Quadrupole mass spectrometer operating in the electron-capture negative ion mode as detector for comprehensive two-dimensional gas chromatography.

A recently introduced rapid-scanning quadrupole mass spectrometer (qMS) with an electron-capture negative ion (ECNI) option, the Perkin-Elmer Clarus 500, was tested as a detector for comprehensive two-dimensional gas chromatography (GC x GC). The parameters influencing the data acquisition rate in the scan mode, such as scan time and inter-scan delay, and in the selected ion monitoring mode, such as dwell time and inter-channel delay, were evaluated. In the scan mode, good-quality mass spectra covering a range of 300 Da can be obtained at an acquisition rate of 23 Hz; in selected ion monitoring, an acquisition rate of 90Hz can be achieved when monitoring a single ion. Compared with electron ionisation, the use of electron-capture negative ionisation causes no extra peak broadening. As applications, mixtures of polychlorinated n-alkanes (PCAs), polybrominated diphenyl ethers (PBDEs) and polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) were analysed. The separation of PCAs based on their number of chlorine substituents was confirmed for the first time by using GC x GC-ECNI qMS in the scan mode and a significantly improved limit of detection was achieved for BDEs (10-150 fg injected) and CDD/Fs (10-700 fg injected) in the selected ion monitoring mode.