Janfelt Christian, Frandsen Helle, Lauritsen Frants R
Department of Chemistry, Copenhagen University, Universitetsparken 5, 2100 Copenhagen Ø, Denmark.
Rapid Commun Mass Spectrom. 2006;20(9):1441-6. doi: 10.1002/rcm.2466.
A mini membrane inlet mass spectrometer (mini-MIMS) of a total weight of 12 kg was constructed using a miniature Multipole mass spectrometer, a small vacuum system and a flexible flat sheet membrane inlet, where the exposed membrane area can be changed by a factor of 80. The variable membrane area together with the possibility of operating the Multipole at pressures up to 1 x 10(-3) Torr made it possible to test the system with three microporous membranes (cellulose, polyether sulfone and polypropylene) normally not compatible with standard electron ionization MIMS systems and a standard non-porous polydimethylsiloxane membrane. We found that the hydrophilic cellulose and polyether sulfone membranes had selectivity characteristics opposite to those of the standard silicone membrane. They demonstrated preferential detection of hydrophilic compounds in hydrophobic organic solvents, whereas the silicone membrane preferentially detects hydrophobic organic compounds in aqueous solution. Using the cellulose membrane, organic contaminants and water could be detected in organic solvents at 10-100 ppm levels by weight, the relative high detection limits primarily caused by interference from a high chemical background from the solvent. When being used with the standard silicone membrane the mini-MIMS behaved just like most standard MIMS systems with detection limits of volatile organic compounds in water at concentrations just below 1 ppm. The hydrophobic microporous polypropylene membrane was not found to be useful with the mini-MIMS.
我们构建了一台总重12千克的微型膜进样质谱仪（mini - MIMS），它采用了微型多极质谱仪、小型真空系统和柔性平板膜进样口，其暴露的膜面积可变化80倍。可变的膜面积以及在高达1×10⁻³托的压力下操作多极质谱仪的可能性，使得该系统能够用三种通常与标准电子电离MIMS系统不兼容的微孔膜（纤维素、聚醚砜和聚丙烯）以及一种标准的无孔聚二甲基硅氧烷膜进行测试。我们发现，亲水性的纤维素膜和聚醚砜膜具有与标准硅氧烷膜相反的选择性特征。它们在疏水性有机溶剂中表现出对亲水性化合物的优先检测，而硅氧烷膜则优先检测水溶液中的疏水性有机化合物。使用纤维素膜时，可在有机溶剂中检测到重量比为10 - 100 ppm水平的有机污染物和水，相对较高的检测限主要是由溶剂的高化学背景干扰所致。当与标准硅氧烷膜一起使用时，mini - MIMS的表现与大多数标准MIMS系统类似，对水中挥发性有机化合物的检测限略低于1 ppm。未发现疏水性微孔聚丙烯膜对mini - MIMS有用。
