摘要：
August, 1982 SHORT PAPERS 957 Spectrophotometric Determination of Magnesium with Beryllon II Zhu Ying-quan and Zhang Lin P.O. Box 82, Chengdu, China and Li Jun-yi Department of Chemistry, Huazhong Normal College, Wuhan, China Keywords : Magnesium determination ; beryllon IT ; spec f r o photometry ; aluminium alloys Beryllon I1 [3-(8-hydroxy-3,6-disulpho-l-naphthylazo)chromotropic acid] is produced by condensation of diazotised H-acid (l-aminonaphth-8-ol-3,6-disulphonic acid) with chromo- tropic acid.l It has been applied as a spectrophotometric reagent for b e r y l l i ~ m , ~ - ~ but has not previously been used to determine magnesium spectrophotometrically. This paper describes conditions for colour development, the composition of the complex and the influence of other ions.I t is satisfactory for the determination of magnesium in aluminium alloys. The proposed method is simple and the reproducibility is good. Experimental Apparatus Instruments Factory). with a glass electrode and a saturated calomel (S.C.E.) reference electrode were used. Visible spectra were recorded with a Model 72 spectrophotometer (Shanghai Analytical A Model pHS-73 pH meter (Tianjin Analytical Instruments Factory) Reagents All solutions were prepared in doubly distilled water. were used. Magnesium solution. hydrochloric acid (1 + 1). standard solution. Beryllon I I solution, 0.1%. Factory) in 100 ml of water. Analytical-reagent grade chemicals Dissolve 0.1000 g of high-purity magnesium metal in 10 ml of Protect it from sunlight and dilute to 20 pg ml-l as a working Dissolve 0.1000 g of beryllon I1 (Shanghai Chemical Reagents958 SHORT PAPERS Analyst, Vol.I07 Recommended Procedure Place an aliquot containing not more than 60 pg of magnesium in a 50-ml calibrated flask. Add 6.0 ml of concentrated ammonia solution (25-28y0) and 5.0 ml of beryllon I1 solution, dilute to the mark with water and mix well. Measure the absorbance at 640 nm in a 1-cm cell against a reagent blank. Determination of Magnesium in Aluminium Alloys Transfer 0.2000g of sample into a 100-ml beaker, cover the beaker and add 10ml of hydrochloric acid (1 + 1) and 2-3 ml of hydrogen peroxide (30%). Heat until the sample has dissolved. Cool, add 40 ml of water and heat to dissolve the salts. Transfer the solution into a 200-ml calibrated flask, dilute to volume with water and mix well.Filter the solution into a 200-ml beaker. Pipette 5ml of the filtrate into a 50-ml calibrated flask, add, with swirling, 5 ml of triethanolamine (TEA) (3 + 2) and then apply the recommended procedure. Remove the cover and carefully evaporate the solution to 1-2 ml. Results and Discussion Absorption Spectra The absorption spectra of beryllon I1 and its complex with magnesium are given in Fig. 1. The wavelength of maximum absorption of the complex was at 640nm and that of the reagent blank at 580 nm (Fig. 1, A). Therefore, 640 nm was adopted as the wavelength to be used throughout this work. 0.3 - W c m 0 + 0.2 - 2 0.1 - A I 1 , I 0 540 580 620 660 700 740 Wavelengthinm Fig. 1. Absorption spectra of A, reagent blank against Mag- water and B, magnesium - Beryllon I1 complex.nesium taken, 40 pg; 1-cm cell. Effect of pH In 50 ml of solution, 2-8 ml of concentrated ammonia solution (25-28y0) (corresponding to pH 11.6-1 1.9) gave maximum and constant absorbance with 40 pg of magnesium, so 6 ml of concentrated ammonia solution (pH 11.8) were added in subsequent determinations. The effect of pH on the absorbance of the complex was investigated. Effect of Reagent Concentration beryllon I1 reagent up to 4 ml and then remains reasonably constant up to 6 ml. 5 ml of beryllon I1 solution were used in subsequent determinations. The results in Fig. 2 show that the absorbance increases with increasing amounts of Hence, Rate of Colour Development up to 10 h after maximum intensity had been reached.Measurement of a solution after various time intervals showed no change in absorbanceAugust, 1982 SHORT PAPERS 959 0.5 ' Q, 0 C 0.3 ' 0, n Q 0 1 2 3 4 5 6 7 Rim I Fig. 2. Effect of Beryllon I1 con- centration ( R ) . Magnesium taken, 40 pg; l-cm cell. Stoicheiometry of the Complex and the molar ratio method.' The stoicheiometry of the complex was determined by the continuous variation method6 Both methods indicate the formation of a 1 : 2 complex. Calculation of the Complex Instability Constant et aZ.,*t9 and was found to be 7.1 x The complex instability constant was calculated according to the procedure of Bent Effect of Foreign Ions The following ions do not interfere when present in the amounts shown in parentheses: Li+, Na+ and K+ (20 mg), Cu2+ (0.2 mg), Ni2+ (0.8 mg), Cr3+ (0.12 mg), Cr6+ (0.8 mg), Mo6+ (0.16 mg), Co2+ (0.08 mg), Pb2+ (0.36 mg) and Zn2+ (0.18 mg).Fe3+ (20 mg) and AP+ (5 mg) can be masked by the addition of TEA and Sr2+ and Ba2+ (8 mg) by the addition of EGTA. Be2+ cannot be tolerated at any level. The effect of foreign ions on the determination of 40 pg of magnesium was examined. Calibration Graph and Sensitivity 0-60 pg of magnesium in 50 ml of solution at 640 nm. (E) was 1.03 x lo4 1 mol-l cm-l. A calibration graph was constructed in the usual way and Beer's law was obeyed for The molar absorptivity coefficient Samples Analysed The results shown in Table I are in reasonable agreement with those obtained by atomic- absorption spectrophotometry. TABLE I DETERMINATION OF MAGNESIUM IN ALUMINIUM ALLOYS The method can be applied to the determination of magnesium in aluminium alloys.Mgfound, % r A \ Sample Atomic-absorption No. Proposed method spectrophotometry Nominal composition, yo 1 0.05 0.048 0.6 Fe, 0.5 Mn, 0.3 Zn, 0.8 Cu, 11.5 Si, 0.049 Mg* 2 0.10 0.099 0.7 Fe, 0.3 Mn, 0.3 Zn, 5.0 Si, 2.0 Cu, 0.10 Mg* 3 0.30 0.31 0.6 Fe, 0.3 Zn, 0.01 Sn, 4.0 Si, 2.0 Cu, 0.5Mn, 0.32 4 0.40 0.41 0.5 Fe, 0.5 Mn, 0.3 Zn, 0.01 Sn, 1.0 Cu, 0.40 Mg* 5 0.50 Mg* 0.495 0.5 Fe, 0.5 Mn, 0.5 Zn, 0.3 Ni, 6.0 Si, 0.1 Cu, 0.52 * Certified value. Mg* Comparison with Other Methods Table 11. is no need for extraction and the complex formed is stable for a long period. The results obtained by using different spectrophotometric reagents are compared in The proposed method is simple and rapid and works over a wide pH range. There960 SHORT PAPERS Analyst, Vol.107 TABLE I1 Reagent Titan Yellow Quinolin-8-01 Xylidyl Blue I Eriochrome Black T Metalphthalein Beryllon I1 COMPARISON OF REAGENTS FOR THE SPECTROPHOTOMETRIC DETERMINATION OF MAGNESIUM Colour 4 Interfering ions stability Reference A/ nm 1 mol-1 cm-l pH range . . 535 1.4 x 103 >12 Al, Ca, Cd, Co, NH,+, 10-30 min 10 . . 405 2.7 x lo3 10.0-10.2 Many metals Stable 11 Ni, Sn, Zn, PO,3- .. 510 3 x 104 8.95 Fe, Cu, A1, Ca, Sr 30 min 12, 13 . . 525 1.8 x lo4 9.6 Analytical group 1-111 Stable 14 metals, PO,+ . . 570 1.8 x lo4 10.2 Al, Cr, Fe, Pb, Ca, Ba, 5 min 15 Mn, Sr . . 640 1.03 x lo4 11.6-11.9 Be, Ca, Fe, A1 10 h This work 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. References Lukin, A. M., and Zavarikhina, G. B., Zh. Anal. Khim., 1956, 11, 393. Suvorovskaya, N. A,, Voskresenskaya, M. M., and Melnikoca, T. A., Nauchn. Soobshch. Inst. Gorn. Markman, A. L., and Galkina, L. L., Uzb. Khim. Zh., 1962, No. 4, 5. Ersitavi, D. I., Brouckek, F. I., and Eristavi, V. D., Tr. Gruz. Politekh. Inst., 1966, NO. 108, 41. Rozenberg, P. A., Lab. Delo, 1963, 9, 11. Job, P., Ann. Chim. (Paris) 1928, 9, 113. Yoe J. H., et al., I n d . Eng. Chem., Anal. Ed., 1944, 16, 111. Bent, H., et al., J . A m . Chem. SOC., 1941, 63, 569. Babko, A. K., “Physicochemical Analysis of Complex Compounds in Solution,” Akademii Nauk Jean, M., Anal. Chim. Acta, 1952, 7, 338. Luke, C . L., and Campbell, M. E., Anal. Chem., 1954, 26, 1778. Mann, C. K., and I’oe, J . H., Anal. Chem., 1956, 28, 202. Mann, C. K., and Yoe, J. H., Anal. Chim. Acta, 1957, 16, 155. Selzer, G., and Ariel, M., Anal. Chim. Acta, 1958, 19, 496. Schwarzenbach, G., Helv. Chim. Acta, 1954, 37, 113. Dela, Moscow, 1960, 6, 63. SSR, Kiev, 1956. Received December 2nd, 1981 Accepted March 52h, 1982
