Excretion of trimethylselenonium ion in human urine

Abstract

A method to permit isolation and measurement of trimethylselenonium ion [TMSe, (CH 3) 3Se +] from 1 liter of human urine was developed. The method was based on precipitation of TMSe with ammonium reineckate, preseparation with anion-exchange resin, and final thermal decomposition and collection of the product in HNO 3. It was tested for recovery and separation from other selenium moieties present in urine using both in vivo-labeled rat urine and human urine spiked with unlabeled TMSe. Recoveries from the former were in the range 76.8–87.0% (mean ± SD: 81.8 ± 3.7%, n = 5), while for the latter they were in the range 72.0–93.0% (mean ± SD for three occasions (%): 80.9 ± 5.5, 81.4 ± 7.8, and 78.9 ± 1.0). The reliability of the method was tested against and HPLC procedure using in vivo-labeled rat's urine. The mean (±SD) percentage of urine radioactivity appearing as TMSe was 36.0 ± 5.7% for the present and 36.2 ± 6.6% for the HPLC method. The mean of deviations, as percentage of the HPLC method, was −0.03 ± 8.8%. The linear regression equation for the two methods was y = −0.805 + 1.029 x ( r 2 = 0.81). Excretion of TMSe was measured in urine samples from several persons (range: 0.18–0.37 μg Se/liter; mean ± SD: 0.26 ± 0.07, n = 9). One subject consumed three separate doses of unlabeled selenite on alternate days (Day 1, 197 μg Se; Day 3, 395; and Day 5, 592). For the first 24 h of each period, TMSe excretions (μg Se/24 h) were 0.24, 0.53, and 0.97, respectively. The corresponding figures for the 24- to 48-h collections were 0.13, 0.34, and 0.53 μg/24 h, respectively. When expressed as percentage of urine Se the range was 0.14–0.44%. It is concluded that this method is reliable for accurate measurement of TMSe from a large (1 liter) volume of human urine, and TMSe constitutes a quantitatively minor fraction of urine selenium in typical North Americans.