The gas chromatography column change procedure is an essential process that needs to be performed carefully to ensure the optimal performance of the instrument. Even experienced gas chromatographers often fail to install columns in the best way possible, which can result in sub-optimal performance or even batch failure. Therefore, it is crucial to get the instrument preparation right, and the beginning is the most important part of the work.
This involves selecting the appropriate column and ferrule for your system and injection type, placing the column nut and ferrule onto the column before cutting at the inlet or detector end, and installing the front end of the column into the GC inlet. Once the column is installed, it is important to check that the correct column dimensions are entered into the GC software and allow the column to purge for twenty minutes to expel any oxygen that has entered the column.
The column should also be conditioned by heating it from 50°C to the maximum temperature of 5°C/minute and holding it for 1 hour. After conditioning, the column should be removed from the inlet and quickly inserted into a septum or a Capillary Column End Cap to minimize the opportunity for air to enter the column.
Finally, it is important to confirm that there is flow through the column by submerging approximately 2.5 cm (1 inch) of the free end of the column in methanol or another solvent compatible with the stationary phase in the column and verifying that a steady stream of bubbles is produced.
GC Shutdown
- On the Total Chrom menu, press run and clear the setup icon.
- Click on the Run icon followed by “Release control”.
- Click on the Run icon followed by and detach.
- Now click on the Admin menu, then “cam administration”, and click on users, followed by the manager.
- Highlight an item that has “Clarus” in it, and then click on the edit menu, followed by remove locks. Make sure that all items with Clarus have been removed.
- Now the computer and GC are detached and GC can be operated by itself.
- Shut off power for the Clarus GC.
Column Removal
- Hydrogen, helium, and air valves back of the GC need to be off.
- After the GC oven is cooled, remove the old column.
- Remove nuts at each end of the column for reuse.
- Remove the septum nut and gas line nut.
- Remove the injection port glass liner by pushing the thin rod in the injection port cavity from inside the oven.
- Glass liner and an “O” ring will come out from the top. Examine the “O” ring, if looks worn out replace it. If the glass liner looks dirty, replace it.
Column Installation
A. Use the same column
If the overall chromatogram is O.K. but some peaks show tailing or are not seen, unravel about a turn and a half of the column at each end. Cut ~ 6-12 inches of each end. Install the column into GC as per directions in step C.
B. New Column
Take out a new column from the box. Unravel about a turn of the column at each end, and cut ~3-4 inches off each end. Install the column into GC as per directions in step C.
ALSO READ: General HPLC Column Care
C. Install column in GC
- Each end of the column needs to stick out ~10 inches beyond the column cage.
- Insert a small nut at the thick end of the column, followed by injection port ferrule. The tapered end of the ferrule goes first inside the 1/16-inch nut.
- Now insert 1/8 inch nut into the thin end of the column. Ferrule has a tapered end and a small diameter protruded end. The protruded end goes inside the nut first.
- Now insert the thicker diameter column with a small nut end into the injection port.
- Insert the thinner diameter column with a big nut into the detector end.
- Loosely tighten both nuts.
- Each end of the column should be visible and sticking out on the top of the instrument. If not take the column out, unravel some more columns, and repeat the steps shown above.
- Cut the column on the injector side approximately flush with the outside port surface.
- Insert glass liner with an “O” ring over the column end. Push the liner down to make it flush with the outside port surface.
- Insert the gas line nut and tighten it.
- Inside the oven, push the column upward, till you feel resistance. Tighten the nut snugly by hand, followed by approximately ¼ turn by wrench.
- Replace the septum in the nut and place the septum nut on.
- On the detector end, cut the column about ½ inches above the detector surface.
- Now push the column up about 3 inches, and cut it again.
- Pull back the column about 2 inches or so.
- Insert a wooden dowel in the detector cavity and let it rest on the detector cavity.
- Push the column slowly up and see that it pushes the dowel up.
- Pull the back of the column so that it does not push the dowel, NOW PULL BACK another ~1/2 inches. Tighten the nut snugly by hand, followed by approximately ¼ turn by a wrench.
- Remove the dowel.
GC Startup
- Turn on all three gases followed by the power switch. Log on to GC.
- Ignite the flame for the detector.
- Go to GC, inject one microliter of heptane, and make sure you see big large peak within 30 seconds.
- On Total Chrome software, click on run, followed by attach icon for the Clarus GC.
- Click on run, followed by the take control icon. Now GC is controlled by computer.
- Go to the setup and type in the next six lines as standard #5, run # 1, 2,3,4,5, and 6.
- Under modify the sequence, for the first run (run #1), choose the Biodiesel conditioning method. It allows to condition of columns faster and better.
- The first few runs will have a few extra peaks and upward drifts in the baseline. As the column gets conditioned, a baseline will get smoother. The last three runs or so will be consistent.
What are the benefits of changing GC columns regularly?
Changing GC columns regularly can provide several benefits, including:
- Improved peak shape and resolution: Over time, GC columns can become contaminated, leading to poor peak shape and reduced resolution. Changing the column regularly can help to maintain optimal performance and ensure that the peaks are well-resolved.
- Increased sensitivity: Contaminants in the column can also lead to increased background noise, which can reduce the sensitivity of the instrument. Changing the column can help to reduce the background noise and increase the sensitivity of the instrument.
- Reduced downtime: If a column is not performing optimally, it may need to be replaced mid-analysis, which can result in downtime and delays in obtaining results. Changing the column regularly can help to prevent unexpected downtime and ensure that the instrument is always ready for use.
- Longer column lifetime: Regular column changes can help to prevent column degradation and extend the lifetime of the column. This can help to reduce the overall cost of running the instrument and ensure that the instrument is always performing optimally.
What are the best practices for GC column maintenance?
Proper maintenance of GC columns is essential to ensure optimal performance and extend the lifetime of the column. Here are some best practices for GC column maintenance:
- Correct installation: Incorrect installation of a new GC column can severely compromise performance and permanently damage the stationary phase. Therefore, it is important to follow the correct column handling procedures when installing a new column.
- Conditioning: Best practice procedures for conditioning new columns should be followed to ensure optimal performance. This involves heating the column from 50°C to the maximum temperature of 5°C/minute and holding it for 1 hour. If using a non-MS detector, monitor the baseline during this time. If the baseline is still gradually falling after 1 hour, continue conditioning until the baseline stabilizes.
- Storage: If the column is not in use, it should be stored properly to prevent contamination and damage. The column should be removed from the instrument and stored in a clean, dry place. If the column is stored in the instrument, maintain a low flow of carrier gas and maintain the oven temperature at 40 – 50°C.
- Regular maintenance: Regular maintenance of the GC instrument includes removing short sections from the inlet end of the column to remove contaminants that are permanently retained on the column. This improves peak shape, resolution, and column lifetime, allowing the best performance to be achieved from both the instrument and the column.
- Leak checking: Leaks in the system allowing room air to enter the column can cause a shortened column life. It is important to maintain the purity of the gas all the way to the column and check for leaks during purge to prevent oxygen and moisture from re-entering the column.
- Rinsing: After completion of analysis, rinsing with a suitable solvent can help remove any contaminants from the column. Most solvents such as water, methanol, chloroform, carbon tetrachloride, etc are fine but for basic stationary phases water and methanol should be avoided.
By following these best practices for GC column maintenance, it is possible to ensure optimal performance, extend the lifetime of the column, and reduce downtime.
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Chromatography