Highly Selective and Sensitive Spectrophotometric Determination of Iron(I I) and CobaIt(I II) with 4-(2- Pyridy lazo) resorcino1(PAR) T a k a o Yotsuyanagi, Ryuji Yamashita, and Kazuo Aomura Lahoratorj of Analytical Chemistry, Faculty of Engineering, Hokkaido University, Sapporo-shi, 060, Japan
VARIOUS AUTHORS (1-8) have reported highly sensitive spectrophotometric determinations of a number of metals utilizing water soluble red complexes formed by metal ions and 442pyridylazo)resorcinol(PAR). However, because of the poor selective nature of PAR, the application of the above procedures to practical samples is limited to special cases where interfering metals were separated by preliminary treatments such as solvent extraction and ion-exchange chromatography. Takeuchi and Shijo ( 9 , IO) reported that cobalt- and nickelPAR chelates are not decomposed by a large excess of EDTA at room temperature. We also have reported a similar behavior of PAR chelates of iron(I1) (11) and chromium(II1) (12). Based on these findings, a selective spectrophotometric method for Fe, Co, Ni, and Cr was proposed in which the interference by other metals can be readily screened out with EDTA (9-12). However, intense mutual interference among Fe, Co, Ni, and Cr which can not be masked by EDTA, makes it difficult to establish a selective PAR method for these metals. We have found that the PAR chelates of Fe”, Co3+,and Pd?+ alone are stable for at least for two hours in boiling aqueous borate buffer solution (pH 9.0) containing a large excess of EDTA, whereas Fe(II1)-, Co(11)-, and all other metal-PAR chelates are decomposed by EDTA within 30 min. Thus, except for palladium(I1) ion, the color of PAR chelate is stable only for iron under reducing conditions and for cobalt under oxidizing conditions. This finding makes it possible to develop a highly selective and sensitive spectrophotometric method for iron and cobalt. EXPERIMENTAL Apparatus. The absorbance measurements were made with a Hitachi 124 Model double-beam spectrophotometer. Toa Electronics Ltd. HM-SA Model pH meter equipped with a glass electrode was used to measure pH. Reagents. A standard iron(I1) solution was prepared by dissolving 0.702 gram of ferrous ammonium sulfate in 50 ml of 0.01N hydrochloric acid solution and diluting to 100 ml (1 ml = 1.0 mg of Fe). A standard cobalt(I1) solution was prepared by dissolving 5.95 grams of cobaltous chloride in (1) F. H. Pollard, P. Hanson, and W. J. Geary, Amd. Chim.Acta, 26, 20 (1959). (2) Y. Shijo and T. Takeuchi, Jup. Anal., 14,115 (1965). (3) I KI.~(II)EDTA. This result indicates that the PAR ligand has a low valence stabilizing property such as that of the o-phenanthroline ligand. This property can be expected from the possibility that PAR forms a chelate-ring with a very similar structure to that of the o-phenanthroline complex. The above analytical methods are accurate, and are applicable in a concentration range of 0.05 ppm through to 0.8 ppm of iron and cobalt. In the case where a higher sensitivity is required than that of the recommended procedure, the extraction of the PAR chelates with tetradecyl-dimethylbenzyl ammonium chloride (TDBA+.Cl-) is recommended (15). Procedure of the extraction is as follows : 50 ml of colored solution is transferred to a 100-ml separatory funnel, to which 1.5 ml of 0.05M TDBA'.Cl- solution was added. The mixture is shaken with 10 ml of chloroform for 10 minutes. The absorbance of the chloroform layer is measured at 522 nm for iron or at 520 nm for cobalt against a blank. By this extraction, an approximately 5-fold increase in sensitivity can be obtained for both iron and cobalt. RECEIVED for review August 9, 1971. Accepted December 21, 1971. (15) T. Yotsuyanagi, R . Yamashita, and K. Aomura, Jap. Anal. 19, 981 (1970).
Loss of Mercury from Water during Storage Robert V. Coyne and James A. Collins US.Air Force Encironmental Health Laboratory, McClellan Air Force Base, Calg. 95652 THEDISCOVERY of significant levels of mercury in fish, water supplies, seed grains, and other edible materials has caused a great deal of emphasis to be placed on improvement of analytical techniques for mercury in terms of both specificity and sensitivity. Numerous modifications in analytical methods for mercury have been published relative t o techniques for urine, blood, water, sediment, geological samples, food products, and animal tissue (1-6). Some recent modifications reported sensitivities in the part per billion range and there is little doubt that such sensitivity is possible from a strict analytical standpoint (7, 8). How(1) E. Berman, At. Absorption Newslett., 6 , 57 (1967). ( 2 ) W. R. Hatch and W. L. Ott, ANAL.CHEM., 40, 2085 (1968). (3) G. W. Kalb, At. Absorption Newslett., 9, 84 (1970). (4) B. B. Mesman and B. S. Smith, ibid., p 81. ( 5 ) R. K. Munns and D. C . Holland, J. Ass. Ofic. Anal. Chem., 54, 202 (1971). (6) V. A. Thorpe, ibid., p 206. (7) R. W. April and D. N. Hume, Science, 170,849 (1970). (8) Y.K. Chau and H. Saitoh, Emir. Sci. Technol.,4,839 (1970).
ever, as early as 1941, reference was made to adsorption of mercuric ions from dilute solutions onto glass surfaces, but no data were presented to support the statement (9). More recently, Shimomura et al. (10, 11) reported their results using isotopic mercury ; the loss of mercury from stored solutions was observed to be proportional to pH, greater losses occurring with higher pH values. In another study using radioactive isotopes, losses up to 82 of added mercury were encountered in unpreserved samples of natural water (8). Greenwood and Clarkson reported loss of mercury in dilute solutions, again using a radioactive mercury tracer; these authors studied a number of container materials under total artificial conditions and, relative to polyethylene, observed mercury adsorption of about 38x in 46 days (12). Other references have been (9) A. E. Ballard and C. D. W. Thornton, Ind. Eng. Chem., 13, 893 (1941). (10) S. Shimomura, Y. Nishihara, and Y. Tanase, Jup. Anal., 17, 1148 (1968). (11) Zbid., 18, 1072 (1969). (12) M. R. Greenwood and T. W. Clarkson, J. Amer. Znd. Hyg. Ass., 31, 251 (1970). ANALYTICAL CHEMISTRY, VOL. 44, NO. 6, MAY 1972
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