2008 Volume 24 Issue 12 Pages 1529-1536
The drift in sensitivity due to carbon deposition on the sampling cone, skimmer cone and ion lenses has been a serious problem in gas chromatography/inductively coupled plasma mass spectrometry (GC/ICP-MS). To overcome this problem, a high-speed switching method between a mixed-gas plasma and a pure-argon plasma (named plasma gas-switching method) using an oxygen permeation tube and a switching valve was developed. This enabled both the cleaning of deposited carbon and an enhancement of the sensitivity; as a consequence, both the repeatability and the sensitivity of polybrominated diphenylether (PBDE) were improved by more than 3 and 4 times, respectively. The drifts of sensitivity over a period of 8 h were less than 5% in most cases. Concerning the analytical performance of thermally labile congeners from octa- to deca-BDE, the detection limits, dynamic ranges of the calibration graphs and unequivalent sensitivities were remarkably improved by using a metal capillary separation column coated with a very thin (0.05 µmm) film of immobilized-polydimethylsiloxane. The detection limits ranged from 0.014 pg (BDE-154) to 0.093 pg (BDE-209), which were equal or superior to the lowest values reported hitherto by GC/MS (high resolution). A remarkable loss of sensitivity for highly-brominated congeners, such as nona- and deca-BDE, was observed in an analysis of PBDE technical mixtures when the solvent was methanol. The loss of sensitivity turned out to be due to an activation of the retention gap used for on-column injection; this problem was solved by changing methanol to isooctane in the sample-preparation step before analysis.