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[7] What do Chromatograms tell us? Peak Shape: Tailing on just a Single Peak in the Chromatogram

20 May 2013

Chromatograms are like fingerprints.  If you can “read” chromatograms well, you often can find a plausible cause. In this series, we will show a series of GC-chromatograms that are obtained from users and discuss some potential causes for the phenomena. Then we can move into some solutions for improvement.

Fig. 1 Only one peak shows strong tailing

The chromatogram in figure 1 was obtained on a new column. A polarity reference test mixture was injected to verify the correctness of installation. All peaks elute as nice sharp peaks, except the last one.  Somehow there is activity in the system for this component. This activity can be in liner, the column or the detection port liner/transfer line;

Check what kind of component is showing the tailing. Is it an acid, a base or a highly polar analyte like a diol?

Often glass wool in liners can show some activity which delays the injection; Also check the injection port temperature;

When installing the column, and using graphite ferrules, some graphite may enter the column; Reinstall and make sure a 2-3 cm piece of the column is cut-off the inlet after the ferrule has been put in place.  If you use a new ferrule, you may consider to “pre-seat” the ferrule. This way it has already grip on the fused silica and simplifies correct installation.  There are special tools available for different GC inlets.

Here is one for Agilent GC’s: 203-03-015.pdf

Also check column position in detection port; Detection port liners can be highly active, which will show first on the most polar analytes.  The column end must be located near the flame tip;

Also ask yourself if you have chosen the right stationary phase and dimensions for the range of analytes. If a thinner film is used, peak shapes often show worse because of the lower elution temperatures.

A good option is to consider the latest generation of bonded phase columns (Rxi-columns). 

These show a higher degree of inertness, which widens the application. The sample in figure 1 was also analyzed on a Rxi-5Sil MS and the result was quite impressive, see fig.2 and 3.  So in this case, it was a column activity problem.

Fig. 2 When the sample was analyzed on a Rxi column with similar dimensions, the problem-peak elutes with better symmetry, allowing more accurate analysis

Fig.3 Zoom of the problem peak.

If the analyte is a base, there are base deactivated GC columns available that perform very well and are durable for amine containing analytes. Special columns are available for volatile amines (Rtx-Volatile amines). See Advanced Capillary Column Technology Improves Analysis of Volatile Amines