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:28 The HNTs and DB-HNTs were prepared using a modified procedure.(27) Experimentally, 20 mg of hydrogen tetrachloroaurate(III) (HAuCl4) was dissolved in 10 mL of 1-octadecene containing 0.
Category: