低流速、低电压微型差分迁移率谱的研究

Research on Low Flow Rate and Voltage Micro Differential Mobility Spectrometry

差分迁移率谱(DMS)是面向现场检测的离子迁移谱(IMS)技术发展热点之一,近年来逐渐从气溶胶检测走向物质成分检测,但现阶段存在传统结构导致的流速(>100 L/min)和电压(>1kV)过大问题。本实验采用厚膜工艺制造的窄间隙离子迁移管,以10.6 eV真空紫外灯为电离源,自行研制了低流速(<7 L/min)、低电压(<30 V)工作条件的差分迁移率谱(DMS),以丙酮、丁酮、邻二甲苯和对二甲苯等VOCs为检测对象,比较了不同流场条件下差分迁移率谱的分辨率、灵敏度变化特性,求解分析了不同离子的离子迁移率。结果表明,鞘气Q_s和载气Q_a流速比Q_s/Q_a是DMS分辨率和灵敏度的关键参数,当流速比Q_s/Q_a=3-9时,所有物质信号强度单调递增;Q_s/Q_a>9时,单调递减。分辨率在Q_s/Q_a=3-6时,单调递增;Q_s/Q_a=6-10时,增长速率逐渐降低并趋向饱和;Q_s/Q_a>10时,出现不稳定跳变。通过总流量Q和分离电压V_d关系求解出的不同物质离子迁移率(K)与参考值符合程度极高,误差小于3%。另外,在S/N=3条件下,丁酮检出限可达0.6μg/L。本工作为应用于物质成分现场检测的差分迁移率谱技术提供了微型化和工作条件优化基础。

Differential mobility spectrometry（DMS）,as a standard tool to detect submicron aerosol particles,is gradually expanding its application to molecular detection in recent years.However,the operating voltage（ 1 kV） and gas flow（ 100 L/min） of DMS are required in charged particles detection,whereas they are too large for field detection of ions.In this work,we designed a UV-DMS device with narrow gap ion drift tube,fabricated by thick film technology and able to operate under low flow rate（7 L/min） and low voltage（30 V）.Four kinds of volatile organic compounds（VOCs）（acetone,2-butatone,o-xylene,p-xylene）were chosen as examples to study the resolution,sensitivity and the obtaining of ion mobility.The results showed that the flow rate ratio of sheath gas and carrier gas Q_s/Q_a was the key parameter of UV-DMS resolution and sensitivity.The sensitivity of all examples increased significantly with Q_s/Q_a from 3 to 9 and then slowly decreased.Meanwhile,the resolution increased markedly with Q_s/Q_a from 3 to 6,and reached saturation during 6 to 10.Both sensitivity and resolution became unstable when Q_s/Q_a was over 10.The ion mobility deviation between experiment and reference was less than 3%.The detection limit was 0.6 μg/L with S/N ratio of 3.This work provided a basis for the miniaturization and parameters optimization of DMS in molecular detection.