Six spectroscopic methods for detection of oxidants in urine: implication in differentiation of normal and adulterated urine.

Six separate methods to detect oxidants in urine were developed. The presence of the oxidants was established by initial oxidation of ferrous to ferric ion and detecting the ferric by chromogenic oxidation or complex formation. The reagents for chromogenic oxidation were N,N-dimethylamoino-1,4-phenylenediamine (DMPDA), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid (ABTS), and 2-amino-p-cresol (APC), and the reagents for the chromogenic complex were xylenol orange (XO), 8-hydroxy-7-iodo-5-quinolinesulfonic acid (HIQSA), and 4,5-dihydroxy-1,3-benzene-di-sulfonic acid (HBSA). All methods showed comparable results when tested for ferric, chromate, permanganate, oxychloride, hydrogen peroxide, oxone, tert-butylhydroperoxide, and cumenehydroperoxide at a concentration of 1.0 mmol/L in water (CV < 7%). The nitrite results are comparable only with DMPDA and APC. Periodate responded to the highest oxidation number (ON = 8) by chromogenic oxidation but lowest (ON = 2) by the chromogenic complex. The iodate responded only to the chromogenic oxidation with ON = 6. The linearity of the procedures was established by chromate in water. The linear concentrations were 0.09-12.00 mE/L for DMPDA, ABTS, APC, and HBSA and 0.09-6.00 mE/L for XO and HIQSA. In all methods, the correlation coefficients were > or = 0.9991 and precisions were within +/- 5.6%. The methods were used to test oxidants in 238 urine specimens. The chromate at 3.0 mE/L in water was used as standard. The correlation coefficients of 0.9600-0.9853 and the ANOVA test (F = 0.90, F(critical) = 2.22 at P(0.48)) indicated that the methods correlated well. The median concentration of oxidants in the specimens was 0.21 mE/L with an average and standard deviation of 0.62 +/- 1.19 (range 0.04-8.83 mE/L). When Grubbs' statistical test was applied to the specimen results, no specimen was found to be outlier or could be considered as adulterated. The Grubbs' test also revealed that the threshold concentration to identify urine adulteration was 29 mE/L at confidence level of 99%.