Smokeless tobacco can contain thousands of analytes, making it an extremely difficult matrix for identification of pesticide residues.
Smokeless tobacco can contain thousands of analytes, making it an extremely difficult matrix for identification of pesticide residues. Many current methodologies incorporate the use of complex, time consuming sample cleanup techniques to eliminate much of the matrix interference prior to analysis by GC–MS.
This application highlights how the increased peak capacity of comprehensive two-dimensional gas chromatography can minimize the need for extensive sample cleanup methods. A GC×GC-TOFMS analysis of a commercially available smokeless tobacco product is shown. A QuEChERS sample extraction was used without dispersive solid phase cleanup.
Calibration curves were generated for 87 pesticides at concentrations from 0.5 to 2000 pg/μL. The correlation coefficients averaged 0.993 for the 87 pesticides. A QuEChERS extract of smokeless tobacco was spiked with these pesticides at 100 pg/μL and analyzed by GC×GC-TOFMS.
All pesticides were detected and identified in the smokeless tobacco extract. Interferences such as wintergreen oil, which would co-elute with pesticide residues in a one-dimensional GC–MS analysis, were eliminated by the increased resolution of GC×GC-TOFMS.
Figure 1: Total ion contour plot showing GCÃC-TOFMS analysis of spiked smokeless tobacco extract.
Figure 1 displays a total ion contour plot for the spiked tobacco extract showing a partial group of the pesticides detected. The region highlighted by the orange rectangle exhibits the y-axis separation of Dichlorvos from an intense peak for wintergreen oil. Figure 2 illustrates that quantitation using (m/z 109) would still result in interference from the wintergreen oil in a one-dimensional separation as both analytes contain this mass fragment. In this example, the GC×GC separation is critical to removing the potential for quantitation bias.
Figure 2: Expanded view of the highlighted region from Figure 1 now displaying only (m/z 109).
In addition to the increased chromatographic resolution, the use of a Time of Flight Mass Spectrometer provides the ability to acquire full mass range spectra without sacrificing sensitivity. This is beneficial for detecting not only target pesticides, but also new and emerging contaminants.
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