Extraneous Peaks in Chromatographic Analysis

Chromatography is a process that allows you to separate compounds based on their affinity to different properties. This separation begins with a mixture of compounds and ends with individual peaks or bands of each compound on its own graph. Compounds can interfere with chromatography in many ways, causing peaks that shouldn’t be there. These extraneous peaks ruin the clarity of your results and make it difficult to understand what your chromatography data are showing you. Recognizing when you have extraneous peaks is important because they can skew your results, but it isn’t always easy to see which peaks are not real. We will explain why this happens, as well as give you some tips on how to identify these fake peaks and get rid of them.

What are extraneous peaks?

A peak that is not a result of the compounds you’re analyzing but rather something else is referred to as an extraneous peak. A peak that isn’t from your sample would show up as a bump on the graph, rather than a smooth line. These extraneous peaks will throw off your chromatography results, making it difficult to draw accurate conclusions. When a peak is too wide, or the solvent has a higher retention time than it should, the graph will look like a hump rather than a peak. A hump can throw off the retention times of your samples, making it difficult to determine what compounds are present.

The presence of extraneous peaks in chromatography results is extremely common. This is due to a variety of issues with the sample or the equipment being used. You may have issues with the sample itself. For example, if you are using a hydrocarbon solvent, you may be pulling in hydrocarbon impurities from the air. These impurities will cause peaks in your chromatography results. Other issues that can cause extraneous peaks include contaminants that are in your sample such as dust, solvent, grease, or even oils from your fingertips. Contaminants, such as the solvent that you use in your sample, can also cause retention time issues, causing bumps on your chromatograph rather than peaks.

Which peaks can be classified as extraneous peaks?

The peaks that are most commonly considered extraneous are those that represent some other component of the equipment rather than a compound in the sample. Some common peaks that may be considered extraneous include: The solvent’s retention time - The solvent will pull the sample upward and directly affect the time the compounds take to reach the detector. The solvent’s baseline - This is the solvent’s retention time without the sample in it. The baseline is important because it is used to determine the start time of the sample. If the baseline is higher than it should be, the sample will be falsely detected. The solvent’s peak width - In order to accurately determine the compounds in the sample, the chromatography column must separate the compounds. This process is referred to as “elution.” The column can only elute the compounds once they’ve reached the top of the column. However, if the column is too wide, compounds may elute before they’re detected. This can result in the compounds being detected on both sides of the sample, making it appear as though there are two compounds in the sample.

The best way to identify extraneous peaks is to compare your chromatograph to a chromatograph diagram. If you are analyzing a sample that has been previously analyzed, then you can compare your results to the previous sample. It is important to note the differences between chromatograph and chromatograph diagrams. A chromatograph is data that you collect through the analysis, while a chromatograph diagram is a representation of the sample’s retention times. - If your chromatograph shows a retention time that is different from the sample diagram, you may have an issue with the retention time of the column. - If your chromatograph shows two peaks, you may have a retention time issue.

There is not any specific regulatory guideline for extraneous peaks that can help the industry to identify the extraneous peak in the chromatogram. Pharmaceutical firms have no specific reporting threshold for extraneous peaks. Some firms consider the extraneous peaks if any peak has 1% area of the main peak and they leave the peaks having an area below 1% and some have their limit of 2% area, which means there is no specific criterion for it and there is no justification for this 1% or 2% reporting threshold.

ICH Guidances ICH Q3A(R2), “Impurities in New Drug Substances" and ICH Q3B(R2), “Impurities in New Drug Products" have details about impurities and degradation products but extraneous peaks are not addressed in these guidelines.

The FDA mentions extraneous peaks only in the "Reviewer Guidance - Validation of Chromatographic Methods" published in 1994. But it doesn't have any reporting threshold.

However, regulatory bodies are focusing on it these days and FDA has issued warning letters when extraneous peaks are not investigated properly. Following are some warning letters issued by the FDA on the investigation of extraneous peaks.

Vega Life Sciences Pvt Ltd
Windlas Healthcare Pvt Ltd
Mylan Pharmaceuticals Inc

Therefore, proper regulatory guidance from FDA or ICH is required for the pharmaceutical industry on extraneous peaks and their reporting threshold. Please add your views on this topic in the comment section.

Conclusion

Chromatography is a great technique for separating compounds and analyzing them. Unfortunately, chromatography can also produce extraneous peaks that can throw off the clarity of your results. The best way to deal with extraneous peaks is to take careful notes on your sample and the equipment that you’re using. This way, you can identify issues with your sample and the equipment and troubleshoot them before they become a problem.

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