Simultaneous Determination of Carbonyls and NO₂ in Exhausts of Heavy-Duty Diesel Trucks and Transit Buses by HPLC following 2,4-Dinitrophenylhydrazine Cartridge Collection

A method combining 2,4-dinitrophenylhydrazine (DNPH) cartridge sampling and high-performance liquid chromatog raphy (HPLC) analysis has been used for the measurement of carbonyl and NO₂ emissions from heavy-duty diesel trucks and transit buses. The reaction of NO₂ with DNPH allows for the simultaneous and unambiguous determination of NO₂ and carbonyl concentrations in exhaust samples. The potential coelution of the NO₂-DNPH derivative with the formaldehyde-DNPH derivative under certain chromatographic conditions was investigated. Successful separation of these two species was achieved allowing for simultaneous determination of carbonyls and NO₂ in the exhaust samples collected from heavy-duty diesel (HDD) trucks and diesel, diesel/electric hybrid, diesel equipped with the continuously regenerating technology (CRT) particle traps, and compressed natural gas (CNG) transit buses tested over various drive cycles. Elevated NO₂ emissions from CRT-equipped buses were observed. The NO₂/NO_x volume ratios for HDD trucks and transit buses are discussed. A comparison of the DNPH derivatization with HPLC/UV−visible detection method with a chemiluminescence analyzer method for NO₂ measurement is presented for a limited number of diesel/CRT and CNG buses.