I need help to find an easy method to quantify the nmol/ml of aldehyde groups introduced in bacterial polysaccharide after periodate oxidation.

I've tried with BCA and microBCA method, but i always seen a strange affect in my sample: more i diluite it, more te response growth (after normalization for diluition factor).

Have someone BCA trick or some other easy method to suggest? (I can't use NMR.)

Thanks