Tips For Better Gas Chromatography Analysis

Most Gas Chromatography analysis related problems fall into one of eight categories. In this article, we’ll take a quick look at some simple troubleshooting for analysts experiencing one of those - retention time shifts.

Retention time shifts are incredibly common and can be attributed to one (or more) of the following:

1. Different column temperature or column dimension
2. Different carrier gas flow rate or average velocity
3. Injector leak
4. Change in solvent
5. Column contamination or even falls out of calibration with age

What now?

These tips and tricks brought to you by Pace Analytical, LLC are generalizations and recommendations for simple troubleshooting of the most common problems.

Different column temperature or dimension

Verify your temperature program or column temperature.

A change in column temperature will shift all peaks in the same direction. A change in temperature program may affect all or some of the peaks. For example, if the retention time shift does not affect early eluting peaks, a change in temperature program is most likely the issue.

Verify column identity.

A change in dimension will cause varying shifts in all peaks (<30 sec), the amount of shift increasing as RT increases. A change in column length due to cutting or maintenance may cause carrier gas flow rates to change.

Different carrier gas flow rate or average velocity

Check gas flow rates.

A change in carrier gas flow rate will also cause all peaks to shift in the same direction.

A slower velocity will increase RT, faster will decrease RT. If the velocity has not changed, check for calculation errors. In some instances, although not common, the pressure regulator or flow controller may be at fault.

Injector Leaks

Check injector septa.

If your GC is equipped with a back pressure regulated injector, a leak may cause a decrease in RT for all peaks. If the RT shifts are inconsistent and changes in direction and size with each injection, a faulty or loose septum is likely to blame.

Change in solvent

If only the peaks nearest the solvent front are affected, the cause us likely the solvent- those closest to the solvent front experiencing the reduction in RT. A change in solvent is also causes corresponding asymmetric or broad peak shape at times.

Column contamination or old age

Injections of high sample concentration can cause a shift in the RT of the corresponding compound. It may also cause surrounding peaks to shift. Rinsing a capillary column using a rinse kit will decontaminate and restore the column. Occasionally a column oven will drift out of calibration, the oven showing a different temperature than the actual. In this case, a service engineer will likely be needed to perform re-calibration. 

Please feel free to contact us for service inquiries related to Gas Chromatography Analysis:

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Minneapolis, MN 55414