NMIJ Certified Reference Material Research Articles

Development of 3β,4α-dihydroxy-5α-androstan-17-one standard solution for doping analyses.

Doping analyses are essential for sporting events because some athletes might use prohibited substances to win games. To obtain reliable results from doping analyses, it is important to use both reliable standard solutions and validated analytical methods at accredited laboratories. Among the focused compounds related to prohibited substances listed by the World Anti-Doping Agency, we developed a certified reference material (CRM) for 3β,4α-dihydroxy-5α-androstan-17-one (DHAS), a metabolite of formestane that is used to conceal prohibited anabolic steroids, in methanol solution (NMIJ CRM 6212-a). To develop a CRM traceable to the International System of Units (SI), we newly applied different analytical methods with an SI-traceable internal standard for quantitative NMR (qNMR) instead of mass balance approach because this CRM solution was required to develop rapidly using a limited amount of high-purity DHAS. One method was gravimetric blending using the purity of DHAS powder evaluated by both qNMR and a combination of qNMR and high-performance liquid chromatography (HPLC), and the other was direct quantification of the DHAS mass fraction in the candidate solution CRM by both qNMR and qNMR/HPLC. Because the values obtained by gravimetric blending and direct quantification of the mass fraction were comparable, the arithmetic mean was applied to obtain the certified value. Considering homogeneity and stability according to ISO Guide 35: 2017, the certified values with expanded uncertainties (coverage factor k = 2, approximate 95% confidence interval) were (135.2 ± 9.5) μg/g for the mass fraction and (107.0 ± 7.5) μg/ml for the mass concentration.

Certified reference material (CRM) of tea powder (BARC - D3201) for K, Ca, P, Mg, Mn, Al, Fe, Ba, Zn, Cu, Sr, Pb, As, Cd, and Hg: Method validation and its production

A certified reference material (CRM) for major and trace elements in black tea powder has been developed at National Centre for Compositional Characterization of Materials/Bhabha Atomic Research Centre (BARC), Hyderabad. The study describes an acid assisted microwave digestion of tea powder followed by quantitation of K, Ca, P, Mg, Mn, Al, Fe, Ba, Zn, Cu and Sr by ICP-AES; Pb, Cd by GFAAS and As, Hg by AFS in the digests. The method was validated in terms of selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), trueness, precision, traceability, ruggedness and combined uncertainty using a CRM of tea powder (NMIJ CRM 7505-a) and spike recovery studies. The obtained values of LOQ ranged from 0.018 % m/m for Ca to 0.35mg kg−1 for Hg. Precision of the method was found to be <5% for all the analytes (K, Ca, P, Mg, Mn, Al, Fe, Ba, Zn, Cu, Sr, Cd and Hg) excepting for Pb and As (6.5 % at 95% confidence level). The obtained LOQ values, trueness and precision established that the validated method could be used for the characterization of candidate tea CRM during homogeneity and stability studies. Candidate tea CRM (∼3.6 Kg) was processed (which included spiking, drying grinding and sieving) and its homogeneity was assessed at various levels with respect to all 15 property values. The assignment of the property values for each element was carried out after an interlaboratory comparison exercise (ILCE), where 11 laboratories from various government and private sectors participated. A total of four techniques inductively coupled plasma mass spectrometry (ICP-MS), inductively coupled plasma atomic emission spectrometry (ICP-AES), graphite-furnace atomic-absorption spectrometry (GFAAS) and atomic-fluorescence spectrometry (AFS) were used during ILCE. Property values were assigned for 14 elements (K, Ca, P, Mg, Mn, Al, Fe, Ba, Zn, Cu, Sr, Pb, Cd, and Hg) along with combined uncertainties. The concentration with expanded uncertainties of the property values were between 0.458 ± 0.025 for Ca (% m/m) to 0.60 ± 0.084 mg kg−1 for Hg. Long-term stability studies suggested that the produced tea CRM is stable at storage temperature (4 °C) for the last two years, whereas, short-term stability studies (at temperatures 4, 25 and 40 °C) established its transportation stability at tested temperatures for a period of three weeks. Preparation and certification of tea CRM (BARC-D3201) was carried out in accordance with ISO Guides 17034 and 35.

Development and Co-Validation of a Certified Reference Material (NMIJ CRM 7204-A) for the Analysis of Trace Elements in Seawater Sample

Abstract A certified reference material (CRM), i.e. NMIJ CRM 7204-a, was characterized for the analysis of 10 regulated trace elements in sample seawater, provided in 500 mL polyethylene bottles. Homogeneity and stability of the elements were investigated by inductively coupled plasma tandem quadrupole mass spectrometry after proper dilution, while mass-shift mode was applied to the measurement of trace elements except for Cd and Pb. A property value was obtained as the weighted mean of the results obtained by different methods with weights based on the reciprocal of the standard uncertainty. Combined uncertainty of a property value was obtained as the root mean square of the standard uncertainties of homogeneity, stability, analysis reproducibility, method-to-method variance, and calibrating standard. In NMIJ CRM 7204-a, the concentration of Cd is approximately 3 µg/kg, while those of other trace elements are around 10 µg/kg. Validity of the certified values was confirmed with analytical results of As and Cd by National Institute of Metrology (NIM, China) and those of Cd and Ni by Korea Research Institute of Standards and Science (KRISS, Korea). The concentrations of Na, Mg, K, and Ca along with the density values at 15, 20, and 25 Celsius were provided as information values.

Development of NMIJ CRM 5207-a tungsten dot-array for the image sharpness evaluation in scanning electron microscopy - structure evaluation and determination of dot-pitch.

We have developed a new certified reference material (CRM) for image sharpness evaluation and magnification calibration for scanning electron microscopy (SEM). Designed to be suitable for the image sharpness evaluation by the derivative method, the CRM has nanoscale tungsten dot-array structure fabricated on silicon substrate, which gives steep contrast transition from the dot to the substrate in SEM image. The pitch of the dot-array was SI-traceably measured as a specified value with relative expanded uncertainty ($k=2$) of ~1.3%, which can be utilized for the magnification calibration of SEM. Since specimens, as one of the image formation parameters, easily affect image sharpness value, our CRM, as a 'pinned specimen', will play an important role to achieve robust and stable image sharpness measurement system.

Development of Artificial Urine Certified Reference Material for Quantification of Neonicotinoid Insecticides.

Neonicotinoid insecticides (neonicotinoids) are widely used, however, they can negatively affect human health. Thus, neonicotinoids and their metabolites in human urine are analyzed globally to assess exposure levels and health risks. To properly assess the exposure levels and health risks, accurate analytical results are a necessity. This study aims to develop urine certified reference material (CRM), NMIJ CRM 7408-a, for the quantification of neonicotinoids. To develop NMIJ CRM 7408-a, commercially available artificial urine was used as the raw material to which the target neonicotinoids were added. Analyses of neonicotinoids in NMIJ CRM 7408-a were carried out by isotope dilution mass spectrometry (IDMS). Sample homogeneity was assessed, with the results showing that acetamiprid, clothianidin, thiacloprid, and thiamethoxam exhibited sufficiently homogeneous distributions in the material. The relative uncertainties due to inhomogeneity were 1.2-7.0%. The results obtained from long-term stability assessment indicated that the target neonicotinoids were stable. The relative uncertainties due to instability were 9.4-17.2% (for an expiry date of 21 months). The characterization for providing concentration values was carried out using one (clothianidin and thiacloprid) or two (acetamiprid and thiamethoxam) analytical methods. The certified values of the target neonicotinoids (acetamiprid, clothianidin, thiacloprid, and thiamethoxam) were 0.19-1.38 µg/kg. This is the first frozen artificial urine CRM in which neonicotinoids were quantified by IDMS and will be useful for evaluating the accuracy of analysis and validation of analytical methods for the determination of neonicotinoids in urine. NMIJ CRM 7408-a, which has been certified for four neonicotinoids, was developed by NMIJ.

A higher order method for the determination of total phosphorus in human serum

Phosphorus is an essential element in the human body and an important clinical biomarker in serum. However, the lack of reference method that is traceable to the International System of Units and matrix-matched certified reference material (CRM) pose a major challenge in the assessment of the accuracy of phosphorus measurements. A higher order measurement procedure for total phosphorus in human serum by standard addition method using high-resolution sector field inductively coupled plasma mass spectrometry was established. In this method, germanium and gallium are used as internal standards. The accuracy of the measurement was evaluated by comparing the results with the certified values of Trace Elements in Tea Leaf Powder (NMIJ CRM 7505-a) and Trace Elements in Milk Powder (NMIJ CRM 7512-a), as well as the reference value of Electrolytes in Frozen Human Serum (NIST SRM 956d). This method had also been applied in an international interlaboratory comparison (CCQM-K139 Elements in Human Serum). The results of this comparison showed that this method is comparable with the methods used by other established national metrology institutes or designated institutes. In addition, the first human serum reference material that is certified for total phosphorus was produced. This reference material is valuable for method development as well as the assessment of the accuracy of phosphorus measurements in clinical laboratories (as quality control).

Applications and Uncertainty Estimation of Single Level Standard Addition Method ICP-MS for Elemental Analysis in Various Matrix.

The standard addition method (SAM) based on gravimetric sample preparation was investigated as an approach for the removal or cancelling of matrix effects in measurements by inductively coupled plasma mass spectrometry (ICP-MS). Deduction of the equations and experimental confirmation of the method are both given in the present work. After measuring both spiked and non-spiked samples by ICP-MS, the concentration of an element could be calculated based on the signal intensity ratio to an internal standard. A practical example was provided for the measurement of Fe in a certified reference material (CRM), i.e. NMIJ CRM 7512-a (milk powder). The validity of the method had been confirmed by the results of international comparisons with various kinds of matrix, including bioethanol, human serum, biodiesel fuel, drinking water, infant formula milk power, and seafood. The suggested method had been applied to measurements of multiple elements in three CRMs, including tap water, milk powder, and tea leave powder, respectively.

Development of a Certified Reference Material (NMIJ CRM 7203-a) for Elemental Analysis of Tap Water.

A certified reference material (CRM), NMIJ CRM 7203-a, was developed for the elemental analysis of tap water. At least two independent analytical methods were applied to characterize the certified value of each element. The elements certified in the present CRM were as follows: Al, As, B, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, Pb, Rb, Sb, Se, Sr, and Zn. The certified value for each element was given as the (property value ± expanded uncertainty), with a coverage factor of 2 for the expanded uncertainty. The expanded uncertainties were estimated while considering the contribution of the analytical methods, the method-to-method variance, the sample homogeneity, the long-term stability, and the concentrations of the standard solutions for calibration. The concentration of Hg (0.39 μg kg-1) was given as the information value, since loss of Hg was observed when the sample was stored at room temperature and exposed to light. The certified values of selected elements were confirmed by a co-analysis carried out independently by the NMIJ (Japan) and the KRISS (Korea).

Development of human serum certified reference material for quantification of polychlorinated biphenyls

ABSTRACTHuman serum certified reference material (CRM), NMIJ CRM 7407-a, for the analysis of polychlorinated biphenyls (PCBs) was developed by the National Metrology Institute of Japan. A pool of commercially available human serum was used as a raw material of the CRM. This sample is in the form of a liquid comprising approximately 4 g stored in a cryogenic polypropylene vial. Homogeneity assessment was performed, and the material was homogeneous enough for PCB 118, PCB 138, PCB 153, and PCB 194: the relative uncertainties due to inhomogeneity were 2.5–10.5%. The results obtained from the stability assessment indicated that the target PCBs were stable: the relative uncertainties due to instability were 0–14.7%. The certification was carried out using two different types of GC columns for each target PCB to avoid interferences on GC separation; the certified values of the target PCBs (PCB 118, PCB 138, PCB 153, and PCB 194) were 9.7–129.8 ng/kg. This is the first frozen human serum CRM in which PCBs were determined by isotope dilution mass spectrometry.

Development of a certified reference material for the determination of perfluorooctanoic acid

A certified reference material (CRM) for the determination of perfluorooctanoic acid (PFOA) has been issued as NMIJ CRM 4056-a by the National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Purity (kg kg -1 ) based on a titration method was determined by subtracting the mass fractions of impurities measured using liquid chromatography/mass spectrometry (LC/MS) from those of acids expressed as PFOA measured by a neutralization potentiometric titration. To validate an obtained result, purity based on a mass balance method was determined by subtracting the mass fractions of impurities, measured using LC/MS, Karl-Fischer titration (KFT), and vacuum evapo- ration, from 1 kg kg -1 . Results from both titration and mass balance methods were in agreement within the accepted limits of uncertainty. The certified purity of NMIJ CRM 4056-a was determined to be 0.959 kg kg -1 , calculated as the mean of the results obtained with the two methods. The standard uncertainty of the certified purity was evaluated from purity evaluations as well as from sample homogeneity and stability obtained from LC/MS and KFT analyses. Consequently, the expanded uncertainty was estimated to be 0.005 kg kg -1 with a coverage factor of k = 2.

A Certified Urea Reference Material (NMIJ CRM 6006-a) as a Reliable Calibrant for the Elemental Analyses of Amino Acids and Food Samples

We examined the reliability of a certified reference material (CRM) for urea (NMIJ CRM 6006-a) as a calibrant for N, C, and H in elemental analyzers. Only the N content for this CRM is provided as an indicative value. To estimate the C and H contents of the urea CRM, we took into account the purity of the urea and the presence of other identified impurities. When we examined the use of various masses of the calibrant (0.2 to 2 mg), we unexpectedly observed low signal intensities for small masses of H and N, but these plateaued at about 2 mg. We therefore analyzed four amino acid CRMs and four food CRMs on a 2-mg scale with the urea CRM as the calibrant. For the amino acid CRMs, the differences in the analytical and theoretical contents (≤0.0026 kg/kg) were acceptable with good repeatability (≤0.0013 kg/kg in standard deviation; n = 4). For food CRMs, comparable repeatabilities to those obtained with amino acid CRMs (≤0.0025 kg/kg in standard deviation; n = 4) were obtained. The urea CRM can therefore be used as a reliable calibrant for C, H, and N in an elemental analyzer.

Development of a Certified Reference Material (NMIJ CRM 7512-a) for the Determination of Trace Elements in Milk Powder

A certified reference material (CRM), NMIJ CRM 7512-a, was developed for the determination of trace elements in milk powder. At least three independent analytical methods were applied to characterize the certified value of each element; all of these analytical methods were based on microwave acid digestions and carried out using different analytical instruments. The certified value was given on a dry-mass basis, where the dry-mass correction factor was obtained by drying the sample at 65°C for 15 to 25 h. The certified values in the units of mass fractions for 13 elements were as follows: Ca, 8.65 (0.38) g kg(-1); Fe, 0.104 (0.007) g kg(-1); K, 8.41 (0.33) g kg(-1); Mg, 0.819 (0.024) g kg(-1); Na, 1.87 (0.09) g kg(-1); P, 5.62 (0.23) g kg(-1); Ba, 0.449 (0.013) mg kg(-1); Cu, 4.66 (0.23) mg kg(-1); Mn, 0.931 (0.032) mg kg(-1); Mo, 0.223 (0.012) mg kg(-1); Rb, 8.93 (0.31) mg kg(-1); Sr, 5.88 (0.20) mg kg(-1); and Zn, 41.3 (1.4) mg kg(-1), where the numbers in the parentheses are the expanded uncertainties with a coverage factor of 2. The expanded uncertainties were estimated considering the contribution of the analytical methods, the method-to-method variance, the sample homogeneity, the dry-mass correction factor, and the concentrations of the standard solutions for calibration. The concentrations of As (2.1 μg kg(-1)), Cd (0.2 μg kg(-1)), Cr (1.3 μg kg(-1)), Pb (0.3 μg kg(-1)), and Y (64 μg kg(-1)) were given as information values for the present CRM.

Characterization of a certified reference material (NMIJ CRM 8301-a) for determination of Cu in bio-ethanol

A certified reference material (CRM) was characterized for the determination of copper (Cu) in bio-ethanol samples. The material for the CRM was made from rice by fermentation and refined by distillation, which was further added with Cu acetate and acetic acid. Because the ionization of Cu in inductively coupled plasma mass spectrometry (ICP-MS) was affected by the content of ethanol in the sample, matrix matched methods were developed for the determination of Cu, where the bio-ethanol samples were 10-times (v/v) diluted to 1molL−1 nitric acid solution. All of the standard solutions for calibration were also adjusted to 1molL−1 nitric acid solution with 10% (volume fraction) ethanol. Determination of the concentration of Cu in the sample was carried out by gravimetric standard addition ICP-MS, isotope dilution (ID-) ICP-MS, and graphite furnace atomic absorption spectrometry (GF-AAS). The property value of Cu was calculated based on the weighted mean of the observed values by these methods, with the reciprocal of the uncertainty of each method as the weight. The deviation factor of sampling for characterization was also taken into consideration for calculating the certified value. The combined uncertainty (3.79%, relative value) of the certified value was calculated as a combination of the uncertainties of homogeneity (3.53%), analytical method (0.64%), method-to-method variance (1.16%), and calibration standard (0.35%). The certified value of Cu in the CRM was (53.7±4.1) ngg−1 (property value±expanded uncertainty, k=2), which is traceable to the International System of Units (SI units) via the Japan Calibration Service System (JCSS).

Development of SI-traceable C-peptide certified reference material NMIJ CRM 6901-a using isotope-dilution mass spectrometry-based amino acid analyses

A certified reference material (CRM) is a higher-order calibration material used to enable a traceable analysis. This paper describes the development of a C-peptide CRM (NMIJ CRM 6901-a) by the National Metrology Institute of Japan using two independent methods for amino acid analysis based on isotope-dilution mass spectrometry. C-peptide is a 31-mer peptide that is utilized for the evaluation of β-cell function in the pancreas in clinical testing. This CRM is a lyophilized synthetic peptide having the human C-peptide sequence, and contains deamidated and pyroglutamylated forms of C-peptide. By adding water (1.00 ± 0.01) g into the vial containing the CRM, the C-peptide solution in 10 mM phosphate buffer saline (pH 6.6) is reconstituted. We assigned two certified values that represent the concentrations of total C-peptide (mixture of C-peptide, deamidated C-peptide, and pyroglutamylated C-peptide) and C-peptide. The certified concentration of total C-peptide was determined by two amino acid analyses using pre-column derivatization liquid chromatography-mass spectrometry and hydrophilic chromatography-mass spectrometry following acid hydrolysis. The certified concentration of C-peptide was determined by multiplying the concentration of total C-peptide by the ratio of the relative area of C-peptide to that of the total C-peptide measured by liquid chromatography. The certified value of C-peptide (80.7 ± 5.0) mg/L represents the concentration of the specific entity of C-peptide; on the other hand, the certified value of total C-peptide, (81.7 ± 5.1) mg/L can be used for analyses that does not differentiate deamidated and pyroglutamylated C-peptide from C-peptide itself, such as amino acid analyses and immunochemical assays.

Accurate determination of arsenic in arsenobetaine standard solutions of BCR-626 and NMIJ CRM 7901-a by neutron activation analysis coupled with internal standard method

Neutron activation analysis (NAA) coupled with an internal standard method was applied for the determination of As in the certified reference material (CRM) of arsenobetaine (AB) standard solutions to verify their certified values. Gold was used as an internal standard to compensate for the difference of the neutron exposure in an irradiation capsule and to improve the sample-to-sample repeatability. Application of the internal standard method significantly improved linearity of the calibration curve up to 1 μg of As, too. The analytical reliability of the proposed method was evaluated by k 0-standardization NAA. The analytical results of As in AB standard solutions of BCR-626 and NMIJ CRM 7901-a were (499 ± 55) mg kg −1 ( k = 2) and (10.16 ± 0.15) mg kg −1 ( k = 2), respectively. These values were found to be 15–20% higher than the certified values. The between-bottle variation of BCR-626 was much larger than the expanded uncertainty of the certified value, although that of NMIJ CRM 7901-a was almost negligible.

Characterization of certified reference material for quantification of polychlorinated biphenyls and organochlorine pesticides in fish

Fish certified reference material (CRM), NMIJ CRM 7404-a, for the analysis of polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) was developed by the National Metrology Institute of Japan, part of the National Institute of Advanced Industrial Science and Technology. Fish samples (Japanese seabass) used for the preparation of the CRM were collected from Tokyo Bay, and the edible part was freeze-dried, pulverized, sieved, homogenized, and sterilized by gamma-irradiation. This sample is in the form of a powder comprising approximately 10 g stored in a brown glass bottle. The certification was carried out using multiple analytical methods such as pressurized liquid extraction, Soxhlet extraction, saponification, and homogenization to ensure the reliability of analytical results; the certified values of target PCBs (PCB 28, PCB 70, PCB 105, PCB 153, and PCB 170) and OCPs (trans-nonachlor, dieldrin, p,p'-DDE, p,p'-DDT, and p,p'-DDD) were 1.05-14.0 microg kg(-1) and 1.57-18.0 microg kg(-1) for PCBs and OCPs, respectively. This is the first fish powder CRM in which PCBs and OCPs were determined by isotope dilution mass spectrometry.