Certification of reference materials for inorganic trace analysis: the INCT approach

This paper presents the work done by the Institute of Nuclear Chemistry and Technology (INCT), Warsaw on a procedure of the certification of matrix reference materials (CRMs) for inorganic trace analysis. The INCT has been involved in preparation and certification of that type of CRMs since 1986 till now. The certification of CRMs is performed on the basis of statistical evaluation of the data obtained from the worldwide interlaboratory comparison. The initially adopted certification procedure has been developed, and the final shape is presented and discussed. The modifications are connected with the new demands of the international standards. The results of analysis of candidate CRMs obtained by the potentially primary procedures based on radiochemical neutron activation analysis (RNAA) and results of analysis of CRM accompanying candidate RMs are applied in the certification process for quality assurance purpose.     

Improvements in the determination of chlorobenzenes and chlorophenols through a stepwise interlaboratory study approach

A systematic quality control programme carried out by a number of laboratories from the European Union and from EFTA countries is described. The programme was designated to improve the analytical state of the art in the determination of selected chlorinated benzenes and chlorinated phenols in different environmental matrices. To that end a stepwise interlaboratory study approach was chosen, analysing, in consecutive order, a clean extract of soil, a raw extract and the soil itself. Eight analytes were selected for the study, i.e. three chlorobenzenes and five chlorophenols. During the programme significant improvements in analytical performance were achieved, as shown by a decrease in within-laboratory coeffficients of variation as well as by acceptable coefficients of variation in the mean value of laboratory means of all analytes in the final matrix analysed, i.e. a natural soil. The results of the programme prompted the European Union to embark upon a pentachlorophenol interlaboratory certification study to produce an industrial soil candidate Certified Reference Material (CRM) [1].     

Improvements in the determination of chlorobenzenes and chlorophenols through a stepwise interlaboratory study approach

A systematic quality control programme carried out by a number of laboratories from the European Union and from EFTA countries is described. The programme was designated to improve the analytical state of the art in the determination of selected chlorinated benzenes and chlorinated phenols in different environmental matrices. To that end a stepwise interlaboratory study approach was chosen, analysing, in consecutive order, a clean extract of soil, a raw extract and the soil itself. Eight analytes were selected for the study, i.e. three chlorobenzenes and five chlorophenols. During the programme significant improvements in analytical performance were achieved, as shown by a decrease in within-laboratory coeffficients of variation as well as by acceptable coefficients of variation in the mean value of laboratory means of all analytes in the final matrix analysed, i.e. a natural soil. The results of the programme prompted the European Union to embark upon a pentachlorophenol interlaboratory certification study to produce an industrial soil candidate Certified Reference Material (CRM) [1]. Received: 28 August 1997 / Revised: 15 October 1997 / Accepted: 21 October 1997     

Preparation and homogeneity study of a mussel candidate reference material for certification of organotin compounds

Organotin compounds are currently determined in various environmental matrices (in particular water, sediment and shellfish) to form the basis of control measures for the levels of contamination, as required in some EC Directives. Accurate measurements are a prerequisite for the enforcement of this legislation, which implies that good quality control of determinations should be ensured. One of the tools for achieving accuracy is to use certified reference materials (CRMs). With regard to tin species, however, CRMs are rather scarce and mainly concern sediment and fish matrices certified for their butyltin content. The present study deals with the preparation of a mussel candidate reference material and the verification of its homogeneity prior to the certification of the contents of butyl- and phenyl-tin compounds. 100kg of mussels (Mytilus edulis) were collected, carefully washed with fresh water in order to eliminate matrix salts and immediately frozen by immersion in liquid nitrogen. The mussels were shelled (in the frozen state) and the edible part was stored in thermally sealed polyethylene bags which were stored at –25 °C. The frozen material was ground in a Teflon-coated grinding mill, spread on sterilized flat trays and freeze-dried. The freeze-dried material was then ground for 15 days in a zirconia ball mill and sieved on a titanium sieve to separate the fibrous part. Successively, the material was mixed for 15 days under argon atmosphere in a special polyethylene-lined mixing drum and bottled in brown Pyrex-glass bottles. 21 bottles were selected during the course of the bottling procedure to verify the within- and between-bottle homogeneity of the overall batch. The within-bottle homogeneity was verified by determining the organotin (butyl- and phenyltins) content for subsamples of 500 mg in ten replicates from one bottle, whereas the between-bottle homogeneity was controlled by one organotin measurement from each of 20 bottles. The analyses were performed by GC-MS. The results showed that the homogeneity of the material makes it suitable as a candidate reference material.     

Preparation and certification of creatinine and urea reference materials with certified purity as a traceability source in clinical chemical measurements

Purity certified reference materials (CRMs) are playing a key role in metrological traceability, because they form the basis for many traceability chains in chemistry. Recently, the National Metrology Institute of Japan (NMIJ) has developed two purity CRMs for creatinine (NMIJ CRM 6005-a) and urea (NMIJ CRM 6006-a), because the concentrations of these two compounds are frequently measured in clinical laboratories for monitoring the renal functions. In the certification of purity CRMs, it is essential that the materials have been thoroughly characterized for purity, and the purity should preferably be determined directly by a primary method of measurements. In the development of these two CRMs, we used the purified materials as candidates. The certified values were assigned based on the results of two different methods; acidimetric titration and nitrogen determination by the Kjeldahl method. Since both methods cannot distinguish some impurities from the target compounds, major impurities in the candidate materials were also identified, quantified, and subtracted. These CRMs can provide a traceability link between routine clinical methods and SI units. Presented at BERM-11, October 2007, Tsukuba, Japan.     

Improvements in the determination of eight polycyclic aromatic hydrocarbons through a stepwise interlaboratory study approach

A summarising account of a systematic stepwise approach based on interlaboratory studies carried out by a number of laboratories from European Union and EFTA countries is given. This approach has been designed to improve the analytical state of the art in the determination of selected polycyclic aromatic hydrocarbons in different environmental matrices. The approach resulted in a certification exercise to produce a sewage sludge as Certified Reference Material (CRM). The results of the programme showed that HPLC and GC are equally reliable for PAH analysis at submicrogram to microgram per gram levels in various environmental matrices. Major improvements were achieved during the programme, resulting in reduced coefficients of variation and between-laboratory differences. Several recommendations emerging from the programme experience are presented.     

Reference materials for PAHs in foodstuffs: Results of the certification exercise of two coconut oil reference materials

This certification exercise was the final stage of a stepwise interlaboratory study approach, organized within the SMT-program of the EC, for the development of certified reference materials (CRMs) for the determination of PAHs in foodstuffs. The certification exercise was carried out by thirteen European laboratories using a variety of extraction and clean-up procedures and different analytical procedures. Two different coconut oil materials were certified for their mass fractions of six selected PAHs.     

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.     

Interlaboratory Study to Improve the Quality Control of Methylmercury Determination in Sediment

The results are presented of an interlaboratory study on methylmercury (MeHg) in sediment carried out by a group of European laboratories within the framework of a project managed by the EC Standards, Measurements and Testing Programme (formerly BCR). The aim of this exercise was to evaluate the performance of current methods used for MeHg determination in sediment in order to improve the state-of-the-art prior to the certification of a candidate reference material. The paper describes the organization of the interlaboratory study, the preparation of the sediment material used, the techniques evaluated and the results obtained by the participating laboratories. The outcome of the collaborative project showed that certification could be contemplated, providing that certain analytical techniques were optimized, especially with regard to extraction methods.     

Development and certification of reference materials for residues of organochlorine and organophosphorus pesticides in beef fat ACSL CRM 1 and 2

Beef fat samples were prepared and tested as candidate reference materials for organochlorine and organophosphorus pesticides. The CRMs consisted of beef fat spiked with pesticide solutions. One sample (ACSL CRM 1) was prepared containing close to 0.2 mg/kg of each of the organochlorine pesticides dieldrin and heptachlor epoxide. A second sample (ACSL CRM 2) was prepared containing close to 0.8 mg/kg of each of the organophosphorus pesticides diazinon, chlorpyrifos and ethion. The spiking levels and homogeneity of the materials were verified. The coefficients of variation of 5 analyses carried out to test between-jar homogeneity for each reference material were dieldrin, 3.5%; heptachlor epoxide, 1.1%; diazinon, 2.1%; chlorpyrifos, 1.2% and ethion, 3.1%. No instability in any of these compounds was detected over a twelve month period. The candidate reference materials were found to be suitable for certification by interlaboratory testing. The certification process was based on a two-stage nested design described in ISO Guide 35. Analysis of results reported by collaborating laboratories provided an assessment of the homogeneity of the reference materials. The certified values together with their upper and lower 95% confidence limits are: ACSL CRM 1*Dieldrin*0.199 mg/kg **(0.188, **0.210 mg/kg) *Heptachlor epoxide*0.194 mg/kg **(0.176, **0.212 mg/kg) ACSL CRM 2*Diazinon*0.805 mg/kg **(0.755, **0.855 mg/kg) *Chlorpyrifos*0.790 mg/kg **(0.728, **0.852 mg/kg) *Ethion*0.813 mg/kg **(0.746, **0.879 mg/kg). A certificate for each material was prepared according to the guidelines set out in ISO Guide 31. Received: 25 April 1997 / Revised: 19 August 1997 / Accepted: 28 August 1997     

Development and certification of reference materials for residues of organochlorine and organophosphorus pesticides in beef fat ACSL CRM 1 and 2

Beef fat samples were prepared and tested as candidate reference materials for organochlorine and organophosphorus pesticides. The CRMs consisted of beef fat spiked with pesticide solutions. One sample (ACSL CRM 1) was prepared containing close to 0.2 mg/kg of each of the organochlorine pesticides dieldrin and heptachlor epoxide. A second sample (ACSL CRM 2) was prepared containing close to 0.8 mg/kg of each of the organophosphorus pesticides diazinon, chlorpyrifos and ethion. The spiking levels and homogeneity of the materials were verified. The coefficients of variation of 5 analyses carried out to test between-jar homogeneity for each reference material were dieldrin, 3.5%; heptachlor epoxide, 1.1%; diazinon, 2.1%; chlorpyrifos, 1.2% and ethion, 3.1%. No instability in any of these compounds was detected over a twelve month period. The candidate reference materials were found to be suitable for certification by interlaboratory testing. The certification process was based on a two-stage nested design described in ISO Guide 35. Analysis of results reported by collaborating laboratories provided an assessment of the homogeneity of the reference materials. The certified values together with their upper and lower 95% confidence limits are: ACSL CRM 1*Dieldrin*0.199 mg/kg **(0.188, **0.210 mg/kg) *Heptachlor epoxide*0.194 mg/kg **(0.176, **0.212 mg/kg) ACSL CRM 2*Diazinon*0.805 mg/kg **(0.755, **0.855 mg/kg) *Chlorpyrifos*0.790 mg/kg **(0.728, **0.852 mg/kg) *Ethion*0.813 mg/kg **(0.746, **0.879 mg/kg). A certificate for each material was prepared according to the guidelines set out in ISO Guide 31.     

Development of a reference material for routine performance monitoring of methods measuring polychorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like polychlorinated biphenyls

Matrix-matched environmental certified reference materials (CRMs) are one of the most useful tools to validate analytical methods, assess analytical laboratory performance and to assist in the resolution of data conflicts between laboratories. This paper describes the development of a lake sediment as a CRM for polychorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DLPCBs). The presence of DLPCBs in the environment is of increased concern and analytical methods are being developed internationally for monitoring DLPCBs in the environment. This paper also reports the results of an international interlaboratory study involving thirty-five laboratories from seventeen countries, conducted to characterize and validate levels of a sediment reference material for PCDDs, PCDFs and DLPCBs.     

Reference materials for PAHs in foodstuffs: Results of the certification exercise of two coconut oil reference materials

This certification exercise was the final stage of a stepwise interlaboratory study approach, organized within the SMT-program of the EC, for the development of certified reference materials (CRMs) for the determination of PAHs in foodstuffs. The certification exercise was carried out by thirteen European laboratories using a variety of extraction and clean-up procedures and different analytical procedures. Two different coconut oil materials were certified for their mass fractions of six selected PAHs. Received: 25 May 1997 / Revised: 5 September 1997 / Accepted: 28 September 1997     

Development of a reference material for routine performance monitoring of methods measuring polychorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and dioxin-like polychlorinated biphenyls

Matrix–matched environmental certified reference materials (CRMs) are one of the most useful tools to validate analytical methods, assess analytical laboratory performance and to assist in the resolution of data conflicts between laboratories. This paper describes the development of a lake sediment as a CRM for polychorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (DLPCBs). The presence of DLPCBs in the environment is of increased concern and analytical methods are being developed internationally for monitoring DLPCBs in the environment. This paper also reports the results of an international interlaboratory study involving thirty-five laboratories from seventeen countries, conducted to characterize and validate levels of a sediment reference material for PCDDs, PCDFs and DLPCBs.     

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.     

Some difficult problems still existing in the preparation and certification of CRMs

Differences between particle size measurements of CRMs by various methods are discussed and the importance of the reliability of such data for proper estimation of the homogeneity of the material is emphasized. On the basis of a very simple model, the dependence of the Ingamells' sampling constant on the average mass of a single particle of the material is derived, and theoretical predictions are compared with the experimental results. Various approaches to the certification of the candidate RMs are briefly reviewed. The merits of the approach being used in this laboratory to evaluate data obtained in the interlaboratory comparison, and to assign certified and information values, is discussed. The conclusions are supported by results obtained for selected trace elements by use of "definitive" (primary) and "very accurate" methods. Some observations on the unusual resistance of some biological materials to wet ashing and the resulting possibility of making analytical errors are mentioned.     

Some difficult problems still existing in the preparation and certification of CRMs

Differences between particle size measurements of CRMs by various methods are discussed and the importance of the reliability of such data for proper estimation of the homogeneity of the material is emphasized. On the basis of a very simple model, the dependence of the Ingamells’ sampling constant on the average mass of a single particle of the material is derived, and theoretical predictions are compared with the experimental results. Various approaches to the certification of the candidate RMs are briefly reviewed. The merits of the approach being used in this laboratory to evaluate data obtained in the interlaboratory comparison, and to assign certified and information values, is discussed. The conclusions are supported by results obtained for selected trace elements by use of “definitive” (primary) and “very accurate” methods. Some observations on the unusual resistance of some biological materials to wet ashing and the resulting possibility of making analytical errors are mentioned.     

Projects for the improvement of the quality of chemical speciation analyses in environmental matrices

Summary The release of organometallic compounds and other chemical forms of elements in the environment has caused great concern because of their possible high toxicity. To validate the analytical techniques, the Community Bureau of Reference (BCR) has undertaken a series of projects for the improvement of the quality of determinations of chemical species in environmental matrices. The implementation of these projects follows a stepwise approach involving intercomparisons to detect and remove sources of errors in different phases of the analytical methods and the certification of the compounds in various matrices. The current projects deal with the determination of the extractable content of trace metals in soils (single extraction) and sediment (sequential extraction), forms of aluminium in water, elements with different oxidation states (e.g. As, Cr and Se) and organic forms (e.g. methylated forms of As in solution, methyl-mercury in fish, arseno-betaine and -choline in solutions, triethyl- and trimethyl-Pb compounds in solution, and butyltin compounds in sediment).Abbreviations AAS atomic absorption spectrometry - CVAAS cold vapour AAS - DPP differential pulse polarography - ECD electron capture detector - ETAAS electrothermal AAS - FIA flow injection analysis - FID flame ionisation detector - FLUOR spectrofluorimetry - FPD flame photometric detector - GC gas chromatography - HG hydride generation - HPLC high performance liquid chromatography - HPLC-AES HPLC atomic emission spectrometry - INAA instrumental neutron activation analysis - ICPAES Inductively coupled plasma AES - MS mass spectrometry - QFAAS quartz furnace AAS - RNAA neutron activation analysis with radiochemical separation     

Development of reference materials for paralytic shellfish poisoning toxins

A project was undertaken to develop mussel reference materials that were certified for their mass fractions of saxitoxin and decarbamoyl-saxitoxin. Fifteen laboratories from various European countries participated. Three of these had major responsibility for substantial parts of the work and overall coordination of the project. The project involved 4 main activities: (1) procurement and characterization of calibrants; (2) improvement of analytical methodology; (3) preparation of reference materials, including homogeneity and stability studies; (4) 2 interlaboratory studies and a certification exercise. The joint activities resulted in 3 homogeneous and stable reference materials: 2 lyophilized mussel materials with and without naturally incurred paralytic shellfish poisoning (PSP) toxins, and a saxitoxin enrichment solution. The reference materials were certified with respect to their saxitoxin and decarbamoyl-saxitoxin content. The lyophilized mussel material with PSP toxins (CRM 542) contained <0.07 mg saxitoxin x 2HCl/kg and 1.59 +/- 0.20 mg decarbamoyl-saxitoxin x 2HCl/kg. The lyophilized mussel material without PSP toxins (CRM 543) contained <0.07 mg saxitoxin x 2HCl/kg and <0.04 mg decarbamoyl-saxitoxin x 2HCl/kg. The certified value of the saxitoxin mass fraction in the saxitoxin enrichment solution (CRM 663) was 9.8 +/- 1.2 microg/g.     

Development of a simple desulfurization procedure for the determination of butyltins in complex sediment samples using gas chromatography-pulsed flame photometric detection

In this study a rapid solid phase extraction (SPE) procedure was developed to minimize the effect of different sulfur species for the determination of butyltin in sediments. The organosulfur species and organotins were firstly retained on C8 cartridges and then organotins were selectively eluted and analyzed by gas chromatography-pulsed flame photometric detection (GC-PFPD). Optimal conditions for the SPE procedure were obtained using an experimental design approach. The method's accuracy was established by analyzing a certified reference material (CRM), BCR-646 freshwater sediment. The experimental values were found to be in agreement with the assigned values for butyltins. Finally, complex sediment samples collected from a Chilean harbor were analyzed using this methodology to demonstrate its analytical potential for the determination of butyltin in environmental samples.