OBJECTIVE: Develop a simple LC-MS-MS method for determination of 25-hydroxymetabolites of vitamin D2 and D3 in serum. DESIGN AND METHODS: 0.1 mL serum was mixed with 0.3 mL deproteinizing mixture containing two deuterated internal standards. Two LC-MS-MS systems were used: Waters Premier with an ESI source and a Hypersil Gold RP 18 50 × 2.1 mm column, and a Thermo Quantum, with an APCI source and a Kinetex RP 18 core-shell 50 × 2.1 mm column. Certified reference material 972 from NIST was used for method calibration. The samples were additionally analyzed with commercial HPLC procedure. RESULTS: Baseline separation of compounds was achieved in 6 min run time. Both systems have limits of detection of 0.5 nmol/L and recovery ranging from 86% to 112%. The measurement of 25-OH-D3 gave comparable results for all procedures; the results of 25-OH-D2 measurement obtained with the HPLC often differed from those obtained with LC-MS-MS methods. CONCLUSIONS: Established procedure performed well for ESI and APCI sources and totally porous and core-shell LC columns. The use of two internal standards enhanced the accuracy of the measurements.
OBJECTIVE: Develop a simple LC-MS-MS method for determination of 25-hydroxymetabolites of vitamin D2 and D3 in serum. DESIGN AND METHODS: 0.1 mL serum was mixed with 0.3 mL deproteinizing mixture containing two deuterated internal standards. Two LC-MS-MS systems were used: Waters Premier with an ESI source and a Hypersil Gold RP 18 50 × 2.1 mm column, and a Thermo Quantum, with an APCI source and a Kinetex RP 18 core-shell 50 × 2.1 mm column. Certified reference material 972 from NIST was used for method calibration. The samples were additionally analyzed with commercial HPLC procedure. RESULTS: Baseline separation of compounds was achieved in 6 min run time. Both systems have limits of detection of 0.5 nmol/L and recovery ranging from 86% to 112%. The measurement of 25-OH-D3 gave comparable results for all procedures; the results of 25-OH-D2 measurement obtained with the HPLC often differed from those obtained with LC-MS-MS methods. CONCLUSIONS: Established procedure performed well for ESI and APCI sources and totally porous and core-shell LC columns. The use of two internal standards enhanced the accuracy of the measurements.