Chromatography Forum

Hi

I'm trying to determine citric acid and oxalic acid by HPLC UV, but no signal detected, the experiment conditions are:

Column: Varian Pursuit C18, reverse phase
Flow: 1.0 mL / min
Mobile phase: 0.005 H2SO4 pH = 2.5
UV detection: 210 nm
Sample Concentration: 1 mg/ml
Solvent: water

Anyone have any suggestions to solve this problem?

thanks a lot

Are you following an established (validated) method? If so, check that you are using the correct mobile phase. Using a 100% aqueous mobile phase on a C18 column is uncommon; you may not get elution of your analytes without at least some organic modifier in there.

Thanka a lot for your suggestions.

There are reports of the manufacturers that these acids can be separated organics C18 columns using aqueous mobile phases, however, I noticed that the stage of my spine has collapsed resulting in loss of retention, can someone give me a suggestion of some mobile phase appropriate?

Hi

I'm trying to determine citric acid and oxalic acid by HPLC UV, but no signal detected
Flow: 1.0 mL / min
Mobile phase: 0.005 H2SO4 pH = 2.5
UV detection: 210 nm
Sample Concentration: 1 mg/ml
Solvent: water
Anyone have any suggestions to solve this problem?

We do citric acid assays here weekly, in concentratio ranges similar to what you're trying, using either conductivity detector or 210nm, and have validated it for our needs. We never looked into oxalic, that's your job. Use a specialty Restek Allure organic acids column, Grace/Alltech Prevail organic acid column or similar; we've never tried C-18 RP for these. Keep conditions the similar to above, we also use dilute H2SO4 as eluent.

A long time ago I used Hypercarb (graphitic carbon) columns for oxalic acid. I don´t remember details, but it was an adaptation of the manufacturer´s method. I didn´t use these expensive coluns instead of C-18 for fun. Oxalic is quite polar, now-a-days I would probably try HILIC.

HW MUELLER is right about the HILIC

http://www.nacalai.co.jp/cosmosil/data/Web/AP-0307.htm

here is a link to one of the possibilities you will be bombarded soon

Simplest method is using sulfonated polystryrene support such as the Bio-Rad HPX-87H or similar column - 55C - 0.6 ml/min flow rate 0.005 M sulfuric acid. You can use UV but you can also use RI (which is more common).