The temperature of the sample port is usually about 50 ☌ higher than the boiling point of the least volatile component of the sample. The most common injection method is where a microsyringe is used to inject sample through a rubber septum into a flash vapouriser port at the head of the column. The carrier gas system also contains a molecular sieve to remove water and other impurities.įor optimum column efficiency, the sample should not be too large, and should be introduced onto the column as a "plug" of vapour - slow injection of large samples causes band broadening and loss of resolution. The choice of carrier gas is often dependant upon the type of detector which is used. Commonly used gases include nitrogen, helium, argon, and carbon dioxide. The carrier gas must be chemically inert. Have a look at this schematic diagram of a gas chromatograph: The column itself contains a liquid stationary phase which is adsorbed onto the surface of an inert solid. The sample is transported through the column by the flow of inert, gaseous mobile phase. The combination of short analysis time and low detection limits make this method a potential candidate for screening large numbers of samples that have been prepared using techniques such as liquid–liquid extraction or solid-phase microextraction.Gas chromatography - specifically gas-liquid chromatography - involves a sample being vapourised and injected onto the head of the chromatographic column. The fast separation time limits on-column degradation of the thermally labile compounds and decreases the peak widths, which results in larger peak intensities and a concomitant improvement in detection limits. The PDECD has the benefit that it uses a pulsed plasma to generate the standing electron current instead of a radioactive source. The new method employs a commercially available pulsed-discharge electron capture detector (PDECD) coupled with a microbore capillary gas chromatography (GC) column in a standard GC oven to achieve on-column detection limits between 5 and 72 fg for the nine explosives studied. ABSTRACT: The detection of a mixture of nine explosive compounds, including nitrate esters, nitroaromatics, and a nitramine in less than 140 sec is described.
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