Chromatography Forum

This post applies to reversed phase gradient impurity methods. Gradient methods often exhibit systemic interferences originating in the weak solvent of a binary solvent system. These peaks elute as the solvent strength increases during the gradient. I've read about a technique (hypothetical?) where a column containing stationary phase is plumbed in-line with the weak eluent (prior to the pump) to trap the lipophilic contaminants. Is there such a system that can clean up the contaminants found in the weak solvent? I envision something similar to a solid phase cartridge with very low resistance to flow.

When doing analysis of perfluorinated compounds (PFAS, PFOA) people often use a column in line between the pump and the autosampler to act as a delay column. It captures any target analytes originating from the Teflon parts of the pump or solvent system, trapping them at initial gradient. As the gradient increases the contaminate will be released but it will be delayed in elution from the target peak in the sample so it doesn't interfere with the quantification.

I guess it could also be done with a column prior to the pumps or mixer that has a phase that would capture the contaminate of interest. If the column becomes saturated though you would see breakthrough of the captured contaminate at that point and require a column cleaning or replacement.

It's a "standard" technique; John Dolan wrote it up in one of his troubleshooting columns:
http://www.lcresources.com/tsbible/hs3420.htm

In amino acid analysers utilising cation-exchange LC and post-column derivatisation with ninhydrin, a column similar to the main analytical column is installed between the pump and injector in order to trap the traces of ammonia from the mobile phase. Both columns are cleaned in the end of each gradient run by washing with a strong alkaline eluent.

My boss tells me that back in the 1980's they would sometimes place small columns packed with chromatography grade silica (10u) in line with the organic solvent lines leading out of the pump. This resulted in a slight cleaning up of the solvents before they entered the column (or mixer). They also used them in AA analysis to retain base from pre-column reactions too. Today, we have high quality solvents so it is not needed for solvent polishing, but they do still get used for AA analysis (or sim) methods.

He said in general, not recommended to do this (place something in-line for polishing). Better to solve the contamination problem using the scientific method first and not try and use a "cheat" to absorb something in line which may effect the method.

Ammonia trap SCX column at the pump outlet is a standard approach at least in one commercial amino acid analyser.

There are a number of dedicated mobile-phase cleaning cloumns available, which can even be used in quaternary HPLC systems for online mobile phase cleanup. While I agree that it's better to find and fix the source of contamination, these might be handy as a quick fix sometimes.
Some examples:
https://mz-at.de/en/chromatography/liqu ... c-columns/

There is another option: Shimadzu sells suction filters with an integrated activated carbon bed. I have ordered some of these, but not tried them yet.
https://www.shimadzu.com/an/products/co ... index.html

[quote="tom jupille"]It's a "standard" technique; John Dolan wrote it up in one of his troubleshooting columns:
http://www.lcresources.com/tsbible/hs3420.htm[/quote]

Thank you for the link; this is the article I remember reading.