Characterization of gas chromatography/negative ion chemical ionization mass spectrometry for ambient measurement of PAN: Potential interferences andlong-term sensitivity drift

Gas chromatography/negative ion chemical ionization mass spectrometry (GC/N ICI MS) is characterized, elucidating instrument performance for the contin uous measurement of peroxyacetyl nitrate (PAN) and its homologues, Chromato grams and linear response at parts per trillion by volume (pptv) levels are examined to evaluate the accuracy of calibration using 4 types of base gas es: dry nitrogen, dry synthetic air, purified compressed air, and thermally PAN-decomposed air. The sensitivity to PAN is further checked against humi dity, which may be a source of interference in ambient measurements. The ex perimental results indicate that oxygen, water vapor, and other trace gases in ambient air do not affect the PAN sensitivity. Although significant sen sitivity drifts were observed during the course of measurements made at a r emote site in Japan, this problem was overcome by performing frequent calib rations with isopropyl nitrate (IPN).