Development of isotope dilution-liquid chromatography/tandem mass spectrometry for the accurate determination of trans- and cis-vitamin K isomers in infant formula.

A method based on isotope dilution-liquid chromatography/tandem mass spectrometry (ID-LC/MS/MS) using a C30 column has been developed for the separate and accurate determination of trans- and cis-vitamin K in infant formula. Vitamin K and the deuterium-labeled internal standard eluted at slightly different retention times experiencing different matrix effects, and this possibly resulted in biased measurement. The matrix effect profiles obtained from post-column infusion experiments showed that atmospheric pressure chemical ionization (APCI) was less susceptible to matrix effects near the retention time than electrospray ionization (ESI); therefore, APCI was used in this study. The developed method was validated by measuring fortified samples, and the results agreed with the gravimetric values. Its repeatability and reproducibly were within 2% relative standard deviation. The relative expanded uncertainty was approximately 5%, indicating that the method was of higher-order metrological quality as a reference method.