Before the ethylenglycol in engine oils can be analysed with gas chromatography (GC) a derivatisation reagent which reacts with the ethylenglycol is added. The sample is heated afterwards and all volatile components are transferred into the GC with a headspace injection. They reach a column which holds the analytes back with varying durations. One after the other the analytes are rinsed off the column and detected afterwards. The identification of the ethylenglycol is based on the retention time.
The concentration is calculated by a comparison of the peak area with prior detected calibration standards of which concentration is known.