Trypsin will work in our included buffer but a digest can be done in most any buffer base (as long as no serine protease inhibitors are present) by adjusting the pH to 8-8.5 and adding CaCl2 to 10 mM. The calcium prevents autolysis of the enzyme. Other salt concentrations are not usually a problem. We generally use the Trypsin at a ratio of 1:20 to 1:100 enzyme:protein so you need an approximate protein concentration which could be determined by SDS PAGE or a Bradford dye protein assay. If the BSA at 0.2 % is the majority of the protein then this would be a 2 mg/ml or 200 ug/100 ul and require about 2 to 10 ug of Trypsin.