Following the steps below will ensure that your Molecular Sieve packed column is ready to use just several hours after installation. You should only use dry (moisture-free) & hydrocarbon-free high-purity Nitrogen as the carrier gas to condition (and/or dry) your column. If using a different carrier gas than nitrogen, temporarily switch out gas supplies when conditioning or drying columns. For additional information, see "Molecular Sieve Packed Columns and Fixed (Permanent) Gas Analysis".
1. Cool all heated zones and then turn off all GC gases. Please allow the current packed column (if one is installed) to depressurize so that its removal from the GC (more specifically, the inlet) doesn’t cause a pressure surge which can expel packing from the column (see Helpful Hints C below for additional information).
2. All molecular sieve columns are fully activated and end capped to prevent moisture diffusion. Remove the column end caps (and silicone ferrule, if present) and attach the appropriate nut & ferrule to the inlet side of the column.
Install the new column into the injection port. Do not connect to the detector at this time. Do not turn on any heated zones. Slowly increase the head-pressure just until carrier gas flow starts exiting from the column.
3. Attach an electronic flow meter (or soap-bubble flow meter) to the outlet of the column and once again begin slowly increasing the head-pressure. When the desired column flow rate has been obtained*, continue to monitor the exiting carrier gas flow rate for five minutes to make sure it is stable.
4. Remove the flow meter and purge the column for an additional 10 minutes. Set the GC oven temperature to 110°C and program the oven to ramp at 5°C/min to 300°C. Heat the GC injection port (if applicable) to the desired temperature, but do not expose the column to higher temperatures than the maximum temperature of the column (350°C). Begin the GC oven program ramp. When 300°C is reached, hold it at this temperature for 3 hours.
5. Cool the GC oven (Do not turn off the carrier gas unless you need to switch out the nitrogen for another carrier gas; if you do, see Steps #1-3 above). Install the column into the detector and heat the detector to the desired temperature, but do not expose the column to higher temperatures than the maximum temperature of the column (350°C).
6. Your column should be ready to use.
A. If you notice any degradation with the chromatography, you may need to “dry” the column. To do so, use hydrocarbon-free & moisture-free nitrogen as the carrier gas. After purging the column for 10 minutes using the flow rates listed below, increase the GC oven temperature to 300°C and hold for 3 hours. This should remove all traces of water vapor (and carbon dioxide). (Additional note: With a dry 5A or 13X column, methane (CH4) elutes before carbon monoxide (CO). If CO elutes with methane, or before methane, your column needs to be dried).
If drying the column doesn’t improve chromatography, you may need to “regenerate/reactivate” the column (a tailing carbon monoxide peak is a common indicator of surface activity; another may be a decrease in response for the oxygen peak**). To do so, use hydrocarbon-free & moisture-free compressed air as the carrier gas. After purging the column for 10 minutes using the flow rates listed below, increase the GC oven temperature to 300C and hold for 3 hours. This should reactivate the surface of the zeolite molecular sieve packing.
** If you experience a decrease in response for the oxygen peak, but the carbon monoxide peak does not tail, the problem may be with the pre-column (stripper column), especially if this pre-column is a porous polymer.
B. Always use high quality gas traps on your carrier gas line. As mentioned earlier, molecular sieve packings like to absorb everything.
C. Never perform any GC maintenance (such as replacing the septum or liner) or remove a packed/micropacked column from a GC, without having the carrier gas turned off and allowing the column/instrument to depressurize. Otherwise the packed column’s bed may collapse or particles may be expelled.
D. If the column is not going to be used for several days, all the instrument’s heated zones should be cooled and the carrier gas turned off. The column should be removed and the ends should be capped to keep air/moisture out of the column. If the column is going to be used the following day, do not cool instrument’s heated zones, leave the carrier gas on, and set the GC oven temperature to 150°C.
E. When using a high sensitivity detector like a HID, DID, FID, etc. a micropacked column (0.53mmID through 1.0mmID) should work well. However, when using a low sensitivity detector like a TCD, consider using a 2.0mmID (1/8”OD) packed column (for capacity).
F. Molecular Sieve columns are extremely retentive. For gas analysis, compounds larger than (and including) C2+ (ethane), or compounds with a boiling point greater than 50°C, should not be injected onto these columns. If you suspect your samples may contain “heavies”, consider using a system which incorporates a pre-column and valve switching.
* Common conditioning carrier gas flow rates for packed/micropacked columns:
0.53mmID (0.74mmOD) = 5mL/min
0.75mmID (0.95mmOD) = 7.5mL/min
1.0mmID (1/16”OD) = 10mL/min
2.0mmID (1/8” OD) = 20mL/min.
Safety Note: If using hydrogen as the carrier gas, please safely vent the hydrogen during the conditioning process. Do not vent the gas into a confined space, like the GC oven. Several of the links in this post contain useful safety information when using hydrogen. GC Carrier Gases – Alternatives to Helium