*2.2. Preparation of Calibration and Quality Control (QC) Standards*

HSG4112(S) 10 mg, HSG4112(R) 10 mg, and HSG4112-d5 (internal standard; IS) 5 mg were weighted and transferred to a 10 mL volumetric flask and ACN was added to the marking line to completely dissolve and store in a refrigerator (4 ◦C). The standard stock solutions of HSG4112(S) and HSG4112(R) were serially diluted to the designated concentrations to prepare the working standard solutions. The IS stock solution was diluted to 100 ng/mL with ACN and used for plasma sample preparation. Working standard solutions (5 µL) were added to plasma (95 µL) to yield calibration standards of 5, 20, 50, 100, 500, 1000, 2000, and 5000 ng/mL. QC samples were prepared at final concentrations of 5(LOQ), 15(low), 400(mid), and 4000(high) ng/mL in the same manner as the calibration standards.
