Rapid detection of synthetic biomarkers of Escherichia coli in water using microAnalyzer: a field dependence study

Abstract

Mixtures of 12 known volatile metabolites of Escherichia coli (2,5-dimethyltetrahydrofuran, dimethyl disulfide, 2-heptanone, 2,5-dimethylpyrazine, benzaldehyde, dimethyl trisulfide, 2-nonanone, nonanal, decanal, 2-undecanone, indole, and 2-tridecanone) were prepared from internal standards in water. The headspace gases were then analyzed using microAnalyzer™, a miniaturized Gas Chromatography-Differential Mobility Spectrometry (GC-DMS) system. Differential mobility spectra showed monomer peaks of the analytes with the observed retention times below 3 min. Dispersion voltages, determining the dependence of signal intensities and compensation voltages of each analyte on the applied radio frequency (RF) voltages, were recorded for positive and negative modes. It was found that at increasing RF voltages the monomer peaks of compounds of lower molecular masses tend to shift to more negative compensation voltages; whereas, those of higher molecular masses tend to shift to more positive compensation voltages. The shift results in increase separation among each peak. The signal intensities for all peaks, however, tend to decrease at higher RF voltages. The RF voltage which gave optimum peaks separation and signal resolution was 1,200 V (corresponds to 24 kV/cm). This study demonstrates the potential of microAnalyzer™ as an integrated gas chromatograph detector for a preliminary screening system in the on-site detection of E. coli in water. The operational principle of the instrument is also presented in this study.