Tolbutamide

PF (Lot: ST007001, purity: 99.4%) was purchased from Nature Standard (Shanghai, China). Tolbutamide (IS, Lot: 100369-201307, purity: ≥ 98.0%) was purchased from Yuanye Biotechnology (Shanghai, China). Verapamil Hydrochloride (Lot: LGVBJ-ET, purity: 98.0%) was subscribed from TCI (Shanghai, China). The structure of PF and Tolbutamide are shown in Figure 1. Acetonitrile, methanol and dimethyl sulfoxide, up to HPLC grade, were purchased from Merck (KGaA, Darmstadt, Germany). Deionized water was collected from a Milli-Q ultra-pure grade water system (Millipore Corp., Massachusetts, MA, USA). All the other chemicals were of analytical or HPLC grade.

LDR (purity >98%), diclofenac (purity >99%), tolbutamide (purity >99%), warfarin (purity >98%), and chlorzoxazone (purity >98%) were obtained from Shanghai Yuanye Biological Technology Co., Ltd. (Shanghai, China). Sodium carboxyl methyl cellulose (CMC-Na) was purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China). Ethylenediaminetetraacetic acid disodium salt (EDTA-Na₂) was purchased from Beijing Solarbio Science and Technology Co., Ltd. (Beijing, China). Methanol and acetonitrile of LC-MS grade were obtained from Sigma-Aldrich (St. Louis, MO). Formic acid of LC-MS grade was purchased from Shanghai Macklin Biochemical Co., Ltd. (Shanghai, China).