Metrological approaches to organic chemical purity: primary reference materials for vitamin D metabolites.
Given the critical role of pure, organic compound primary reference standards used to characterize and certify chemical Certified Reference Materials (CRMs), it is essential that associated mass purity assessments be fit-for-purpose, represented by an appropriate uncertainty interval, and metrologically sound. The mass fraction purities (% g/g) of 25-hydroxyvitamin D (25(OH)D) reference standards used to produce and certify values for clinical vitamin D metabolite CRMs were investigated by multiple orthogonal quantitative measurement techniques. Quantitative (1)H-nuclear magnetic resonance spectroscopy (qNMR) was performed to establish traceability of these materials to the International System of Units (SI) and to directly assess the principal analyte species. The 25(OH)D standards contained volatile and water impurities, as well as structurally-related impurities that are difficult to observe by chromatographic methods or to distinguish from the principal 25(OH)D species by one-dimensional NMR. These impurities have the potential to introduce significant biases to purity investigations in which a limited number of measurands are quantified. Combining complementary information from multiple analytical methods, using both direct and indirect measurement techniques, enabled mitigation of these biases. Purities of 25(OH)D reference standards and associated uncertainties were determined using frequentist and Bayesian statistical models to combine data acquired via qNMR, liquid chromatography with UV absorbance and atmospheric pressure-chemical ionization mass spectrometric detection (LC-UV, LC-ACPI-MS), thermogravimetric analysis (TGA), and Karl Fischer (KF) titration.
Material Measurement Laboratory, Chemical Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8392, USA. michael.nelson@nist.gov.
Michael A
MA
Nelson
Material Measurement Laboratory, Chemical Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8392, USA.
Mary
M
Bedner
Material Measurement Laboratory, Biosystems and Biomaterials Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8392, USA.
Brian E
BE
Lang
Information Technology Laboratory, Statistical Engineering Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8392, USA.
Blaza
B
Toman
Material Measurement Laboratory, Chemical Sciences Division, National Institute of Standards and Technology, Gaithersburg, MD, 20899-8392, USA.
Katrice A
KA
Lippa
D001499:Bayes Theorem; D002853:Chromatography, Liquid / Q000379:methods / Q000592:standards*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards*; D013058:Mass Spectrometry / Q000379:methods / Q000592:standards*; D012015:Reference Standards; D012996:Solutions; D013818:Thermogravimetry; D014807:Vitamin D / Q000031:analogs & derivatives / Q000302:isolation & purification*
D012996:Solutions; D014807:Vitamin D
Data combination; Metrology; Primary standard; Purity; Vitamin D; qNMR