The US National Institute of Standards and Technology (NIST) developed a Standard Reference Material® (SRM®) 3949 Folate Vitamers in Frozen Human Serum to replace SRM 1955 Homocysteine and Folate in Human Serum. The presence of increased endogenous levels of folic acid and 5-methyltetrahydrofolate (5mTHF) in SRM 3949, enhanced folate stability via addition of ascorbic acid, and inclusion of values for additional minor folates are improvements over SRM 1955 that should better serve the clinical folate measurement community. The new SRM contains folates at three levels. To produce SRM 3949, pilot sera were collected from 15 individual donors, 5 of whom were given a 400-µg folic acid supplement 1 h prior to blood draw to increase serum levels of 5mTHF and folic acid for the high-level material. To stabilize the folates, 0.5

The production and demand for hand sanitizers have increased dramatically during the coronavirus disease 2019 (COVID-19) health emergency. To be deemed effective and safe, hand sanitizers should contain at least 60 % alcohol (typically ethanol) as well as minimal amounts of harmful impurities regulated by the Food and Drug Administration (FDA). To help ensure product potency and safety through sound measurements, the National Institute of Standards and Technology (NIST) developed and evaluated four instrumental measurement approaches for their applicability in measuring ethanol and impurities in 72 hand sanitizers representing a range of brands and formulations. The methods included gas chromatography with flame ionization detection (GC-FID), liquid chromatography with ultraviolet absorbance detection (LC-UV), quantitative nuclear magnetic resonance spectroscopy (qNMR), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). All four instrumental methods can determine and provide comparable results for ethanol, the principle disinfectant in different hand sanitizer formulations. All methods can also confirm the presence of other alcohols potentially present in significant quantities (? percent levels) such as methanol, a harmful impurity, and isopropanol, which can be either the primary disinfectant or an approved denaturant in some formulations. Two of the methods, qNMR and GC-FID, were also able to determine impurities at the requisite sensitivity levels ( g/g) set by the FDA limits. This report presents descriptions and key results from each method. In addition, a discussion regarding the applicability and strengths and weaknesses of each measurement approach for the analysis of hand sanitizers is presented and discussed.

The off-flavor compounds geosmin and 2-methylisoborneol (2-MIB) are well-known to impact the quality of farmed freshwater fish species, but little is known about off-flavors in marine aquaculture. To begin addressing this knowledge gap, a method for determining geosmin and 2-MIB using LC with atmospheric pressure chemical ionization (APCI) MS detection was developed. While 2-MIB was readily detected using LC-APCI/MS, geosmin exhibited on-column degradation that was independent of column chemistry and could not be eliminated. Optimized conditions were identified that balanced the separation and ionization efficiency of 2-MIB and geosmin while minimizing geosmin degradation, but the overall method sensitivity for geosmin was reduced by the on-column losses. The method was used with direct aqueous injections to determine the volatilization rates of geosmin and 2-MIB at ppb levels during aeration under laboratory conditions in both salt water and pure water to simulate marine and fresh water aquaculture, respectively. The volatilization rates of both compounds were 30% faster in salt water than in fresh water with or without aeration, but aeration was found to enhance the rate by a factor of 2.5 in both water types. The LC-APCI/MS method was combined with stir bar sorptive extraction (SBSE) to achieve greater sensitivity for determining off-flavors in recirculating aquaculture system (RAS) water. Using SBSE-LC-APCI/MS, the LODs for geosmin and 2-MIB were 70 ng/kg (part per trillion) and 6 ng/kg, respectively. The on-column losses resulted in a relatively high LOD for geosmin that renders this method unsuitable for determining geosmin at the low ng/kg levels expected in RAS. SBSE using both grab water samples and an in-situ diving unit were used to evaluate 2-MIB levels in the culture water of two separate marine RAS that were supporting the growth of European sea bass but had differing levels of water treatment. 2-MIB was readily detected using both SBSE approaches in the RAS with less sophisticated treatment when the animal stocking density was at its highest (50 kg/m(3)) but was not detected in the more sophisticated RAS regardless of stocking density. Geosmin was not detected in either system, but the results were inconclusive given its higher LOD. These limited results suggest that the anaerobic water treatment components, present only in the more sophisticated RAS, maintained the level of 2-MIB below the LOD. Published by Elsevier B.V.

The comparison required the assignment of the mass fraction of folic acid present as the main component in the comparison sample. Performance in the comparison is representative of a laboratory's measurement capability for the purity assignment of organic compounds of medium structural complexity [molecular weight range 300–500] and high polarity (pKOW < −2). Methods used by the eighteen participating NMIs or DIs were based on a mass balance (summation of impurities) or qNMR approach, or the combination of data obtained using both methods. The qNMR results tended to give slightly lower values for the content of folic acid, albeit with larger associated uncertainties, compared with the results obtained by mass balance procedures. Possible reasons for this divergence are discussed in the report, without reaching a definitive conclusion as to their origin. The comparison demonstrates that for a structurally complex polar organic compound containing a high water content and presenting a number of additional analytical challenges, the assignment of the mass fraction content property value of the main component can reasonably be achieved with an associated relative standard uncertainty in the assigned value of 0.5% Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Vitamin D is a fat-soluble vitamin that occurs primarily in two forms, vitamin D2 and vitamin D3. Vitamin D3 is produced naturally when skin is exposed to UV radiation, is naturally-occurring in foods (generally of animal origin), and is fortified in some foods and dietary supplements. Vitamin D2 occurs in food (generally plant sources) and until recently was the form most often used in dietary supplements. Vitamin D is metabolized in the body to produce several closely related, hydroxylated species (metabolites), with 25-hydroxyvitamin D3 [25(OH)D3] and 25-hydroxyvitamin D2 [25(OH)D2] as the most common metabolites measured in human serum. Concentrations of total vitamin D in human serum, calculated as the sum of 25(OH)D2 and 25(OH)D3, are typically in the 16 ng/g to 30 ng/g (40 nmol/L to 75 nmol/L) range, with 25(OH)D3 usually accounting for more than 90 % of the total. An epimer of 25(OH)D3, 3-epi-25(OH)D3, can be present at levels up to 10 % of 25(OH)D3 concentration. Seven National Metrology Institutions participated in the Track C Key Comparison CCQM-K132 low-polarity analytes in a biological matrix: vitamin D metabolites in human serum. Participants were requested to evaluate the mass fractions, expressed in ng/g, of 25(OH)D3, 25(OH)D2, and 3-epi-25(OH)D3 in two human serum materials, termed Serum Pool I and Serum Pool II. Due to the known low levels of 3-epi-25(OH)D3 in both materials and the very low level of 25(OH)D2 in Serum Pool I, the study protocol stated that key comparison reference values (KCRVs) would be assigned only to 25(OH)D3 in both materials and 25(OH)D2 in Serum Pool II. Results for 3-epi-25(OH)D3 were requested to evaluate the separation technologies employed; 3-epi-25(OH)D3 needs to be chromatographically separated from 25(OH)D3 for proper quantification of 25(OH)D3. Results for 25(OH)D2 in Serum Pool I were requested to explore measurement performance at its low level. All participants used isotope dilution liquid chromatography with tandem mass spectrometry detection (ID LC-MS/MS) for the measurement of the vitamin D metabolites. Successful participation in CCQM K132 demonstrates capabilities in analysis of low molecular mass (100 g/mol to 500 g/mol) and low-polarity (nonpolar, pKow < −2) analytes at the 1 ng/g to 500 ng/g mass fraction range in complex biological matrixes with core competencies for sample preparation and analysis using ID LC-MS/MS. This study extends the mass fraction capability range to 105 to 106 times lower than that demonstrated in previous CCQM Key Comparisons for cholesterol in serum, another nonpolar clinical analyte. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

The National Institute of Standards and Technology (NIST) has developed Standard Reference Material (SRM) 972a Vitamin D Metabolites in Frozen Human Serum as a replacement for SRM 972, which is no longer available. SRM 972a was developed in collaboration with the National Institutes of Health's Office of Dietary Supplements. In contrast to the previous reference material, three of the four levels of SRM 972a are composed of unmodified human serum. This SRM has certified and reference values for the following 25-hydroxyvitamin D [25(OH)D] species: 25(OH)D2, 25(OH)D3, and 3-epi-25(OH)D3. The value assignment and certification process included three isotope-dilution mass spectrometry approaches, with measurements performed at NIST and at the Centers for Disease Control and Prevention (CDC). The value assignment methods employed have been modified from those utilized for the previous SRM, and all three approaches now incorporate chromatographic resolution of the stereoisomers, 25(OH)D3 and 3-epi-25(OH)D3.

Since 2005, the National Institute of Standards and Technology (NIST) has collaborated with the National Institutes of Health (NIH), Office of Dietary Supplements (ODS) to improve the quality of measurements related to human nutritional markers of vitamin D status. In support of the NIH-ODS Vitamin D Initiative, including the Vitamin D Standardization Program (VDSP), NIST efforts have focused on (1) development of validated analytical methods, including reference measurement procedures (RMPs); (2) development of Standard Reference Materials (SRMs); (3) value assignment of critical study samples using NIST RMPs; and (4) development and coordination of laboratory measurement QA programs. As a result of this collaboration, NIST has developed RMPs for 25-hydroxyvitamin D2 [25(OH)D2], 25(OH)D3, and 24R,25-dihydroxyvitamin D3 [24R,25(OH)2D3]; disseminated serum-based SRMs with values assigned for 25(OH)D2, 25(OH)D3, 3-epi-25(OH)D3, and 24R,25(OH)2D3; assigned values for critical samples for VDSP studies, including an extensive interlaboratory comparison and reference material commutability study; provided an accuracy basis for the Vitamin D External Quality Assurance Scheme; coordinated the first accuracy-based measurement QA program for the determination of 25(OH)D2, 25(OH)D3, and 3-epi-25(OH)D3 in human serum/plasma; and developed methods and SRMs for the determination of vitamin D and 25(OH)D in food and supplement matrix SRMs. The details of these activities and their benefit and impact to the NIH-ODS Vitamin D Initiative are described.

Chemical measurement methods are designed to promote accurate knowledge of a measurand or system. As such, these methods often allow elicitation of latent sources of variability and correlation in experimental data. They typically implement measurement equations that support quantification of effects associated with calibration standards and other known or observed parametric variables. Additionally, multiple samples and calibrants are usually analyzed to assess accuracy of the measurement procedure and repeatability by the analyst. Thus, a realistic assessment of uncertainty for most chemical measurement methods is not purely bottom-up (based on the measurement equation) or top-down (based on the experimental design), but inherently contains elements of both. Confidence in results must be rigorously evaluated for the sources of variability in all of the bottom-up and topdown elements. This type of analysis presents unique challenges due to various statistical correlations among the outputs of measurement equations. One approach is to use a Bayesian hierarchical (BH) model which is intrinsically rigorous, thus making it a straightforward method for use with complex experimental designs, particularly when correlations among data are numerous and difficult to elucidate or explicitly quantify. In simpler cases, careful analysis using GUM Supplement 1 (MC) methods augmented with random effects meta analysis yields similar results to a full BH model analysis. In this article we describe both approaches to rigorous uncertainty evaluation using as examples measurements of 25-hydroxyvitamin D3 in solution reference materials via liquid chromatography with UV absorbance detection (LC-UV) and liquid chromatography mass spectrometric detection using isotope dilution (LC-IDMS).

Two independent analytical approaches, based on liquid chromatography with absorbance detection and liquid chromatography with mass spectrometric detection, have been developed for determination of isoflavones in soy materials. These two methods yield comparable results for a variety of soy-based foods and dietary supplements. Four Standard Reference Materials (SRMs) have been produced by the National Institute of Standards and Technology to assist the food and dietary supplement community in method validation and have been assigned values for isoflavone content using both methods. These SRMs include SRM 3234 Soy Flour, SRM 3236 Soy Protein Isolate, SRM 3237 Soy Protein Concentrate, and SRM 3238 Soy-Containing Solid Oral Dosage Form. A fifth material, SRM 3235 Soy Milk, was evaluated using the methods and found to be inhomogeneous for isoflavones and unsuitable for value assignment. Graphical Abstract Separation of six isoflavone aglycones and glycosides found in Standard Reference Material (SRM) 3236 Soy Protein Isolate

The National Institute of Standards and Technology (NIST), in collaboration with the National Institutes of Health Office of Dietary Supplements and the Vitamin D Standardization Program, has recently issued a new serum-matrix Standard Reference Material (SRM): 2973 Vitamin D Metabolites in Frozen Human Serum (High Level). SRM 2973 was designed to provide a serum material with a total 25-hydroxyvitamin D [25(OH)D] concentration near 100 nmol/L to complement the existing serum-based SRMs with values assigned for total 25(OH)D between 20 and 80 nmol/L. Values were assigned for 25-hydroxyvitamin D₂ [25(OH)D₂], 25-hydroxyvitamin D₃ [25(OH)D₃], 3-epi-25(OH)D₃ , and total 25(OH)D [the sum of 25(OH)D₂ + 25(OH)D₃] using the NIST isotope dilution LC with tandem MS (MS/MS) reference measurement procedure (RMP) and related methods. SRM 2973 has a certified value of 98.4 ± 2.1 nmol/L for 25(OH)D₃ and reference values of 1.59 ± 0.05 nmol/L for 25(OH)D₂ and 5.23 ± 0.20 nmol/L for 3-epi-25(OH)D₃ . In addition, a candidate RMP for 24R,25-dihydroxyvitamin D₃ [24R,25(OH)₂D₃] based on LC-MS/MS was used to assign values to SRM 2973 and the existing SRM 972a Vitamin D Metabolites in Frozen Human Serum. Reference values for 24R,25(OH)₂D₃ were assigned to SRM 2973 (7.51 ± 0.26 nmol/L) and the four levels of SRM 972a: Level 1 (6.38 ± 0.23 nmol/L), Level 2 (3.39 ± 0.12 nmol/L), Level 3 (3.88 ± 0.013 nmol/L), and Level 4 (6.32 ± 0.22 nmol/L). The development of SRM 2973 [with a higher concentration of 25(OH)D₃] and the addition of values for 24R,25(OH)₂D₃ assigned to both SRM 972a and SRM 2973 provide laboratories involved in vitamin D measurements with improved QA tools.

Certain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately.Such identification is not intended to imply recommendation

Comparability Study, were asked to use the methodology of their choice to measure concentrations of 25-hydroxyvitamin D in pooled human serum control

Comparability Study, were asked to use the methodology of their choice to measure concentrations of 25-hydroxyvitamin D in pooled human serum control and study

Reference standards for the vitamin D metabolites 25-hydroxyvitamin D 3 , 25-hydroxyvitamin D 2 , and 3-epi-25-hydroxyvitamin D 3 were evaluated using liquid chromatography (LC) with ultraviolet (UV) absorbance and mass spectrometric (MS) detection to assess purity. The chromatograms for solutions of all three 25(OH)D compounds, obtained using a pentafluorophenyl (PFP) stationary phase, revealed peaks that increased in area over time and had MS spectra that were nearly identical to the parent compound, indicating isomers had formed in solution that were unrelated to the reference standard purity. However, when the purity evaluations were completed with a cyanopropyl stationary phase, the isomeric products coeluted with the parent compounds and were not observable. The rates of formation of the isomeric products were found to increase when heated and were confirmed to be pre-25-hydroxyvitamin D compounds using spectral information from both MS detection and nuclear magnetic resonance (NMR) spectroscopy. The rates of conversion of 25(OH)D 3 to pre-25(OH)D 3 was studied in solutions of ethanol and bovine serum albumin (BSA) in phosphate-buffered saline (PBS). The solutions prepared with BSA/PBS were found to form twice as much pre-25(OH)D 3 as the solutions in ethanol. The isomerization of 25(OH)D in solution has implications for calibration of 25(OH)D in clinical measurements, which are discussed.

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 1H-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.

Comparability Study, were asked to use the methodology of their choice to measure concentrations of 25-hydroxyvitamin D in pooled human serum control and study materials distributed by NIST.The study materials consisted of SRM 972a Vitamin D Metabolites in Human Serum Level 4 and VitDQAP-II (a material designed