Optimization of capillary GC/FTIR for complex sample analysis

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Virginia Tech


Optimization of capillary gas chromatography-Fourier Transform Infrared (GC-FTIR) spectrometry has been accomplished by studying various columns, lightpipe designs, FTIR detectors and spectroscopic parameters. For adequate separation of complex samples the efficiency of WCOT (Wall Coated Open Tubular) fused silica capillary columns was found to be unmatched by packed columns or wide bore glass capillaries. A consequence of using more narrow bore columns, however, is lower sample capacity and less IR detectability. Two 6 cm light pipes and a more narrow 40 cm lightpipe were compared with respect to both optical throughput and eluent band broadening. FTIR spectroscopic parameters such as mirror velocity and number of scans coadded were examined in order to achieve an optimum signal to noise ratio. The complexity of a particular sample has been shown to dictate certain spectroscopic parameters. The sensitivity differences of two liquid-nitrogen cooled FTIR detectors used in the GC-FTIR experiments have been determined with reference to using them with either a long or short lightpipe.

The capability of optimized capillary GC-FTIR has been demonstrated in the analysis of model compound mixtures and comp lex petroleum products including test aviation jet fuels. Major attention was given to the detection and identification of aliphatic and aromatic components in the highly complex samples. Computerized library search routines have been used to tentatively identify eluting components by infrared spectral matching to quality vapor phase library file spectra. Gas chromatography-mass spectrometry (GC-MS) data are also included for the same jet fuel samples to directly compare extent of information provided and relative spectroscopic sensitivities.