Selenium in plants by mass spectrometric techniques: developments in bio-analytical methods - Plenary Lecture

Various plants can accumulate Se up to the thousands of ppm. These are called accumulators and they have potential to remediate areas contaminated with this metalloid. Some of them, like Arabidopsis thaliana or Brassica juncea (Indian mustard) have been investigated in terms of the Se metabolic pathway. To date few studies have been done for selenium speciation with most studies reporting total selenium concentration in various parts of the plant. This present report summarizes some of the studies carried out in terms of: extraction of Se species, cleaning procedures, separation methodologies and mass spectrometric techniques employed. The use of inductively coupled plasma mass spectrometry (ICP-MS) in conjunction with liquid or gas chromatographic techniques (HPLC and GC) as separation techniques provide an attractive methodology for determining Se species in plants. Some of the species produced by the plant, such as Se-methylselenocysteine or Se-methylselenomethionine can be identified at ppb levels by RP-HPLC-ICP-MS, while others needed to be further characterized by ES-MS. The coupling of GC-ICP-MS using solid phase microextraction (SPME) as sample preparation system is also evaluated for the determination of the Se/S volatile species in the head-space of Brassica juncea seedlings. Detection limits on the ppt level (7-300 ppt depending on the species) and adequate precision for Se and S species suggest GC-ICP-MS as an excellent methodology for determination of volatiles with minimum sample preparation.