Cryogenic preconcentration-direct FID method for measurement of ambient NMOC: refinement and comparison with GC speciation

A method for measuring total nonmethane organic compounds (NMOC) In the atmosphere has been refined to reduce measurement variability and evaluated for possible use In connection with the control of hydrocarbon emissions. The method, a simplification of the conventional gas chromatographlc (GC) speciation technique, uses cryogenic preconcentration and flame ionization detection but does not use a GC column. Tests to compare this simplified method to the GC speciation technique, using actual ambient air samples, were carried out. Test results showed that the sensitivity and precision of the simplified method approach those of the speciation technique. Other test results verified that the use of stainless steel sample canisters for collection and temporary storage of NMOC samples Is acceptable and contributes little additional variability to the method.