Isotopic Analysis of Atmospheric Formaldehyde by Gas Chromatography Isotope Ratio Mass Spectrometry

Little is known about the isotopic composition of formaldehyde in the atmosphere, a chemical intermediate in hydrocarbon oxidation. Here, we present a promising new method to analyze the carbon (delta 13C) and hydrogen (delta D) isotopic composition of atmospheric formaldehyde. The direct isotopic analytical technique described uses continuous-flow gas chromatography-isotope ratio mass spectrometry, which provides flexibility for either isotopic analysis without correction for derivative functional groups. Current levels of precision of measurement are +/-1.1 and +/-50 per thousand (1 sigma) for delta 13C and delta D analyses, respectively. Concentration of formaldehyde in ambient air is also determined, coincident with isotopic measurement, to a precision of +/-15%. The method has the required sensitivity for analyses of formaldehyde in urban air on relatively small volume grab samples of whole air (10-70L STP), potentially providing high temporal resolution. This is particularly advantageous for studying formaldehyde given its short lifetime and large variability in the atmosphere.