Ghost Peaks in Chromatography: What They Are, Why You Should Be Aware of Them

Ghost peaks in chromatography are unwanted peaks that appear at an interval less than the expected retention time. These peaks are generally caused by interactions of other compounds or metabolites with the solvent and stationary phase, which leads to a decrease in separation. They are also caused by interference from impurities or high noise levels. This post will look at ghost peaks in chromatography and what you can do about them.

What are Ghost Peaks?

If a compound appears less than the expected retention time this is known as a "ghost peak". This will appear as a peak with a different retention time to the compounds that were injected on the same chromatogram. This can occur due to the factors discussed below. Ghost peaks in chromatography are unwanted peaks that appear at an interval less than the expected retention time. These peaks are generally caused by interactions of other compounds or metabolites with the solvent and stationary phase, which leads to a decrease in separation. They are also caused by interference from impurities or high noise levels.

Why should We be Concerned about Ghost Peaks?

Ghost peaks can be problematic for two reasons. The first reason is that it is often difficult to identify the actual compound responsible for the ghost peak. This can lead to inaccurate quantifications or identification of the compound. The second issue is that a ghost peak can make it difficult to assess the quality of the separation. In a pharmaceutical analysis it is very important because if you are looking for any impurity, the presence of a ghost peak means that your unable to identify the impurity or you are unable to determine the concentration of the impurity you are looking for.

Causes of a Ghost Peak

There are many reasons for the appearance of the ghost peak during analysis. Sometimes it may appear due to noise or impurity present in the sample, presence of any compound in stationary phase or in mobile phase, interaction between the sample and stationary phase or sometimes due to the low flow rate.

How to Fix the Problem of Ghost Peaks 

This is very unfortunate that there is no any single solution to solve the problem of ghost peaks. But these are some solutions to minimize the occurrence of ghost peaks. You should ensure to use the correct mobile phase, reduce the noise level, mix the sample properly before injecting, chose correct flow rate and ensure the column and sample temperature is correct. Finally, you can check whether you are dealing with a ghost peak. To do this, you need to select the retention time of the ghost peak and then add a few minutes to it. If you find that a peak appears, you will have identified the ghost peak.

Conclusion

Ghost peaks in chromatography are caused by a variety of factors, including the presence of impurities or other compounds in the sample, the presence of compounds in the stationary phase or solvent, or interactions between other compounds and the stationary phase. The risk of ghost peaks can be reduced by thoroughly cleaning the vessel and solvent, using the correct mobile phase, and reducing the noise level. These issues can be identified by using the retention time of the ghost peak and adding a few minutes to it.