*2.8. Sample Preparation for Targeted Metabolite Identification and Quantification*

Fifteen randomly selected samples (ECT = 5, CCT = 5, and CTL = 5) were quantified for the target metabolite. Erythrocytes (6 × <sup>10</sup>8) were lysed in 200 <sup>μ</sup>L of ddH2O containing 100 ppb of debrisoquine sulfate (Sigma) as an internal control. The lysate was extracted in 800 μL of warmed methanol. The sample was incubated at RT for 15 min to precipitate proteins and centrifuged at 16,000× *g* for 30 min at 4 ◦C. The supernatant was transferred to a new tube, dried under nitrogen gas, and stored at −80 ◦C. Prior to analysis, the sample was dissolved in 200 μL of ddH2O containing 0.1% formic acid. The procedure was carried out according to the method of Tang et al. [26].
