A new simple and sensitive high-performance liquid chromatographic procedure with tandem mass spectrometry detection (HPLC/MS/MS), to determine L-carnitine (LC), D3-L-carnitine (D3-LC), acetyl-L-carnitine (ALC), acetyl-D3-L-carnitine (D3-ALC), propionyl-L-carnitine (PLC) and propionyl-D3-L-carnitine (D3-PLC) in plasma, was developed. Sample preparation consisted of only deproteinization of plasma samples with a mixture of acetone–methanol before injection in HPLC. The detection was achieved by multiple reaction monitoring. A chloro-derivative of L-carnitine was used as internal standard. The limits of detection, calculated for a S/N ratio ∼3, were 1 nmol/mL for LC and D3-LC, and 0.1 nmol/mL for ALC, D3-ALC, PLC and D3-PLC. The limits of quantitation were 5 nmol/mL for LC and D3-LC, 1 nmol/mL for ALC and D3-ALC, and 0.25 nmol/mL for PLC and D3-PLC. The recovery of the procedure was in the range 80–96% for the six analytes, 88.2% for the internal standard. Validation was performed within the following concentration ranges: 5–160 nmol/mL for LC and D3-LC, 1–32 nmol/mL for ALC and D3-ALC, and 0.25–8 nmol/mL for PLC and D3-PLC. Linearity was assessed during both intraday and interday sessions, and coefficients of regression were always higher than 0.99. Precision and accuracy were in the ranges 0.38–5.5% and 0.01–3.92%, respectively. The method is suitable for the quantitation of the three endogenous carnitines and their deuterated homologues in plasma in a single analysis.
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Tallarico et al. (1998) studied this question.