Megabore versus Microbore as the Optimal Column for Fast Gas Chromatography/Mass Spectrometry

The use of a short megabore (0.53 mm ID) column for fast gas chromatography/mass spectrometry (GC/MS) was compared with the use of a short microbore (0.1 mm ID) capillary column and demonstrated to be superior. Several aspects and experimental parameters that affect fast GC/MS are demonstrated and discussed. These aspects include the acceptable column flow rate, column internal diameter and length, mass analyzer, GC/MS interface properties, ionization method and the inter-relationship between these features. The microbore column provides, at best, a modest gain in chromatographic resolution, however, the accompanying loss in concentration sensitivity is severe due to greatly reduced sample introduction rate and other effects. We claim that, with fast GC/MS analysis the mass spectrometer and ionization methods play a major role in the overall separation capability and that enhanced mass spectrometric separation is more useful than the modest gain achieved with the microbore column. Thus, the use of a supersonic molecular beam with electron ionization or hyperthermal surface ionization contributes greatly to fast GC/MS. This contribution is further enhanced due to the high flow-rate, fast injection that minimizes the time spent on GC temperature programming and cooling. It is demonstrated that fast GC/MS does not necessarily require time-of-flight mass analysis and that the conjectured problem of mass spectral skewing is negligible even with microbore columns. It is emphasized and demonstrated that compatibility with advanced tools for fast sample preparation is an important consideration for an effective fast GC/MS analysis with real-world samples. Fast GC/MS analysis, without extraction, of the pesticide diazinon in the herb chervil is shown using a novel direct sample introduction device, a short megabore column and electron ionization in a supersonic molecular beam.