Technical note: Concerns on the use of ozone scrubbers for gaseous carbonyl measurement by DNPH-coated silica gel cartridge

Abstract

2,4-Dinitrophenylhydrazine (DNPH) is a typical derivatizing agent coated on sorbent cartridges for detection of carbonyl compounds at ambient levels. However, airborne oxidant of ozone (O3) can react with DNPH to form side products that can interfere with the accurate detection of carbonyls. It is the most critical interferer degrading carbonyl-DNP-hydrazone formed on the cartridge during sampling, resulting in underestimation of carbonyl concentrations; this strong oxidant can be removed by installing a denuder or scrubber coated or filled with potassium iodide (KI) upstream. The purpose of this study is to demonstrate and discuss the usage of novel KI-filled ozone traps in affecting carbonyl collection efficiency of DNPH-coated silica gel cartridges in field and laboratory settings. Results of the study showed that measured carbonyls concentrations were 4.9-13.5% lower in samples collected without any ozone traps compared to those collected with a commercially available ozone scrubber or KI denuder. Although ozone can be reduced efficiently by KI, both environmental relative humidity (RH) and byproducts formed from the oxidation of KI with ozone, namely iodine (I2) and hydroxyl ion (OH-), can inhibit derivatization kinetics and contribute to degradation of the carbonyl-DNP-hydrazones formed during sampling. Placement of an acid-permeated polyethylene filter between the ozone scrubbers and the DNPH-coated cartridge notably improved carbonyl collection efficiency by neutralizing the byproduct OH-. End-users of the DNPH method should consider these findings and evaluate the performance of ozone scrubbers accordingly during sampling events. © Taiwan Association for Aerosol Research.