SPECIATION OF 4 SELENIUM-COMPOUNDS USING HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY WITH ONLINE DETECTION BY INDUCTIVELY-COUPLED PLASMA-MASS SPECTROMETRY OR FLAME ATOMIC-ABSORPTION SPECTROMETRY

An analytical method for the speciation of selenomethionine, selenocys tine, selenite and selenate by high performance liquid chromatography (HPLC) with atomic spectrometric detection is presented. An organic po lymeric strong anion exchange column was used as the stationary phase in combination with an aqueous solution of 6 mmol L-1 of salicylate io n at pH 8.5 as the mobile phase which allowed the isocratic separation of the four selenium analytes within 8 minutes. The separated seleniu m species were detected on-line by flame atomic absorption spectrometr y (FAAS) or inductively coupled plasma mass spectrometry (ICP-MS). The signal-to-noise ratio of the FAAS detector was optimized using a hydr ogen-argon entrained-air flame and a slotted-tube atom trap (STAT) in the flame. The limit of detection (3 sigma) achieved by the HPLC-FAAS system was 1 mg L-1 of selenium (100 mu L injections) for each of the four selenium species. More powerful selenium detection was achieved u sing an ELAN 5000 ICP-MS instrument. Selenium was measured at m/z = 82 . The ICP-MS signal intensity was enhanced by a factor of 3-4 after ad dition of 3% methanol to the chromatographic mobile phase and by using an increased plasma power input of 1300 W. The limit of detection ach ieved under these conditions was 1 mu g L-1 (100 mu L injections). The HPLC-ICP-MS system was used for selenium speciation of selenite and s elenate in aqueous solutions during a BCR certification exercise and f or selenium speciation in the certified reference material, BCR No. 40 2 White Clover. Extraction experiments revealed that the selenium spec ies in the biological material were extractable only in the presence o f water in the extraction medium. The results indicated that selenate and a compound of unknown identity U were present in the plant sample.