Countering the Effects of Media Interferences and Background Contamination in Collection of Low Concentration Aldehydes and Ketones in Engine Exhaust with Dinitrophenylhydrazine (DNPH) Derivatization 2011-01-2060

This paper discusses a method developed to counter the variability of media interferences for the measurement of aldehydes and ketones in automotive exhaust. Dinitrophenylhydrazine (DNPH) Derivatization Methodology for the collection of aldehyde and ketone compounds in vehicle exhaust has been in use for over thirty years. These carbonyl compounds are captured by passing diluted exhaust gas through a sample medium containing DNPH. The sampling medium can take the form of DNPH dispersed on a solid sorbent or as a DNPH solution in a solvent such as acetonitrile. Carbonyl compounds react readily to form DNPH derivatives which are stable and which absorb ultra-violet (UV) light, facilitating quantitative measurement. However, when the procedure was developed, emissions rates from vehicles were much higher than the current (2010) emissions levels. The current levels of background carbonyl-DNPH derivative present in commercially-prepared, unsampled DNPH cartridges are well above typical instrument level of detection (LOD) and limit of quantitation (LOQ); moreover, these levels vary significantly from cartridge to cartridge. The variance also differs for each of the fourteen-plus compounds quantified. Variability in the background concentration of the carbonyl-DNPH derivative affects the accuracy of these measurements. This effect becomes more pronounced in relative terms as modern, ultra-low emissions vehicles are concerned. Thus, a procedure was needed to quell the effects of the day-to-day and cartridge-to-cartridge variation from a large emissions measurement program involving modern (2008 model year) vehicles.