溴代烷烃光致化学电离质谱在线测量大气中甲醛和乙二醛的方法研究

As the important oxidation intermediates in the atmospheric photochemical cycle, formaldehyde and glyoxal are commonly used as indicators of VOCs’ oxidation processes and sources. However, Formaldehyde and acetaldehyde in the atmospheric have short life, low concentration, and fast temporal and spatial variation. Therefore, an accurate and high sensitive online measurement method is demanding. Chemical ionization mass spectrometry is a kind of high sensitive online measurement technology, but the existing ionization methods such as PTR suffer from the ion interferences that cannot meet the measurement requirements for formaldehyde and glyoxal in the atmosphere. This application intends to develop a photoionization-generated bromoalkane cation chemical ionization method for measurement of formaldehyde and glyoxal. The method utilizes the vacuum ultraviolet (VUV) to generate high-intensity reagent ions by photoionization of bromoalkane, then the sample are ionized by reaction with the brominated reagent ions via ion association reactions. The formed brominated adduct ions can improve the accuracy of identification according to the isotopic abundance ratio characteristics of Br element (79Br:81Br=50.6%:49.4%). In order to improve the measurement sensitivity of formaldehyde and glyoxal, the high-pressure ion-molecular collision ionization reaction and radio frequency electric ion focusing technology will be utilized, which will achieve sufficient chemical ionization and high transmission efficiency. This method can provide a new tool for the in-depth study of atmospheric photochemical reaction process and atmospheric VOCs tracing.

甲醛和乙二醛作为大气光化学循环中重要的VOCs氧化中间产物，常被用作VOCs氧化过程及来源的指示物。然而大气中甲醛和乙二醛寿命短，浓度低，时空变化快，需要一种准确在线高灵敏测量方法。化学电离质谱法是一种在线高灵敏测量技术，但现有PTR等电离方法存在产物离子受干扰严重问题，无法满足大气甲醛和乙二醛的测量需求。本申请拟发展一种测量大气甲醛和乙二醛的溴代烷烃光致化学电离质谱法。该方法利用真空紫外（VUV）光电离溴代烷烃产生高强度溴代试剂离子，试剂离子再与样品通过离子缔和反应电离，形成溴代加和产物离子，可根据溴元素（79Br:81Br=50.6%:49.4%）显著同位素丰度比特征，提高识别的准确性。另外，利用高气压下离子-分子碰撞电离反应并结合射频电场驱动的离子反应区，以实现充分化学电离和高效离子传输，提高甲醛和乙二醛的测量灵敏度。该方法可为深入研究大气光化学反应过程以及VOCs溯源提供新工具。

甲醛和乙二醛作为大气光化学循环中重要的VOCs氧化中间产物，常被用作VOCs氧化过程及来源的指示物。然而大气中甲醛和乙二醛寿命短，浓度低，时空变化快，需要一种准确在线高灵敏测量方法。化学电离质谱法是一种在线高灵敏测量技术，但现有PTR等电离方法存在产物离子受干扰严重问题，无法满足大气甲醛和乙二醛的测量需求。本项目发展了一种测量大气甲醛和乙二醛的溴代烷烃光致化学电离质谱法。针对甲醛的高灵敏快速检测，研制了一种光致CH2Br2+化学电离源，实现对甲醛分子的高效化学电离，对甲醛的检出限低于1 ppbv。此外，发展了一种团簇介导 CH2Br2+化学电离源，将乙二醛的灵敏度提高了2个数量级，检出限低至0.05 ppbv。最终，考察了湿度对检测的影响，建立了在线标定方法，并成功应用于实际大气中甲醛和乙二醛的检测，可为深入研究大气光化学反应过程以及大气污染物溯源提供技术支持。另外，本项目发展的电离方法还成功实现了人体呼出气中甲醛和食用接触用纸中乙二醛的高灵敏检测，有望推广至医疗诊断和食品安全领域。