Speciation of organic selenium compounds by reversed-phase liquid chromatography and inductively coupled plasma mass spectrometry. Part II. Sector field instrument with high mass resolution

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Abstract
The speciation of four selected organic Se compounds (selenocystine, selenocystamine, selenomethionine and selenoethionine) was studied by coupling high-performance liquid chromatography (HPLC) to inductively coupled plasma mass spectrometry (ICP-MS) with hydraulic high pressure nebulization (HHPN) for sample introduction into a double focusing magnetic sector field instrument in order to overcome problems from spectral interferences. Reversed-phase chromatography with methanol as the eluent was applied to the separation of the organic Se compounds. The nature of the interferences due to methanol was elucidated by application of high mass resolution. Finally, a mass resolution of R = 1400 was found to be sufficient for resolution of the interferences from the isotopes of analytical significance with which, in comparison with low resolution operation (cf. Part I), detection limits were improved to between 0.002 ng ml−1 for selenocystine and 0.01 ng ml−1 for selenocystamine. With respect to a sample volume of 200 µl, this enabled micro analysis of the compounds with a content below 2 pg.

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