GAS-CHROMATOGRAPHIC DETERMINATION OF ACETONITRILE IN AIR USING A THERMIONIC DETECTOR

A gas chromatographic procedure for the determination of acetonitrile (CH3CN) in air is described, based a thermionic nitrogen-selective detector. The lower limit of detection is 15 pg of CH3CN for a blank value of 5.0 ± 3.2 pg. The method involves the collection of air in 2-dm3 vessels (glass or stainless steel) and preconcentration of acetonitrile by cryogenic trapping. Preconcentration by sorption on modified Chromosorb 102 was found unsuitable due to undesirable memory effects. Air samples stored In containers for periods longer than 3 days generally show a rise In CH3CN concentration, so that air samples must be processed within a few days. Precautions against contamination in the gas handling system or by Intrusion of laboratory air also are important. Calibration tests based on gaseous and liquid dilution series lead to comparable accuracies of about 4% In each case but a better reproducibility for liquid calibration mixtures. Air samples taken over the Atlantic Ocean, In the Bay of Helgoland, during aircraft ascents over Europe, and in the urban air of Mainz indicate the range of CH3CN mixing ratios in the troposphere from 52.6 ± 13.1 pptr in background air to 731 ± 82 pptr In polluted city air. © 1990, American Chemical Society. All rights reserved.