Arnold R. Johnson, Jr.'
Universily of Wyoming Laramie
Neothorin Spot Test for Zirconium and Hafnium
Various color reactions of Neothorin2 with metal ions have been described by Fritz and B r a d f ~ r d ,K~~ t e i n i k o v Kuznetsov: ,~ and others. Although the reaction with zirconium has been reported, it has not been mentioned that under proper conditions Neothorin is almost specific for zirconium and hafnium. The only probable interferences are Ti(IV), Th(IV), and U(IV).O Neither has it been mentioned that this reagent can he used to differentiate between zirconium and hafnium. A simple but sensitive spot test for the identification of and differentiation between zirconium and hafnium is, therefore, described in this paper. I n strong hydrochloric or perchloric acid solution, zirconium produces a blue-violet solution or precipitate while that of hafnium is red-violet. However, in mixtures, the zirconium color tends to mask the hafnium color. Even though this is the case, it is often possible to detect hafnium in the presence of zirconium. The spot test described may, therefore, be used for the identification of zirconium, of hafnium, and of mixtures of zirconium and hafnium in solutions and in solids (such as oxides and ores) after appropriate treatment. Zirconium and hafnium test solutions may he prepared in a number of ways depending upon the starting material. Probably the simplest method is to dissolve the tetrachlorides or oxychlorides in strong hydrochloric or perchloric acid. The spot test may then be carried out by placing one drop of the test solution on a porcelain spot plate and adding 1 drop of 0.10% aqueous Neothorin reagent. If zirconium or a mixture of zirconium and hafnium is present, a blue-violet solution and/or precipitate will form, depending on the concentration. If hafnium only is present, a redviolet solution and/or precipitate will form. Unknown solutions may be tested in the same manner as the knowns. However, in this case, a drop of strong HC1 or HClOl should be added to make certain the test solution is strongly acidic. In the absence of zirconium and hafnium, an orange solution is obtained even in the presence of most other cations. These reactions may also be carried out in test tubes or on strips of filter paper. If the unknown is an oxide or ore, then a few mg of 'Address after September 1: Department of Chemistry, Minot State College, Minot, North Dakota, 58701. lNeothorin (Arsenazo; Arsenazo I); a-(l,&dihydroxy-3,6disulfo-2naphthylazo) henzenearsonic acid; or a Na salt. Available from K & K Laboratories, Inc., 121 Express Street, Engineers Hill, Plainview, New York, 11803. C.. Anal. Chem. 30,1021 (1958). "FRITZ,J. S., AND BRADFORD, "UTEINIKOY,A. F., Zavodsk. Lab., 24, 1050 (1958); Anal. Abstr. 6 , 2473 (1959). 6 K u z ~ ~ ~ sV.o vI.,, Zh. Analit. Khim. 7 , 226 (1952); Chem. Abst. 47, 1534c (1953). 'FRITZ, J. S., Private communication.
the sample is placed in a small (No. 0000) porcelain crucible and sufficient sodium peroxide is added to cover the sample. This mixture is carefully fused over a burner until no further evolution of oxygen is noted from fused mixture. After cooling, several dropsof 6 M HCI or HCIOl are cautiously added to the melt to dissolve some of the sample and to ensure that the resulting solution is strongly acidic. A drop of this solution is then placed on a spot plate and the remainder of the procedure as described for solutions is carried out. Although practically no cation interference is observed, several anions interfere due to the masking of the color reaction. It is, therefore, necessary to make certain that the zirconium or hafnium is free from such anions as sulfate, citrate, tartrate, oxalate, phosphate, fluoride, and other anions which form complexes with zirconium or hafnium. Chloride, perchlorate, nitrate, and acetate do not interfere. In the presence of a high concentration of iron(III), the test is best carried out by using perchloric acid in place of hydrochloric acid. Perchloric acid can also be used in the other tests as well. Nitric acid is not as satisfactory as hydrochloric or perchloric acid and sulfuric acid cannot be used since the sulfate ion masks the color reaction. As previously mentioned, zirconium and hafnium can be distinguished from each other because of the differences in the colors produced with Neothorin. This difference is enhanced if the reaction is carried out in HC1 media rather than HCIOa. In mixtures of the two solutions, the zirconium color tends to mask the hafnium color. However, if a drop of 30% H202solution is added to the mixed complexes, the Zr color is bleached to an orange color whiie the Hf is bleached to a pink to pink violet color. This often makes it possible to detect hafnium in the presence of zirconium depending upon the relative amounts present. This latter test is more distinctive if it is carried out in HCIOarather than HC1. By running and comparing known solutions of Zr, of Hf, and of mixtures, it is therefore possible to determine whether a sample contains only Zr, only Hf, or in many cases a mixture of the two. Unfortunately, this test will not detect a trace of one of these elements in the presence of the other. The sensitivity of this method is about 37 for both Zr and Hf. At low concentrations the test is often improved by adding more than one drop of the Neothorin reagent. I t is also often advantageous to add more than one drop of the Neothorin solution and/or H2O2 when carrying out the bleaching reactions in mixtures of Zr and Hf. The best conditions for a specific application can readily he found by modifying the procedures suggested in this paper. Volume 42, Number 8, August 1965
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