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

摘要

A high temperature diaphragm valve-based two-dimensional (2D) gas chromatography (GC x 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 degrees C. Use of the diaphragm valve allowed for the use of uncoupled carrier gas flows for D-1 (first column dimension) and 2D (second column dimension), with a D-1 flow rate of 1 ml/min, and a D-2 flow rate 3 ml/min. The 3 ml/min flow rate on D-2 was selected to ensure compatibility with most TOFMS detectors. For valve-based modulation, a 5 mu l sample loop coupled with a 60 ms pulse width was selected, providing sufficient sensitivity concurrent with an acceptable D-2 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 degrees C to 450 degrees C was used to initially study instrument performance. For a 120 min separation and a modulation period P-M of 2 s, average peak widths-at-base of 10 s and 94 ms were achieved for the alkanes on the D-1 and D-2 dimensions, respectively. Hence, the D-1 peak capacity is (1)n(c)similar to 700,and the 2D peak capacity can in principle be (2)n(c)similar to 20. Thus the ideal 2D peak capacity could in principle approach n(c,2D)similar to 14,000 using the 120 min D-1 run time. The limit of detection (LOD) for docosane, a representative analyte, was determined to be 1.5 ppm injected concentration when 2 mu l 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 20 min and a short modulation period P-M of 1 s. Average peak widths-at-base of 5.4 s and 166 ms were achieved on the D-1 and D-2 dimensions, respectively. This yielded a (1)n(c)similar to 220 and a (2)n(c)similar to 6. Therefore, the 2D peak capacity is n(c,2D)similar to 1320 with the 20 min diesel separation. (C) 2016 Elsevier B.V. All rights reserved.