Pyrrolidone modified magnetic COF materials for the quantitative determination of 25-hydroxyvitamin D in human serum <i>via</i> isotope dilution mass spectrometry

Vitamin D is indispensable for regulating the balance of calcium and phosphate and preserving the health of the skeletal system. Rapid and accurate detection of vitamin D content in the blood is crucial. In this work, we synthesized a magnetic COF material modified with pyrrolidone and <i>p</i>-aminobenzoic acid (Fe₃O₄@COF@Au@PABA@APP) for quantifying 25-hydroxyvitamin D from serum <i>via</i> isotope dilution mass spectrometry. The developed method demonstrated excellent linearity (<i>R</i>² > 0.99) across the 1-200 ng mL^-1 calibration range, a low detection limit (0.50 ng mL^-1), a good recovery rate (97.69%-103.16%), and low intra-day (<6.04%) and inter-day (<7.50%) variations. The measurement uncertainties for 25-OH VD₂ and VD₃ were determined to be about 3.46% and 3.60%, respectively. The VD in the serum of 20 volunteers was successfully measured by this method, which proved that the method had remarkable reliability and repeatability.