Determination of carbonyl pollutants adsorbed on ambient particulate matter of type PM2.5 by using magnetic molecularly imprinted microspheres for sample pretreatment and capillary electrophoresis for separation and quantitation.

Abstract

The authors describe a method for the determination of carbonyl pollutants adsorbed on ambient particulate matter (diameter < 2.5 μm; PM2.5). 2,4-Dinitrophenylhydrazine (DNPH) was used to derivatize carbonyl compounds. Magnetic molecularly imprinted polymers (MMIPs) selective for 2,4-DNPH were synthesized to remove excess of the derivatization reagent 2,4-DNPH. Micellar electrokinetic chromatography (MEKC) was then applied to the separation of DNPH-derivatized carbonyl compounds. The increased sensitivity of MEKC with UV detection and the sample cleanup resulted in drastically reduced sampling times (15 min) with detection limits ranging from 0.005-0.068 μg·m-3 for different carbonyls. The method was applied to continuous monitoring of carbonyl compounds on ambient PM 2.5 for two consecutive months. The concentrations and gas-to-particle ratios of carbonyls were determined, and a statistical method was used to evaluate the correlation among different carbonyls. It was observed that the total concentration of carbonyls, especially of multi-carbon carbonyls, increases with the level of air pollution. The level of isovaleraldehyde rises sharply and accounts for 37% of total carbonyls on days with extremely humid haze. The ratio of acetaldehyde to propionaldehyde (C2/C3) decreases with the duration and heaviness of haze conditions. Results indicate that anthropogenic emissions and the characteristics of the atmosphere (e.g. temperature, sunlight, and relative humidity) are the main factors that lead to abnormally high levels of isovaleraldehyde and other carbonyls in ambient PM 2.5. Graphical abstract Schematic of a method for the determination of carbonyl pollutants adsorbed on ambient fine particle of type PM2.5. Magnetic molecularly imprinted polymers (MMIPs) were synthesized to remove the excess derivatization reagent (2,4-DNPH) in air sample prior to CE separation.