Critical study of fluorimetric determination of selenium in urine

Different steps for the fluorimetric determination of Se in urine have been investigated. A HNO₃---HClO₄ (4:1) mixture is useful for urine digestion, and reduction of Se(VI) to Se(IV) is effectively carried out with HCl (6M). Selenium(VI) present after the digestion process constitutes 14.5–36.6% of total Se. An optimum pH of 1.80±0.05 and the addition of 1 ml of 2,3-diaminonaphthalene (DAN) (0.1%, w/v) are established in the formation of Se—DAN complex. Heating to 60°C, a time of incubation of 15 min is recommended to assure the complete formation of Se—DAN complex. A volume of 5 ml of cyclohexane and vigorous shaking for 45 sec is necessary for the extraction process. With this optimized method, the detection limit of selenium was 0.82 μg/l., within-day precision for a 50.0 μg/l. standard solution and urine (27.3 μg/l.) were 2.4 and 2.7% and between-day for the urine was 3.9% (33.9 μg/l.). Analytical recovery of 0.5 ml of Se standard (250 μg/l.) added to 1 ml of urine was 99.9±2.9% (95.8–104.4, n = 12). Normal levels of selenium excretion in urine obtained from healthy people were 27.9±8.7 μg/day (13.2–44.1), not observing significant differences (P < 0.05) between sexes.