Lambertus Gordon, Sacks Richard
Department of Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
Anal Chem. 2005 Apr 1;77(7):2078-84. doi: 10.1021/ac040174p.
A series-coupled ensemble of microfabricated GC columns made by dry reactive ion etching of silicon substrates is evaluated for use with pneumatic selectivity enhancement techniques for targeted pairs of volatile organic compounds. Each column is 3.0 m long with a 150 miceom wide by 240 microm deep cross section. Dynamic coating was used to prepare a nonpolar column with a dimethyl polysiloxane stationary phase and a moderately polar column with a trifluoropropylmethyl polysiloxane stationary phase. Each column generates 5000-6000 theoretical plates. The columns are operated in series with the nonpolar column connected to a split inlet, the polar column connected to a flame ionization detector, and a valve connected between the column junction point and the inlet to the first column. When the valve is closed, the effluent from the first column passes directly into the second column. When the valve is open, both ends of the first column are at the inlet pressure, and flow stops in this column while increased flow is obtained in the second column. For analyte pairs that are separated by the first column but coelute from the column ensemble, the valve is opened for a few seconds after the first component of the pair has passed into the second column but the second component is still in the first column. The result is enhanced separation of the pair in the ensemble chromatogram. Relatively thick cross-linked stationary-phase films are used to increase retention for volatile compounds. The combination of air carrier gas and stationary-phase film thickness in the range 1-2 microm requires the use of relatively low average carrier gas velocities (typically less than 10 cm/s) for adequate resolving power of the column ensemble. Selectivity enhancement under isothermal conditions for a 14-component mixture of volatile organic compounds is demonstrated where neither of the columns alone nor the column ensemble without selectivity enhancement could obtain a complete separation.
通过对硅基片进行干法反应离子蚀刻制成的一系列串联微加工气相色谱柱，被评估用于针对挥发性有机化合物目标对的气动选择性增强技术。每根色谱柱长3.0米，横截面宽150微米、深240微米。采用动态涂覆法制备了具有二甲基聚硅氧烷固定相的非极性色谱柱和具有三氟丙基甲基聚硅氧烷固定相的中等极性色谱柱。每根色谱柱产生5000 - 6000个理论塔板数。这些色谱柱串联运行，非极性色谱柱连接到分流进样口，极性色谱柱连接到火焰离子化检测器，并且在色谱柱连接点和第一根色谱柱的进样口之间连接一个阀。当阀关闭时，第一根色谱柱的流出物直接进入第二根色谱柱。当阀打开时，第一根色谱柱的两端处于进样口压力，该色谱柱中的流动停止，而第二根色谱柱中的流量增加。对于被第一根色谱柱分离但从色谱柱组合中同时洗脱的分析物对，在该对的第一个组分进入第二根色谱柱但第二个组分仍在第一根色谱柱后，将阀打开几秒钟。结果是在组合色谱图中该对的分离得到增强。使用相对较厚的交联固定相膜来增加挥发性化合物的保留。空气载气和1 - 2微米范围内的固定相膜厚度的组合要求使用相对较低的平均载气速度（通常小于10厘米/秒）以获得色谱柱组合的足够分离能力。在等温条件下对14种挥发性有机化合物混合物的选择性增强得到了证明，在此情况下，单独的任何一根色谱柱或没有选择性增强的色谱柱组合都无法实现完全分离。
