First derivative spectrophotometric determination of uranium(VI) and vanadium(V) in natural and saline waters and some synthetic matrices using PAR and cetylpyridinum chloride

The aim of this study was to determine the Se concentration in urine samples under routine clinical laboratory conditions. The sample was completely mineralised using a focused microwave oven with a mixture of nitric acid and sulphuric acid for 14min. Se was measured by using hydride generation-atomic fluorescence spectrometry (HG-AFS). Complete recovery was achieved for SeCys, SeMet and TMeSe species. The method was validated by analysing the standard reference material SRM 2670 urine (normal and elevated levels), and by regular participation in Interlaboratory Exercises. Detection limit and precision in terms of reproducibility and repeatability were established. A study of the stability of digested samples and pre-reduced solutions over time was performed to propose the optimised method for routine analysis.