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:This remaining supernatant was then used to resuspend the hR vesicle pellet at a concentration of;0.1 mM. FTIR samples were made from these suspensions with slight modifications to previously published procedures (Braiman et al., 1987; Dioumaev and Braiman, 1997b).
Category: