Different pretreatment methods were applied depending on food type. One piece of simulated gum or commercial chewing gum in 15 mL of DW was stirred overnight. Thus, washed gum base in DW was collected and further washed with 5 mL of acetone (Samchun Pure Chemical Co., Ltd., Pyeongtaek, Gyeonggi-do, Korea) twice and 5 mL of ethanol (Samchun Pure Chemical Co., Ltd.), and then, all washed solutions were pooled. Finally, 1 mL of the pooled solution was pre-digested with nitric acid (Samchun Pure Chemical Co., Ltd.) and hydrogen peroxide (Samchun Pure Chemical Co., Ltd.).
The TiO2-containing simulated sugar powder, other commercial foods (0.2 g), such as candy, chocolate, jelly, sauces, and snacks, and the cell samples were directly subjected to pre-digestion with nitric acid and hydrogen peroxide. nitric acid (10 mL) was added to each sample and heated to 180–200 °C in order to digest organic materials. hydrogen peroxide (1 mL) was then added and heating was continued, and this procedure was repeated until the solution was colorless and clear. The pre-digested samples were resuspended in 1 mL of deionized and distilled water (DDW), and centrifuged at 10,000 rpm for 20 min. Then, the precipitate was washed twice with 2 mL of ethanol and re-suspended in 20 μL of ethanol for SEM-EDS analysis [27 (link)].
The TiO2-containing simulated sugar powder, other commercial foods (0.2 g), such as candy, chocolate, jelly, sauces, and snacks, and the cell samples were directly subjected to pre-digestion with nitric acid and hydrogen peroxide. nitric acid (10 mL) was added to each sample and heated to 180–200 °C in order to digest organic materials. hydrogen peroxide (1 mL) was then added and heating was continued, and this procedure was repeated until the solution was colorless and clear. The pre-digested samples were resuspended in 1 mL of deionized and distilled water (DDW), and centrifuged at 10,000 rpm for 20 min. Then, the precipitate was washed twice with 2 mL of ethanol and re-suspended in 20 μL of ethanol for SEM-EDS analysis [27 (link)].