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L-carnitine

Determining free and bound L-carnitine in foodstuffs using HPLC-MS/MS

L-carnitine

The amino acid L-carnitine plays an essential role in the energy metabolism of human, animal and plant cells. It functions as a receptor molecule for activated fatty acids in cytosol and in cell organelles such as the mitochrondia. The human body can form L-carnitine from the amino acids methionine and lysine, but also ingests it, predominantly from meat. L-carnitine is used in medicinal products and dietary supplement products.

Detection principle 

L-carnitine is extracted from the sample material (eg milk powder-based baby food) using an acetonitrile/water mixture at 60°C. To determine the bound L-carnitine, the sample material is also subjected to an alkali fusion. After HPLC separation on a reverse phase, and after electrospray ionisation, the L-carnitine content is determined using mass spectrometry (MS/MS) on the basis of characteristic disintegration of the quasi-molecule ions. Quantification takes place with an isotype-labelled D3-Carnitine, which was added to the sample material to be extracted before extraction began.

Fig 1: Standard solution (content represents 3 mg/100g sample):
The two characteristic mass transfers (quantifier 162 → 85 and qualifier 162 → 103) of the L-carnitine (top) and the two characteristic mass transfers (165 → 85 and 165 → 105) of the isotope-labelled D3-L-carnitine (bottom)

Fig 2: Sample of milk powder-based baby food (content: 3.9 mg/100g):
The two characteristic mass transfers (quantifier 162 → 85 and qualifier 162 → 103) of the L-carnitine (top) and the two characteristic mass transfers (165 → 85 and 165 → 105) of the isotope-labelled D3-L-carnitine (bottom)

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