National Institute Of Standards And Technology Standard Reference Material Research Articles

Optimizing Zr-doped MC-ICP-MS sample-standard bracketing to simultaneously determine 87Sr/86Sr and δ88Sr for high sample-throughput

In recent years, the increasing demand for extensive strontium (Sr) datasets across various scientific fields has prompted the development of fast, precise, and reliable protocols. These protocols aim to achieve high sample-throughput without compromising data quality. A novel method termed the zirconium (Zr) doped sample-standard bracketing (SSB) has been recently introduced for isotope measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This method allows for simultaneous acquisition of 87Sr/86Sr and δ88Sr data without the need for sample spiking. However, the reliability of this method in handling large datasets and ensuring long-term reproducibility requires additional documentation. A comprehensive examination of the reliability of Sr isotope data over two years involves the implementation of systematic tests on reference materials from the National Institute of standards and technology (NIST) with the standard reference material (SRM) numbers: 1400, 1515, 987, 2910b, 1486, as well as a Hawaiian volcano observatory basalt (BHVO-1). The results of this study lead to the definition of a set of quality control parameters. The developed protocol applies various controls to ensure precise matching of Sr and Zr concentrations for both the samples and the bracketing standard (NIST SRM 987), along with the identification of instrumental biases. The outlined quality control ensures the reproducibility of the results (87Sr/86Sr = 0.710247 ± 0.000026, 2SD, n = 557; and δ88Sr = 0.001 ± 0.053 ‰, 2SD, n = 537 for NIST SRM 987), proving invaluable for archaeological, geological, and ecological studies requiring the fast acquisition of extensive datasets (n > 100) to create isotopic baselines.

Estimation of measurement uncertainty for the quantification of protein by ID-LC–MS/MS

The emergence of mass spectrometry (MS)-based methods to quantify proteins for clinical applications has led to the need for accurate and consistent measurements. To meet the clinical needs of MS-based protein results, it is important that the results are traceable to higher-order standards and methods and have defined uncertainty values. Therefore, we outline a comprehensive approach for the estimation of measurement uncertainty of a MS-based procedure for the quantification of a protein biomarker. Using a bottom-up approach, which is the model outlined in the “Guide to the Expression of Uncertainty of Measurement” (GUM), we evaluated the uncertainty components of a MS-based measurement procedure for a protein biomarker in a complex matrix. The cause-and-effect diagram of the procedure is used to identify each uncertainty component, and statistical equations are derived to determine the overall combined uncertainty. Evaluation of the uncertainty components not only enables the calculation of the measurement uncertainty but can also be used to determine if the procedure needs improvement. To demonstrate the use of the bottom-up approach, the overall combined uncertainty is estimated for the National Institute of Standards and Technology (NIST) candidate reference measurement procedure for albumin in human urine. The results of the uncertainty approach are applied to the determination of uncertainty for the certified value for albumin in candidate NIST Standard Reference Material® (SRM) 3666. This study provides a framework for measurement uncertainty estimation of a MS-based protein procedure by identifying the uncertainty components of the procedure to derive the overall combined uncertainty.Graphical

Utilization of a NIST SRM: a case study for per- and polyfluoroalkyl substances in NIST SRM 1957 organic contaminants in non-fortified human serum

The National Institute of Standards and Technology (NIST) generates and maintains thousands of Standard Reference Materials (SRMs) to serve commerce worldwide. Many SRMs contain metrologically traceable mass fractions of known organic chemicals and are commercially available to aid the analytical chemistry community. One such material, NIST SRM 1957 Organic Contaminants in Non-Fortified Human Serum, was one of the first materials issued by NIST with measurements for per- and polyfluoroalkyl substances (PFAS) listed on the Certificate of Analysis and was commercially available in 2009. Since the release of SRM 1957, nearly 400 units have been sold to date, and over 50 publications related to PFAS measurements have included this material for multiple analytical purposes, such as a quality control material, for interlaboratory comparison, as an in-house comparison tool, for inter- and intra-day measurement accuracy, as an indicator of isomeric patterns of PFAS, and for other uses. This perspective details the ways SRM 1957 is utilized by the analytical community and how data have been reported in the literature. A discussion on accurately comparing SRM data to generated data is included. Furthermore, we conducted an in-depth investigation around additional applications for NIST SRMs, such as a matrix-matched reference material, and for the identification of targeted compounds during high-resolution mass spectrometry data collection. Ultimately, this manuscript illustratively describes the ways to utilize a NIST SRMs for chemicals of emerging concern.

Comparison of the terpene lactones and flavonols contents in G. Biloba commercial samples and the NIST standard reference materials using LC/UV/MS

The leaf extract of Ginkgo biloba has purported value for improving mental capacities in Alzheimer's patients. The flavonols and the terpene lactones are considered to be the two major groups of active components that influence human health. Almost all the clinical studies regarding G. Biloba were using either EGb 761®, a proprietary extract of G. Biloba leaves, or an extract prepared according to the standard set by it. Consequently, most of the commercial G. Biloba products were labeled with their content accordingly. This paper studied the compositions of both flavonols and terpene lactones of seven commercially available G. Biloba products and three standard reference materials (SRM 3246 G. Biloba leaves, SRM 3247 G. Biloba extract, and SRM 3248 G. Biloba tablet) from the National Institute of Standards and Technology (NIST). In this study, a chromatographic method with UV and mass spectroscopic detection was employed for the determination of the compositions of flavonols and the terpene lactones in Ginkgo products using gradient reversed-phase HPLC. Methanol-water (1:1) extracts of terpene lactones and flavonols out of G. Biloba products and NIST SRMs were analyzed qualitatively and quantitatively. While the relative compositions of the flavonol glycosides were similar for the NIST SRMs, those for the commercial G. Biloba products varied significantly. The relative concentrations of terpene lactones were also shown significant differences among products, but not as dramatic as that of flavonols.

Influence of Shear Lip Symmetry on the Fracture Behavior of Charpy Specimens

Abstract An investigation was conducted at the National Institute of Standards and Technology (NIST) on the influence of shear lip symmetry on the fracture behavior (absorbed energy and data scatter) of Charpy specimens at different energy levels, corresponding to NIST low-energy, high-energy, and super-high-energy certified verification specimens. Whenever both shear lips are on the same tested specimen half (symmetrical fracture), absorbed energy tends to be lower than when each specimen half includes one shear lip (asymmetrical fracture). Fracture type does not have a significant effect on impact toughness or variability at low- or high-energy levels, but its influence becomes significant above 200 J. Specifically, super-high-energy specimen lots do not fulfill the NIST requirement (sample size < 5.0) when both fracture types are combined, whereas they may become acceptable if only symmetrical or asymmetrical fractures are considered. This tendency is particularly clear for the 9310 (3-nickel) steel, which is currently under consideration for the reinstatement of super-high-energy specimens in the NIST Standard Reference Materials catalog. The most effective method for preventing the formation of shear lips, and therefore avoiding this type of bimodal behavior, is to side-groove the Charpy specimens for a total thickness reduction of 10 %.

Standard Reference Material (SRM) 2378 fatty acids in frozen human serum. Certification of a clinical SRM based on endogenous supplementation of polyunsaturated fatty acids.

Dietary fatty acids can be both beneficial and detrimental to human health depending on the degree and type of saturation. Healthcare providers and research scientists monitor the fatty acid content of human plasma and serum as an indicator of health status and diet. In addition, both the Centers for Disease Control & Prevention (CDC) and the National Institutes of Health - Office of Dietary Supplements are interested in circulating fatty acids (FAs) because they may be predictive of coronary heart disease. The National Institute of Standards and Technology (NIST) provides a wide variety of reference materials (RMs) and Standard Reference Materials® (SRM®s) including blood, serum, plasma, and urine with values assigned for analytes of clinical interest. NIST SRM 2378 Fatty Acids in Frozen Human Serum was introduced in 2015 to help validate methods used for the analysis of FAs in serum, and consists of three different pools of serum acquired from (1) healthy donors who had taken fish oil dietary supplements (at least 1000mg per day) for at least one month (level 1 material), (2) healthy donors who had taken flaxseed oil dietary supplements (at least 1000mg per day) for at least one month (level 2 material), and (3) healthy donors eating "normal" diets who had not taken dietary supplements containing fish or plant oils (level 3 material). The use of dietary supplements by donors provided SRMs with natural endogenous ranges of FAs at concentrations observed in human populations. Results from analyses using two methods at NIST, including one involving a novel microwave-assisted acid hydrolysis procedure, and one at the CDC are presented here. These results and their respective uncertainties were combined to yield certified values with expanded uncertainties for 12 FAs and reference values with expanded uncertainties for an additional 18 FAs.

Development of a Northern Continental Air Standard Reference Material.

The National Institute of Standards and Technology (NIST) recently began to develop standard mixtures of greenhouse gases as part of a broad program mandated by the 2009 United States Congress to support research in climate change. To this end, NIST developed suites of gravimetrically assigned primary standard mixtures (PSMs) comprising carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-natural air balance at ambient mole fraction levels. In parallel, the National Oceanic and Atmospheric Administration (NOAA) in Boulder, Colorado, charged 30 aluminum gas cylinders with northern hemisphere air at Niwot Ridge, Colorado. These mixtures, which constitute NIST Standard Reference Material (SRM) 1720 Northern Continental Air, were certified by NIST for ambient mole fractions of CO2, CH4, and N2O relative to NIST PSMs. NOAA-assigned values are also provided as information in support of the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) Program for CO2, CH4, and N2O, since NOAA serves as the WMO Central Calibration Laboratory (CCL) for CO2, CH4, and N2O. Relative expanded uncertainties at the 95% confidence interval are <±0.06% of the certified values for CO2 and N2O and <0.2% for CH4, which represents the smallest relative uncertainties specified to date for a gaseous SRM produced by NIST. Agreement between the NOAA (WMO/GAW) and NIST values based on their respective calibration standards suites is within 0.05%, 0.13%, and 0.06% for CO2, CH4, and N2O, respectively. This collaborative development effort also represents the first of its kind for a gaseous SRM developed by NIST.

Determination of Chloride in Infant Formula and Adult/Pediatric Nutritional Formula by Potentiometric Titration: Single-Laboratory Validation, First Action 2015.07.

A potentiometric method for determination of chloride was validated against AOAC Standard Method Performance Requirement (SMPR(®)) 2014.015. Ten AOAC Stakeholder Panel on Infant Formula and Adult Nutritionals (SPIFAN) matrixes, including National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 1849a, were tested in duplicate on 6 independent days. The repeatability (RSDr) ranged from 0.43 to 1.34%, and the intermediate reproducibility (RSDiR) ranged from 0.80 to 3.04%. All results for NIST SRM 1849a were within the range of the certified concentration (701 ± 17 mg/100 g). Recovery was demonstrated with two overspike levels, 50 and 100%, in the 10 SPIFAN matrixes. Samples were tested in duplicate on 3 different days, and all results were within the SMPR requirement of 95 to 105%. The LOQs of the method for powdered products and ready-to-feed or reconstituted products were 20 mg/100 g and 2.2 mg/100 mL, respectively. A wide analytical range from the LOQ to 99.5% chlorine content can be reached with an appropriate dilution factor, but in practice, the upper analytical value observed in routine matrix testing was approximately 1080 mg/100 g in skim milk powder. This is a rapid, simple, and reliable chlorine-testing method applicable to infant formula, adult nutritionals, and ingredients used in these dairy-based products, such as skim milk powder, desalted whey powder, whey protein powder, and whole milk powder.

Development of a southern oceanic air standard reference material.

In 2009, the United States Congress charged the National Institute of Standards and Technology (NIST) with supporting climate change research. As part of this effort, the Gas Sensing Metrology Group at NIST began developing new gas standard mixtures for greenhouse gas mixtures relevant to atmospheric measurements. Suites of gravimetrically prepared primary standard mixtures (PSMs) were prepared at ambient concentration levels for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-air balance. In parallel, 30 gas cylinders were filled, by the National Institute of Water and Atmospheric Research (NIWA) in Wellington, New Zealand, to high pressure from pristine southern oceanic air at Baring Head, New Zealand, and shipped to NIST. Using spectroscopic instrumentation, NIST analyzed the 30 cylinder samples for mole fractions of CO2, CH4, and N2O. Certified values were assigned to these mixtures by calibrating the instrumentation with the PSM suites that were recently developed at NIST. These mixtures became NIST Standard Reference Material (SRM) 1721 Southern Oceanic Air and are certified for ambient mole fraction, the first of their kind for NIST. The relative expanded uncertainties corresponding to coverage intervals with 95% probability are no larger than 0.06% of the certified values, representing the smallest uncertainties to date ever assigned to an NIST gas SRM.

Evaluation of bilirubin interference and accuracy of six creatinine assays compared with isotope dilution–liquid chromatography mass spectrometry

ObjectivesThe aim of this study was to estimate bilirubin interference and accuracy of six routine methods for measuring creatinine compared with isotope dilution–liquid chromatography mass spectrometry (ID–LC/MS). Design and methodsA total of 40 clinical serum samples from 31 patients with serum total bilirubin concentration >68.4μmol/L were collected. Serum creatinine was measured using two enzymatic reagents and four Jaffe reagents as well as ID–LC/MS. Correlations between bilirubin concentration and percent difference in creatinine compared with ID–LC/MS were analyzed to investigate bilirubin interference. Bias estimations between the six reagents and ID–LC/MS were performed. Recovery tests using National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 967a were also performed. ResultsBoth the enzymatic methods showed no bilirubin interference. However, three of the four Jaffe methods demonstrated significant bilirubin concentration-dependent interference in samples with creatinine levels <53μmol/L, and two of them showed significant bilirubin interference in samples with creatinine levels ranging from 53.0 to 97.2μmol/L. Comparison of these methods with ID–LC/MS using patients' samples with elevated bilirubin revealed that the tested methods failed to achieve the bias goal at especially low levels of creatinine. In addition, recovery test using NIST SRM 967a showed that bias in one Jaffe method and two enzymatic methods did not achieve the bias goal at either low or high level of creatinine, indicating they had calibration bias. One enzymatic method failed to achieve all the bias goals in both comparison experiment and recovery test. ConclusionsIt is important to understand that both bilirubin interference and calibration traceability to ID–LC/MS should be considered to improve the accuracy of creatinine measurement.

Investigating adsorption/desorption of carbon dioxide in aluminum compressed gas cylinders.

Between June 2010 and June 2011, the National Institute of Standards and Technology (NIST) gravimetrically prepared a suite of 20 carbon dioxide (CO2) in air primary standard mixtures (PSMs). Ambient mole fraction levels were obtained through six levels of dilution beginning with pure (99.999%) CO2. The sixth level covered the ambient range from 355 to 404 μmol/mol. This level will be used to certify cylinder mixtures of compressed dry whole air from both the northern and southern hemispheres as NIST standard reference materials (SRMs). The first five levels of PSMs were verified against existing PSMs in a balance of air or nitrogen with excellent agreement observed (the average percent difference between the calculated and analyzed values was 0.002%). After the preparation of a new suite of PSMs at ambient level, they were compared to an existing suite of PSMs. It was observed that the analyzed concentration of the new PSMs was less than the calculated gravimetric concentration by as much as 0.3% relative. The existing PSMs had been used in a Consultative Committee for Amount of Substance-Metrology in Chemistry Key Comparison (K-52) in which there was excellent agreement (the NIST-analyzed value was -0.09% different from the calculated value, while the average of the difference for all 18 participants was -0.10%) with those of other National Metrology Institutes and World Meteorological Organization designated laboratories. In order to determine the magnitude of these losses at the ambient level, a series of "daughter/mother" tests were initiated and conducted in which the gas mixture containing CO2 from a "mother" cylinder was transferred into an evacuated "daughter" cylinder. These cylinder pairs were then compared using cavity ring-down spectroscopy under high reproducibility conditions (the average percent relative standard deviation of sample response was 0.02). A ratio of the daughter instrument response to the mother response was calculated, with the resultant deviation from unity being a measure of the CO2 loss or gain. Cylinders from three specialty gas vendors were tested to find the appropriate cylinder in which to prepare the new PSMs. All cylinders tested showed a loss of CO2, presumably to the walls of the cylinder. The vendor cylinders exhibiting the least loss of CO2 were then purchased to be used to gravimetrically prepare the PSMs, adjusting the calculated mole fraction for the loss bias and an uncertainty calculated from this work.

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry for the determination of Cr, Fe, Cu, Zn and Se in cereals

Ultrasonic slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (USS-ETV-ICP-MS) has been applied to determine Cr, Fe, Cu, Zn and Se in several cereal samples. Thioacetamide was used as the modifier to enhance the ion signals. The background ions at the masses of interest were reduced in intensity significantly by using 1.0mLmin−1 methane (CH4) as reaction cell gas in the dynamic reaction cell (DRC). Since the sensitivities of Cr, Fe, Cu, Zn and Se in different matrices were quite different, standard addition and isotope dilution methods were used for the determination of Cr, Fe, Cu, Zn and Se in these cereal samples. The method detection limits estimated from standard addition curves were about 1, 10, 4, 12 and 2ngg−1 for Cr, Fe, Cu, Zn and Se, respectively, in original cereal samples. This procedure has been applied to the determination of Cr, Fe, Cu, Zn and Se whose concentrations are in μgg−1 (except Cr and Se) in standard reference materials (SRM) of National institute of standards and technology (NIST), NIST SRM 1568a Rice Flour and NIST SRM 1567a Wheat Flour and two cereal samples purchased from a local market. The analysis results of reference materials agreed with certified values at 95% confidence level according to Student's T-test. The results for the real world cereal samples were also found to be in good agreement with the pneumatic nebulization DRC ICP-MS results of the sample solutions.

Analysis of the Transient Hot-Wire Method to Measure Thermal Conductivity of Silica Aerogel: Influence of Wire Length, and Radiation Properties

When the transient hot-wire method is used to measure the thermal conductivity of very low thermal conductivity silica aerogel (in the range of 10 mW/m·K at 1 atm) end effects due to the finite wire size and radiation corrections must be considered. An approximate method is presented to account for end effects with realistic boundary conditions. The method was applied to small experimental samples of the aerogel using different wire lengths. Initial conductivity results varied with wire length. This variation was eliminated by the use of the end effect correction. The test method was validated with the NIST (National Institute of Standards and Technology) Standard Reference Material 1459, fumed silica board to within 1 mW/m·K. The aerogel is semitransparent. Due to the small wire radius and short transient, radiation heat transfer may not be fully accounted for. In a full size aerogel panel radiation will augment the phonon conduction by a larger amount.

Quality Determination of Biomass for Combustion: A New High-Throughput Microwave Digestion Method Prior to Elemental Analysis by Inductively Coupled Plasma–Optical Emission Spectroscopy

A high content of minerals in biomass feedstock may cause fouling, slagging, and corrosion in the furnace during combustion. Here, a new pressurized microwave digestion method for biomass digestion prior to elemental analysis is presented. This high-throughput method is capable of processing approximately 48 samples per hour with reduced laboratory hazards and waste because only a very small volume of hydrofluoric acid is used. Concentrations of 12 elements (Al, Ca, Cd, Cu, Fe, K, Mg, Mn, Na, P, Si, and Zn) were determined using inductively coupled plasma–optical emission spectroscopy (ICP–OES). National Institute of Standards and Technology (NIST) standard reference materials (SRMs) 1515 apple leaves and 1575a pine needles were used for method validation. Recoveries of the 12 elements in the NIST SRMs ranged from 93 to 115%. A comparison of the high-throughput method with the European Union (EU) standard method showed agreements in the range from 98 to 115% (except for Al) when the elements were quantified in plant material of the energy crop Miscanthus × giganteus.

Comparative physicochemical and biological characterization of NIST Interim Reference Material PM2.5 and SRM 1648 in human A549 and mouse RAW264.7 cells

The epidemiological association between exposure to fine particulate matter (PM2.5) and adverse health effects is well-known. Here we report the size distribution, metals content, endotoxin content, and biological activity of National Institute of Standards and Technology (NIST) Interim Reference Material (RM) PM2.5. Biological activity was measured in vitro by effects on cell viability and the release of four inflammatory immune mediators, from human A549 alveolar epithelial cells or murine RAW264.7 monocytes. A dose range covering three orders of magnitude (1–1000μg/mL) was tested, and biological activity was compared to an existing Standard Reference Material (SRM) for urban PM (NIST SRM 1648). Robust release of IL-8 and MCP-1 from A549 cells was observed in response to IRM PM2.5 exposures. Significant TNF-α, but not IL-6, secretion from RAW264.7 cells was observed in response to both IRM PM2.5 and SRM 1648 particle types. Cytokine or chemokine release at high doses often occurred in the presence of cytotoxicity, likely as a result of externalization of preformed mediator. Our results are consistent with a local cytotoxic and pro-inflammatory mechanism of response to exposure to inhaled ambient PM2.5 and reinforce the continued relevance of in vitro assays for mechanistic research in PM toxicology. Our study furthers the goal of developing reference samples of environmentally relevant particulate matter of various sizes that can be used for hypothesis testing by multiple investigators.

Uncertainty of 222Rn Concentrations in the Usepa Radiation and Indoor Environments National Laboratory Exposure Chamber

The U.S. Environmental Protection Agency (EPA) operates an environmentally controlled chamber for purposes of exposing various radon and decay product measurement equipment to known (222)Rn concentrations. Exposure durations range from 1 h to several months, and (222)Rn concentrations vary between 37 and 4,440 Bq m(-3). Radon concentrations are generated from Ra sources mounted on the chamber, but concentrations are continuously measured using equipment calibrated using (222)Rn generated from Ra laboratory standards made from a National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) and verified through an aliquot measured by the NIST. The (222)Rn concentrations that are used to calibrate the equipment in the chamber are produced from bubbling a measured volume of air through the (226)Ra laboratory standard solution. This paper describes the process to derive an average chamber concentration during the exposure period. This includes the generation of laboratory (226)Ra standards from the original NIST SRM, (222)Rn emanation into a measured volume of air and transfer to Rocky Mountain Glassworks stainless steel scintillation cells to generate individual cell calibration factors, the calibration of larger mounted flow-through scintillation cells, and the reduction of cumulative chamber scintillation cell counts over various time periods. Each step is associated with an uncertainty based on measured and estimated factors, and each step adds an additional uncertainty to the cumulative total. The methods used follow guidance in the 1993 ISO Guide to the Expression of Uncertainty in Measurement and NIST Technical Note 1297. Chamber exposures of 96 h and (222)Rn concentrations between 150 and 2,700 Bq m(-3) are associated with a combined standard uncertainty of 4.1% (1 s). Ninety-six hour (96 h) exposures of lower (222)Rn concentrations of between 150 - 370 Bq m(-3) are associated with a combined standard uncertainty of 5%. Results indicate that there are measures that can be taken to reduce the estimated uncertainty slightly. The calculations used in this analysis have been incorporated into the computer code used to track chamber concentrations and exposures so that estimated uncertainties can be associated with each exposure.

Determination of fortified and endogenous folates in food-based Standard Reference Materials by liquid chromatography-tandem mass spectrometry

The National Institute of Standards and Technology (NIST) is developing a wide variety of Standard Reference Materials (SRMs) to support measurements of vitamins and other nutrients in foods. Previously, NIST has provided SRMs with values assigned for the folate vitamer, folic acid (pteroylglutamic acid), which is fortified in several foods due to its role in prevention of neural tube defects. In order to expand the number of food-based SRMs with values assigned for folic acid, as well as additional endogenous folates, NIST has developed methods that include trienzyme digestion and isotope-dilution liquid chromatography-tandem mass spectrometric (LC-MS/MS) analysis. Sample preparation was optimized for each individual food type, but all samples were analyzed under the same LC-MS/MS conditions. The application of these methods resulted in folic acid values for SRM 1849a Infant/Adult Nutritional Formula and SRM 3233 Fortified Breakfast Cereal of (2.33 ± 0.06) μg/g and (16.0 ± 0.7) μg/g, respectively. In addition, the endogenous folate vitamer 5-methlytetrahydrofolate (5-MTHF) was detected and quantified in SRM 1849a Infant/Adult Nutritional Formula, candidate SRM 1549a Whole Milk Powder, and candidate SRM 1845a Whole Egg Powder, resulting in values of (0.0839 ± 0.0071) μg/g, (0.211 ± 0.014) μg/g, and (0.838 ± 0.044) μg/g, respectively. SRM 1849a Infant/Adult Nutritional Formula is the first food-based NIST SRM to possess a reference value for 5-MTHF and the first certified reference material to have an assigned 5-MTHF value based on LC-MS/MS. The values obtained for folic acid and 5-MTHF by LC-MS/MS will be incorporated into the final value assignments for all these food-based SRMs.

Characterization of NIST standard reference materials by next generation sequencing

The National Institute of Standards and Technology (NIST) offers certified Standard Reference Materials (SRMs) for laboratories which perform DNA-based human identity testing. Developed by the Applied Genetics Group at NIST, forensic DNA SRMs are well characterized for relevant markers such as autosomal and Y-chromosomal short tandem repeats (STRs) and mitochondrial DNA (mtDNA) sequence. Characterization of the SRMs has been performed by capillary gel electrophoresis fragment-based genotyping analysis and/or Sanger type sequencing. New technologies, commonly referred to as next generation sequencing (NGS), now offer an opportunity to validate the certified DNA-based reference materials using an orthogonal method and thereby increase the confidence in the certified values of the materials. The increased sensitivity of NGS will facilitate expansion of the information content of NIST SRMs through the characterization of new features which are beyond the ability of fragment-based analysis or Sanger sequencing to detect. This work will also lead to the availability of Certified Reference Materials for laboratories wishing to implement and validate NGS technology in the field of forensics.

Determination of essential and toxic metals in blood by ICP-MS with calibration in synthetic matrix

A high throughput method has been developed and validated for the analysis of heavy metals in blood using inductively coupled plasma mass spectrometry (ICP-MS) with an integrated sample introduction system with discrete sampling (ISIS-DS). Blood analyses are performed using an Agilent 7700x ICP-MS in helium collision mode. For this study, we selected a metal panel that included As, Cd, Hg, Mn, Pb, and U. Blood specimens, reference material and intermediate calibration standards were diluted 50 times with a diluent composed of n-butanol, NH4OH, H4EDTA, Triton X-100 and five internal standards (ISTDs). A 50 times dilution alone however does not dissipate the blood matrix effect. We found that the addition of NaCl and CaCl2 to calibration standards created a synthetic matrix (SM) environment leading to excellent analytical accuracy for all metals in the study, with results for lead nearly identical to isotopic dilution technique results. In addition, our study demonstrated that under matrix-match conditions for blood samples and calibration standards, any ISTD can be selected for any analyte regardless of first ionization potential or atomic mass (i.e., 55Ge is an acceptable ISTD for 238U or 205Tl for 55Mn, etc.). This method was initially validated using the following external reference materials: four levels of NIST standard reference material (SRM) 955c samples supplied by the National Institute of Standards and Technology (NIST), Wisconsin State Laboratory of Hygiene (WSLH) blood sample pools that were used to prepare Filter Paper Blood Lead proficiency testing (PT) samples (June 2011 event), and multi-element blood samples supplied by the Institute National de Sante Publique Quebec (INSPQ). When calibration standards were prepared without the matrix-match components, notable differences between present study results and respective reference or mean values were observed. This approach may offer a universal technique to improve the accuracy of ICP-MS results for metal analyses in any complex matrix. This method is currently being used to analyze human blood specimens as part of the California Environmental Contaminant Biomonitoring Program (CECBP).

An improved candidate reference method for serum potassium measurement by inductively coupled plasma-mass spectrometry

BackgroundIn 2002, the National Institute of Standards and Technology (NIST) established a reference method for serum potassium based on inductively coupled plasma-mass spectrometry (ICP-MS). The aim of this study was to develop an inexpensive and improved candidate reference method for accurate and precise determination of serum potassium. MethodsSerum samples were diluted with 1% HNO3 supplemented with 59Cobalt as isotope internal standard, and potassium was measured by ICP-MS. The new method was evaluated with NIST standard reference materials (SRMs), according to the Clinical and Laboratory Standard Institute's evaluation protocols. ResultsAt 4.300 and 4.678mmol/l levels, the present method demonstrated analytical imprecision of 0.09% and 0.14%, and recoveries of 99.67% to 99.88%, respectively. The bias between the target values of SRMs were −0.02% to +0.28%, respectively. This method was linear between 0.0000 and 6.87mmol/l (R2=1.000). The method had an uncertainty (U95%) of 0.76%. ConclusionsThe proposed ICP-MS method to measure serum potassium is precise and accurate, with high sensitivity and specificity. It may be considered as a candidate reference method for the determination of serum potassium.