Determination of l- and d-carnitine in dietary food supplements using capillary electrophoresis–tandem mass spectrometry

This paper reports the application of a capillary electrophoresis–electrospray ionisation-tandem mass spectrometry methodology for the unequivocal identification and the quantitative determination of the two enantiomers of the non-protein amino acid carnitine (l- and d-Carn) in 22 dietary food supplements, including drinks, biscuits, capsules and tablets. MS/MS experiments were optimised to achieve the high sensitivity and selectivity required for food analysis. A comparison of the slopes obtained by the external standard and the standard additions calibration methods indicated the absence of matrix interferences in these food samples. Good precision (RSDs ranged from 2.3% to 4.3% for migration times, and from 2.1% to 10.5% for corrected peak areas) and acceptable accuracy established by means of recovery studies (from 85% to 102%) were obtained. The limit of detection was about 10 ng/mL (S/N = 3) enabling the determination of enantiomeric impurities (d-Carn) up to 0.025% of Carn in foods. This chiral method illustrated is suitable for routine qualitative and quantitative analyses of Carn in foods. The results showed contents for l-Carn comprised from 47% to 115% with respect to the labelled content of l-Carn. Percentages obtained for the d-enantiomer ranged from 0.4% to 5.9%, except for one of the samples analysed, that contained the racemate (49.3% d-Carn). The use of the racemate is not allowed by legislation, which corroborated the high potential of the developed method in the control of the quality and safety of foods containing Carn.