The determination of vitamin D 3 in bovine milk by liquid chromatography mass spectrometry

Abstract

A renewed international interest in vitamin D status has revealed significant deficiencies in several populations, including Australia. Vitamin D exists in two forms, cholcalciferol (D 3) and ergocalciferol (D 2). The main source of vitamin D 3 is from exposure of 7-dehydrocholesterol present in the skin to UV irradiation. However, there is an absolute requirement for vitamin D through proper dietary intake if humans live in the absence of sunlight or exclusively indoors. Bovine milk is considered to be a good dietary source of vitamin D 3, even though the levels are quite low. This paper describes robust methods using liquid chromatography–linear ion trap mass spectrometry (LC–MS n) and liquid chromatography–tandem mass spectrometry (LC–MS/MS) to measure the levels of vitamin D 3 in fresh bovine milk (0.05 μg/100 ml), commercial (natural and fortified) milk samples (0.01–2 μg/100 ml) and a dairy based infant formula (8 μg/100 g), without the need for extensive clean-up procedures. The limits of quantification (LOQ) are 0.01 μg/100 ml and 0.02 μg/100 ml for LC–MS n and LC–MS/MS, respectively. Recoveries of vitamin D 3 added to the samples prior to saponification were satisfactory (range 60–90%). 25-Hydroxyvitamin D 3 was not present in any of the samples analysed (LOQ = 0.01 μg/100 ml, recovery range 30–40%).