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:The mitochondrial transmembrane potential was measured using flow cytometry of cells stained with 5,5′,6,6′- tetrachloro-1,1′,3,3′-tetraethylbenzimidazolcarbocyanineiodide (JC-1) (Cossarizza et al., 1993) as described previously (Dymkowska et al., 2006).
Category: