In GC, samples are vaporized in the injection port, and sample constituents are then separated as they are moved along the length of the column by the carrier gas. Separation of the constituents is achieved because each compound possesses a characteristic rate of dissolution into the stationary phase and revolatilization into the mobile phase that is dependent upon the characteristics of the compound, and the stationary phase used in the method (see Fig. 1) . The extent of separation can be increased or decreased to some extent by altering the temperature of the oven in which the chromatographic column is housed. Some advanced GC systems also incorporates hardware that allows for variable injection port temperatures to increase analyte separation. However, the main means of increasing the separation of the analyte from other sample constituents is the choice of the stationary phase/column used in the method. As each analyte exits the column, it is detected and quantified by a detector (e.g., mass spectrometer, electron capture, flame ionization detectors, etc.). Gas chromatography is generally characterized by great analytical sensitivity, often as low pg/ml, but it is limited by the need to volatilize the compounds of interest. Compounds with high boiling points are difficult to vaporize and cannot be quantified by GC very readily . For this reason, HPLC has been more widely used.
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