Improved Measurement of Ozone and Carbonyls Using a Dual-Bed Sampling Cartridge Containing <i>trans</i>-1,2-Bis(2-pyridyl)ethylene and 2,4-Dinitrophenylhydrazine-Impregnated Silica

Abstract

We have previously developed a new method using trans-1,2-bis-(4-pyridyl)ethylene (4-BPE) and 2,4-dinitrophenylhydrazine (DNPH) for the simultaneous determination of ozone and carbonyls in air using a two-bed cartridge system. In this method, 4-BPE was used to capture ozone. However, the method suffered from long reaction times in the eluate, low solubility of the DNPH derivative, and a strong dependence on atmospheric moisture. These problems could be overcome by using trans-1,2-bis-(2-pyridyl)ethylene (2-BPE) in place of 4-BPE. The efficiency of the reaction of ozone with 2-BPE to form pyridine-2-aldehyde (2PA) is higher than the corresponding reaction with 4-BPE. Under the optimized elution conditions, the reaction times of 2PA and 4PA with DNPH are within 15 and 120 min, respectively. In the elution from the sampling cartridge, 2PA formed from 2-BPE and ozone is easier to dissolve in the elution solvent. A stronger influence of humidity was observed in ozone recovery by the 4-BPE/DNPH method. 2-BPE exhibits a maximum reaction efficiency of 84% at 32% relative humidity (RH), while 4-BPE attains a maximum reaction efficiency of 82% at 49% RH. Humidity has much less influence on the reaction of 2-BPE with ozone. Above 18% RH, the reaction efficiency of 2-BPE with ozone is in the range 80-84%. Thus, 2-BPE is the more useful reagent for ozone analysis. The concentrations of ozone and carbonyls by the improved 2-BPE/DNPH method corresponded with the mean value by an ozone auto analyzer in an air monitoring station and a DNPH cartridge coupled with a KI-ozone scrubbing cartridge.