The baseline starts creeping up on a Tuesday. By Thursday there are small peaks in blank runs that shouldn’t be there, and the peaks that should be sharp have grown tails. Someone opens the catalogue and starts pricing a new column, which is a reasonable instinct and often the wrong one.
A GC column sits at the end of a chain of small parts, and many of the problems that show up in the chromatogram start somewhere along that chain. Checking the gas chromatography supplies upstream (filters, septa, liners, ferrules) usually takes less time and money than replacing the column. It also tends to find the real fault.
Start Where the Gas Starts
Carrier gas is the first thing to touch the system, and its purity affects everything after it. Gas filters exist to strip out moisture, oxygen and hydrocarbons before they reach the inlet. Some are designed for a single contaminant, others as combined triple filters, and there are versions specific to helium or hydrogen carriers.
Oxygen and moisture are particularly unkind to stationary phases at high oven temperatures. A filter past its useful life gives no warning of its own; the first sign is usually in the data. Many labs track filter changes by date or indicator rather than waiting for symptoms, which turns a guess into a routine.
Why Does a Small Septum Cause Big Peaks?
Because it sits at the hottest, busiest point of the inlet and gets pierced on every injection. As a septum ages it can shed material and release volatile compounds. That’s a common source of ghost peaks that appear even in blank runs.
Repeated needle strikes can also core the septum, dropping small fragments into the liner below. Those fragments then sit in the sample path. A septum costs very little compared with a column, and replacing it on a schedule based on injection count is one of the cheapest checks in the whole system.
The Liner Sees Everything First
Every sample hits the inlet liner before it reaches the column. Non-volatile residue, septum particles and matrix build up there over time. Active sites on a dirty liner can cause tailing and loss of sensitive compounds that looks remarkably like a column problem.
Liners come in different designs for split and splitless work, packed-column analysis and specific instruments. Matching the liner to the injection technique matters as much as keeping it clean. Of all the gas chromatography supplies in a lab drawer, the liner is probably the one most worth inspecting before anything gets replaced.
Leaks also make retention times drift and baselines noisy, which can send troubleshooting in the wrong direction. Checking fittings with a leak detector after any column change, and replacing ferrules rather than reusing tired ones, prevents a whole category of confusing results.
