Pulsed flow modulation two-dimensional comprehensive gas chromatography–tandem mass spectrometry with supersonic molecular beams

Abstract

Pulsed flow modulation (PFM) two-dimensional comprehensive gas chromatography (GC × GC) was combined with quadrupole-based mass spectrometry (MS) via a supersonic molecular beam (SMB) interface using a triple-quadrupole system as the base platform, which enabled tandem mass spectrometry (MS-MS). PFM is a simple GC × GC modulator that does not consume cryogenic gases while providing tunable second GC × GC column injection time for enabling the use of quadrupole-based mass spectrometry regardless its limited scanning speed. The 20-ml/min second column flow rate involved with PFM is handled, splitless, by the SMB interface without affecting the sensitivity. The combinations of PFM GC × GC–MS with SMB and PFM GC × GC–MS-MS with SMB were explored with the analysis of diazinon and permethrin in coriander. PFM GC × GC–MS with SMB is characterized by enhanced molecular ion and tailing-free fast ion source response time. It enables universal pesticide analysis with full scan and data analysis with reconstructed single ion monitoring on the enhanced molecular ion and another prominent high mass fragment ion. The elimination of the third fragment ion used in standard three ions method results in significantly reduced matrix interference. GC × GC–MS with SMB improves the GC separation, and thereby our ability for sample identification using libraries. GC–MS-MS with SMB provides better reduction (elimination) of matrix interference than GC × GC–MS. However, it is a target method, which is not always applicable. GC × GC–MS-MS does not seem to further reduce matrix interferences over GC–MS-MS and unlike GC × GC–MS, it is incompatible with library identification, but it is beneficial to have both GC × GC and MS-MS capabilities in the same system.