Cryotrapping of CO2-rich atmospheres for the analysis of volatile metal compounds using capillary GC-ICP-MS

A cryotrapping GC-ICP-MS method for the determination of volatile metal compounds (VOMS) ill 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 ill 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 N-2 and in a N-2-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.