Airborne aldehydes are measured by drawing a volume of air through a cartridge containing silica coated with 2,4-dinitrophenylhydrazine (DNPH), which is eluted with a solvent and analysed using high performance liquid chromatography with UV detection. The method cannot measure acrolein, and suffers from interferences from ozone and nitrogen dioxide, making sampling difficult in polluted environments. Using this method to measure the aldehydes in the London Underground maintenance sites, where the exhaust emissions are high, the method failed to deliver results.
The aim of the thesis was to fully understand the limitations of using the DNPH method in a polluted environment, and to develop an improved measurement method. It was found that the DNPH not only suffers from interference from ozone and nitrogen dioxide, but carbon monoxide also causes interference and destroys the DNPH. The destruction of the DNPH by NO2, CO and ozone was quantified and an equation for the calculation of the amount of DNPH required for sampling of aldehydes in a polluted environment was proposed.
Based on these findings, several other derivatisation reagents (3-methoxybenzothiazolin-2-one hydrazine (MBTH), 2,3,4,5,6-pentafluorophenyl hydrazine (PFPH), O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA), 2-diphenylacetyl-1,3-indandioine-1-hydrazine (DAIH), 4-hydrazinobenzoic acid (HBA)), were evaluated in the presence of NO, NO2 and CO. The evaluation of alternative derivatisation reagents resulted in the identification of PFBHA to be the superior alternative to DNPH due to its low reactivity towards NO2, NO and CO. A method using PFBHA as the derivatisation reagent was developed, using silica gel coated with hydroquinone as the sorbent material. The new method has a 100 % method recovery as well as collection efficiencies above 90 % for all three of the aldehydes.
The LOD for formaldehyde, acetaldehyde and acrolein were determined to be 2.40, 6.49, and 2.70 g/m3, respectively, when sampling at 1.0 L/min for 8 hours. The concentrations of these aldehydes were measured at a train maintenance depot. The results were compared to those obtained using the DNPH method. The DNPH method underestimated the aldehyde concentrations by between 18 – 93 %, depending on the concentration of NO2, and CO present. A reliable method for the measurement of airborne aldehydes in polluted environments was developed.
