抄録
The two-step high performance liquid chromatography (HPLC) method, that is, preparative HPLC (reverse-phase) followed by analytical HPLC (normal-phase), is used as the Japanese official method to determine the content of vitamin D in food. We first performed an interlaboratory study to estimate precision of the official method using the certificated formula milk (NIST, SRM 1849). The relative standard deviations (RSDs) of the official method for intermediate precision and reproducibility were 16.5 and 18.6%, respectively. We considered that non-polar insoluble interferences may disturb re-dissolution of vitamin D in the sample solutions which are applied to the preparative HPLC (reverse-phase). Therefore, we investigated a modified method in which preparative HPLC (normal-phase) was followed by analytical HPLC (reverse-phase), in order to reduce the insoluble substances. An interlaboratory study using 4 commercial formula milk available in Japan showed that the intermediate- and reproducibility-RSD of the modified method were ranged from 6.7 to 12.9% and from 7.4 to 18.9%, respectively. These results suggest good performance of the modified method.
