Less than one minute low-pressure gas chromatography - mass spectrometry

Abstract

Conventional gas chromatography - mass spectrometry (GC-MS) takes 20–40 min per sample, which is undesirably slow in any application if speed can be increased while still meeting analytical needs. In this study, we achieved reasonably good separations with full analysis cycle times of less than 1 min by combining for the first time low-pressure (LP) GC-MS with low thermal mass (LTM) resistive-heating for rapid temperature ramping and cooling of the capillary column. The analytical column is threaded into the LTM thin-walled metal tubing in an instrumental device known as “LTM Fast GC” that is mounted at the top of the gas chromatograph in a detector port. The column inlet and outlet are connected to the GC injector and MS transfer line as usual. For LPGC-MS, a 40 cm, 0.1 mm. i.d. uncoated flow restrictor capillary connected at the injector is coupled with a 2.6 m, 0.25 mm i.d., 0.25 µm film thickness analytical column leading to the MS. Thus, the inlet operates at normal GC pressures, but the analytical column is under vacuum, which increases the optimal helium carrier gas flow velocity thereby increasing speed of full range separations while maintaining acceptable quality of chromatography. This column configuration in LTM-LPGC-MS trades a 64-fold gain in speed of analysis vs. standard GC-MS for a 4-fold loss in chromatographic peak capacity, thereby converting analysis time from minutes into seconds in common applications. For example, jet fuel containing fatty acid methyl esters (akin to biofuel) was separated in 25 s with <1 min full analysis cycle time. An EPA Method 8270 mixture of 76 analytes was also analyzed in <1 min full cycle time by LTM-LPGC-MS. Other examples include very fast analysis of heroin in a street drug powder and elucidation of a new organic synthetic compound. In this report, we describe and discuss the several advantageous and practical features of LTM-LPGC-MS, as well as its trade-offs.