It is a very challenging analytical problem since your mixture is quite complex. Ion chromatography stationary phases may be the most convenient way. It may not be compatible with organic solvents like DMF (ACN is fine on many Dionex IonPac Systems). Do you have access to voltammetry? The following article seems a like a decent solution for non-aqueous systems: Simultaneous Determination of Oxalate and Carbonate, Analytical Letters, 20:2, 213-221.

What range of concentrations do you expect? There is another way (provided interferences are absent) that you extract oxalate and carbonate in water (i.e. remove organic solvents) and precipitate the two anions with calcium ions. Assuming only oxalate and carbonate are present, one can do redox titration of a known weight of calcium oxalate and calcium carbonate mixture with KMnO4. After oxalate determination, the difference will give carbonate content.

It is a very challenging analytical problem since your mixture is quite complex. Ion chromatography stationary phases may be the most convenient way. It may not be compatible with organic solvents like DMF (ACN is fine on many Dionex IonPac Systems). Do you have access to voltammetry? The following article seems a like a decent solution for non-aqueous systems: Simultaneous Determination of Oxalate and Carbonate, Analytical Letters, 20:2, 213-221.

What range of concentrations do you expect? There is another way (provided interferences are absent) that you extract oxalate and carbonate in water (i.e. remove organic solvents) and precipitate the two anions with calcium ions. Assuming only oxalate and carbonate are present, one can do redox titration of a known weight of calcium oxalate and calcium carbonate mixture with KMnO4. After oxalate determination, the difference will give carbonate content.

Thanks for your answer. 

It will be a complex electrochemical mixture (CO2 reduction). I don't think the titration approach will be amenable to the system because it will be on very small scales and there will be catalysts and additives that could interfere with the observations. 

Kyle

Ion chromatography is perhaps the best way to go in this case. Both carbonate and oxalate are retained on IC columns. You will not be able to distinguish between carbonate and bicarbonate in IC (one single peak) with NaOH or any basic eluent.

Idris,

Have you done this with 13C NMR? They have no protons so will not be detectable in proton NMR. 13C will take a while and I don't trust that the integrations will be accurate. 

-Kyle

Kyle, 

I was also going to suggest quantitative 13C NMR with a standard for oxalate and for carbonate. I only have experience trying to detect them qualitatively, but for that, we usually do 13C NMR with standards along with FTIR with standards. 

I would make a calibrate curve for 13C NMR with known concentrations of the standards, then run your sample and compare the integrations.

Be careful with oxalate though because I think that can decompose into CO2 and formate. Might want to look into this.

It depends on your matrix and the approx. concentrations. Providing more information in your question is always a help.

If oxalate and bicarbonate are present in modest quantities, you can drive off the CO2 by acidifying a sample, warming, neutralizing, and precipitating the oxalate with calcium. (Yes, gravimetry, when you have a department full of sophisticated instruments.)

A second sample can have the CO2 gas driven off by bubbling nitrogen through the acidified sample. The CO2 can be trapped and precipitated by a calcium or strontium chloride solution and measured (gasp!) gravimetrically.

Ion chromatography will work, of course, but with this mixture, there are just so many ways it can go wrong. Worse if there are other components in the matrix.