Analysis of atmospheric organic compounds by thermal desorption-comprehensive two-dimensional gas chromatography-flame ionization detection

Abstract

As a new separation technology developed in the 1990s, comprehensive two-dimensional gas chromatography (GC×GC) has many advantages, such as high resolution, high sensitivity, and large peak capacity. In this work, a GC×GC system coupled with a flame ionization detector (FID) was set up for the measurement of atmospheric organic compounds. Using a thermal desorption (TD) as injector and a cold/hot jet modulator for the GC×GC modulation, the TD-GC×GC-FID system is able to separate various types of C₅–C₁₅ atmospheric organic compounds within only one chromatographic run, including non-methane hydrocarbons (NMHCs), oxygenated volatile organic compounds (OVOCs) and halogenated hydrocarbons. Qualitative analysis was made using a quadruple mass spectrometer in combination with standard gases, and quantitative analysis using external standards combining with FID mass correction factors. The mean standard deviations of the first and second dimension retention times of the target compounds are less than 0.6 s and 0.02 s, respectively. The mean relative standard deviations of the peak volumes are 4.5% for NMHC and 14.3% for all compounds. The average <italic>r</italic>² of the calibration curve exceeds 0.99. The average detection limit is 6.04 ng and the average recovery is around 111%. In the analysis of air samples from an urban site in Beijing January, 2010, more than 400 peaks of organic compounds was detected, of which 103 compounds have been identified including alkanes, alkenes, mono- and poly-aromatics, aldehydes, ketones, alcohols, esters, halogenated hydrocarbons, etc. The total concentration of the quantified constituents averaged 51.3×10^-9 <italic>V/V</italic>. The proportions of OVOCs, aromatics, alkanes, halogenated hydrocarbons, and alkenes were approximately 51%, 30%, 15%, 3%, and 1%, respectively. The top 3 components was ethanol (9.84×10^-9 <italic>V/V</italic>), acetone (6.72×10^-9 <italic>V/V</italic>), and toluene (3.48×10^-9 <italic>V/V</italic>). The TD-GC×GC-FID system can be used as a platform for simultaneous measurements of different groups of atmospheric organic compounds.