High-speed cryo-focusing injection for gas chromatography: Reduction of injection band broadening with concentration enrichment

Abstract

In order to maximize peak capacity and detection sensitivity of fast gas chromatography (GC) separations, it is necessary to minimize band broadening, and in particular due to injection since this is often a major contributor. A high-speed cryo-focusing injection (HSCFI) system was constructed to first cryogenically focus analyte compounds in a 6cm long section of metal MXT column, and second, reinject the focused analytes by rapidly resistively heating the metal column via an in-house built electronic circuit. Since the cryogenically cooled section of column is small (∼750nl) and the direct resistive heating is fast (∼6000°C/s), HSCFI is demonstrated to produce an analyte peak with a 6.3ms width at half height, w1/2. This was achieved using a 1m long column with a 180μm inner diameter (i.d.) operated at an absolute head pressure of 55psi and an oven temperature of 60°C, with a 10V pulse applied to the metal column for 50ms. HSCFI was also used to demonstrate the head space sampling and fast GC analysis of an aqueous solution containing six test analytes (acetone, methanol, ethanol, toluene, chlorobenzene, pentanol). Using Henry’s law constants for each of the analytes, injected mass limits of detection (LODs) were typically in the low pg levels (e.g., 1.2pg for acetone) for the high speed separation. Finally, to demonstrate the use of HSCFI with a complex sample, a gasoline was separated using a 20m×100μm i.d. column and the stock GC oven for temperature programming, which provided a separation time of 200s and an average peak width at the base of 440ms resulting in a total peak capacity of 460 peaks (at unit resolution).