UPLC-ESI-MS/MS for determining trans- and cis-vitamin K1 in infant formulas: method and applications

A simple and sensitive method of determining vitamin K1 isomers (cis-and trans-forms) was developed for routine monitoring of supplemented infant formulas. The proposed method involves the applications of the lipase hydrolysis and the liquid-to-liquid extraction. After the hydrolysis and extraction procedures, the vitamin K1-enriched extract was directly injected into the ultra-performance liquid chromatography–tandem mass spectrometry system (UPLC-MS/MS). The components were detected using electrospray ionization (ESI) in positive-ion and quantified by multiple-reaction monitoring (MRM) mode. trans-vitamin K1 was separated from the biologically inactive cis-isomer through a C30 column (4.6 × 150 mm, 3 µm), and vitamin K1-d7 was used as an internal standard. Calibration curves were linear over the range of 9.3–464.75 ng ml−1 for trans-vitamin K1 (r2 > 0.999) and 1.71–85.25 ng ml−1 for cis-vitamin K1 (r2 > 0.999). The limit of detection for trans- and cis-vitamin K1 was 0.011 µg 100 g−1 and 0.01 µg 100 g−1. The limit of quantification was 0.037 µg 100 g−1 and 0.031 µg 100 g−1, respectively. The intra- and inter-batch variations (RSD%) were less than 5 %. The proposed method was applied to determine vitamin K1 isomers in milk-based, soy-based and rice-based infant formulas, and the cis-vitamin K1 isomer contributes to 7.05–17.21 % of the total vitamin K1 in certain infant formulas.