Which method you use to measure the total antioxidant capacity? Depending on the technique you use and how you want to preserve the samples, will be the most suitable diluent.
In total GSH assay, for example, we use phosphate buffer pH = 7 but we use it in the day and discard. In the case of wanting to preserve the dilution for future measurements, however, we use buffer Tris-base pH = 7.6.
Thank you Carolina for your suggestions. We use ABTS to quantify total antioxidant capacity in blood serum samples. We are going to use tris- base. Thanks again!!!