URINE SELENIUM DETERMINATION BY ELECTROTHERMAL ATOMIC-ABSORPTION SPECTROMETRY - INFLUENCE OF URINARY PHOSPHATES ON THE TRIMETHYLSELENONIUM ION SIGNAL

A feasibility study to determine inorganic selenium and its organic me tabolites in urine by means of ETAAS with Zeeman-effect background cor rection is presented in detail. The procedure in itself is rather simp le: dilution of the urine prior to digestion with a nitric acid-hydrog en peroxide mixture and direct analysis of the digest by ETAAS using c opper (100 mu g) and magnesium nitrate (200 mu g) as the chemical modi fier. Matrix matched calibration is used. There is little emphasis on the various instrumental parameters (charring and atomization curves) and the choice of chemical modifiers. Instead, the focus is on the beh aviour of TMSe(+) (trimethylselenonium ion) in urine and on ways of im proving its recovery from a urine sample. The effect of the specific g ravity, the digestion procedure, the amounts and nature of various ino rganic anions, pre-dilution of the urine before testing and modifier c oncentration on the TMSe(+) signal is clearly demonstrated. Actual dat a from real exposed workers show the effect of the concentration of ph osphates on the recovery; of TMSe(+) (78 +/- 21%) in individual spot s amples. It can be seen that the suppression effect of phosphates on th e TMSe(+) signal in urine is more pronounced and more correlated in te st samples spiked with phosphates (with the same urine matrix) than in various workers' spot samples where the phosphates were experimentall y determined. This proves that phosphates are only partly responsible for this suppression effect and that most probably some unknown chemic al species are involved.