Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:Protein concentrations were determined using the DC‚Ñ¢ protein assay following the manufacturer‚Äôs instructions with bovine serum albumin as standard (Bio-Rad, Mississauga, Ontario) [21].
Category: