Detection of volatile organic compounds associated with E. coli using headspace correlation gas chromatography

A dynamic headspace correlation gas chromatography (HS-cGC) approach to detect volatile organic compounds associated with Escherichia coli (E. coli) in nutrient broth is described. E. coli identification was achieved by detecting microbial volatile organic compounds (mVOCs) produced by the bacteria in the sample matrix. Headspace of the test solution was introduced into the separation column up to 256 times in a single analysis using a pseudo-random binary modulation sequence (PRBS). A convoluted chromatogram was recorded and later cross-correlated with the injection pattern to generate a correlogram. Inoculated samples starting from single cell inoculum were distinguished from sterile controls after 11 h enrichment. Conventional culture-based plating methods need analysis time on the order of days, but HS-cGC reduced the time-to-detection by approximately one-full day compared to culture-based plating methods. Quantitative comparison of key figures of merit between dynamic HS-cGC and static headspace-comprehensive two-dimensional gas chromatography (HS-GC × GC) is also presented. Here mixed standards were analysed to determine linearity, method detection limit (MDL), limit of quantification (LOQ), and repeatability. The correlation technique demonstrated MDL in the range of 0.5 to 2.0 mg/L and LOQ 2.0 to 5.5 mg/L for the target compounds. These results surpassed the static HS-GC × GC which exhibited a higher MDL (20 to 40 mg/L) and LOQ (80 to 150 mg/L), with comparable linearity and repeatability. With analytical figures of merit 20-40 times better (lower MDL and LOQ) than the previously described GC × GC approach, the HS-cGC methodology is an attractive alternative for trace target analyte determination. HS-cGC has a high potential to complement conventional culture-based plating methods to ramp up surveillance to detect pathogens and/or spoilage microbes in the food setting.