Spot Test

Addition of four to five drops of 3% hydrogen peroxide in approximately 200 ^L of urine adulterated with PCC (~6-7 drops from a transfer pipette) caused rapid formation of a dark brown color and a dark brown precipitate appeared on standing. In contrast, unadulterated urine turned colorless after addition of hydrogen peroxide (26).

3.6.4. Other Tests for Detecting Chromate

Freslew et al. (27) described a capillary ion electrophoresis technique for detecting chromate ion, as well as nitrite ion, in urine specimens suspected of adulteration. The DPC colorimetric test for chromate, which can be easily automated, can serve as a screening test. Capillary electrophoretic analysis can be used to confirm the presence of chromate in adulterated specimen, if necessary. A good correlation was observed between chromate concentrations in urine using the colori-metric test and the capillary electrophoretic analysis (28). Paul described six spectro-scopic methods for detection of oxidants including chromate. The presence of oxidants (as adulterants in urine) was established by initial oxidation of ferrous to ferric ion and then detecting ferric ion by chromogenic oxidation or complex formation. The author used N,N-dimethylamino-1,4-phenylenediamine, 2, 2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) or 2-amino-para-cresol for chromogenic oxidation. The reagents for the chromogenic complex formation were xylenol orange, 8-hydroxy-7-iodo-5-quinolinesulfonic acid and 4,5-dihydroxy-1, 3-benzene-di sulfonic acid (29).

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