same as for Saltzman's iodide method for which most other oxidants interfere postively, SO2 interferes negatively, and about one-tenth of all NO2 present is measured as 0 3 ( 4 ) . All data in this paper have been reported as ozone concentrations, but it should be pointed out that, a t low levels of oxidant, values obtained are probably representative of an indeterminate mixture of ozone and other oxidants. In conclusion, we feel that this modification of Saltzman's iodide method for ozone determinations has application as a calbration method in the 5-ppb to 100-ppb range for ozone detection devices.
ACKNOWLEDGMENT We express our sincere thanks to E. A. Butler of our department for his advice throughout this project and to E.
M. Chamberlain and W. H. Edwards of the University of Utah Biology Department for the use of their equipment in the ozone dilution experiment.
LITERATURE CITED (1) S. R . Goates, J. S. Bradshaw, and N. F. Mangelson, Roc. Utah Acad. Sci., Arts, Lett., 51, part 2, 26 (1974). (2) B. E. Saltzman and N. Gilbert, Anal. Cbem., 31, 1914 (1959). (3) M. Katz in "Air Pollutants". 2nd ed., Vol. 11, A. C. Stern, Ed., Academic Press, New York, N.Y., 1968, pp 86-90. (4) E. E. Saltzman and A. F. Wartberg, Anal. Cbem., 37, 779 (1965). (5) S.L. Kopczyns, Anal. Cbem., 43, 1126(1971).
RECEIVEDfor review March 5, 1975. Accepted April 28, 1975. This research was supported by the Genealogical Society of the Church of Jesus Christ of Latter-Day Saints.
Rapid Extractive Spectrophotometric Determination of Haf nium(IV) with 4-( 2- Py ridy lazo)resorcino1 B. Subrahmanyam and M. C. Eshwar Department of Chemistry, Indian Institute of Technology, Bombay 400076, India
Numerous methods are available for the determination of zirconium in the presence of hafnium, but very few methods are known for the determination of hafnium in the presence of zirconium ( I ) . The present study deals with the spectrophotometric determination of hafnium in the presence of zirconium. Even though a large number of reagents are potentially useful for determination of hafnium, only a few reagents have been studied in detail, such as arsenazo(II1) ( 2 ) , chromeazurol S ( 3 ) , 6,7-dihydroxy-2,4-diphenylchroman (41, methylthymol blue ( 5 ) , and xylenol orange (6-10). 4(2-Pyridylazo)resorcinol, PAR, was investigated for determination of zirconium(1V) ( 1 1 ) in these laboratories. Zirconium reacted with PAR a t pH 2.5 giving a 1:l orange-red chelate in the presence of ascorbic acid, exhibiting a maximum absorbance a t 540 nm. I t has been observed that hafnium gives a color reaction with PAR; hence, a detailed investigation has been taken up. The method proposed is simple, rapid, sensitive, and enables the determination of trace amounts of hafnium in the presence of threefold excess of zirconium.
EXPERIMENTAL Apparatus and Reagents. A Perkin-Elmer Model 402 spectrophotometer was used for absorbance measurements with matched 10-mm quartz cells. A Cambridge pH meter was used for pH adjustments. One gram of hafnium metal (99.9% pure, Fluka A.G.) was dissolved in a minimum amount of 40% hydrofluoric acid in a platinum dish. The solution was oxidized with a few drops of concentrated nitric acid and heated gently to expel oxides of nitrogen. The solution was then treated with 10 ml of concentrated sulfuric acid, evaporated to dryness, dissolved in 20 ml of water, and transferred to a one-liter calibrated flask. Twenty ml of concentrated sulfuric acid was added t o this solution, and diluted to the mark. This solution contained 1 mg of hafnium per ml. A diluted solution containing 10 pg of hafnium per ml was prepared from stock solution by appropriate dilution. Aqueous solution of 4-(2-pyridylazo)resorcinol(monosodium salt), 0.1%, was prepared from a pure sample (E. Merck) in double distilled water. All other reagents were of AnalaR grade (BDH). 1692
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Buffer solution of pH 2.5 was prepared by mixing 83 ml of 0.1M HCI (BDH AnalaR) and 500 ml of 0.1M potassium hydrogen phthalate and making up to 1 liter. General Procedure. An aliquot of hafnium solution containing
