High-performance liquid chromatography–ultrasonic nebulizer high-power nitrogen microwave-induced plasma mass spectrometry, real-time on-line coupling for selenium speciation analysis

The coupling of a high-power nitrogen (N2) microwave-induced plasma (MIP) mass spectrometry – (MS) (1.3 kW) with high-performance liquid chromatography, connected with concentric nebulizer (CN), ultrasonic nebulizer (USN) and a hydride generation (HG) systems, for the optimization and determination of selenium compounds, has been carried out. The MIP-MS system fulfils the ideal requirement being an on-line real-time chromatographic detector for Se speciation analysis. Interchanging of MIP-MS system fabricated nebulizer (concentric) with an ultrasonic nebulizer increases about 3.4–12 (peak height) and 6.5–10 (peak area) times ion signals for the selenium compounds. The detection limits for selenate, selenite, trimethylselenonium ion (TmSe), selenomethionine (Semet) and selenoethionine (Seet) (in Milli-Q-water) obtained with the optimized HPLC–USN-N2MIP-MS system are 0.11, 0.14, 0.09, 0.14 and 0.10 μg L−1, respectively, about 12–48 times lower than the HPLC–CN-MIP-MS and 1.5–4.4 (peak height) times lower compared to the HPLC–CN-inductively coupled plasma (ICP)–MS coupling. Considering peak area, the repeatability (R.S.D. for three successive analyses) and intermediate precision (R.S.D. for three successive analyses performed on three different days), achieved for five Se compounds are 0.8–5.6, and 1.1–5.9%, comparable with the HPLC–CN-ICP-MS, HPLC–HG-MIP-MS and HPLC–CN-MIP-MS systems. The combined HPLC–USN-N2MIP-MS has been adequately applied for the determination of Se compounds in certified National Institute for Environmental studies human urine CRM No. 18. The results reasonably agree with the HPLC–CN-ICP-MS values. This encouraging combination may be an alternative ion source of mass spectrometry for coming generation in regard to the selenium speciation analysis.