Poly-DL-alanine, acetaminophen, betaine hydrochloride, and drug standards were purchased from Sigma-Aldrich (St. Louis, MO). Drug CCS calibrants were obtained as descried previously.20 (link) Human liver microsomes (HLM) and S9-fraction (S9) pooled from 100 male and 100 female individuals were purchased from Sekisui XenoTech (Kansas City, KS). C12, C14, and C16 benzalkonium chlorides (BACs) and the synthetic precursors necessary for synthesizing additional BACs and ω-hydroxy BAC analogs were purchased from Sigma-Aldrich (St. Louis, MO). Synthesis of BACs and their ω-OH analogs is detailed in the Supporting Information.