Direct measurement of atmospheric formaldehyde using gas chromatography pulsed discharge ionisation detection

摘要

A gas chromatographic system has been developed for the direct analysis of atmospheric formaldehyde and other oxygenated hydrocarbons. This method utilises the trapping of analytes in a loop cooled with liquid nitrogen, separation by gas chromatography and then subsequent detection using a pulsed discharge helium ionisation detector (pdHID), The detection limit of this instrument is estimated to be 32 parts per trillion by volume (pptv) for 0.21 of gas sampled at a flow rate of 30 mi min(-1) (SPN at 4:1), A number of other compounds have been monitored simultaneously using this method, including higher molecular weight aldehydes and acetone, Continuous measurement of formaldehyde can be performed with a time resolution of 15 min, with longer analysis times required for inclusion of other species. Calibrations were performed using a permeation tube instrument for both formaldehyde and acetone. A linear response has been observed for formaldehyde sample volumes of 60-200 mi of a 272 ppbv sample (20-68 ng), For acetone a linear response was observed from 175-360 mi of a 30 ppbv standard (12-26 ng), A flame ionisation detector (FID) was also utilised during system development to confirm separation of formaldehyde from atmospheric hydrocarbons. [References: 22]