Determination of low-level carbon in tungsten wire by combustion gas chromatography

A combustion gas-chromatographic technique for the determination of trace amounts of carbon in tungsten wire is described. The method involves the oxidation of the tungsten wire in a quartz oven at 1000 degrees . The liberated gases are swept into a cooled sample-loop in a gas-sampling valve. Upon completion of the oxidation process, the contents of the sample loop are introduced into a gas Chromatograph. The use of a 3-ft long column of silica gel allows separation of carbon dioxide and oxygen. The presence of oxygen requires that the hot-wire detector used be equipped with filament-protecting circuitry. Calibration curves are constructed by using organic and tungsten carbide standards. A limit of detection of 0.2 microg carbon can be achieved with a precision of better than 10%.