Multipoint calibration of a gas chromatograph using cryogenic preconcentration of a single gas standard containing volatile organic compounds

Abstract

Methodology Is described for the use of a cryogenic preconcentration technique to increase the sample amount of trace volatile toxic organic compounds In a gas matrix for analysis by gas chromatography A gas chromatograph equipped with a flame-ionization detector was set up for the analysis of such gas mixtures in a nitrogen balance gas. A system was assembled to preconcentrate cryogenically the gas sample and then Inject it onto the chromatographic column. The system was evaluated for analytical precision and to determine If it could be used to construct a calibration curve for the instrument using a single calibration gas standard. An experiment was also performed to determine the trapping efficiency for the organic compounds using the system as constructed. The operating procedure evaluated for cryogenically preconcentrating the sample involved trapping the sample for different time Intervals at a set sample flow rate. The analytical data from this procedure were plotted for each compound in the gas standard using linear forced zero regression. Results indicate that the method is very linear over the concentration range of 1-13 nmol/mol (parts per billion) for the operating conditions studied. This determination of linearity now allows the use of one calibration gas standard to develop a calibration range for an instrument.