Peak shifting is when peaks are not appearing on your chromatogram at their expected retention times. This is a problem because the GC software uses those expected retention times to identify which analyte peaks are which. Once peaks shift significantly, the software will either misidentify the peaks, or miss detecting them altogether. Either case results in faulty measurements, so it’s a serious problem that must be addressed. 

There really are only a few reasons why peaks shift:  either the GC oven temperature has changed, or the carrier gas flow through the GC columns has changed, or the GC columns have degraded.   

Since the temperature of modern process GC ovens is so well controlled, monitored and alarmed, a change in oven temperature is rarely the reason for peak shifting problems these days.   

A change in carrier gas flow, however, is much more common, and can be caused by leaks, blockages, system pressure changes, and other mishaps. To determine if a flow change is your problem, try measuring your carrier gas flows and comparing them to those listed in your GC’s flow setup procedure.  If you see major discrepancies, you then have to chase down the root cause, be it a leak, blockage, or something else. 

Column degradation can occur for a variety of reasons too, and shifting peaks may be just one of multiple tell-tale symptoms of this problem in your chromatogram. To learn more about chromatogram interpretation and troubleshooting process GCs, consider contacting R. Aaron Eidt at Peak Performance Analytical Consulting today!