Chromatography Forum

In order to get a good peak,I have to use mobile phase with oxalic acid for LC/MS/MS(ESI).My sample are of serum and urine,I want to know whether oxalic acid will bring contamination to MS?Thank you for your reply!

Oxalic acid is not volatile. Therefore it is not suitable in eluents for MS applications.

Wasn´t there a chain recently where someone suggested that oxalic decomposs so does not interfere with MS??? (I don´t like to use "Search" here).

I think HW Mueller might be refering to:
viewtopic.php?f=3&t=13115&hilit=oxalic

Someone wrote there that they were using ammonium oxalate without the source getting blocked by solids, so whatever the reason, it sounds like it has worked for someone, once, somewhere!

I think HW Mueller might be refering to:
Someone wrote there that they were using ammonium oxalate without the source getting blocked by solids, so whatever the reason, it sounds like it has worked for someone, once, somewhere!

I am always amazed by some junior analysts in the lab struggling with too many options from too many publications for one set of analytes. The conclusion can always be like UV has lower LOD than MS/MS, any compound can be separated on any column, any additive can be used for ESI MS and so on.

In one recent LC/GC application note, a note from a reputable instrument manufacture claims that the 3uM column is a UHPLC column. What a diversified analytical world!

As with so many other things, it depends on your mass spectrometer and the concentration of oxalic acid. I did use oxalic acid once on an LC-MS. It did work; I did getting clogging (not contamination) but it was easy enough to unclogg the source between sets. However, I wasn't doing quantitative work at the time. I was using a max of 5 mM oxalic acid.

There are more column choices now, but there are also off-axis sources, which mitigate clogging. You probably could use small amounts of oxalic acid with some of them. However, I might look at different columns first where I didn't need a chelator in the mobile phase to get sharp peaks.

I have read an article where they used oxalic acid but the temperature of the ESI had to be ~400oC or so so that it decomposed the acid to CO2 and water etc. Sorry but I can't remember the article off the top of my head.