Gas chromatography coupled to electron capture negative ion mass spectrometry with nitrogen as the reagent gas – an alternative method for the determination of polybrominated compounds

Abstract

Gas chromatography in combination with electron capture negative ion mass spectrometry (GC/ECNI-MS) is a sensitive method for the determination of polybrominated compounds in environmental and food samples via detection of the bromide ion isotopes m/z 79 and 81. The standard reagent gas for inducing chemical ionization in GC/ECNI-MS is methane. However, the use of methane has some drawbacks as it promotes carbonization of the filament and ion source. In this study, we explored the suitability of nitrogen as reagent gas for the determination of brominated flame retardants (polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), allyl-2,4,6-tribromophenyl ether (ATE) and 2,3-dibromopropyl-2,4,6-tribromophenyl ether (DPTE)) and halogenated natural products (for instance, methoxylated tetrabrominated diphenylethers and polybrominated hexahydroxanthene derivatives). An ion source temperature of 250 degrees C and a nitrogen pressure of 7 Torr in the ion source gave the highest response for m/z 79 and 81 of virtually all investigated polybrominated compounds. Using these conditions, nitrogen-mediated GC/ECNI-MS usually gave higher sensitivity than the method with methane previously used in our lab. In addition, the ion source was not contaminated to the same degree and the lifetime of the filament was significantly increased. Moreover, the response factors of the different polybrominated compounds with the exception of 2,4,6-tribromophenol were more uniform than with methane. Nitrogen is available at very high purity at relatively low price.