An automatic cryotrapping and cryofocussing system for parallel ICP-MS and EI-MS detection of volatile arsenic compounds in gaseous samples

Abstract

A new GC-ICP-MS/EI-MS coupling is presented, which enables the quantification and identification of volatile metal and metalloid compounds in gaseous samples simultaneously. The proposed assembly is fully controlled using Windows compatible software to ensure precise and reproducible analytical results. The cryotrapping (CT) system is critical for sensitive and precise detection of volatile arsenic compounds. Thus, the CT trap was newly designed and factors affecting CT efficiency were comprehensively optimized, especially the trapping materials, trapping flow rates, heating rates and trapping temperatures. Silanized glass beads (2 mm) as the packing material in the CT trap greatly increased the trapping efficiency. A relatively high trapping flow rate (200 mL min⁻¹) gave the best recoveries. An adequate heating rate (e.g. 11.3 watt × 360 s) was required to desorb arsenic and to prevent thermal decomposition. Liquid argon was demonstrated to be the most appropriate coolant, since this prevented freezing of O₂ and blockage of the trap. In comparison, cryofocusing (CF) was less dependent on aforementioned parameters. Thick film chromatography allowed baseline separation of different arsine compounds at room temperature and eliminated the interference from xenon. Analysis of volatile arsenic with more complicated structures such as triethylarsine using a CT-CF technique is suitable for qualitative but not for quantitative purposes due to lower stability of these compounds. The resulting detection limits and RSD of arsine and methyl arsines with ICP-MS detection are 0.12–0.41 pg arsenic, and 0.76–1.29%, which is remarkably lower than those in previous studies.