Introducing the Lucidity Gas Sampling Valve for GC-FID!
Typically, the sample for a GC-FID is either solid or a liquid states. These samples are often mixed with a solvent to extract the analyte of interest, then that liquid solution is injected into the GC-FID. If the analyte of interest is volatile enough, then headspace is used, this is where the solid or liquid sample is placed into a gas tight vial and heated until the analyte is evolved as a gas. A gas tight syringe is used to pull the sample and inject into the GC-FID. But, what do you use when your sample is already a gas?
This is where a gas sampling valve (GSV) comes into play. We’ve had a lot of requests for such a valve, so we’ve decided to create such a solution. The Lucidity GSV is made of a 6 port gas switching valve connected to a sample loop, in this case a 250 μL loop.
Schematic of a gas switching valve
The valve is heated to some set temperature, and held there until the sample is introduced. The sample is introduced via a solenoid valve into the sample side of the switching valve, through the sample loop and out of the waste port. The solenoid valve is then closed, the sample allowed to come to atmospheric pressure, then the valve is moved to the inject position. Moving to this position puts the sample loop in line with the carrier gas and the GC column.
To test out the GSV I used a small bottle of propane that I had from my garage. Once connected to the GSV through a solenoid valve, I was ready to test the GSV operation.
The propane tank was opened, the solenoid valve opened and sample allowed to enter into the switching valve into the 250 μL sample loop. The GC method was loaded and readied using the details below:
| Lucidity GC-FID Conditions | |||
|---|---|---|---|
| Carrier | Hydrogen | ||
| Control | Pressure | ||
| Flow | 1.0 mL/min | ||
| Split ratio | 100:1 | ||
| Column | MXT-624 | 30 m x 0.25 mm, 1.40 um | |
| Injector | 200 ℃ | ||
| FID | 200 ℃ | ||
| Oven Program | |||
| Rate | Temperature | Hold Time | |
| 40 ℃ | 4 min | ||
| GSV Program | |||
| Temperature | 80 ℃ | ||
| Sample Loop Size | 250 μL | ||
For my first attempt I did go with a large sample loop to ensure that there would be enough sample to be seen by the FID. I now know that I don’t need such a large sample loop for a pure substance.
Chromatogram of propane injected by the GSV
The chromatogram shows quite a bit of tailing, which could be caused by the size of the sample loop or the choice of column. Both of these are easily remedied but not the focus of this experiment. The goal of this experiment was to ensure that the GSV was functionating correctly and that we could see peaks using this new sampling device. As shown by the above chromatogram, the experiment was a success.
We will be sharing more results from this project in the coming weeks and months, and if you would like more information or would like to work with us on this project contact us below.