Manufacture And Application Study Of Micromachined Gas Chromatography Columns Based On MEMS

Microfabricated gas chromatography columns are seen as the core of micro total analytical systems as they are smaller in size and lower in power compared to conventional capillary columns.Thus,studies regarding their properties have gained extensive interest around the world.In this paper,we discuss different layout configurations of the MEMS-based gas chromatography column,studies regarding the bilayer film as a novel stationary phase for gas chromatographic separation,and the microcolumn integrated study of the micro gas chromatography system.The main results and central conclusions from this paper are outlined as follows:1.According to the plate theory and rate theory of gas chromatography columns,the distribution of the channel air flow plays a critical role in peak separation.A simulation using the finite element method(FEM)shows the flow field distribution in an 8-channel microcolumn and demonstrates the optimization of the splitter structure at the column entrance.The results from this study demonstrate that the flow field distribution of the multicapillary microcolumn exhibits greater uniformity compared to that of the open tubular column.This is useful in terms of increasing gas-stationary phase interactions.The eight-capillary gas chromatographic column is fabricated using a series of MEMS techniques,and SE-54 was chosen as the stationary phase using the static coating procedure in this paper.All malodorous mixture components were perfectly separated in both columns using systemic peaks.In the case of the 8-channel microcolumn with the short separation time,the unit plate number was higher compared to the conventional capillary column.2.The cascaded gas chromatography column which combines one-and two-channel columns with different stationary phases in the absence of a modulator is utilized to separate stimulants of chemical warfare agents and interfering vapors.The linked column increases the sample capacity and is able to achieve a high separation efficiency due to the complementary advantage of having two different stationary phases.3.The optimization of the column layout configurations of the microcolumn are described in this paper.A serpentine microcolumn configuration with a long,straight segment was found to be the ideal layout configuration according to previous studies.The flow distribution across the open tubular column revealed that molecules within the center part of the channel experience a higher velocity than those near the tube walls.Thus,the open tubular column experiences a strong “laminar flow effect”.The wavy column is first fabricated in the paper which can remarkably decrease the “laminar flow effect”.The wavy column is comprised of upper arcs and lower arcs that are connected alternatively in series.Wavy columns with different radii and angles are simulated using FEM.Results demonstrate that a wavy column with a width of 40 ?m,an arc angle of 136°,and a radius of curvature of 14.3 ?m represent the optimum parameters in our experiment.In order to overcome the low plate number of the single-channel wavy column,a multi-capillary gas chromatographic wavy column was fabricated to enable a higher column efficiency for the separation of alkanes,benzene mixtures,and food ester additives.In addition,we also designed a semi-packed wavy microcolumn in this study.In order to achieve an even flow velocity profile,a wavy channel was used instead of a straight long segment,and the position,shape,and size of the embedded posts were explored using FEM.4.This work presents the investigation of bilayer film(reduced graphene oxide/zinc oxide)as a new type of stationary phase for gas chromatographic separation on a microcolumn.Reduced graphene oxide is immobilized onto the column wall through solgel-derived Zn O particles as a supporting material between the RGO film and the channel wall.To test the separation performance,three kinds of organic mixtures containing polar and nonpolar components are injected into the column.The long retention time is found for most compounds especially for alcohols,which may be due to strong interactions between RGO and compounds via the formation of hydrophobicity,hydrogen bonding,and ?-? stacking.5.The microcolumn is integrated in micro-total analytical systems with smaller size,lower power and higher efficiency,instead of the traditional capillary column.The platinum electrode temperature control system and thermo electric cooler temperature control system are prepared in the paper.Temperature accuracy of both temperature control systems are lower than the commercial chromatography system,while the sample still be separated well in the system we prepared.