| The development and use of field portable instruments for on-site analysis is a growing area of research. The instruments are being designed for applications ranging from environmental monitoring to homeland security. One of the design routes for these instruments are meso and micro-scale gas chromatographs for sampling, separation, and detection of organic compounds in large volume air samples.; A meso-scale gas chromatograph, under development at the University of Michigan, uses ambient air as a carrier gas and microfabricated sensors as detectors to eliminate the need for onboard gas tanks. This reduces instrument size and weight, but the use of air as a carrier gas also reduces the optimal carrier gas velocity, which increases analysis time. A 9-m column assembly was chosen (as a compromise between resolving power and analysis time) based on spreadsheet models of the Golay-Guiochon equation.; Selectivity enhancement techniques are used enabling faster separations of target mixtures. A-series coupled tandem column ensemble containing a non-polar first column and a polar second column was used to enhance the separation of compounds separated by the first column but coeluting from the column ensemble. Methods were developed using transient changes in junction point pressure or independent temperature control of the two columns. A series of 3 pressure pulses were used to enhance the separation of a 13 component mixture with 3 coelutions while adding only ∼10 s to the total analysis time. This was successfully repeated using temperature pulses of the second column instead of pressure pulses. A delay of the temperature ramp on the second column was used in conjunction with a single temperature pulse to enhance the separation of an 18 component mixture with 3 coelutions.; The operation of a multi-bed sorption trap, which was developed to quantitatively remove organic vapors from large volume air samples, and inject them as a 1--2 s wide plugs onto the separation column, was modified to use fast heating rates and split flow operation to minimize injection plug widths. Injection-plug-widths as small as 89 ms, 210 ms and 520 ms were obtained in the split mode for n-pentane, n-octane and n-undecane, respectively. |
