A UPLC–MS/MS method for determination of endogenous <scp>l</scp> ‐carnitine and acetyl‐ <scp>l</scp> ‐carnitine in serum of patients with depression

A simple, rapid, and selective ultra-performance liquid chromatography-tandem mass spectrometry method for determination of l-carnitine (LC) and acetyl-l-carnitine (ALC) in human serum was developed. Acetyl-l-carnitine-d3 (ALC-d3 ) was selected as internal standard (IS). After protein precipitation with acetonitrile-water (1 mL, 2:1, v/v), the analytes and IS were separated on a 2.5-μm XSelect HSS T3 C18 column by gradient elution with methanol-water (containing 0.01% ammonia water) as the mobile phase at a flow rate of 0.2 mL/min. Analytes were detected with multiple reaction monitoring using a positive scan mode with electrospray ionization. Good linearity (R2 &gt; 0.999) was observed in the concentration range for LC and ALC. The inter- and intra-day values of relative error were -10.4% to 10.0% with CVs less than 9.84%. The average recoveries of the two analytes were 91.29%-98.23%. Blood samples containing LC and ALC were stable under various storage conditions. Normal, haemolytic, and hyperlipidaemic serum had no significant effect on the quantification of LC and ALC. This method was successfully applied to study the concentrations of endogenous LC and ALC in the serum of patients with first-episode depression.