Chromatography Forum

Hi, I'm looking for a way to extract both citric and oxalic acids from the urine. Urine organic acids (I guessed) are interfering the separation of oxalic acid using a RP column with UV detector

thanks

Hello,

Urine cannot be directly injected onto a column as it contains several protein and amino acid compounds which will bind to the packing material, therefore some kind of sample preparation will need to be carried out beforehand. Passing it through either a PLRP-S or C18 SPE cartridge should remove these compounds, and probably help with those that are interfering with the separation of citric and oxalic acid. It will, however, let all other dissolved organic acids (such as lactic acid, uric acid etc.) through as well.

What column are you actually using for this separation, as another approach would be to try using a ligand exchange HPLC column instead. I have been doing some work recently on a Hi-Plex H column (from Polymer Laboratories) which gives a very good separation of oxalic and citric acid, which may help to resolve them from any other interfering compounds in your sample. I can provide you with further details about this if required.

Hope this helps,

Steve.

Hi Y,

While you can retain critic acid on an aqueous-compatible RP column in highly aqueous mobile phase in ion-suppression mode (low pH), it is very diffcult to obtain decent retention for oxalic acid which elutes close to the void, and is heavily affected by sample matrix (see this link http://www1.dionex.com/en-us/columns_ac ... s6953.html).

On the other hand, oxalic and citric acids can be separated by ion chromatography with ease if you have the capability in the lab. Much better lower detection limit can be achieved at the same time. You can find some useful information in the following link (see peaks 23 and 28): http://www1.dionex.com/en-us/columns_ac ... s3609.html

In case you prefer to use a standard HPLC system with UV detection. A mixed-mode column should be considered. Figure 6 in the document provided by the following link could be what you need - http://www1.dionex.com/en-us/webdocs/48 ... 021407.pdf.

Please let me know if you have questions.

Good luck,

Hi, steve
thanks for advising...
yes, I understand the need for proper extraction and sample clean up before injecting into HPLC. currently, i just filtered (normal filtration), centrifuged and dilute the sample before injecting, i hope it will help to clean it up from the protein and amino acids.
yes, I'm interested in your suggestion of using ligand-exchange column. i will check it out from the internet first or get back to you. I'm using the genesis RP C18 column.

Thanks

Hi, XiaoDong,

thanks for the very useful link. I definitely believe it will be suitable to separate the organic acids in urine. I'm looking a way to try it out. Let you know the result after I've try on it.

Thanks