Long term stability of organic selenium species in aqueous solutions
Résumé
Long term stability of organic selenium compounds (selenocystine, selenomethionine, trimethylselenonium ion) has been studied over a one year period for 2 analyte concentrations: 25 and 150 μg/L Se, at pH 4.5 in the dark, under different storage conditions: temperature of -20°C, 4°C, 20°C, 40°C; in Pyrex, Teflon, or polyethylene containers; in an aqueous matrix or in the presence of a chromatographic counter ion (pentyl sulfonate at 10-4 mol/L concentration). Light effects have also been tested. The stability of the selenium species was monitored by HPLC-ICP/MS. Storage conditions can drastically alter the stability of organic selenium species. Organoselenium compounds were shown to be stable in the dark over a one year period in an aqueous matrix at pH 4.5 in Pyrex containers at both 4°C and 20°C. Pyrex vials exposed to natural sunlight at room temperature resulted in a steady decrease of the selenoamino acid concentration. Teflon containers caused losses of less than 25% at both 4°C and 20°C in the dark. However, polyethylene vials presented, at all temperatures tested, a rapid decrease of the TMSe+ concentration. The stability of the Se species studied did not show significant differences between 4°C and 20°C in any container material used. Storage of solutions at 40°C led to slight differences between the Pyrex and Teflon containers. However, polyethylene presented a drastic decrease of the three species over time at this higher temperature. Solutions frozen at -20° C in polyethylene vials did not stabilize the TMSe+ signal. Finally, concentrations and matrices of the samples did not significantly affect the stability of the species. © Springer-Verlag 1998.