Abstract:

Carbonyl compounds （CCs） are a pivotal class of oxygenated volatile organic compounds in ambient air， which are mainly derived from natural emissions， primary emissions from anthropogenic sources， and secondary formation due to atmospheric oxidation. Various classes of CCs have different impacts on human health， and play critical roles in atmospheric photochemical reactions， ozone production， and the formation of secondary organic aerosols. At present， the number of CCs in ambient air determined by traditional methods is limited， especially for high molecular weight monocarbonyl compounds （HMW-MCs） and dicarbonyl compounds （DCs）. If more CCs can be accurately determined， it will be beneficial for the study of atmospheric oxidation mechanisms and the formulation of pollution control strategies.In this study， an analytical method was developed that enables simultaneous determination of the 40 CCs in ambient air with a single injection， utilizing high-performance liquid chromatography-triple quadrupole mass spectrometry. First， the 16 CCs-2，4-dinitrophenylhydrazine （DNPH）-derivatized single standards were prepared using purified DNPH crystals in the laboratory. Second， the remaining 24 commercial CCs-DNPH-derivatized hybrid standards were purchased. Finally， all the above standards were mixed in a certain proportion to prepare the 40 CCs-DNPH-derivatized hybrid standards for later use. The sample collection procedures （sampling flow rate and sampling duration）， the pretreatment methods （elution volume and constant volume）， the chromatographic analysis conditions （chromatographic column， the concentration of ammonium acetate， etc.） and the mass spectrometry analysis conditions （ion source parameters， fragmentation voltage， collision energy， etc.） were optimized. Ambient air samples were collected using DNPH cartridges （at a flow rate of 1 L/min， for 4 h）， eluted with 4 mL of acetonitrile and diluted to a final volume of 5 mL （the acetonitrile naturally flowed through the DNPH cartridges in the opposite direction to the sampling direction） in a vacuum drying chamber， and then filtered through a 0.22 μm organic filter membrane and transferred to 1.5 mL brown sample bottles prior to instrumental analysis. Chromatographic separation was performed using a Sepax BR-C18 column （250 mm×4.6 mm， 5 μm） with mobile phases consisting of 1.0 mmol/L ammonium aqueous solution and acetonitrile under gradient elution conditions. The analysis was performed at a column temperature of 50 ℃ with an injection volume of 5 μL. The target analytes were identified using negative electrospray ionization （ESI^-） and multiple reaction monitoring （MRM） modes and quantified using the external standard method. The results showed that the 40 CCs exhibited good linearities within the mass concentration range of 2.5–200 μg/L， with the determination coefficients （R²） exceeding 0.997 8. The method detection limits and method quantification limits were established within the ranges of 0.001–0.03 μg/m³ and 0.005–0.12 μg/m³， respectively. The blank spiked recoveries of the target analytes at low， middle， and high concentration levels （0.05， 0.1， and 0.2 μg） ranged from 75.2% to 119.0%， while the relative standard deviations （RSDs， n=7） ranged from 0.4% to 4.2%. This analytical method was applied to the monitoring of ambient samples in the Pearl River Delta region. Except for 2-furaldehyde and isophorone， 38 CCs were effectively detected. Among these， formaldehyde， acetaldehyde and nonanal consistently showed higher concentrations across all sampling sites. Overall， the concentrations of low molecular weight monocarbonyl compounds （LMW-MCs） were moderately higher than those of HMW-MCs， and substantially higher than those of DCs. Compared with conventional methods， this method effectively overcame the limitations in existing approaches regarding the limited variety and detection difficulties of DCs and HMW-MCs. Additionally， it also improved the chromatographic resolution of target analytes which have similar retention times and the same ion pairs. Overall， this method was simple and rapid， offering excellent sensitivity， precision， and chromatographic resolution. It was suitable for the determination of the abovementioned 40 CCs in ambient air．

Key words: carbonyl compounds （CCs）, ambient air, high performance liquid chromatography-triple quadrupole mass spectrometry （HPLC-MS/MS）