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• A 9-pound package containing the sampling pump, battery pack, support electronics, <br /> flame ionization detector, hydrogen gas cylinder, and an optional gas chromatography <br /> (GC} column, and <br /> • A hand-held meter/sampling probe assembly <br /> ' The OVA is generally calibrated to methane but can be calibrated to the species of interest <br /> The OVA can operate in two modes <br /> Survey mode During normal survey mode operation, a sample is drawn into the probe and <br /> ' transmitted to the detector chamber by an internal pumping system When the sample reaches the <br /> FID it is ionized as described above and the resulting signal is translated on the meter for direct- <br /> reading concentration as total organic vapors or recorded as a peak on a chart The meter display is <br /> an integral part of the probe/readout assembly and has a scale from 0 to 10 that can be set to read 0 <br /> to 10, 0 to 100, or 0 to 1000 ppm <br /> ' Gas chromatography mode GC is a technique for separating components of a sample and <br /> qualitatively or quantitatively determining them The sample to be separated is injected into a column <br /> packed with an inert solid, a carrier gas (hydrogen) flows through the column As the carrier gas <br /> forces the sample through the column, the separate components of the sample are retained on the <br /> ' column for different periods of time The amount of time a substance remains on the column, which <br /> is called its retention time, is a function of its affinity for the column material, column temperature, <br /> and flow rate of the carrier gas Under present instrumental conditions, each component elutes from <br /> the column at a different but reproducible length of time As the components elute from the column, <br /> ' they flow into the detector <br /> Since the output of the detector is connected to a strip chart recorder, separate peaks are <br /> recorded for each component This readout is called a gas chromatogram Since the retention times <br /> are reproducible, if the retention time of an unknown agrees with the retention time of a known, <br /> ' recorded under the same set of analytical conditions, the unknown is tentatively identified In <br /> addition, the area under each peak is proportional to the concentration of the corresponding sample <br /> ' component If these areas are compared to the areas of standards, recorded under identical analytical <br /> conditions, the concentration of the sample components can be calculated Note that if the "base" of <br /> 0 - 13 <br /> 1 <br />