Figure 2. Thermochemolytic-gas chromatography-electron impact/mass spectrometry (THM-GC-EI/MS) of purified phthiocerol dimycocerosate (PDIM) waxes.

The selected ion monitored EI/MS chromatogram shows the target fragment ions m/z 101 and m/z 88, resulting from the major trimethyl C₂₉ and tetramethyl C₃₀, and C₃₂ mycocerosates released by thermochemolysis of the PDIMs. A minor proportion of a tetramethyl C₃₁ mycocerosate is also indicated. The characteristic doublet peaks are due to racemisation during the alkaline hydrolysis. The method relied on recognizing comparable proportions of the combined C₂₉/C₃₀ peak and the C₃₂ peak, as was the case in all the positive specimens. Some minor variation in the ratios of the individual peaks was observed, but this did not affect the diagnostic ratios.