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:AY9944 (trans-1,4 bis-(2-dichlorobenzylaminomethyl)cyclohexane dihydrochloride) (1 ŒºM as a working solution), N-acetylcysteine (NAC) and monodansylcadaverine (MDC) were from Sigma (St. Louis, MO).
Category: