Submitted to: Journal of Chromatography A
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 22, 2007
Publication Date: January 26, 2007
Citation: Hoh, E., Mastovska, K., Lehotay, S.J. 2007. Optimization of separation and detection for comprehensive two-dimensional gas chromatography-time-of-flight mass spectrometry analysis of polychlorinated dibenzo-p-dioxins and dibenzofurans. Journal of Chromatography A. 1145:210-221. Interpretive Summary: The 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are among the most toxic compounds known, and these chemicals should be monitored at ultra-trace levels in food and the environment to protect human health and the ecosystem. The current predominant method of analysis is too expensive and cumbersome, often taking $1,000 per sample and a full week of labor-intensive sample preparation. The common type of analytical instrument used for detection of PDCD/Fs is also very expensive, bulky, and requires an expert operator. In this research study, we evaluated comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF) as an alternative approach to lower costs and speed analysis of PCDD/Fs. This manuscript describes the systematic optimization and evaluation of GC×GC-TOF conditions to achieve the best separation and lowest detection limits. This report will be very useful to analytical chemists using the GC×GC-TOF approach for any analysis, particularly for PCDD/Fs, and is the first step in the development of a faster and less costly method to extract, separate, detect, and identify PCDD/Fs at ultra-trace levels in food and other matrices.
Technical Abstract: The 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are among the most toxic compounds known. The current predominant method of analysis is too expensive and cumbersome, and comprehensive gas chromatography coupled to time-of-flight mass spectrometry (GC×GC-TOF) has the potential to lower the costs and speed analysis of PCDD/Fs. In this study, GC×GC-TOF parameters were evaluated and optimized to yield complete separation of the 17 most important PCDD/F congeners from PCB interferences, and to attain the lowest detection limits. The optimization study entailed evaluation of oven temperature programs, column flow rates, ion source temperatures, electron ionization energy, data acquisition rate, and various GC×GC parameters. After optimization, all 17 PCDD/Fs were separated in <60 min, and in particular, the critical pair of 2,3,7,8-tetrachloro dibenzo-p-dioxin (TCDD) and pentachlorobiphenyl congener CB126 did not co-elute chromatographically. Accurate identification and determination of all analytes could be made using their clean full mass spectra. In GC×GC, the modulation period and start time were the most important factors that affected sensitivity and selectivity for the analysis of the PCDD/Fs. The modulation period should be '4 s to preserve separations achieved in one dimensional GC, and the modulation start time was important to achieve one large slice and 2 smaller symmetrical slices of TCDD to maximize its detection sensitivity. After optimization, the method could identify 0.25 pg of TCDD injected from its full mass spectrum.