Synthesis of Diatomaceous Earth-Aminopropyltriethoxysilane

D-APDMS used in the NA extraction processes was prepared as follows [24 (link),25 (link),26 (link)]. Diatomaceous earth (DE) was washed with distilled water (DW) for 30 min with stirring. The sediment containing impurities was removed after a short period of settling under gravity. APDMS was used to prepare D-APDMS. Briefly, 5 mL of APDMS was pipetted dropwise into 100 mL 95% (v/v) ethanol solution, which was acidified with acetic acid (pH 5) and combined with 2 g DE. The mixture was incubated for 4 h at room temperature (RT) with stirring. Then, D-APDMS was washed with ethanol, dried under vacuum overnight, and stored at RT until use.