Determination of trimethylselenonium ion and total selenium in human urine by graphite furnace atomic absorption spectrometry

Abstract

Determination of trimethylselenonium ion (TMSe⁺) and total selenium in human urine by graphite furnace atomic absorption spectrometry (GFAA) was studied. It is necessary to separate TMSe⁺ from other selenium compounds in urine and to digest TMSe⁺ to inorganic selenium completely without any loss of selenium, so that ion exchange column chromatograph and pressure decomposition technique were applied prior to the analysis by GFAA. Method: (1) Separation of TMSe⁺; ml of urine was placed on an ion exchange column (1×20 cm) containing Dowex 50 W-X8(H⁺) resin suspended in 1 N NH₄OH. The column was washed with 50 ml of 1 N NH₄OH, distiled water, and HC1(0.05 N, 0.1 N, 0.5 N, 1.0 N and 4.0 N). TMSe⁺ was eluted with 4.0 N HCL and the first 5 ml of the eluent was discarded and then 40 ml was collected as TMSe⁺ fraction. A 10 ml aliquot of the TMSe⁺ fraction was transferred into the pressure decomposition vessel and heated for 80 min at 200 °C. After cooling the vessel in water, 2 ml of 20 % hydroxylamine hydrochloride was added to the digested solution and the whole was boiled for 10 min. The selenium in the solution wan extracted with 1 ml of 0.02 % dithizone in carbon tetrachloride.(2) Ashing for the determination of total selenium; 1 ml of urine was taken into a pressure decomposition vessel containing 5 ml of 5 N HNO₃ and heated for 80 min at 200 °C. Hydrochloric acid was added to the digested solution to be adjusted with ca. 4 N of HC1 concentration and the selenium was extracted with dithizone in carbon tetrachloride. (3) Analysis; A 20μl aliquot of the extract was injected into the carbon tube with a microsyringe. The carbon tetrachloride was evaporated by heating for 20 s at 100 °C.Then 50 μl of 0.1% nickel solution to the residue and the selenium was determined according to the operating conditions in Table 1. The proposed method could determine TMSe⁺ in human urine with a recovery of (82102) %, and with a variation coefficient of (3.76.2) %, and total selenium in urine a recovery of (94101)0/0. Detection limits of TMSe⁺ in urine was 1.0 ng/ml and total selenium was 0.5 ng/ml.