Comprehensive Vitamin Biomarker Quantification

The concentrations of total vitamin B₁ in whole blood and urine were measured by the high-performance liquid chromatography (HPLC)-postlabeled fluorescence method of Kimura et al.19 (link) The concentration of total vitamin B₂ in whole blood was determined by the HPLC–lumiflavin method of Ohkawa et al,20 with slight modifications. The concentration of vitamin B₂ in urinary excretion was analyzed according to the method of Ohkawa et al.21 (link) Pyridoxal phosphate (a coenzyme of vitamin B₆) in plasma was determined using the HPLC method.22 4-PIC, a catabolite of vitamin B₆, was measured in urine by the HPLC method.23 (link) Concentrations of vitamin B₁₂ in plasma and urine were assayed by the microbiological method with Lactobacillus delbrueckii subsp. lactis ATCC 7870.24 The total nicotinamide content in whole blood was measured by the method of Shibata et al.25 (link) The quantities of Nam, 2-Py, and 4-Py in urine were measured simultaneously by the HPLC method of Shibata et al.26 (link) The content of MNA was measured by the method of Shibata.27 Plasma and urinary folates were determined by the microbioassay method using Lactobacillus casei ATCC 2733.28 (link) Plasma and urine contents of reduced and oxidized ascorbic acid and 2,3-diketogluconic acid were determined by the HPLC method.29