Simultaneous Detection of o- , m- , p-Xylene by High-field Asymmetric Waveform Ion Mobility Spectrometry

本研究以自制的FAIMS设备为实验平台。设备集成离子源、分离电压电源、补偿电压电源、离子迁移管分析器、弱电流探测器、测控系统等关键模块。离子源采用10. 6 eV 的真空紫外灯(Heraeus，UK)；DV源采用频率为1 MHz，占空比为30%的不对称方波，分离电场可调节范围为0-1500V；CV为范围在-30 ~30 V的缓变电压；离子迁移管分离电极尺寸为 15×10×0.5 mm。载气采用南京上元工业气体厂生产的纯度为99. 999% 高纯氮气，样品气由南京上元工业气体厂提供，其组分为N2和气态样品，纯度大于99.95%。仪器工作方式如图2所示，样品气和载气在高精度流量计控制下，通过调节两路气路流量的相对大小控制进样浓度及载气流速。载气依次经过分子筛及冷阱去除水汽及其他杂质，最后与样品气充分混合后由FAIMS进气口进入分析器进行分离和检测。实验首先对单一物质进行分析，依次获取邻、间、对二甲苯在不同分离电压下的CV-I谱图，提取CV-DV指纹信息。通过对比分析指纹识别信息选取物质特征峰及有效分离区间、初步确定混合物异构体最佳分离电压，然后通过CV-I谱图叠加的方式分析峰高、半峰宽对特征离子峰有效读取的影响、从而进一步确定二甲苯异构体最佳分离条件，最后基于特征离子峰及最佳分离条件开展二甲苯异构体混合物同时检测实验，通过分析混合物CV-I谱图离子峰与单一物质特征离子峰对应程度，从而实现二甲苯混合物的同时分离检测。

This study employs a self-fabricated FAIMS device as the experimental platform. The device integrates key modules including an ion source, separation voltage power supply, compensation voltage power supply, ion mobility tube analyzer, weak current detector, and measurement and control system. The ion source utilizes a 10.6 eV vacuum ultraviolet lamp (Heraeus, UK); the separation voltage (DV) source adopts an asymmetric square wave with a frequency of 1 MHz and a duty cycle of 30%, with the separation electric field adjustable in the range of 0–1500 V; the compensation voltage (CV) is a slowly varying voltage ranging from -30 to 30 V; the separation electrode of the ion mobility tube has dimensions of 15 × 10 × 0.5 mm. The carrier gas is high-purity nitrogen (99.999% purity) produced by Nanjing Shangyuan Industrial Gas Factory; the sample gas, also provided by the same manufacturer, consists of N2 and gaseous samples with a purity exceeding 99.95%. The operating workflow of the instrument is illustrated in Figure 2. Controlled by high-precision flow meters, the relative flow rates of the two gas paths are adjusted to regulate the sample injection concentration and carrier gas flow velocity. The carrier gas first passes through a molecular sieve and a cold trap to remove water vapor and other impurities, then fully mixes with the sample gas, and enters the analyzer via the FAIMS inlet for separation and detection. The experiment begins with the analysis of single substances, sequentially acquiring CV-I spectra of ortho-, meta-, and para-xylene under varying separation voltages, and extracting CV-DV fingerprint information. Through comparative analysis of the fingerprint recognition data, the characteristic peaks of target substances and effective separation intervals are identified, and the optimal separation voltage for separating the isomer mixture is preliminarily determined. Subsequently, the impacts of peak height and half-peak width on the effective readout of characteristic ion peaks are analyzed by superimposing CV-I spectra, thereby further confirming the optimal separation conditions for xylene isomers. Finally, simultaneous detection experiments for xylene isomer mixtures are conducted based on the characteristic ion peaks and optimal separation conditions. By analyzing the correspondence between the ion peaks in the CV-I spectra of the mixture and the characteristic ion peaks of individual pure substances, simultaneous separation and detection of xylene mixtures is achieved.