morin is very highly a x o r b a n t in the ultraviolet region and care must be used not to have too much reagent present; the fluorescence intensity of the aluminum chelate with morin is very sensitive to temperature changes even from 15 O to 30" C; salicylidene-o-aminophmol decomposes easily in alcohol or water solutions. It should be noted that the above comparisons were all made with a 1P28 electron multiplier phototube. A grating o r phototube more sensitive at the particular emission wavelength would improve the results of a reagent. F o r example, the lP2El electron multiplier phototube is far more sensitive to the emission of the first two reagents above than to the emission of the last o n the list. For general purposes in the qualitathe and quantitative determination of aluminum where only parts per million are of interest we prefer the purified AAGR as a reagent. This material is very easily obtained and purified; the alcohol solution is very
stable, the emission is easily separated from an ultraviolet excitation of the sample by a common filter and the emission is well within the sensitive range of a low priced stable phototube. Of the above reagents, the soft red fluorescent light emitted by the AI-PBBR chelate makes this reagent readily applicable to visual comparisons. The AI-NSAHF gives the most intense emission of the chelates tested. ACKNOWLEDGMENTS The authors are indebted to Susan Delaney and H. Feinstein for checking various parts of this research. Received for review July 27, 1966. Accepted December 21, 1966. Work supported in part by the National Science Foundation.
Spectrophotometric Determination of Periodate in Presence of Iodate Using Aluminum Hydroxide S. N, Bhattacharyya and P. K. Chetia Saha institute of Nuclear Physics, Nuclear Chemistry Division, 92, Ackarya Prafulla Chandra Road, Calcutta-9, India
PERIODATE CAN BE determined in slightly acidic o r alkaline solutions by its absorption at 222 m p according t o earlier reports ( 1 , 2 ) . In the case of kinetic studies of radiation-induced decomposition of iodate, it is necessary to determine small amounts of various oxiclation states of iodine in the presence of a large excess of iodate. It has been found that iodate ion in aqueous solution alscl shows appreciable absorption in the ultraviolet region of the spectrum. Simultaneous spectrophotometric determination (3) of two components in a mixture may be made if there is cnly a slight overlapping of absorption spectra. But no such suitable condition could be observed in the case of iodate and periodate. A compensation technique, ( 4 ) which eliminates the spectrum of one component by putting the same amount of the component in the reference cell, is sometimes useful. But in a multicomponent system the method is not always convenient from the point of view of versatility, easy manipulation, accuracy, and precision. I t would be useful if one could find an easy method for separating periodate from the bulk '3f iodate and then, having recourse to spectrophotometry. Attempts have therefore been made to find a suitable coprecipitant for carrying out the small amounts of periodate and measuring the absorbance at a suitable wavelength in the presence of the coprecipitant. Recently Fe(OH)3 has been found (5) to be a good coprecipitant for periodate. But ferric ion has an appreciable a x o r p t i o n in the ultraviolet region of the spectrum. The aim of the present investigation is to find
(I) M. S . McDonald, J. Thompsett, and J. F. Mead, ANAL.CHEM., 21, 315 (1949). (2) C. E. Crouthamel, H. \ . Meek, D. S. Martin, and C . V. Banks, J . Am. Chern. Soc., 71, 3031 (1949). (3) V. C . Vespe and D. F. .3oltz, ANAL.CHEM., 24, 664 (1952). (4) D. 2.Robinson, Zbid.,23,273 (1951). (5) A. I. Novikov and E. I. Finkel'shtein, Z/z. Analit. Khim., 19, 541 (1964); C . A . 61, 496 c (1964).
whether AI(OH)3 can serve as a suitable coprecipitant for carrying out periodate in the presence of a large excess of iodate, and whether the periodate thus carried can be determined conveniently through spectrophotometry in the presence of the coprecipitant. EXPERIMENTAL Apparatus. Absorbances were measured in a Hilger Uvispek photoelectric spectrophotometer, using 1-cm silica cells. Reagents. Analytical grade reagents were used during the course of the present investigation. Carrier free was procured as iodide from the Atomic Energy Establishment, Trombay, Bombay. The labeled iodate (KI*03) solution was prepared by passing CI2through the acidic solution of the iodide containing I 1 3 I . Procedure. Measured amounts of KI03 and KIOl were taken from their respective stock solutions; to these were added known amounts of aluminum sulfate and ammonium chloride solutions. The volume was made to 50 ml. Aluminum was precipitated by passing ammonia gas; the solution was continuously stirred during the course of precipitation. The precipitate was filtered and washed with about 50 ml of water. The Al(OH), precipitate was then dissolved by percolating 20 ml of 6 N H2S04through the filter paper and the solution was made up to 50 ml with water. The absorbance was measured against the blank in 1-cm silica cells at 210 mp.
RESULTS AND DISCUSSION The absorption spectra of periodate in aqueous solution at different p H have been studied by Crouthamel et al. (2). The absorption maximum observed at 222 m p tends to be flattened with the decrease of pH. A t lower pH, the sensitivity in the limit of detection is thus reduced. Spectral characteristics of periodate at high acidity in 2.4N H2S04medium have been studied. Figure 1 shows that the absorption maximum of periodate shifts toward a lower wavelength a t 210 mp. VOL. 39, NO. 3, MARCH 1967
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Figure 1. Absorption spectra of 5.0 X 10-jM potassium periodate solution in 2.4N H2S04 medium
Table I. Determination of Periodate in Presence of Iodatea Initial K I 0 4 , moleslliter molar ratio, KIOa :KIOs Taken Found 2.00 x 10-6 1:500 2.02 x 10-5 3.00 x 10-5 1 :332 2.99 x 10-5 2.00 x 10-5 1.98 x 10-5 1 :250 5.00 x 10-5 5.08 X 10-5 1 :loo 10.00 x 10-5 1 :50 9.81 x 10-5 4.00 x 10-5 1 :25 3.90 x 10-5 2.82 X 2.85 X 1:1.4 0 6.4 mg of aluminum was precipitated in a total volume of 50 ml.
In order to determine the optimum amount of carrier necessary to carry out all periodate, amounts of the aluminum carrier were varied and the results are shown in Figure 2. We have taken 6.4 mg of aluminum for carrying out all periodate in a volume of 50 ml of the solution. The effect of ammonium chloride o n the extent of coprecipitation was also studied. The amount of ammonium chloride was varied from 0.05M to 2.OM and it was found that the ammonium chloride does not show any appreciable effect o n the amount of coprecipitation of periodate. This indicates that the mechanism involved in the process of carrying of periodate by Al(OH), is not due to usual surface adsorption, when the extent of coprecipitation should have been influenced by the large amount of chloride ion present. I t may be due to some form of internal adsorption where the periodate ion, unlike the iodate, is internally adsorbed in the lattice of the carrier. That Al(OH), does not take up traces of iodate when precipitated in the presence of a large excess of iodate was tested by using as radioactive indicator. Varying amounts of potassium iodate were taken, to which was added a known amount of labeled KI*O3 solution, and the same amount of AI(OH), was precipitated. The precipitate was filtered, washed, and dissolved in sulfuric acid as described above. The activity in the filtrate and in the precipitate was determined by means of a liquid counter. It was observed that all activity passes into the filtrate and no appreciable activity could be detected in the precipitate. This indicates that when
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Figure 2. Coseparation of periodate with AI(OH)3, precipitated in a total volume of 50 ml Concn. of periodate
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A1(OH)3 is precipitated in the presence of a large excess of iodate, the uptake of iodate by Al(OH)3 is negligible. In order to find whether the system conforms to Beer’s law, varying amounts of periodate were taken, and 6.4 mg of aluminum was precipitated in their presence in a total volume of 50 ml. The precipitate was filtered, washed with water, and dissolved in sulfuric acid as has been described previously, and the absorbances of the solutions were measured against the blank at 210 mp. I t was found that in the range of concentration, 1 X 10-6 to 18 X lO-5M K1O4, the system obeys Beer’s law and themolar absorptivity was calculated to be 2.87 X 103. It should be pointed out that a similar value of molar absorptivity was obtained when the periodate alone in 2.4N H z S 0 4 medium was measured at 210 mk in the absence of any coprecipitant. This again clearly indicates that serves as a faithful coprecipitant for the periodate ion. To test the suitability of the method in the presence of large excesses of iodate the same procedure was adopted with different initial molar ratios of iodate and periodate. The results are shown in Table I. Although the absorbance measurements were made in the far ultraviolet region of the spectrum and the absorbances of the solutions that were measured were relatively low, the results agree to within a fair degree of accuracy; as low as 2 X lO-5M periodate can be determined accurately in the presence of 1 x 10-2M iodate. The method is very simple, easily adaptable and reproducible, and gives fairly accurate results in the determination of periodate from mixtures having molar ratios ranging from 1 :1 to 1 :500 for periodate :iodate. ACKNOWLEDGMENT The authors thank B. C. Purkayastha, Head of the Nuclear Chemistry Division, for his continuous encouragement in this work and for going through the manuscript. Thanks are also due to Shyamoli Sen of this Division for preparing the labeled iodate solution.
RECEIVED for review September 19, 1966. Accepted November 21,1966. One of the authors (P. K . Chetia) is indebted t o the Government of Assam for a research scholarship.
