DIRECT ANALYSIS OF THIN-LAYER CHROMATOGRAPHY SPOTS BY THERMAL EXTRACTION-GAS CHROMATOGRAPHY MASS-SPECTROSCOPY

A method of direct analysis of separated or overlapped silica gel thin-layer chromatographic (TLC) spots is demonstrated with seven naphthalene compounds, four polycyclic aromatic hydrocarbons (PAHs), and three pesticides. The TLC spot is scraped off and loaded into the sample cell of a thermal extraction-gas chromatography-mass spectrometer (TE- GC-MS), where the TLC spot is gradually heated and the analytes are thermally extracted, separated, and finally detected with an ion trap mass spectrometer (ITD). This thermal desorption method is milder than laser desorption and permits analytes to be desorbed and analyzed in a straightforward manner without extensive decomposition. Analytes are identified at the level of 20 ng/spot, and a detection limit of several hundred picograms is reported for the analysis of seven naphthalene compounds when the split ratio is 5:1. This method can be applied to thermally stable substances that can be desorbed from TLC silica gel. © Oxford University Press 1992.