any methods to reduce NH4OAc background for IC analysis? or any alternate soil extraction procedures available for cation analysis with IC in order to determine CEC?
Yes, With IC you will detect ammonium ion and acetate ion (however there may be other sources of acetate and ammonium ions). Have you considered using the spectrophotometric Bertholet reaction to quantitate just ammonium ion?
A soil sample is extracted with an excess of 1 M ammonium acetate solution. The amounts of exchangeable sodium, potassium, calcium and magnesium in the extract are determined by flame photometry (Na and k) and by atomic absorption spectrophometry (ca and Mg). lanthanum or strotium is added as a releasing agent to prevent formation of refractory compounds which may interfere with determinations (e.g. phosphate),
I think your best bet in this situation is to use ICP-OES or Flame AA for your analysis. With that much NH4 you will really have a difficult time getting good peaks for the other cations. We used to run into a similar problem when trying to run NH4+ on samples with high sodium. The peaks are so close together, we had to resort to Ammonia electrode.
First, I agree with the statements above to use an alternative analytical approach. ICP or AAS the easiest way to go.
Let's assume that you do not have access to either of the methods. Depending on the sample pH a degassing step (e.g., vacuum) might help to reduce the ammonium concentration. Ammonium acetate is volatile, and you might be able to reduce its concentration. How much? I don't know. I think it depends on the sample pH. So here lies the dilemma. If you want to use IC for the determination of group I and II elements, acidification is necessary, while the vacuum degas benefits from higher pH values.
I still prefer the use of an alternative analytical approach, but I hope that this suggestion is of some help.