Critical study of fluorimetric determination of selenium in urine

Different steps for the fluorimetric determination of Se in urine have been investigated. A HNO(3)HClO(4) (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 degrees 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 mug/l., within-day precision for a 50.0 mug/l. standard solution and urine (27.3 mug/l.) were 2.4 and 2.7% and between-day for the urine was 3.9% (33.9 mug/l.). Analytical recovery of 0.5 ml of Se standard (250 mug/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 mug/day (13.2-44.1), not observing significant differences (P < 0.05) between sexes.