amounts up to at least 10 times that the neptunium on a mole basis. Bnions Chloride Fluoride Dichromate Permanganate Sulfate Bisulfate Persulf ate Sulfamate Nitrite Oxalate Citrate
Cations Sodium Potassium Calcium Aluminum Ferric Chromic Nickel Silver Uranyl Plutonyl
Allowance must be made for substances which consume the oxidant during the oxidation step. Absorptivity. With the system described, the absorptivity of sexivalent neptunium at the 1.23-micron peak is 0.189. LITERATURE CITED
(1)7Hoff~n;n,D. C., “Progress in Nuclear hnergy, Series IX, “Analytical Chem-
istry,” Vol. 2, p. 181, Pergamon Press, New York, 1961. (2) Katz, J. J., Seaborg,. G. T., “Th; Chemistry of the Actinide Elements, p. 223, Wiley, New York, 1957. (31 Keder. W. E.. General Electric Co., . ,Richland, Wash., private communication, 1958. (4) Waggener, W. C., J . Phys. Chem. 62, 382-3 (1958). RECEIVEDfor review July 16, 1962. Accepted February 21, 1963. All work performed under Contract No. AT(45-1)1350 between the U. S. Atomic Energy Commission and General Electric Co.
A N e w Spectrophotometric Method for the Determination of Microgram Amounts of Selenium G. F. KIRKBRIGHT and JOHN H. YOE Praff Trace Analysis I aborafory, Deparfmenf o f Chemistry, Universify o f Virginia, Charloftesville,
b The oxidation of phenylhydrazine p-sulfonic acid b y selenious acid has been investigated. Measurement of the absorbance at 520 m p of the azo dyestuff formed when the diazonium oxidation product i s coupled with 1 naphthylamine i s the basis of a new spectrophotometric method for trace amounts of selenium. The effect of acidity, reagent concentration, and rate of reaction has been studied for both the oxidation and coupling processes. The reaction has a practical sensi.ivity of 0.01 pg. 2f selenium per sq. cm. for log lo/T = 0.005. The tolerances toward diverse ions have been investigated. The interference of iron and copper has been eliminated b y solvent extraction of their cupferron complexes. The method has been applied to the analysis of synthetic samples containing selenium and various foreign ions.
B
(2) and, more recently, Kolthoff and Elving ( 7 ) have reviewed the methods available for the determination of selenium. TKOtypes of method are available for the apectrophotometric determination of selenium-Le., those which involve reduction of selenium(1V) to elemental form, oftcn with the simultaneous production of a colored oxidation product, and those in which a colored or fluoresccnt piazselenol is formed by reaction of selenious acid with an aromatic o-diamine. We have investigated a reaction of the first type. Postowsky, Lugowkin, and NIandrJ-k (8) investigated the oxidation of arylhydrazines by selenious acid. They found that the arylhydrazines were
VU.
oxidized to diazonium salts, which could be coupled with aromatic amines to produce intensely colored azo dyestuffs. Feigl and Demant ( 3 ) have employed this reaction for the detection of small amounts of arylhydrazines, and we now report its utilization for the spectrophotometric determination of microgram amounts of selenium. The solubility, stability in aqueous solution, and sensitivity toward oxidation by selenious acid of phenylhydrazine, naphthylhydrazine, m- and p nitrophenylhydrazine, and phenylhydrazine .n-sulfonic acid were examined semiquantitatively. Phenylhydrazine p-sulfonic acid was selected as the most stable and sensitive reagent. I-and %Naphthol, 1- and 2-naphthylamine, and several naphthylaminesulfonic acids were examined as reagents for the coupling reaction with the diazonium salt oxidation product. 1Naphthylamine was chosen as the most favorable reagent for coupling in acid
The coupling reaction is identical with that involved in the sensitive Griess (1, 5,6)reaction for the detection and determination of nitrite. The results of our investigation of the optimum conditions for Reaction B confirm those of Rider and Mellon (Q), who made a critical examination of the use of this coupling reaction in the spectrophotometric determination of traces of nitrite. The determination of the optimum conditions for the oxidation and coupling reactions is described.
selenium in acid solution :
ml., boil gently for several minutes,
EXPERIMENTAL
Apparatus. Beckman spectrophotometers, Alodel DU and DK-2, with matched I-cm. Corex cells. Beckman uH meter &{ode1 G with -generalpurpose glass electrode. Reagents. STANDARD SELEXICM SOLUTION. Dissolve 1.000 gram Of chemically refined selenium shot (Johnson, ‘latthey and ‘O., Ltd*, spectrographically standardized H.S.) in ml. of 12AT HC1 and ml. of
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ANALYTICAL CHEMISTRY
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