Pseudo-Sadtler retention indices were calculated using persistent trace level capillary column artifacts, evident in the gas chromatography–mass spectrometry analysis of a natural product extract. The artifacts consisted mainly of a series of polymethylcyclosiloxanes eluting during a linear temperature program. These were used to determine retention indices of structures in the extract, and these indices were then compared with those derived from the more traditional n-alkanes calibration method.