Routine clinical determination of carotene, vitamin E, vitamin A, 25-hydroxy vitamin D3 and trans-vitamin K1 in human serum by straight phase HPLC

A universal extraction procedure is described for fat‐soluble vitamins in human serum. Methods are presented for routine quantitative analysis by isocratic straight phase HPLC with UV‐detection of (α + β)‐carotene, vitamin E. (α‐tocopherol) and vitamin A (all‐trans‐retinol) in one single run, and of vitamin K1 (trans‐phylloquinone) and 25‐hydroxy vitamin D3 after sample clean‐up using disposable reversed‐phase cartridges. The limits of detection, precisions and selectivities of the developed assays are shown to be satisfactory after more than three years' experience. The routine clinical determination of fat‐soluble vitamins can be performed in less than 5 mL of serum. Analyses of external quality control and randomly taken outpatient samples are shown to be of great value in assessing laboratory performance.