Technical Tips

A Technical Tip by Kory Kelly
GC Product Manager

Everyone has most likely been plagued with additional peaks in a chromatogram from time to time. The key is to determine the source of these unwanted peaks and eliminate them. Possible sources of unexpected peaks can come from nearly everywhere ranging from but not limited to incorrect sample preparation, electronic noise, accidentally introduced contaminants, and sample carryover left in the detector, column, syringe, or inlet.

A common source of additional peaks in a chromatogram that have been problematic for column manufacturers has been due to septum bleed. It is common practice to install a new septum in the inlet when a new column is installed. This new and unconditioned septum can often be a source of contamination that will result in peaks in the chromatogram. Users see the additional peaks and instantly blame them on the column as the peaks were not present before the column was installed. Chromatographers with mass spectra identification can even identify the peaks as silicon containing compounds and realize that the stationary phase of the column contains silicon and further cements the notion that the column is bad.

In reality, the peaks seen in the spectrum are actually due to septum bleed. Septa are made of the same polymers that comprise the stationary phase of the column giving compounds that would be similar with column bleed compounds. The fact that peaks are seen shows that the compounds are being separated by the column, which means that they were introduced in the front of the column. If the column was bleeding, peaks would not be seen as the column would bleed form the whole length of the column at the same time and would not result in a peak but a general rise in the baseline as the temperature increases.