What happened to my GC column?14 Jan 2013
GC columns are commonly marketed for multiple methods/analyses, which is usually not an issue. Sometimes, however, when a column (or column set) has been used for one analysis, it may no longer work for another analysis. This is especially true when one analysis contains very dirty samples (or derivatized samples), and another contains very reactive compounds. Dirty samples (and derivatized samples) may introduce unwanted activity into the column (and injection port liner) which renders the instrument too reactive to perform other types of analyses. For example, let’s say you have an instrument which recently analyzed PCB’s in transformer oil, and now you plan to analyze low level pesticides; there is a good chance you are going to have difficulty meeting the requirements (detection limits) for the pesticide analysis. The same type of situation may occur after analyzing derivatized samples, or those containing elemental sulfur. I had discussed these topics previously in my series Capillary GC Column Killers.
Ideally, one would have a dedicated instrument and column for each analysis, but this is often not realistic. However, having a dedicated column (and injection port liner) for a difficult analysis may well be worth the investment.
Generally speaking, here are a few things to consider when making the column selection for your next project.
1. What type of samples/compounds has the column been exposed to, and could this lead to problems with your next project? To minimize instrument downtime, always keep a new, backup column available in case the new project does not work with the current column.
2. Injection port liners are also susceptible to the same problems encountered by columns after certain analyses; always keep a few new ones on hand.
3. Don’t forget routine maintenance, like swabbing out the injection port with cotton-tipped wooden handle swabs and an appropriate solvent. Change all inlet consumables, and trim the analytical column (not just the guard column - remember, a guard column only traps non-volatile residue; if unwanted material makes it into the analytical column, it may get trapped in the sticky polymer, leading to column activity).
4. If activity is still an issue after routine maintenance, “prime” the system with several injections of a high-concentration standard, followed by a solvent blank to make sure there is no compound carryover.
5. If contamination is the issue, perform routine maintenance first (see #3), and then bake-out the instrument according to the instrument manufacturer's recommendations (but never overnight - an hour or two should be more than enough).
6. If contamination continues to be an issue, change the split vent trap. If a replacement is not available, turn on the split flow (at a flow rate of approximately 2mL/min) and leave it on overnight. This may help prevent contamination from working its way back into the injection port.
7. If a jagged baseline is the issue, and especially if your column is a high-polarity or a non-bonded phase, limit the temperature ramp, both increasing (oven heating) and decreasing (oven cooling) temperature rate to 20°C/min.
Hopefully this post will provide some useful information for those who may have experienced sudden column (and/or instrument) issues, and for ways to keep it from happening in the future. Thanks for reading.