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A = reagent blank (0.1 M CaCI2) Β = A + 50 ppm Br03_ (based on 1-g sample) C = Β + 10 ppm ICV
t
< 3,
0.05
I
-0.6
-0.8
-1.0
-1.2
-1.4
-1.6
-1.8
-2.0
Potential (volts vs. S C E )
Figure 2. Differential pulse polarographic determination of iodate and bromate
sensitivity of the method being ade quate for concentrations well below the specified limit. The degree of sep aration is affected by both cobalt and chloride concentrations; in testing co balt nitrate hexahydrate the cobalt wave is shifted to a slightly more nega tive position. For cobalt nitrate the ACS NH 4 + limit is 0.20%, and a sam ple of 0.10 g is sufficient. Polarographic determination of ni trate (or nitrite) requires addition of a redox catalyst to yield a reductive wave. We have used the procedure of Kolthoff, Harris, and Matsuyama (7), in which uranyl acetate is the catalyst, and found it to be suitable for testing a number of reagent chemicals (6). Among these are sodium chloride, al kali bromides, magnesium sulfate, and calcium sulfate, which have ACS lim its ranging from 5 to 50 ppm NOe - . There have been no nitrate require ments for ammonium salts or ammo nium hydroxide because the reduc tion-distillation method cannot be ap plied. With the availability of polaro graphic methods, these compounds appear to deserve further consider ation. If it is of interest to distinguish nitrite from nitrate, one can use the
procedure of Chang et al. (8), in which only nitrite forms the reducible deriv ative diphenylnitrosamine. lodate, bromate, and chlorate
Currently, only 11 reagents have ACS requirements that include tests for one or more of these anions. The determinations are based on liberation of iodine, hence they are not specific for any one oxidant. Alkali iodides are tested for iodate, whereas alkali and ammonium bromides are tested for bromate. Alkali chlorides are exam ined for chlorate plus nitrate, and al kali nitrates for iodate plus nitrite. Often the limits cannot be specified precisely because the tests depend on visual observation of color produced by addition of acid, iodide (if needed), and starch. Polarography is capable of distin guishing between bromate and iodate, which have long been known to yield well-separated reductions (Figure 2). The responses shown in these tests clearly allow measurement at present ACS limits of 10 ppm Br0 3 ~ or about 3 ppm IO3 - , using 1-g samples. The committee has recently adopted po larographic procedures for testing so-
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^Φ=
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ANALYTICAL CHEMISTRY, VOL. 57, NO. 1, JANUARY 1985 · 31 A
