Gas Chromatography


Gas Chromatography is a method used for separating a gaseous mixture into its individual components. It is often paired with Mass Spectrometry for identification. Gas Chromatography is used in many different fields, but some of the most common are forensics and medicine. One of the big challenges faced in gas chromatography is that normal gas chromatographs (GCs) are large (see Figure 1) and require a lot of power. This restricts them from being portable. Portable GCs would allow for on-site analysis, requiring smaller samples and yielding faster analysis times. Our group focuses on creating portable GCs on silicon wafers in BYU’s cleanroom using common microfabrication techniques. 

Figure 1 - A conventional gas chromatograph

Figure 2 shows the elements of a GC. The main component is a long tube through which the gas flows, called the column. The inside of the column is coated in a polymer called the stationary phase. A sample is injected into the column and is carried by a carrier gas (or mobile phase), typically helium or nitrogen. As the sample flows through the column, molecules react with the stationary phase and are slowed. Different molecules in the sample react differently with the stationary phase and travel through the column at different rates, allowing for separation. As the gas leaves the column, it is detected by the detector and recorded. Figure 3 shows an example recording, or chromatogram. Each of the peaks represents a different molecule that has been detected. 


Figure 2 - The components of a gas chromatograph


Figure 3 - An example output from a GC detector


A layout of our GC design is shown in Figure 4. A cross section of the channel is also pictured (Figure 5). The column is 5.8 m long, 150 µm wide, and 70 µm deep. The whole GC fits on a 100 mm silicon wafer. After manufacturing the GC chips in the cleanroom, we use a technique called silk-screening to print heaters onto the outside surface of the wafers. Heating the GC in this manner allows a negative thermal gradient to be applied across the column. This is beneficial because as the sample travels down the column, the molecules that are farther along will be at a lower temperature, causing them to travel more slowly than the molecules that aren’t as far along in the column (see Figure 6). This causes focusing, ultimately producing narrower and taller peaks in the chromatogram. A completed GC chip with silk-screened heaters is pictured in Figure 7. Funding for this project has been provided by Perkin Elmer. 

Figure 4 - The layout of our GC design

Figure 5 - A cross-sectional SEM image of the GC channels

Figure 6 - Focusing caused by a thermal gradient

Figure 7 - Completed GC chip with silk-screened heaters


**1 and 2 were found on Wikipedia: https://en.wikipedia.org/wiki/Gas_chromatography** 



Publications

  1. " Fundamentals and Developments in Microchip Gas Chromatography Column Technology ", Abhijit Ghosh, Carlos Vilorio, Aaron R. Hawkins, and Milton L. Lee,  in review Talanta.
  2. " Extending the Upper Temperature Range of Microchip Gas Chromatography Using a Heater/Clamp Assembly", Abhijit Ghosh, Jacob E. Johnson, Jonathan G. Nuss, Brittany A. Stark, Aaron R. Hawkins, Luke T. Tolley, Brian D. Iverson, H. Dennis Tolley and Milton L. Lee,  Journal of Chromatography A 1517, 134-141 (2017).
  3. " Axial thermal gradients in microchip gas chromatography", Anzi Wang, Sampo Hynynen, Aaron R. Hawkins, Samuel E. Tolley, H. Dennis Tolley, Milton L. Lee,  Journal of Chromatography A 1374, 216-223, (2014).  
  4. " Effect of Thermal Control in Microchip Thermal Gradient Gas Chromatography", Abhijit Ghosh, Austin R. Foster, Aaron R. Hawkins, Brian D. Iverson, Milton L. Lee, H. Dennis Tolley, Luke Tolley, Carlos R. Vilorio,  Pittcon, Orlando, FL, February 26 – March 1, (2018).  
  5. " Temperature Control for Microchip Thermal Gradient Gas Chromatography", Abhijit Ghosh, Aaron R. Hawkins, Brian D. Iverson, H Dennis Tolley, Jacob E. Johnson, Jonathan G. Nuss, Luke T. Tolley, and Milton L. Lee,  Pittcon, Chicago, IL, May 5 (2017).  

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