Abstract

A cryotrapping GC-ICP-MS method for the determination of volatile metal compounds (VOMs) in gases from anaerobic environments has been developed. The major gases CH₄ and CO₂ have to be separated from the less volatile metal compounds. The inert capillary cryo-trap was submerged in liquid nitrogen or in a dry-ice/acetone slush, the latter preventing the condensation of CH₄ but not CO₂ and water. Cartridges filled with 4–5 g of NaOH were installed in front of the cryotrap in order to eliminate water and especially CO₂ before the cryogenic preconcentration step of the VOMs. The cryo-trap was hyphenated to a capillary GC-ICP-MS, which directly enabled multielemental speciation of the VOMs in the gas samples. The effect of CO₂ in the gas sample on the ICP-MS was monitored by a continuous internal standard (an added indium solution of 10 ng mL⁻¹). The reproducibility of the retention time and intensities as well as the recovery rates for VOMs were investigated using an in-house gas standard containing AsH₃, MeAsH₂, Me₂AsH, Me₃As, SbH₃, MeSbH₂, Me₂SbH, Me₃Sb, SnH₄, MeSnH₃, Me₂SnH₂, Me₃SnH, BuSnH₃ in N₂ and in a N₂–CH₄–CO₂ mixture. The stannane standards showed recovery rates of about 90%, while the different arsenic standards recorded recovery rates between 80 and 90%. Care has to be taken if antimony species have to be measured since their recovery rates vary between 30 and 75%, due to a chemical reaction with NaOH, which consequently reduces the volatility of the compounds and hence no memory effect can be identified originating from the NaOH cartridge.