Mass spectrometry method for measuring vitamin B6 in body fluid

A method for detecting the presence or amount of pyridoxal 5′-phosphate in a sample by tandem mass spectrometry, comprising:

• (i) adding an internal standard to a sample;
• (ii) ionizing pyridoxal 5′-phosphate and the internal standard in the sample in positive ion mode to generate a parent ion of pyridoxal 5′-phosphate having a mass/charge ratio of 248.03+/−1 and a parent ion of the internal standard having a mass/charge ratio of 154.04+/−1;
• (iii) generating one or more daughter ions of said parent ions, wherein said one or more daughter ions comprise a daughter ion of pyridoxal 5′-phosphate with a mass/charge ratio of 150.00+/−1 and a daughter ion of the internal standard having a mass/charge ratio of 136.00+/−1;
• and
• (iv) detecting the presence or amount of one or more said ions generated in step (iii), and determining the presence or amount of said pyridoxal 5′-phosphate in said sample from the presence or amount of one or more said ions.