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:5 mg), GST-53BP2(715-1005) (1 mg), GST-GL(1-257) (1 mg), and GSTGL(94–257) (1 mg) were separated on duplicate SDS–12.
Category: