Quantification of the influence of NO2, NO and CO gases on the determination of formaldehyde and acetaldehyde using the DNPH method as applied to polluted environments

Airborne aldehydes have a significant impact on human health, especially in confined spaces such as tunnels, vehicle depots, industrial and construction sites where combustion devices are in operation. The standard method for the measurement of aldehydes (formaldehyde and acetaldehyde) uses the 2,4-dinitrophenylhydrazine (DNPH) derivatisation method. However this method has been reported to be prone to interference from ozone and NO2. The interference from these compounds have been viewed as chromatographic interferences on the quantification of formaldehyde. However, in these polluted environments, elevated levels of NO2 along with NO and CO are normally present. This study quantifies the impact these gases have on the quantification of formaldehyde and acetaldehyde, by evaluating the chromatographic interferences, consumption of the DNPH during sampling, and the effect these gases have on the capture and retention of the aldehydes on the DNPH cartridge during sampling. For the first time, CO was shown to react with DNPH and interfere with the determination of acetone. The reaction product of CO with DNPH was determined to be a compound that could be mistaken for acetone-DNPH. It has been found that the presence of NO, NO2 and CO in the sampled air consumes the DNPH cartridges, which results in the loss of formaldehyde and acetaldehyde during long-term sampling, and therefore extra capacity of DNPH is required for the measurement of formaldehyde and acetaldehyde in polluted environments. These findings reveal a potential risk of underestimation of formaldehyde and acetaldehyde measurements in a polluted workspaces such as a diesel engine operated environment where NOx and CO concentration levels could be high.