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:Under chemical ionization (CI), ions with mass-to-charge ratios (m/z) of 331, 333, and 337 were monitored for glucose, and ions with m/z ratios of 375 and 376 were monitored for mannitol (6).
Category: