Discard the rear foam plug. Do not discard the glass sampling tube, it can be reused. Seal the vials with PTFE-lined septa and allow them to desorb for one hour. Shake the vials by hand periodiocally during this time. If necessary, transfer aliquots of the samples to the vials used in GC analysis.
Any compound having a similar retention time to that of the analyte is a potential interference.
Generally, chromatographic conditions can be altered to separate interferences from the analyte. Retention time on a single column is not proof of chemical identity. Analysis by an alternate GC column, detection by an FPD in the sulfur mode and confirmation by mass spectrometry are additional means of identification. Construct a calibration curve by plotting detector response versus standard concentration. Determine the concentration of fonofos in each sample from the calibration curve.