Determination of ethylene oxide and acetaldehyde in petrochemical exhaust based on thermal desorption- gas chromatography-mass spectrometry

Ethylene oxide （EO） and acetaldehyde are key components of volatile organic compounds （VOCs） emissions in the petrochemical industry. The ozone formation potential of acetaldehyde is several orders of magnitude higher than that of EO. Therefore， accurately identifying and measuring these compounds is essential for developing effective ozone control strategies. However， separating EO from acetaldehyde presents a considerable analytical challenge due to their isomeric nature and comparable volatilities. In this study， a novel analytical method based on thermal desorption-gas chromatography-mass spectrometry （TD-GC-MS） technology was developed to simultaneously collect， separate， and quantify EO and acetaldehyde. Optimization was performed on the GC column temperature program， thermal desorption temperature， and thermal desorption flow rate to achieve effective separation. Compounds were separated on a TG-624 SiIMS GC column （60 m×0.25 mm×1.4 μm） with a carrier gas flow rate of 1.2 mL/min. To separate EO from acetaldehyde， the GC column temperature was specifically optimized to enhance their differences in desorption rates from the stationary phase. The temperature was initially held at 30 ℃ for 3 min， then ramped at 5 ℃/min to 120 ℃， held for 3 min. Both full scan and selected ion monitoring modes were employed for target detection. During thermal desorption， the thermal desorption temperature was set at 180 ℃， the cold trap temperature was set at -30 ℃ for capturing desorbed targets， and the secondary desorption flow rate was set at 16 mL/min with the corresponding split ratio of 12.3. The method's performance was evaluated under optimized experimental conditions. Within the range from 1 to 10 ng/tube， the method showed strong linearity with correlation coefficients above 0.99 for EO and acetaldehyde. Method detection limits were determined to be 0.16 ng/tube for EO and 0.21 ng/tube for acetaldehyde. Thermal desorption efficiencies for both targets exceeded 95% with samples spiked at 2 and 10 ng/tube. Recovery efficiencies spiked at 2， 5 and 10 ng/tube ranged from 80.3% to 106.8%， with relative standard deviations ranging from 4.5% to 9.2%. This method was applied to VOCs samples collected from aftertreatment exhaust streams of two petrochemical units， where different concentrations of EO and acetaldehyde were detected. This study thus established a reliable method for the simultaneous collection， identification and quantification of EO and acetaldehyde in petrochemical emission matrices. Furthermore， this method can also be used for monitoring these compounds in diverse emission sources and ambient air， thereby providing essential data to support the management and control of reactive VOCs.