This document specifies a method for the quantitative determination of vitamin D₂ and/or vitamin D₃ in infant formula, and adult nutritionals in solid (i.e. powders) or liquid (i.e. ready-to-feed liquids and liquid concentrates) forms using liquid chromatography-mass spectrometry. The application range runs from 0,15 µg/100 g (limit of quantification) to 59 µg/100 g for vitamin D₂ and from 0,25 µg/100 g to 65 µg/100 g for vitamin D₃.