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:…spectrometry (Hu et al. 2014), liquid chromatography coupled with photodiode array detector (Yu et al. 2014), mass spectrometry detector (Won et al. 2014) and nuclear magnetic resonance spectroscopy (Hilbert et al. 2015) can rapidly provide complex chemical information and clarify the…
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