczenko, Z., Spectrophotometric Determination of Elements, ser. ed. Chalmers, R. A., Ellis Honvood, Chichester, 1976, pp. 154, 215, 227, 309, 556, 569 and 592. 18 Pritchard, D. T., Analyst, 1967, 92, 103. 19 Balt, S., and van Dalen, E., Anal. Chim. Acta, 1962, 27, 416. 20 Pease, B. F., and Williams, M. B., Anal. Chem., 1959,31,1044. Paper 0/04129G Received September loth, 1990 Accepted January 3rd, I991

ISSN:0003-2654    

DOI:10.1039/AN9911600541

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST, MAY 1991, VOL. 116 545 BOOK REVIEWS Journal of Chromatography: Volume 500 Edited by R. W. Giese, J. K. Haken, K. Macek, L. R. Snyder and E. Heftmann. Pp. i x + 707. Elsevier, Amsterdam, 1990. Price Dfl 220.00. ISSN 0021 9673. Among the first major scientific journals were those founded by the national chemical societies, J. Chem. SOC., J. Am. Chem. SOC., Berichte, and many others. Smaller groups with more specialist interest generated more closely defined journals, The Analyst, Faraduy Trans., Fresenius J. Anal. Chem., etc. Then in the 1950s and 60s with the post-war resurgence of the chemical industry with the developments in synthetic polymers, pharmaceutical and consumer items, came a sudden flurry of new titles, often from commercial publishers. Some addressed broad areas, such as Tetrahedron and Tetrahedron Lett.Others were more directed and of these J. Chromatogr. must have been one of the most successful. Founded 32 years ago, in 1958, in response to the developments of what was then only a fledgling technique, the Journal of Chromatography has grown in scope and impor- tance and has now reached Volume 500, with new volumes being added at the rate of 37 per year, reflecting the enormous growth and continual importance of separation methods in chemistry over these years. This hard-bound commemorative volume remembers these early days and the development of chromatography with a collection of photographs collected by Michael Lederer, the Editor of the Journal for many years. These range from scenes of the early editorial office set in the snow of the Swiss alps, the founders and many of the pioneers of chromatography, and ends with the younger generation of the Frei family. Many were taken during the social functions at chromatography symposia around the world and depict the conviviality and friends hips within the chromatographic community .The 500th Volume also contains over 30 original papers with the common feature that each includes as an author a member of the editorial board. The topics as always reflect the wide scope of the journal from SFC, TLC, HPLC and GLC to CZE and with a coverage from the basic understanding of the techniques to their applications. Roger M . Smith Field Desorption Mass Spectrometry Laszlo Prokai. Practical Spectroscopy Series: Volume 9. Pp.vi + 291. Marcel Dekker. 1990. Price $99.75 (USA and Canada); $1 19.50 (Export). ISBN 0824783034. Field desorption mass spectrometry (FDMS) became at least partially eclipsed by fast atom bombardment mass spec- trometry (FAB-MS) and related techniques following their introduction in the early 1980s, but has enjoyed renewed interest in some areas more recently. This book, Volume 9 in the Practical Spectroscopy Series, therefore provides both an excellent introduction to the technique and, for those who used FD in pre-FAB days, a timely reminder of the advantages. The book is divided into four readable chapters: Principles; Experimental Techniques and Methods; General Practice; and Applications. Each chapter contains a com- prehensive set of literature references.Chapter 1 summarizes the current state of knowledge concerning the processes involved in producing ions by both field ionization (the forerunner of FD) and by FD. The treatment is extensive and perhaps more mathematical than some readers would prefer, but by the end of the chapter one is left in no doubt as to the complexity of the processes operating during the FD experiment. Having thus grasped (hopefully) a better understanding of these processes, the practitioner may well feel able to obtain better experimental results. Probably the most important factor in the successful application of FDMS is the preparation of suitable activated emitters; the author accordingly spends some time in Chapter 2 explaining the most widely used high temperature activation process (using benzonitrile) and then goes on to consider the various alternative methods available.The preparation of emitters from different materials, e.g., silicon emitters and various metal dendrites, is also considered and their advan- tages and disadvantages are discussed. Chapter 2 continues with an examination of sample supply techniques and means of controlling the emitter heating current, both important for the production of good quality spectra and concludes with several aspects of instrument design. In ‘General Practice’ (Chapter 3) the author discusses the operational details such as sample interactions, the use of additives and derivatization which can all be of considerable assistance in the quest for high-quality spectra. Although FD is more widely known for its ability to provide relative molecular mass information on otherwise intractable mol- ecules, many examples have appeared in the literature where structural information has been derived; this aspect is also discussed and, in common with most areas of this book, illustrated with examples taken from the literature.A comparison of FD with the other common ionization tech- niques helps to put the technique into perspective, and concludes the chapter. A comprehensive review of all the applications work to date would probably fill an entire volume of this size, so it comes as no surprise that the author has been selective in his approach. He refers the reader to the annual Analytical Chemistry reviews and the Royal Society of Chemistry Specialist Periodical Reports for more comprehensive coverage of recent applications.Four main areas of application have been selected for attention, viz., biochemical, medical and phar- maceutical applications; environmental analysis; the charac- terization of fossil fuels and petrochemicals; and the analysis of inorganic and organometallic compounds. These are dealt with in such a way as to give the reader a clear insight into the type of work recently undertaken in each area, with numerous well-chosen examples from the literature. This reviewer felt that this book provided excellent com- prehensive coverage of a much underrated technique. It would prove a valuable addition to the library of any mass spectroscopist involved with, or contemplating involvement with, FDMS. D. Cutlow Steroici Analysis in the Pharmaceutical Industry: Hor- monal Steroids, Sterols, Vitamin D, Cardiac Glycosides Edited by S. Gorog.€//is Horwood Series in Analytical Chemistry. Pp. x + 398. Ellis Horwood. 1990. Price f69.50. ISBN 0 7458 0099 8 (Ellis Horwood); 0 470 21 178 4 (Hal- sted Press). The primary production of bulk steroids together with secondary formulation has been in operation for the past 40 years, but as Professor Gorog rightly observes the majority of publications on steroid analysis originate from medical or academic sources. Clearly there is an element of technical security included in some industrial processes, with perhaps less need for industrial analysts to publish their work, so that this book is a novel enterprise. The book consists of an introductory chapter which reviews the complicated procedures leading to the production of a new synthetic steroid drug.The second chapter, on the methods546 ANALYST, MAY 1991, VOL. 116 used in steroid analysis, correctly occupies almost half of the book, and begins with spectroscopy. The majority of this section is directed to the newer techniques of NMR and mass spectrometry, because the value of ultraviolet spectrometry has declined since the advent of HPLC, although as the author claims, it can still play a part in structural characterization. Infrared spectrometry is noted for the key role played in the early development of steroid synthesis, at least one company favouring Nujol mulls rather than potassium bromide discs suggested by the author as universally used.Chromatography is the most important technique for industrial steroid analysis, owing to the excellent separations possible with these stable compounds, but is discussed in less detail because it has featured more widely in other steroid publications. Thin-layer chromatography had a revolutionary impact, compared with paper chromatography which only rates a passing mention. It remains the favoured technique for control of impurities. Gas chromatography is discussed briefly but was overshadowed by the introduction of high-perfor- mance liquid chromatography, the specific steroid assay procedure. The more limited applications of protein binding and electroanalytical methods, particularly during research and development of a new synthetic steroid, are also mentioned.The third chapter is concerned with the structural elucida- tion of steroids, and begins by stressing that there is normally no limit to the amount of material available, a luxury not always appreciated within the industry. Structure determina- tions can range from the limited applications of ultraviolet spectrometry for steroids with double bonds (using the Fieser-Woodward rules) to complex X-ray diffractometry , and are illustrated by examples from the author’s laboratory. The importance is stressed of identifying by-products and establishing impurity profiles in order to satisfy regulatory authorities. The fourth chapter is fundamental to the aim of the book and is given prominent space as it concerns analytical control during steroid production. The starting material is of crucial importance and the author puts the emphasis on diosgenin, although hecogenin is also successfully used. In-process control and bulk steroid purity assays are discussed. Chapter 5 deals with the analytical aspects of the studies both before and after formulation. There are useful tables on formulations although the steroids could have been grouped more logically. Stability testing of formulated (secondary) products is reviewed but stability testing at the primary, bulk-drug stage is hardly mentioned although it is very important when production first begins. The final chapter on steroids in biological media includes a useful reminder that the health control of production staff is also important. The over-all impression is of a worthwhile addition to the literature on steroids. P. J. Stevens

ISSN:0003-2654    

DOI:10.1039/AN9911600545

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

ANALYST, MAY 1991, VOL. 116 547 CUMULATIVE AUTHOR INDEX JAN UARY-MAY 199 1 Abbas, Nurcddin M.. 409 Akiyama. Hideaki, 501 AI-Tamrah. S. A . , 183 Alarie. Jean Pierre, 117 Alcgret, Salvador, 473 Alexiades, Costas A., 361 Alfassi, Zeev B., 35 Altesor, Carmen, 69 Alvi, S. N., 405 Alwarthan, A. A., 183 Analytical Methods Committee, Anderson. Fiona. 165 AntonijeviC, Biljana, 477 Apak, Regat. 89 Apostolakis, John C.. 233 Askal, Hasan F.. 387 Asselt, Kees van. 77 Attiyat, Abdulrahman S . , 353 Baba, Jun-ichi, 45 Balasubramanian, N., 207 Barnes. Ramon M., 489 Baykut, Fikret. 89 Beh, S. K., 459 Berlot. Pedro E., 313 BiCaniC, Dane, 77 Birch, Brian J., 123 Bisagni, E., 159 Blais, J., 159 Bond, A. M.. 257 Bowyer, James R., 117 Bratinova. Stefanka P.. 525 Brown. Richard H . . 437 Bunaciu. Andrei A ., 239 Cacho. Juan, 399 Candillier, Marie-Paule, 505 Cardwell. Terence J.. 253 Cattrall, Robert W., 253 Cepeda, A., 159 Chan, Wing Hong. 39. 245 Chang, Wen-Bao, 213 Chen. Danhua. 171 Chcn, Guo Nan, 253 Chen, Zcweng, 273 Cheung, Yu Man, 39 Ci, Yun-Xiang, 213, 297 Ciesiclski, Witold, 85 Cohcn, Arnold L.. 15 Cogofref, Vasile V.. 239 Costa-Bauza, A.. 59 Covington, Arthur K., 135 Cowan, Faye J.. 339 Crcsser. Malcolm. 141 Das. Pradip K.. 321 Dawson, Bernard S. W., 339 de Faria, Lourival C.. 357 de la Torrc, M.. 81 de Oliveira Neto. Graciliano. Deb, Manas Kanti. 323 Dcbayle, Pascal, 409 Dcsai, M., 463 DeVasto. Joseph K.. 443 Dol. Isabel, 69 Dona, Anne-Marie, 533 Donnclly, Garret, 165 Efstathiou, Constantinos E., Elagin, Anatoly. 145 Ellis, Andrew T., 333 Erta5, F.Nil. 369 Esmadi. Fatima T., 353 Evans, Otis, 15 Favier, Frederic, 479 Favie r. Jan - Pa u I, 77 Feher, Zsofia, 483 Feng, Y. P., 469 Fernandez-Band. Beatriz. 305 415, 421 357 373 Fernandez-Gamez, F., 81 Fernandez MuCfio, Miguel A., Fernandez-Romcro. J . M., 167 Ferris, Marie M., 379 Fleming, Paddy, 195 Florido, Antonio, 473 Fogg, Arnold G . , 249, 369 Fouques, Dominique, 529 Gaind, Virindar S . , 21 Garcia Mateo, J . V., 327 Georgiou. Constantinos A., 233 Gielen. Johanncs W. J., 437 Glab, Stanislaw. 453 Goodlet. G., 469 Gordon. Rhea L . , 511 Grases. F., 59 Grayeski. Mary Lynn, 443 Griepink, Bernardus, 437 Guitart, Ana, 399 Gupta, V. K.. 391 Gushikem, Yoshitaka. 281 Hamilton, Ian C., 253 Harper, Alexander, 149 Harris. N. K., 469 Hart, John P., 123 Haswell, Stephen J ., 333 Hawke, David T., 333 Hendrix, James L., 49 Hcrnandez Cordoba, Manuel, Hcrnandez Orte. Puri. 399 Himberg, Kimmo, 265 Hocquellet, Pierre, 505 Hofstetter, Alfons. 65 Hollander, Jacobus C. Th., 437 Hong, Jian, 213 Hong, Sung 0.. 339 Hulanicki, Adam, 453 Husain, Sajid, 405 Ioannou, Pinelopi C., 373 lonescu, Mariana S . , 239 Ishida. Junichi, 301 Ishida, Ryoei, 199 Islam, M. M., 469 Israel, Y echeskel, 489 Ivanova, Christina R., 525 Jacobs, Betty J . , 15 Jana, Nikhil R., 321 JCdrzejewski. Wlodzimierz. 85 Jerrow, Mohammad. 141 Jiang, Jian. 395 Jic. Niaqin, 395 Jones. Michael H., 449 Kakizaki. Teiji, 31 Kataky, Ritu, 135 Keating, Paula. 165 Keramidas, Vissarion Z . , 361 Kharoaf. Maher A , , 353 Kielbasinski, Piotr, 85 Knochen, Moises, 69 Kolbe, Ilona, 483 Koncki, Robcrt, 453 Konishi, Tctsuro, 261 Konstantianos, Dimitrios G., Koupparis, Michael A., 233 Kubota.Lauro T., 281 Kudzin, Zbigniew H . , 85 Kumar, B. S. M.. 207 Lan, Chi-Ren. 35 Landry, Jacques. 529 Langelaan, Fred G. G. M., 437 Lazaro, F.. 81 Lee, Albcrt Wai Ming, 39, 245 Leonard, Michael A., 379 Li. Jie, 309 Lin, Chang-shan. 277 269 517 373 Linares, Pilar. 305 Liu, Dao-Jie, 497 Liu, Ren-Min, 497 Liu, Shaopu, 95 Liu, Weiping, 273 Liu, Xue-zhu, 277 Liu, Zhao-Lan, 213 Liu, Zhongfan, 95 Locascio, Guillermo A., 313 Lopez Garcia. Ignacio, 5 17 Lu, Qiongyan, 273 Lubbers, Marcel, 77 Lucas, S., 463 Luque de Castro. M. D., 81, Lyons, David J . . 153 McCallum, Leith E., 153 McDonnell, M. B., 463 Mahuzier, G . , 159 March, J. G.. 59 Marr, lain, 141 Marsel, Joie.317 Martinez Calatayud, J.. 327 Masuda, Toshihiko, 501 MatoviC, Vesna, 477 Matthies, Dietmar, 65 Mattusch, Juergen, 53 Menjyo, T., 257 Metcalf, Richard C., 221 Mikoiajczyk, Marian, 85 Miller. James N.. 3 MilosavljcviC, Emil B., 49 Mishra, Neera, 323 Mishra, Rajendra Kumar, 323 Mitrakas, Manassis G., 361 Moody, G . J.. 459, 469 Morcira, Jose C.. 281 Morcira, Josino C. ~ 249, 369 Morimoto, Kazuhiro, 27 Mueller, Helmut, 53 Mukhtar, Sarfraz, 333 Mufioz dc la Pefia. Arsenio, 291 Nagaosa, Y., 257 Nageswara Rao, R., 405 Nakagawa, Genkichi, 45 Nakamura, Masaru, 301 NedeljkoviC. Mirjana, 477 Nelson, John H . , 49 Nicholas, C. V., 463 Nicholson, Patrick E., 135 Nicuwenhuize, Joop, 347 Niinivaara. Kauko. 265 NikoliC, Sneiana D., 49 Nobbs, Peter E., 153 Nukatsuka. Ishoshi, 199 O’Dea.John, 195 Ohzeki, Kunio, 199 Ojanpera, Ilkka, 265 O’Kennedy, Richard. 165 Omar, Nabil M.. 387 Ortiz Sobejano. Francisca, 517 Osborne, William J . , 153 Pal, Tarasankar, 321 Pidivan, Cornelia, 239 Pambid, Ernesto R., 409 Parker, David, 135 Parker, Glenda F., 339 Pascal, Jean Louis, 479 Pasquini. Celio, 357 Patel, Khageshwar Singh, 323 Peck. David V., 221 Pharr, Daniel Y., 511 Pickral, Elizabeth A.. 511 Pinto, Ivan, 285 Poley-Vos, Carla H., 347 Popova, Sijka A.. 525 Prognon, P., 159 Prownpuntu, Anuchit, 191 167, 171, 305 Pungor, Erno, 483 Rios, Angel, 171 Roianska, Barbara, 521 Ruan, Chuanmin, 99 Sakai. Tadao, 187 Sakurada, Osamu, 31 Saleh, Gamal A., 387 Salinas, Francisco, 291 Sargi, L., 159 Sarkar, Mitali, 537 Saunders, Kevin J., 437 Scollary, Geoffrey R., 253 Selnau, Henry E ., 511 Sepaniak, Michael J . , 117 Sherigara, B. S., 285 Shi, Yingyo, 273 Shijo, Yoshio. 27 Shinde, Vijay M., 541 Shivhare, Priti, 391 Si, Zhi-Kun, 309 Simal Lozano, Jesus ,269 Simonovska, Breda. 317 Singh, Raj P., 409 Soledad Duran, Maria, 291 Stoyanoff, Robert E., 21 Strauss. Eugen, 77 Suetomi, Katsutoshi, 261 Sugawara, Kazuharu, 131 Sultan, Salah M., 177, 183 Sundaramurthi, N. M., 541 Taga, Mitsuhiko, 31, 131 Takahashi, Hitoshi. 261 Takeda. Kikuo, 501 Tanaka, Shunitz, 31, 131 Tatehana. Miyoko. 199 Thomas, J. D. R., 459,469 Thompson, Robert Q., 117 Tikhomirov, Sergei, 145 Titapiwatanakun, Umaporn, Tong, Po Lin. 245 Troll, Georg, 65 Tsang, Kwok Yin, 245 Tseng, Chia-Liang, 35 Tiitem, Esma, 89 Udupa, H. V. K., 285 Uehara, Nobuo, 27 Vadgama, P . , 463 Valchrcel. Miguel, 81, 171, 305 van Delft, Wouter, 347 van den Akker. Adrianus H . , Vandendriessche, Stefaan, 437 Vazquez, M. L.. 159 Verchere, Jcan-Franqois, 533 Vo-Dinh, Tuan, 117 Volynsky, Anatoly, 145 Vuori, Erkki, 26.5 Wada, Hiroko, 45 Wang. Fang. 297 Waris, Matti, 265 Werner, Gerhard, 53 Wilson. B. William, 449 Wring, Stephen A . , 123 Wu, Weh S . , 21 Xu, Qiheng, 99 Yamaguchi, Masatoshi. 301 Yamaguchi, Tokio. 501 Yang. Mo-Hsiung. 35 Yuchi. Akio. 45 Zhang, Xiao-song, 277 Zhu. Gui-Yun. 309 191 347

ISSN:0003-2654    

DOI:10.1039/AN9911600547

出版商:RSC    

年代:1991

数据来源: RSC