High temperature diaphragm valve-based comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry

Abstract

A high temperature diaphragm valve-based two-dimensional (2D) gas chromatography (GC×GC) with time-of-flight mass spectrometry (TOFMS) instrument, with the valve mounted directly in the GC oven, is demonstrated with separations up to 325°C. Use of the diaphragm valve allowed for the use of uncoupled carrier gas flows for 1D (first column dimension) and 2D (second column dimension), with a 1D flow rate of 1ml/min, and a 2D flow rate 3ml/min. The 3ml/min flow rate on 2D was selected to ensure compatibility with most TOFMS detectors. For valve-based modulation, a 5µl sample loop coupled with a 60ms pulse width was selected, providing sufficient sensitivity concurrent with an acceptable 2D peak capacity. A 44-component mixture of alkanes, alcohols, and polyaromatic hydrocarbons (including n-alkanes of heptane to triacontane) whose boiling points range from 98°C to 450°C was used to initially study instrument performance. For a 120min separation and a modulation period PM of 2s, average peak widths-at-base of 10s and 94ms were achieved for the alkanes on the 1D and 2D dimensions, respectively. Hence, the 1D peak capacity is 1nc~700, and the 2D peak capacity can in principle be 2nc~20. Thus the ideal 2D peak capacity could in principle approach nc,2D~14,000 using the 120min 1D run time. The limit of detection (LOD) for docosane, a representative analyte, was determined to be 1.5ppm injected concentration when 2µl of liquid sample was injected with a 20:1 split. A separation of diesel fuel demonstrated the practical utility of the instrument with this complex sample using a relatively fast run time of 20min and a short modulation period PM of 1s. Average peak widths-at-base of 5.4s and 166ms were achieved on the 1D and 2D dimensions, respectively. This yielded a 1nc~220 and a 2nc~ 6. Therefore, the 2D peak capacity is nc,2D~1320 with the 20min diesel separation.