Certified sediment reference materials for trace element analysis from the National Metrology Institute of Japan (NMIJ)

Two types of sediment reference material (NMIJ 7302-a and 7303-a) for trace elements analysis have been prepared and certified by the National Metrology Institute of Japan in the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). The original materials were collected from a bay near industrial activity in Kyushu (NMIJ CRM 7302-a; marine sediment) and from Lake Biwa (NMIJ CRM 7303-a; lake sediment). The sediment materials were air-dried, sieved, homogenized, packaged in 1000 glass bottles (60 g each), and radiation sterilized. Certification of these CRM for trace elements was conducted by NMIJ, where each element was determined by at least two independent analytical techniques. Isotope-dilution inductively coupled plasma mass spectrometry (ICP–MS) was applied for certification of all the elements except mono-nuclide elements such as As and Co. Other techniques such as ICP–MS with quadrupole mass spectrometry and sector-field mass spectrometry, inductively coupled plasma atomic emission spectrometry (ICP–AES), and atomic absorption spectrometry (AAS), were also used. Certified values have been provided for 14 elements (Sb, As, Cd, Cr, Co, Cu, Pb, Hg, Mo, Ni, Se, Ag, Sn, and Zn) in both CRM.     

Development of a candidate certified reference material of cypermethrin in green tea

This paper presents the preparation of a candidate certified reference material (CRM) of cypermethrin in green tea, GLHK-11-01a according to the requirements of ISO Guide 34 and 35. Certification of the material was performed using a newly developed isotope dilution mass spectrometry (IDMS) approach, with gas chromatography high resolution mass spectrometry (GC–HRMS) and gas chromatography–tandem mass spectrometry (GC–MS/MS). Statistical analysis (one-way ANOVA) showed excellent agreement of the analytical data sets generated from the two mass spectrometric detections. The characterization methods have also been satisfactorily applied in an Asia-Pacific Metrology Program (APMP) interlaboratory comparison study. Both the GC–HRIDMS and GC–IDMS/MS methods proved to be sufficiently reliable and accurate for certification purpose. The certified value of cypermethrin in dry mass fraction was 148 μg kg⁻¹ and the associated expanded uncertainty was 14 μg kg⁻¹. The uncertainty budget was evaluated from sample in homogeneity, long-term and short-term stability and variability in the characterization procedure. GLHK-11-01a is primarily developed to support the local and wider testing community on need basis in quality assurance work and in seeking accreditation.     

Development of melamine certified reference material in milk using two different isotope dilution mass spectrometry techniques

A new certified reference material (CRM) of melamine in milk GLHK-11-02 was developed aiming to address the great demand from the testing community after the melamine crises. The material was prepared by adding an appropriate quantity of melamine into the skimmed milk samples and the final product was in the form of fine lyophilized powder. Characterization of the material relied on two newly developed gravimetric isotope dilution mass spectrometry (IDMS) methods, one using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and another gas chromatography-mass spectrometry (GC-MS). Experimental parameters with crucial effects on the performance of the two IDMS methods were thoroughly investigated. These included purity of standard used, equilibration time of isotopes, efficiency of extraction methods as well as possible interferences from the matrix and melamine analogues. Precision was found to be excellent with a coefficient of variation of 2.5% for the LC-IDMS/MS (n=46) and 1.9% for the GC-IDMS (n=30) respectively. Using one-tail Student's t-test at 95% confidence interval, analytical data sets generated from the two methods were found to exhibit no significant difference. Measurement accuracy of the methods was further verified through an Asia Pacific Metrology Program (APMP) pilot study. Analytical results of the present LC-IDMS/MS for the two milk test samples at the concentration level of about 0.45 and 3.5 mg kg(-1) were proven to be very good. There were excellent overlaps between our results and the assigned reference values, and the absolute deviation was less than 3.2%. Both the LC-IDMS/MS and GC-IDMS methods were shown to be sufficiently reliable and accurate for certification of the melamine CRM. Certified value of melamine in dry mass fraction in GLHK-11-02 was 1.14 mg kg(-1). Expanded uncertainty due to sample inhomogeneity, long term and short term stability and variability in the characterization procedure was at 7.1% or 0.08 mg kg(-1). The CRM is primarily used to provide a complete method validation for and to improve the technical competence of melamine analysis to food and chemical testing laboratories.     

Application of isotope dilution mass spectrometry to research of certified reference materials

This paper briefly describes the method and applications of isotope dilution mass spectrometry(IDMS). Primary standard solutions with various natural isotope abundances were used to certify the concentration of enriched isotope solutions by IDMS. Then these enriched isotopes were used to certify unknown samples by IDMS. Li, K, Mg, Fe, Cu, Ni, Cd, Mo, Pb, etc in CRMs were certified and very good results were obtained in three international comparisons by IDMS. Received: 15 June 2000 Accepted: 26 October 2001     

Availability of reference materials: COMAR the database for certified reference materials

COMAR is the international database for certified reference materials. A new user-friendly web-based version, COMAR², has been developed by BAM and CONET Consulting AG which will be available in December 2002. The advantages of COMAR² are briefly explained.Presented at the International ILAC/IAF Conference on Accreditation in Global Trade, 23-25 September 2002, Berlin, Germany     

Species specific isotope dilution for the accurate and SI traceable determination of arsenobetaine and methylmercury in cuttlefish and prawn

Methods based on species specific isotope dilution were developed for the accurate and SI traceable determination of arsenobetaine (AsBet) and methylmercury (MeHg) in prawn and cuttlefish tissues by LC-MS/MS and SPME GC-ICPMS. Quantitation of AsBet and MeHg were achieved by using a ¹³C-enriched AsBet spike (NRC CRM CBET-1) and an enriched spike of Me¹⁹⁸Hg (NRC CRM EMMS-1), respectively, wherein analyte mass fractions in enriched spikes were determined by reverse isotope dilution using natural abundance AsBet and MeHg primary standards. Purity of these primary standards were characterized by quantitative ¹H-NMR with the use of NIST SRM 350b benzoic acid as a primary calibrator, ensuring the final measurement results traceable to SI. Validation of employed methods of ID LC-MS/MS and ID SPME GC-ICPMS was demonstrated by analysis of several biological CRMs (DORM-4, TORT-3, DOLT-5, BCR-627 and BCR-463) with satisfying results.     

Homogeneity and stability of reference materials

 Homogeneity and stability are two crucial characteristics of any certified reference material (CRM). Utmost care must be taken during preparation to create materials as homogeneous and stable as possible. Degradation can generally be minimised by reducing the water activity of the material to a level between 0.15 and 0.35. However, careful preparation by itself is not enough. Positive demonstration of homogeneity and stability is required from the perspective of implementing uncertainty calculus according to the Guide to the Expression of Uncertainty in Measurement (GUM). In many cases, homogeneity and stability studies fail to give sufficient quantitative information on homogeneity and stability, mainly because of a lack of measurement repeatability and insufficient number of replicates. In this work, some solutions to these problems and their implications are presented. Received: 25 April 2000 / Accepted: 12 September 2000     

A high-accuracy method of analysis of 19-norandrosterone in human urine as utilised for the international laboratory intercomparison CCQM-P68

A high-accuracy exact-matching isotope dilution mass spectrometry (IDMS) method for 19-norandrosterone (19-NA) in human urine was developed at NMIA for the certification of a freeze-dried human urine reference material (CRM NMIA MX002). The method utilised GC/HRMS analysis following hydrolysis, solvent extraction, HPLC fractionation and derivatisation. The method development included investigation of all potential analytical biases for the different stages of the method and included development of a confirmatory LC/MS/MS method. The measurement uncertainty of the reference method was rigorously investigated with the achieved expanded uncertainty being less than 4% at the 95% level of confidence. The method was used in the Comité Consultatif pour la Quantité de Matière (CCQM) pilot study CCQM-P68 which was an interlaboratory intercomparison for the analysis of 19-NA in human urine in which four national metrology institutes (NMIs) participated in. The agreement in the results from the NMIA method with those from the other NMIs was excellent.     

Improvement of the traceability of reference materials certified for purity: evaluation of a semi-preparative high-performance liquid chromatography approach

A semi-preparative high-performance liquid chromatography process was evaluated as a tool to quantitatively determine the purity or percentage mass fraction content (% m/m) of organic compounds. The method is simple and does not require the identification and subsequent quantitation of organic-related structure impurities. A protocol was developed and tested on four reference materials certified for purity from 95% m/m to 99.3% m/m. Comparing the purity results of each certified reference material using the new approach with their respective certified values showed no significant analytical bias. Semi-preparative high-performance liquid chromatography has proved the potential to be a primary method directly traceable to mass with an uncertainty statement written down also in terms of mass with expanding uncertainty ranging from 0.8% to 1.3% m/m compared to 0.3 to 2.0% m/m for the certified purity values at the 95% confidence interval.     

Certification of methylmercury in cod fish tissue certified reference material by species-specific isotope dilution mass spectrometric analysis

A new cod fish tissue certified reference material, NMIJ CRM 7402-a, for methylmercury analysis was certified by the National Metrological Institute of Japan in the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Cod fish was collected from the sea close to Japan. The cod muscle was powdered by freeze-pulverization and was placed into 600 glass bottles (10 g each), which were sterilized with γ-ray irradiation. The certification was carried out using species-specific isotope dilution gas chromatography inductively coupled plasma mass spectrometry (SSID–GC–ICPMS), where ²⁰²Hg-enriched methylmercury (MeHg) was used as the spike compound. In order to avoid any possible analytical biases caused by nonquantitative extraction, degradation and/or formation of MeHg in sample preparations, two different extraction methods (KOH/methanol and HCl/methanol extractions) were performed, and one of these extraction methods utilized two different derivatization methods (ethylation and phenylation). A double ID method was adopted to minimize the uncertainty arising from the analyses. In order to ensure not only the reliability of the analytical results but also traceability to SI units, the standard solution of MeHg used for the reverse-ID was prepared from high-purity MeHg chloride and was carefully assayed as follows: the total mercury was determined by ID–ICPMS following aqua regia digestion, and the ratio of Hg as MeHg to the total Hg content was estimated by GC–ICPMS. The certified value given for MeHg is 0.58 ± 0.02 mg kg⁻¹ as Hg. Figure NMIJ CRM 7402-a: cod fish tissue for MeHg analysis     

Development and application of an ultratrace method for speciation of organotin compounds in cryogenically archived and homogenized biological materials

An accurate, ultra-sensitive and robust method for speciation of mono, di, and tributyltin (MBT, DBT, and TBT) by speciated isotope-dilution gas chromatography-inductively coupled plasma-mass spectrometry (SID-GC-ICPMS) has been developed for quantification of butyltin concentrations in cryogenic biological materials maintained in an uninterrupted cryo-chain from storage conditions through homogenization and bottling. The method significantly reduces the detection limits, to the low pg g(-1) level (as Sn), and was validated by using the European reference material (ERM) CE477, mussel tissue, produced by the Institute for Reference Materials and Measurements. It was applied to three different cryogenic biological materials-a fresh-frozen mussel tissue (SRM 1974b) together with complex materials, a protein-rich material (whale liver control material, QC03LH03), and a lipid-rich material (whale blubber, SRM 1945) containing up to 72% lipids. The commutability between frozen and freeze-dried materials with regard to spike equilibration/interaction, extraction efficiency, and the absence of detectable transformations was carefully investigated by applying complementary methods and by varying extraction conditions and spiking strategies. The inter-method results enabled assignment of reference concentrations of butyltins in cryogenic SRMs and control materials for the first time. The reference concentrations of MBT, DBT, and TBT in SRM 1974b were 0.92 +/- 0.06, 2.7 +/- 0.4, and 6.58 +/- 0.19 ng g(-1) as Sn (wet-mass), respectively; in SRM 1945 they were 0.38 +/- 0.06, 1.19 +/- 0.26, and 3.55 +/- 0.44 ng g(-1), respectively, as Sn (wet-mass). In QC03LH03, DBT and TBT concentrations were 30.0 +/- 2.7 and 2.26 +/- 0.38 ng g(-1) as Sn (wet-mass). The concentration range of butyltins in these materials is one to three orders of magnitude lower than in ERM CE477. This study demonstrated that cryogenically processed and stored biological materials are a promising alternative to conventional freeze-dried materials for organotin speciation analysis, because these are, at present, the best conditions for minimizing degradation of thermolabile species and for long-term archival. Finally, the potential of the analytical method was illustrated by analysis of polar bear (Ursus maritimus) and beluga whale (Delphinapterus leuca) liver samples that had been collected in the Arctic and archived at the Marine Environmental Specimen Bank. Significant concentrations of butyltin compounds were found in the samples and provide the first evidence of the presence of this class of contaminant in the Arctic marine ecosystem. Figure Eye catch image.     

Trends in the certification of reference materials

The certification of reference materials is still a rapidly developing area. Mostly driven by demands from laboratories, new reference materials are produced, and even new categories of materials are developed, such as genetically modified organism materials or materials for qualitative analysis. Even in more classical areas, such as the certification of chemicals for purity, there are important new insights, in particular in modelling the measurements and the property values. Laboratories are asking increasingly for uncertainty budgets of reference materials that are compatible with the concepts of the Guide to the expression of uncertainty in measurement, thus putting stronger demands to improve not only the quality of the materials, but also of the science and technology behind a certification. Three important issues are highlighted to exemplify these trends: the further interpretation of homogeneity and stability data, the appreciation of asymmetry due to mathematical constraints (relevant for, e.g., purity and trace analysis), and the certification of reference materials for qualitative measurement.Presented at BERM-9—9th International Symposium on Biological and Environmental Reference Materials, 15–19June 2003, Berlin, Germany     

Preparation and certification of a reference material for the determination of nutrients in seawater

There is an urgent need for natural water reference materials certified for nutrients. In 1996, NRC collected seawater for a proposed CRM at a depth of 200 m in the North Atlantic; this was immediately filtered through 0.05-m cartridge filters into 50-L carboys. The water was later homogenized in the NRC laboratories in Ottawa and stabilized via gamma irradiation. Over six years of stability testing no significant deterioration was detected. In addition to the usual customary standard colorimetric procedures, alternative analytical methods were developed to enable the certification process. The production of a CRM called MOOS-1 will be discussed. Certified values, with uncertainty components addressing the homogeneity, stability, and characterization of the material, were calculated to be: orthophosphate=1.56±0.07 µmol L^–1, silicate=26.0±1.0 µmol L^–1, nitrite=3.06±0.15 µmol L^–1, and nitrite and nitrate=23.7±0.9 µmol L^–1.     

Matrix certified reference materials for environmental monitoring from the National Metrology Institute of Japan (NMIJ)

Matrix certified reference materials (CRMs) are playing an increasingly important role in environmental monitoring in Japan. The National Metrology Institute of Japan (NMIJ)/National Institute of Advanced Industrial Science and Technology (AIST) has been developing matrix CRMs for environmental monitoring since 2001, and has issued nine kinds of CRMs as NMIJ CRMs. The development of the CRMs was conducted in NMIJ in cooperation with candidate material producers. The isotope dilution mass spectrometry (IDMS) was principally adopted to give reliable certified values. Meanwhile, two or more analytical methods, whose levels of accuracy were well evaluated, were applied to avoid any possible analytical bias. Two typical certification processes, the certification of river water CRMs for trace element analysis and that of marine sediment CRMs for PCB and organochlorine pesticide analysis, are outlined as examples. Presented at -- “BERM-10” -- April 2006, Charleston, SC, USA.     

Preparation and characterization of organic calibration solutions for development of certified reference materials at the National Metrology Institute of Japan

Certified reference materials (CRMs) are playing an increasingly important role in environmental monitoring in Japan. The National Metrology Institute of Japan (NMIJ)/National Institute of Advanced Industrial Science and Technology (AIST) has been developing CRMs of organic calibration solutions since 2003, and has issued several NMIJ CRMs. The development of these materials was conducted at the NMIJ in cooperation with candidate material producers. The freezing-point depression method was principally adopted for assessment of the purity of starting materials to give reliable certified values. Gas chromatography with flame ionization detection (GC–FID) and/or high-performance liquid chromatography (HPLC), which are based on independent principles and whose levels of accuracy are well evaluated, were applied in combination with other methods to avoid any possible analytical bias. Purity assessment is outlined for two typical examples, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDD) and 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (p,p′-DDT), which were used as starting materials for a CRM under development. Methods adopted for gravimetric preparation and ampouling of solutions were qualified and optimized to reduce the uncertainties of certified values due to these factors. Furthermore, a new experimental scheme for assessment of stability and preparation variation is proposed for the proper estimation of uncertainties. Presented at BERM-11, October 2007, Tsukuba, Japan.     

加湿气体标准物质水含量分析

利用称量法、饱和蒸气压法、流量法3种不同原理的方法分析加湿气体标准物质中加湿量(水分的变化量),测定结果分别为4.66,4.68,4.70 g。依据3种方法的测量模型计算得到3个湿度量值的标准不确定度分别为0.016,0.025,0.666 g。为加湿后气体湿度值的量值溯源提供了3种可靠的方法,为加湿气体标准物质的制备和水含量溯源提供了新思路。     

NIES certified reference materials for arsenic speciation

 The National Institute for Environmental Studies (NIES) recently prepared two candidate certified reference materials (CRMs) for arsenicals to meet the growing demand for the quality assurance of arsenic speciation analysis. The NIES candidate CRM No. 14 Brown Alga was prepared from Hijiki seaweed for the certification of inorganic arsenic content, and No. 15 Scallop was prepared from adductor muscle of scallop for the certification of arsenobetaine content. The preparation of the candidate CRMs is briefly described. Cooperative analyses for total arsenic content of the candidate CRMs have been underway. The preliminary speciation analysis at NIES revealed difficulty in establishing suitable conditions for extracting arsenic species from the materials. Chromatograms of arsenic species by a high performance liquid chromatography-inductively coupled plasma mass spectrometric detection system are presented to provide information about arsenic species present in these candidate CRMs.     

Certification of mono-, di-, and tributyltin compounds in marine sediment certified reference material by species-specific isotope dilution mass spectrometric analysis using synthesized <Superscript>118</Superscript>Sn-labeled butyltins

A new marine sediment reference material (NMIJ CRM 7301-a) for butyltins analysis was prepared and certified by the National Metrological Institute of Japan, National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). The original material of the sediment was collected at a bay near industrial activities in Japan. The sediment material was air-dried, sieved, homogenized, and packaged into 1,000 glass bottles (60 g each). Certification of NMIJ CRM 7301-a was carried out at NMIJ using two different types of species-specific isotope dilution mass spectrometry: isotope dilution–ethylation–gas chromatography/inductively coupled plasma mass spectrometry (GC/ICPMS) and isotope dilution–ethylation–gas chromatography/mass spectrometry (GC/MS). A mixture of ¹¹⁸Sn-enriched monobutyltin, dibutyltin, and tributyltin was synthesized in our laboratory and was used as a spike for both techniques. Certified values are given for tributyltin (0.044±0.004 mg kg^–1 as Sn), dibutyltin (0.056±0.006 mg kg^–1 as Sn, and monobutyltin (0.058±0.013 mg kg^–1 as Sn), being at lower levels than currently available sediment CRMs for the analysis of organotins.     

Certification of methylmercury content in two fresh-frozen reference materials: SRM 1947 Lake Michigan fish tissue and SRM 1974b organics in mussel tissue (Mytilus edulis)

This paper describes the development of two independent analytical methods for the extraction and quantification of methylmercury from marine biota. The procedures involve microwave extraction, followed by derivatization and either headspace solid-phase microextraction (SPME) with a polydimethylsiloxane (PDMS)-coated silica fiber or back-extraction into iso-octane. The identification and quantification of the extracted compounds is carried out by capillary gas chromatography/mass spectrometric (GC/MS) and inductively coupled plasma mass spectrometric (GC/ICP-MS) detection. Both methods were validated for the determination of methylmercury (MeHg) concentrations in a variety of biological standard reference materials (SRMs) including fresh-frozen tissue homogenates of SRM 1946 Lake Superior fish tissue and SRM 1974a organics in mussel tissue (Mytilus edulis) and then applied to the certification effort of SRM 1947 Lake Michigan fish tissue and SRM 1974b organics in mussel tissue (Mytilus edulis). While past certifications of methylmercury in tissue SRMs have been based on two independent methods from the National Institute of Standards and Technology (NIST) and participating laboratories, the methods described within provide improved protocols and will allow future certification efforts to be based on at least two independent analytical methods within NIST.     

Certification of butyltins and phenyltins in marine sediment certified reference material by species-specific isotope-dilution mass spectrometric analysis using synthesized <Superscript>118</Superscript>Sn-enriched organotin compounds

A new marine sediment certified reference material, NMIJ CRM 7306-a, for butyltin and phenyltin analysis has been prepared and certified by the National Metrological Institute of Japan at the National Institute of Advanced Industrial Science and Technology (NMIJ/AIST). Candidate sediment material was collected at a bay near industrial activity in Japan. After air-drying, sieving, and mixing the material was sterilized with γ-ray irradiation. The material was re-mixed and packaged into 250 glass bottles (15 g each) and these were stored in a freezer at −30 °C. Certification was performed by use of three different types of species-specific isotope-dilution mass spectrometry (SSID–MS)—SSID–GC–ICP–MS, SSID–GC–MS, and SSID–LC–ICP–MS, with ¹¹⁸Sn-enriched organotin compounds synthesized from ¹¹⁸Sn-enriched metal used as a spike. The ¹¹⁸Sn-enriched mono-butyltin (MBT), dibutyltin (DBT), and tributyltin (TBT) were synthesized as a mixture whereas the ¹¹⁸Sn-enriched di-phenyltin (DPhT) and triphenyltin (TPhT) were synthesized individually. Four different extraction methods, mechanical shaking, ultrasonic, microwave-assisted, and pressurized liquid extraction, were adopted to avoid possible analytical bias caused by non-quantitative extraction and degradation or inter-conversion of analytes in sample preparations. Tropolone was used as chelating agent in all the extraction methods. Certified values are given for TBT 44±3 μg kg⁻¹ as Sn, DBT 51 ± 2 μg kg⁻¹ as Sn, MBT 67 ± 3 μg kg⁻¹ as Sn, TPhT 6.9 ± 1.2 μg kg⁻¹ as Sn, and DPhT 3.4 ± 1.2 μg kg⁻¹ as Sn. These levels are lower than in other sediment CRMs currently available for analysis of organotin compounds.