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

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 P_M 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 ¹n_c~700, and the ²D peak capacity can in principle be ²n_c~20. Thus the ideal 2D peak capacity could in principle approach n_c,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 P_M of 1s. Average peak widths-at-base of 5.4s and 166ms were achieved on the ¹D and ²D dimensions, respectively. This yielded a ¹n_c~220 and a ²n_c~ 6. Therefore, the 2D peak capacity is n_c,2D~1320 with the 20min diesel separation.