I have a ghost peak problem with Oxalic acid.

I analyse oxalic, malic, citric, maleic malonic, succinic, valeric and iso-valéric.

Cond: Column Aminex HPX-87H 300x7.8, H2SO4 0.001N was the eluent, flow 0.5ml/min, T°C: 60, 50µL inj.

Sample Extrac. : 5g compost + 40ml H2SO4 2N. I use this concentration of H2SO4 because many oxalate was under iron or Al form in my sample.

My problem is just before oxalic peaks a big ghost peak appear, and I don't see my oxalic peaks!! Do you have any purification méthode info to remove this ghost peak. INFO: Solvent peak:8.8min, ghost peak 11.1min, oxlaic 11.8min.

Can you help me or do you have any article about this subjet.

Thanks
Mike

I think it`s not a ghost peak but a component in your matrix. Do you have any idea about the nature of your matrix peak? If not you could try to find application notes for Aminex and similar columns from different suppliers in order to get an idea which kind of compound might be disturbing. If you are using different detectors a spectrum of your interfering peak could help identifying it, but I think it is quite likely that your matrix peak is a sugar a sugar alcohol or another organic acid, so UV won`t help too much. Without knowing which compound to remove this could be quite tedious but you could try different SPE methods.

If you can`t identify your interfering compound you could try to get better resolution by changing acid concentration or temperature but this will give you only limited changes in selectivity on that kind of column.
So you could try different brands of ion exclusion columns (look at BioRad, Dionex, Macherey&Nagel, Benson.....).
If this doesn`t help you might try to couple two columns in series (maybe a special sugar column in the Ca2+ form) and a ion exclusion column.
Also have a look at:Jupille et al., Amer. Lab.,13, 80 (1981)