Reference Materials For Calibration Research Articles

Specifications for trueness and precision of a reference measurement system for serum/plasma 25-hydroxyvitamin D analysis

Background The divergence in analytical quality of serum/plasma 25-hydroxy-vitamin D analysis calls for defining specifications for a reference measurement system. Methods Fundamentally, in a reference measurement system, there should be a relationship between the analytical specifications for higher- (reference) and lower-order (routine) measurements. Therefore, when setting specifications, we started with limits for routine imprecision (CV rou) and bias ( B rou) using 4 models: (1) the misclassifications in diagnosis, (2) biological variation data (reference interval (RI) and monitoring), (3) expert recommendations, and (4) state-of-the-art performance. Then, we used the derived goals to tailor those for reference measurements and certified reference materials (CRMs) for calibration by setting the limits for CV ref at 0.5 CV rou, B ref at 0.33 B rou , max. uncertainty ( U max) at 0.33 B ref. Results The established specifications ranged between CV rou ≤ 22%, B rou ≤ 10%, CV ref ≤ 11%, B ref ≤ 3.3%, U max 1.1% (model 3) and CV rou ≤ 4%, B rou ≤ 2.6%, CV ref ≤ 2%, B ref ≤ 0.9%, U max 0.3% (model 2, monitoring). Conclusions Model 2 (monitoring) gave the most stringent goals, model 3, the most liberal ones. Accounting for state-of-the-art performance and certification capabilities, we used model 2 (RI) to recommend achievable goals: for routine testing, CV rou ≤ 10%, B rou ≤ 5%, for reference measurements, CV ref ≤ 5%, B ref ≤ 1.7%, and for CRMs, U max 0.6%.

Evaluation of laser induced breakdown spectroscopy for the determination of micronutrients in plant materials

Laser induced breakdown spectroscopy (LIBS) has been evaluated for the determination of micronutrients (B, Cu, Fe, Mn and Zn) in pellets of plant materials, using NIST, BCR and GBW biological certified reference materials for analytical calibration. Pellets of approximately 2 mm thick and 15 mm diameter were prepared by transferring 0.5 g of powdered material to a 15 mm die set and applying 8.0 tons cm − 2 . An experimental setup was designed by using a Nd:YAG laser operating at 1064 nm (200 mJ per pulse, 10 Hz) and an Echelle spectrometer with ICCD detector. Repeatability precision varied from 4 to 30% from measurements obtained in 10 different positions (8 laser shots per test portion) in the same sample pellet. Limits of detection were appropriate for routine analysis of plant materials and were 2.2 mg kg − 1 B, 3.0 mg kg − 1 Cu, 3.6 mg kg − 1 Fe, 1.8 mg kg − 1 Mn and 1.2 mg kg − 1 Zn. Analysis of different plant samples were carried out by LIBS and results were compared with those obtained by ICP OES after wet acid decomposition.

Standard Reference Materials to support measurement of fatty acids

AbstractThe National Institute of Standards and Technology offers a variety of natural‐matrix and solution‐based Standard Reference Materials (SRM) that are characterized for fatty acid composition. The natural‐matrix SRM are intended primarily for use as control materials, but other uses include method validation, the development of new analytical methods, and use as a component in achieving traceability of measurements. The use of complex‐matrix reference materials for instrument calibration is not recommended; solution calibrants are better suited to this task. In addition to calibration, solution SRM can be used as spiking solutions for fortification of samples, in studying extraction recoveries, for developing chromatographic separations, and as authentic standards for identifying constituents in more complex‐matrix extracts. The use of SRM to support the measurement of fatty acids is relevant to a broad spectrum of applications including compliance with and accuracy of nutritional labeling, food manufacturing tolerances (e. g., infant formulas), traceability of measurements for food exports, clinical nutritional measurements, and characterization of alternative energy sources (e. g., biodiesel). Currently, nearly 30 SRM are available with certified, reference, and information values reported for fatty acids. Additional SRM are under development that will complement these reference materials by providing fatty acid profiles in different types of matrices.

Report on CCQM-P98: Quantitative analysis of thin Fe–Ni alloy films using a certified alloy reference material for calibration of testing methods

The pilot study P98 on quantitative surface analysis of alloy films was performed by the Surface Analysis Working Group (SAWG) of the Consultative Committee for Amount of Substance (CCQM). The aim of this pilot study is to ensure the equivalency in the measurement capability of national metrology institutes (NMIs) for the quantification of thin alloy films. Nine laboratories including five NMIs, three companies and one university participated in this pilot study. The majority of the participants used x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES), which are useful methods for the quantitative analysis of thin alloy films or structured surfaces made of them. The compositions of the certified reference material and the other test samples were determined by inductively coupled plasma mass spectrometry (ICP-MS) using the isotope dilution method. The in-depth and lateral homogeneities of the composition were confirmed by secondary ion mass spectrometry (SIMS) using a C60 ion source.In this pilot study, the quantification of Fe–Ni alloy films has been proven to be a good candidate as a subject for a CCQM key comparison. The measured slope and offset values of participants' XPS, AES or EPMA data versus compositions obtained by ICP-MS are considered in detail. Data sets for the compositions obtained either by relative sensitivity factors (RSFs) determined from (a) pure metal films or by RSFs from (b) a certified reference alloy film are compared with the result that the average offset value is substantially reduced from 0.725 to 0.038 for the Fe51–Ni49 alloy film test sample. This result means that the RSFs obtained from an alloy film are much more appropriate than those RSFs from pure metals for the quantification of alloy films because a matrix effect can be successfully covered in the first case. This is the right way to improve the equivalency in the measurement capabilities of participants. Similar results have been observed in an analysis of data obtained with the Fe28–Ni72 and Fe78–Ni22 test films. The compositions measured by XPS using RSFs determined from an alloy film showed the minimum in deviation from the nominal values.Main text.To reach the main text of this paper, click on Final Report.The final report has been peer-reviewed and approved for publication by the CCQM Working Group on Surface Analysis.

In situ analysis of major and trace elements of anhydrous minerals by LA-ICP-MS without applying an internal standard

Here we describe an internal standard-independent calibration strategy for LA-ICP-MS analysis of anhydrous minerals and glasses. Based on the normalization of the sum of all metal oxides to 100 wt.%, the ablation yield correction factor (AYCF) was used to correct the matrix-dependent absolute amount of materials ablated during each run. A Y C F = 100 ∑ j = 1 N ( c p s sam j × l j ) , l j = C rm j / c p s rm j , where cps sam j and cps rm j are net count rates of analyte element j of the sample and reference material for calibration, C rm j is concentration of element j in the reference material, N is the number of elements that can be determined by LA-ICP-MS. When multiple reference materials were used for calibration, l value can be calculated with regression statistics according to the used reference materials. Applying an AYCF and using the USGS reference glasses BCR-2G, BHVO-2G and BIR-1G as reference materials for external calibration, analyses of MPI-DING reference glasses generally agree with recommended values within 5% for major elements (relative standard deviation (RSD) = 0.3–3.9% except for P 2O 5, n = 11), and 5–10% for trace elements. Analyses of anhydrous silicate minerals (clinopyroxene, orthopyroxene, olivine, plagioclase and garnet) and spinel generally agree with the results of electron microprobe analysis within 0.2–7% for SiO 2, Fe 2O 3, MgO and CaO. RSD are generally < 5% for elements with concentrations > 0.1 wt.%. The results indicate that, by applying an AYCF and using USGS reference glasses as multiple reference materials for calibration, elements of these anhydrous minerals can be precisely analyzed in situ by LA-ICP-MS without applying internal standardization. The different element fractionations between the NIST glasses and those glasses with natural compositions indicate that NIST SRM 610 is a less than ideal reference material for external calibration of analyses of natural silicates.

Analysis of coupled Sr/Ca and 87Sr/ 86Sr variations in enamel using laser-ablation tandem quadrupole-multicollector ICPMS

We present in this study results obtained with a laser-ablation coupled with both a quadrupole and a multi-collector ICPMS. The simultaneous in situ Sr/Ca and 87Sr/ 86Sr measurements along growth profiles in enamel allows the concomitant diet and migration patterns in mammals to be reconstructed. Aliquots of the powdered international standard NIST “SRM1400 Bone Ash” with certified Sr and Ca contents, was sintered at high pressure and temperature and was adopted as the reference material for external reproducibility and calibration of the results. A total of 145 coupled elemental and isotopic measurements of herbivores enamel from the Kruger National Park, South Africa, gives intra-tooth Sr/Ca and 87Sr/ 86Sr variations that are well larger than external reproducibility. Sr/Ca profiles systematically decrease from the dentine-enamel junction to the outer enamel whereas 87Sr/ 86Sr profiles exhibit variable patterns. Using a simple geometric model of hypsodont teeth growth, we demonstrate that a continuous recording of the 87Sr/ 86Sr variations can be reconstructed in the tooth length axis. This suggests that the mobility of a mammal can be reconstructed over a period of more than a year with a resolution of a ten of days, by sampling enamel along growth profiles. Our geometric model of hypsodont teeth growth predicts that an optimal distance between two successive profiles is equal to the enamel thickness. However, this model does not apply to the Sr/Ca signal which is likely to be altered during the enamel maturation stage due to differential maturation processes along enamel thickness. Here, the observed constant decreases of the Sr/Ca ratios in the ungulates of Kruger National Park suggests that they did not changed of diet, while some of them were migrating.

Development of Cu and Zn Isotope MC‐ICP‐MS Measurements: Application to Suspended Particulate Matter and Sediments from the Scheldt Estuary

The present study evaluates several critical issues related to precision and accuracy of Cu and Zn isotopic measurements with application to estuarine particulate materials. Calibration of reference materials (such as the IRMM 3702 Zn) against the JMC Zn and NIST Cu reference materials were performed in wet and/or dry plasma modes (Aridus I and DSN‐100) on a Nu Plasma MC‐ICP‐MS. Different mass bias correction methods were compared. More than 100 analyses of certified reference materials suggested that the sample‐calibrator bracketing correction and the empirical external normalisation methods provide the most reliable corrections, with long term external precisions of 0.06 and 0.07‰ (2SD), respectively. Investigation of the effect of variable analyte to spike concentration ratios on Zn and Cu isotopic determinations indicated that the accuracy of Cu measurements in dry plasma is very sensitive to the relative Cu and Zn concentrations, with deviations of δ65Cu from −0.4‰ (Cu/Zn = 4) to +0.4‰ (Cu/Zn = 0.2). A quantitative assessment (with instrumental mass bias corrections) of spectral and non‐spectral interferences (Ti, Cr, Co, Fe, Ca, Mg, Na) was performed. Titanium and Cr were the most severe interfering constituents, contributing to inaccuracies of −5.1‰ and +0.60‰ on δ68/64Zn, respectively (for 500 μg l−1 Cu and Zn standard solutions spiked with 1000 μg l−1 of Ti or Cr). Preliminary isotopic results were obtained on contrasting sediment matrices from the Scheldt estuary. Significant isotopic fractionation of zinc (from 0.21‰ to 1.13‰ for δ66Zn) and copper (from −0.38‰ to 0.23‰ for δ65Cu), suggest a control by physical mixing of continental and marine water masses, characterized by distinct Cu and Zn isotopic signatures. These results provide a stepping‐stone to further evaluate the use of Cu and Zn isotopes as biogeochemical tracers in estuarine environments.

Development of certified reference materials of high-purity volatile organic compounds: purity assay by the freezing-point depression method

For accurate measurement of concentrations of substances by instrumental analysis, reliable calibration standards are needed. In Japan, national reference materials are supplied under the national standards dissemination system named the Japan Calibration Service System (JCSS). In JCSS, calibration standards for the analysis of environmental pollutants are supplied. For the traceability to the SI of reference materials for calibration in JCSS, the National Metrology Institute of Japan (NMIJ) is developing high-purity reference materials of volatile organic compounds (VOCs) as NMIJ CRMs. The freezing-point depression method, which has potential as a primary method of measurement, is employed for the determination of property value. In this paper, a development scheme of certified reference materials of high-purity VOCs is described.

Round Robin Test on Validation of Cyclohexane as a Reference Material for Calibration of Differential Scanning Calorimeters

Round Robin Test on Validation of Cyclohexane as a Reference Material for Calibration of Differential Scanning Calorimeters

Consensus Characterization of 16 FMR1 Reference Materials: A Consortium Study

Fragile X syndrome, which is caused by expansion of a (CGG)(n) repeat in the FMR1 gene, occurs in approximately 1:3500 males and causes mental retardation/behavioral problems. Smaller (CGG)(n) repeat expansions in FMR1, premutations, are associated with premature ovarian failure and fragile X-associated tremor/ataxia syndrome. An FMR1-sizing assay is technically challenging because of high GC content of the (CGG)(n) repeat, the size limitations of conventional PCR, and a lack of reference materials available for test development/validation and routine quality control. The Centers for Disease Control and Prevention and the Association for Molecular Pathology, together with the genetic testing community, have addressed the need for characterized fragile X mutation reference materials by developing characterized DNA samples from 16 cell lines with repeat lengths representing important phenotypic classes and diagnostic cutoffs. The alleles in these materials were characterized by consensus analysis in nine clinical laboratories. The information generated from this study is available on the Centers for Disease Control and Prevention and Coriell Cell Repositories websites. DNA purified from these cell lines is available to the genetics community through the Coriell Cell Repositories. The public availability of these reference materials should help support accurate clinical fragile X syndrome testing.

Investigation of chromium(III) acetylacetonate as a calibration reference material for atomic absorption spectroscopy

It is shown that chromium(III) acetylacetonate meets the requirements of calibration reference materials: it is homogeneous, soluble in water and organic solvents, and its solutions are stable. Chromium(III) acetylacetonate has been successfully used as a calibration reference material in the analysis of chromium in iron-base alloys. The procedure involves chromium acetylacetonate extraction using methyl isobutyl ketone followed by direct atomic absorption analysis of the organic extract. The detection limit of the procedure is 10 ng g−1.

Gas-Liquid Chromatographic Determination of Milk Fat and Cocoa Butter Equivalents in Milk Chocolate: Interlaboratory Study

A collaborative trial was conducted to validate an analytical approach comprising method procedures for determination of milk fat and the detection and quantification of cocoa butter equivalents (CBEs) in milk chocolate. The whole approach is based on (1) comprehensive databases covering the triacylglycerol composition of a wide range of authentic milk fat, cocoa butter, and CBE samples and 947 gravimetrically prepared mixtures thereof; (2) the availability of a certified cocoa butter reference material for calibration; (3) an evaluation algorithm, which allows reliable quantitation of the milk fat content in chocolate; (4) a subsequent correction to take account of the triacylglycerols derived from milk fat; (5) mathematical expressions to detect the presence of CBEs in milk chocolate; and (6) a multivariate statistical formula to quantitate the amount of CBEs in milk chocolate. Twelve laboratories participated in the validation study. CBE admixtures were detected down to a level of 0.5 g CBE/100 g milk chocolate, without false-positive or -negative results. The applied quantitation model performed well at the statutory limit of 5% CBE addition to milk chocolate, with a prediction error of 0.7%, and HorRat values ranging from 0.8 to 1.5. The relative standard deviation for reproducibility (RSDR) values for quantitation of CBEs in analyses of chocolate fat solutions ranged from 2.2 to 3.8% and for analyses of real chocolate samples, from 4.1 to 4.7%, demonstrating that the whole approach, based solely on chocolate fat blends, is applicable to real milk chocolate samples.

Determination of Tetrachloroethylene and Other Volatile Halogenated Organic Compounds in Oil Wastes by Headspace SPME GC–MS

Oil wastes and slops are complex mixtures of hydrocarbons, which may contain a variety of contaminants including tetrachloroethylene (perchloroethylene, PCE) and other volatile halogenated organic compounds (VHOCs). The analytical determination of PCE at trace levels in petroleum-derived matrices is difficult to carry out in the presence of large amounts of hydrocarbon matrix components. In the following study, we demonstrate that headspace solid-phase microextraction (HS-SPME) combined with GC–MS analysis can be applied for the rapid measurement of PCE concentration in oil samples. The HS-SPME method was developed using liquid paraffin as matrix matching reference material for external and internal calibration and optimisation of experimental parameters. The limit of quantitation was 0.05 mg kg−1, and linearity was established up to 25 mg kg−1. The HS-SPME method was extended to several VHOCs, including trichloroethylene (TCE) in different matrices and was applied to the quantitative analysis of PCE and TCE in real samples.

A Challenge for High‐Performance Full‐Field Strain Measurement Systems

Abstract: The advent of digital imaging technology and huge increases in data‐processing power have led to enormous advances in optical techniques for evaluating strain fields. A standardised test material designed for evaluating the capabilities of the most sophisticated optical systems using these techniques is described. The standardised test material presents a significant challenge to optical techniques for full‐field strain evaluation by employing complicated and reproducible strain fields for which analytical solutions are available. The design philosophy and process employed in developing the standardised test material are described and sample results are presented. The relationship between a standardised test material and reference material for calibration is discussed.

Fit-for-purpose shellfish reference materials for internal and external quality control in the analysis of phycotoxins

The need for reference materials for quality control of analysis of foodstuffs has been stressed frequently. This has been particularly true in the phycotoxins field, where there is a great shortage of both pure calibration standards and reference materials. Worldwide there are very few independent bodies that produce certified reference materials for phycotoxins, the main producers currently being the National Research Council Canada and the Japanese Food Research Laboratory. Limited availability of contaminated shellfish and algae, as well as the time and knowledge necessary for the production of adequate reference materials, continuously lead to limited editions of certified reference materials and even more limited production of in-house reference materials. The restricted availability of in-house quality control materials promotes the rapid use of the limited certified reference materials, which in turn hampers the production of the suite of materials required globally for complete protection of public health. This paper outlines the various options that analysts can pursue in the use of reference materials for internal and external quality control, with a view to optimising the efforts of both reference materials users and reference materials producers. For this purpose, the logical sequence is reviewed from the discovery of a new bioactive compound in shellfish, through initial method development up to regulation for food safety purposes including accepted reference methods. Subsequently, the requirements for and efforts typically spent in the production and characterisation of laboratory reference materials, certified reference materials and other test materials used in inter-laboratory studies or proficiency testing, in the area of marine biotoxins are evaluated. Particular emphasis is put on practical advice for the preparation of in-house reference materials. The intricate link between reference material characterisation and method performance is outlined to give guidance on the appropriate in-house method validation in the rapidly developing field of phycotoxins.

Metrological traceability: I make it 42; you make it 42; but is it the same 42?

The paper reproduces a talk given at a 2-day symposium on quality assurance in chemistry held in Brisbane, Australia in 2005. Intended for an audience of analysts in the field, the theme of the symposium drew inspiration from the series of books by Douglas Adams “The Hitchhiker's Guide to the Galaxy”. An introduction to basic concepts of metrological traceability is followed by a discussion of practical steps to ensure metrological traceability of field measurement results. The relationship between metrological traceability and comparability of measurement results is discussed. To achieve metrological traceability in the field, the use of appropriate certified reference materials for calibration is recommended. Examples of atmospheric carbon dioxide and roadside breathalyzer measurements are given.

The calibration of XRF polyethylene reference materials with k0-NAA and ICP-AES

Due to the lack of commercially available polyethylene reference materials for the calibration of X-ray fluorescence spectrometers (XRF), DSM Resolve, in cooperation with PANalytical, prepared and calibrated such a set of standards in 2005. The reference materials were prepared based on the addition of additives to virgin polyethylene. The mentioned additives are added to improve the performance of the polymers. The elements present in additives are tracers for the used additives. The reference materials contain the following elements: F, Na, Mg, Al, Si, P, S, Ca, Ti and Zn in the concentration range of 5 mg/kg for Ti, up to 600 mg/kg for Mg. The calibration of the reference materials, including a blank, was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES) and Neutron Activation Analysis ( k 0-NAA). ICP-AES was used to determine the elements Na, Mg, Al, P, Ca, Ti and Zn whereas k 0-NAA was used for F, Na, Mg, Al, Ca, Ti and Zn. Over the complete concentration range, a good agreement of the results was found between the both techniques. This project has shown that within DSM Resolve, it is possible to develop and to calibrate homogenous reference materials for XRF.

Trace Element Analysis of Fused Whole‐Rock Glasses by Laser Ablation‐ICP‐MS and PIXE

The concentrations of fifty trace elements, including relatively volatile elements and transition metal elements, in fused glasses of Geological Survey of Japan rock reference materials GSJ JR‐2, JA‐1, JA‐2, JB‐1a, JB‐3, JGb‐1 and JF‐1 were determined by particle (proton) induced X‐ray emission (PIXE) and laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS). The fused glasses were prepared by rapid fusion and subsequent quenching in welded platinum capsules and were found to be homogeneous for major elements and for trace elements with concentrations of more than 1 μg g‐1 within the observed precision (± 10% mean) on a 70 μm sampling scale. The values obtained by PIXE and LA‐ICP‐MS for the transition elements (Cr, Mn, Fe, Ni and Cu), the relatively volatile elements (Zn, Ga, Rb and Pb) and the refractory elements (Y, Zr, Nb and Th) with concentrations greater than a few μg g‐1 showed good agreement (within 10 % relative difference). The values for almost all the elements detected at concentrations higher than 1 μg g‐1 as determined by LA‐ICP‐MS also agreed well with the reference values (mean relative difference &lt; ± 10%), except for B and Cu. The good agreement confirmed the appropriateness of the NIST SRM 600 series glass calibration reference material for LA‐ICP‐MS analysis of glasses with variable major‐element compositions for almost all elements. The concentrations of Cu in all the samples were lower than the reference values, which was attributed to adsorption of the transition metals onto the platinum capsule during preparation.

Gluten Determination by Gliadin Enzyme-Linked Immunosorbent Assay Kit: Interlaboratory Study

An interlaboratory study with 10 participants was performed to obtain validation and performance data for an enzyme-linked immunosorbent assay (ELISA) kit developed for quantitative gluten determination in foods. The ELISA kit used for this study is based on 2 monoclonal and 1 polyclonal antibody developed by Immunotech, a Beckman Coulter Co. This kit did not show any false positive results or cross-reactivity with oat, rice, maize, and buckwheat. The gliadin standard from the Working Group on Prolamin Analysis and Toxicity was included in the kit as reference material for calibration. All participants obtained a gliadin ELISA kit with Standard Operational Procedure and a form for recording test results. The study included 13 samples labeled as "gluten-free" and 2 samples spiked by wheat flour. Seven samples had gliadin content below the limit of quantitation (LOQ) of the method, and 1 sample exceeded the highest calibration level. Gliadin content in the range from 10 to 157 mg/kg (1st day) and from 11 to 183 mg/kg (2nd day) was found in 7 samples (including 2 spiked samples). Results of these samples were used for further statistical analysis and evaluation. The Cochran, Dixon, and Mandel statistical tests were applied for detection of outliers. The LOQ of the kit was estimated.

Calibration of laser ablation inductively coupled plasma mass spectrometry for quantitative measurements of lead in bone

Lead accumulates in bone over many years or decades. Accordingly, the study of lead in bone is important in determining the fate of ingested lead, the potential for remobilization, and for the application of bone lead measurements as a biomarker of lead exposure. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) was used to measure the spatial distribution of lead in bone on the micrometer scale. In general, LA-ICP-MS studies are somewhat limited by the lack of matrix-matched standards and/or reference materials for calibration and validation purposes. Here we describe the application of pressed pellets prepared from New York State Department of Health candidate Reference Materials for Lead in Bone (levels 1 through 4), to provide a linear calibration for (208)Pb/(43)Ca in the concentration range <1 to 30 μg g(-1). The limit of detection was estimated as 0.2 μg g(-1). The measured lead values for pelletized NIST SRM 1486 Bone Meal and SRM 1400 Bone Ash were in good agreement with certified reference values. Using this approach, we quantitatively measured the spatial distribution of lead in a cross-section of goat metacarpal from a lead-dosed animal. The lead content was spatially variable in the range of 2 to 30 μg g(-1) with a complex distribution. In some sections, lead appeared to be enriched in the center of the bone relative to peripheral areas, indicating preferential accumulation in trabecular (spongy) rather than cortical bone. In addition, there were discrete areas of lead enrichment, or hot spots, of 100 to 200 μm in width.