Quality and comparability of measurement of potentially toxic elements in urban soils by a group of European laboratories

A study has been conducted to assess the quality and comparability of measurement of aqua-regia-soluble cadmium, chromium, copper, iron, manganese, nickel, lead, and zinc in urban soils within a small cohort of European research laboratories specializing in soil science or environmental analytical chemistry. An initial survey indicated that highly variable levels of analytical quality control (e.g. use of certified reference materials) were routinely implemented in participant laboratories. When a set of soil samples—differing in metal contents and in characteristics such as pH and organic-matter content—were exchanged and analysed, approximately 20% of results differed from target values by more than 25%. A principal-component analysis was applied to data for chromium, copper, nickel, lead, and zinc, and proved successful in assessing overall laboratory performance. The study indicates that greater prominence needs to be given to quality assurance and control if comparable data are to be generated in international, collaborative research projects.     

Quality assurance of X-ray spectrometry for chemical analysis

Three different techniques, energy dispersive X-ray fluorescence, total reflection X-ray fluorescence and particle induced X-ray emission were used to initiate an evaluation program on quality assurance (QA) procedures applied to X-ray spectrometry for chemical analysis. The use of standard methodologies to assure the statistical control of measurement data is the main objective of this work. Certified Reference Materials were used and up to 15 certified elements were analyzed to carry out the QA procedures. For the internal quality control, z-scores were calculated and control charts were produced. The plotted elemental data illustrate statistically controlled methodologies for the majority of the determinations. Even the cases where the control charts exhibit values out of control limits, the z-scores are below 3 in absolute value, indicating satisfactory results. Concerning external quality control the statistical methods applied showed that the results obtained for the three techniques are comparable, although some significant differences occur, mainly due to sample preparation. Therefore, the techniques are traceable to certified reference materials and the data gathered so far, enable to initiate a database for QA procedures.     

Evaluation of measurement uncertainties for the determination of total metal content in soils by atomic absorption spectrometry

In this work estimation of measurement uncertainties associated with the total metal content in soils was done by an intralaboratory approach based on method validation and quality control data, and using two certified reference materials (CRM). CRM and soil samples were analyzed following procedures based on the methods that are applied to silicate materials. All elements were determined by atomic absorption spectrometry following a quality assurance program previously established. Quality control actions were implemented in order to provide reliable data. The precision under within-laboratory reproducibility conditions was estimated from triplicate analysis. The trueness component was determined as recovery of the analyte from CRMs: soil sample, SO-2 and river clay sediment, LGC 6139. Combined measurement uncertainty was expressed in terms of precision and recovery uncertainties and the later further split on CRM replicate analysis and uncertainty of the certified value components. The results obtained are critically discussed on the basis of the different contributions. For the selection of the reference material, the CRM dependent terms are critically compared in order to fulfill specific requirements. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Computer-aided quality assurance and certification of reference materials in the DANREF network

A network between 6 Danish laboratories with experience in quality assurance and quality control has been established with the aim of supporting the use and production of high-quality certified reference materials in Denmark. One of the tasks of the network was to develop a PC-program for computer-aided quality assurance and certification of reference materials produced by the network laboratories. This paper describes the design and features of the DANREF PC-program and shows examples of computer-aided evaluation of selected studies on reference materials. The program provides the network laboratories with the possibility to carry out harmonized statistical evaluation and documentation of homogeneity, stability and intercomparison studies in accordance with international guidelines and standards, e.g. ISO guide 35.     

Quality of electron probe X-ray microanalysis determinations obtained from laboratory reference materials of the coppery alloys and basaltic glasses

Nine coppery alloys and five basaltic glasses have been quantitatively evaluated as the reference materials to employ in electron probe X-ray microanalysis. The optimum conditions for measurements were selected considering the dependence of intensity and detection limit on the conditions of the X-ray radiation excitation and analytical signal recording. The homogeneity of basaltic glasses and coppery alloys has been examined. The dependence of electron probe X-ray microanalysis accuracy on the homogeneity of reference materials was studied in the reference materials of coppery alloys.Six data sets comprising the average concentrations, standard deviations, relative standard deviations, confidence interval and the z-score of data quality were calculated for 50 control samples: 10 alloys, 14 glasses, 2 metals, 24 minerals and oxides. The average compositions of every control sample were derived in 8–16 analyses. The measured values were corrected for matrix effects applying the original program. These series of concentrations have been compared with each other and with the certified/recommended values using 2-pair selective Student's t-test.The results gained from both laboratory reference materials and certified glass reference materials show comparable accuracy. The quality of all available results complies with the “applied geochemistry” category of performance (2nd category). The laboratory reference materials give comparable accuracy to certified reference materials and can be used for calibrating microprobe techniques, as well as data quality control. The application of laboratory reference materials in microanalysis of silicate minerals and coppery alloys allows reliable analytical data to be acquired. The applications in mineralogy and metallurgy can be extended successfully to the targets when certified reference materials are not available.     

The role of certified reference materials in ensuring the quality of spectrochemical measurements – the present status in Romania

 The objective of quality assurance programme for spectrochemical measurements is to reduce the measurement errors to accepted limits. Reference materials are being widely used as measurement standards in the fields of industrial production, environmental protection and clinical chemistry, and are playing an important role in ensuring the quality of measurement results. This paper presents some aspects, practices and examples of the activity of the Reference Materials Laboratory of the National Institute of Metrology, Bucharest, in the field of spectrochemical measurements. An attempt to describe the role and use of reliable certified reference materials to ensure the quality of spectrochemical measurements is presented. A short review of the locally available certified reference materials used in spectrochemical measurements is given. The use of reference materials data in estimating the measurement uncertainty is discussed. An interlaboratory comparison, recently organized in Romania, is also presented as a useful response to the need for quality assurance of spectrochemical results. Received: 20 March 1999 / Accepted: 25 February 2000     

k0-NAA, a valuable tool for reference-material producers

The main concern of producers of certified reference materials (CRM) is the preparation of high-quality products with demonstrated homogeneity and stability, combined with a well established set of certified characteristics. CRM producers must, furthermore, comply with other constraints imposed by the ISO Guide 34: ·*production processes, production control, and certification analyses should be performed by expert laboratories, using validated protocols documented in their respective quality assurance manuals; ·*laboratory mean values and the corresponding “expanded” uncertainties, must be used for the determination of the certified values, as recommended by the ISO Guide to the Expression of Uncertainties in Measurements (GUM); and ·*when possible, traceability of the certified value to the SI units, using appropriately validated and/or primary methods, must be ensured. k₀-NAA, i.e. neutron activation analysis with k₀ standardization, is one of the analytical techniques implemented at the Reference Material Unit of IRMM; it meets the first two requirements.     

Certified reference materials for the quality control of EDTA- and acetic acid-extractable contents of trace elements in sewage sludge amended soils (CRMs 483 and 484)

 The ecotoxicity and mobility of trace elements in soils are often evaluated through analytical results resulting from operationally-defined determinations (single and sequential extractions), e.g. based on EDTA, acetic acid etc. extractions. The significance and comparability of these results is highly dependent on the procedures used (standardized protocols or standards adopted by international bodies) and their quality control relies on the availability of reference materials certified following these strictly applied procedures. Recognizing the need to harmonize some of the extraction schemes currently used for soil analysis, the Measurements and Testing Programme (formerly BCR) has organized a series of interlaboratory studies, the first aim of which was to evaluate EDTA- and acetic acid-extraction procedures and the second objective was to certify reference materials for their extractable trace element contents. Two sewage amended soils have been prepared for this purpose, originating respectively from Scotland and Catalonia. This paper describes the preparation, homogeneity and stability studies, and gives an overview of the certification campaign. Received: 6 May 1996/Revised: 14 June 1996/Accepted: 27 June 1996     

Analytical quality control by solid sampling GFAAS in the production of animal tissue reference materials: lead and cadmium in bovine liver reference materials

Summary The function of solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) in the laboratory-internal preparation, production and standardization of bovine liver reference material is described. Analytical quality assurance was achieved by using a wet digestion decomposition procedure and GFAAS (WD-GFAAS) as well as three different methods of SS-GFAAS. It will be shown, that SS-GFAAS is an adequate and efficacious method of analytical quality control in the production of reference materials. Details are given about the preliminary steps of sample selection and preparation, applying SS-GFAAS both as a screening method and for the detection of contamination during the production of the reference materials. The element contents of the four bovine liver materials measured after decomposition with nitric acid in the open system by GFAAS and also by Flame-AAS, using the slotted tube atom trap, are compared statistically with the results obtained by SS-GFAAS. In solid sampling analyses three different systems were applied: a solid sampling ZAA-spectrometer with platform-boat, a D₂AA-spectrometer with solid sampling graphite tube and platform-drawer and an autoprobe-D₂AA-spectrometer with solid sampling autoprobe and graphite tube.     

Quality Assurance in Mycotoxin Analysis

Mycotoxin analysis in food and biological fluids is receiving more and more concern, in view also of increasing involvement by the European Union regarding legislation. Basically all the analytical steps regarding mycotoxin analysis have to be performed according to accurate criteria which are strictly connected to the quality of results in terms of reliability. The only rationale for reducing this difficulty is to apply quality assurance principles. Quality assurance principles define, in fact, the rules to be observed for performing this analysis with a degree of uncertainty that is as low as may be possible. In particular sampling techniques, if carried out improperly, give rise to uncertainty concerning the representativeness of samples that is so critical as to induce a dramatic source of errors in the final analysis. Therefore it seems appropriate to plan training courses for personnel on the various side-effects related to the available sampling and subsampling techniques depending on the commodity. Other contributions to the overall error derive from improper methodologies used by technicians in the pre-treatment step of the samples (incorrect use of glassware, standard solutions, etc.), and finally from the operations involved in the whole analytical procedure. In addition, the use of reference materials and certified reference materials together with the utilization of validated methods of analysis will be dealt with as concrete procedures for obtaining the certainty of final results of good quality. This aspect takes on a relevant outcome if applied to official control activities from authorized bodies acting at a national level.     

Nuclear forensics—metrological basis for legal defensibility

The admissibility of nuclear forensics measurements and opinions derived from them in US Federal and State courts are based on criteria established by the US Supreme Court in the case of Daubert v. Merrell Dow and the 2000 Amendment of Rule 702 of the Federal Rules of Evidence. These criteria are being addressed by new efforts that include the development of certified reference materials (CRMs) to provide the basis for analytical method development, optimization, calibration, validation, quality control, testing, readiness, and declaration of measurement uncertainties. Quality data is crucial for all stages of the program, from R&D, and database development, to actual casework. Weakness at any point in the program can propagate to reduce the confidence of final conclusions. The new certified reference materials will provide the necessary means to demonstrate a high level of metrological rigor for nuclear forensics evidence and will form a foundation for legally defensible nuclear chemical analysis. The CRMs will allow scientists to devise validated analytical methods, which can be corroborated by independent analytical laboratories. CRMs are required for ISO accreditation of many different analytical techniques which may be employed in the analysis of interdicted nuclear materials.     

Quality assurance in environmental research: emissions and fate of platinum

Summary Quality assurance in environmental research is related to reliable analytical methods. According to this fact great efforts were taken in the German Cooperative Project sponsored by the Ministry of Research and Technology Emissions of Precious Metals to ensure the quality of all analytical data from various research groups. As there are only few certified reference materials (CRMs) for platinum available and the application of reference materials is an important measure in quality assurance and quality control actions in every laboratory, several materials have been prepared with low and elevated platinum contents as reference samples for this project. These reference samples were a catalyst sample with elevated platinum content, a dust reference material with low platinum content and a catalyst reference material with low platinum content. With these reference samples and the Canadian geological reference material SU-1a interlaboratory studies were conducted and the results of these are presented in this paper.Dedicated to Professor Dr. Wilhelm Fresenius on the occasion of his 80th birthday     

Electrothermal atomic absorption spectrometric determination of vanadium in extracts of soil and sewage sludge certified reference materials after fractionation by means of the Communities Bureau of Reference modified sequential extraction procedure

A modified three-step sequential extraction procedure proposed by the Commission of European Communities Bureau of Reference (BCR) was applied to certified reference materials of three different soil groups (rendzina, luvisol, cambisol) and sewage sludge of different composition originating from a municipal water treatment plant in order to assess potential mobility and the distribution of vanadium in the resulting fractions. Analysis of the extracts was carried out by electrothermal atomic absorption spectrometry with Zeeman background correction using transversely heated graphite atomizers. Extracts showed significant matrix interferences which were overcome by the standard addition technique. The original soil and sludge certified reference materials (CRMs) and the extraction residue from the sequential extraction were decomposed by a mixture of HNO₃–HClO₄–HF in an open system. The content of V determined after decomposition of the samples was in very good agreement with the certified total values. The accuracy of the sequential extraction procedure was checked by comparing the sum of the vanadium contents in the three fractions and in the extraction residue with the certified total content of V. The amounts of vanadium leached were in good correlation with the certified total contents of V in the CRMs of soils and sewage sludge. In the soils examined, vanadium was present almost entirely in the mineral lattice, while in the sewage sludge samples 9–14% was found in the oxidizable and almost 25% in the reducible fractions. The recovery ranged from 93–106% and the precision (RSD) was below 10%.     

Determination of Hg,As, Pb,and Cd in Orchard Soils by Sequential Injection Vapor Generation Atomic Fluorescence Spectrometry

An analytical procedure was developed for determination of Hg, As, Pb, and Cd in soil samples using sequential injection vapor generation atomic fluorescence spectrometry (SI-VG-AFS) with sample preparation by microwave digestion system. The effects of analytical conditions on the fluorescence intensity were investigated and optimized. Under the optimized condition, the detection limits of the method were 5, 68, 40, and 3 ng L^?1 for Hg, As, Pb, and Cd, respectively. The accuracy of method was verified by the determination of the certified reference soil, and the recoveries for Hg, As, Pb, and Cd were in the range of 98.7–106.1%. The proposed method has been successfully applied to determine the heavy metals in navel orange orchard soils in Ganzhou, and the environmental quality of the orchard soils was assessed based on the content of the heavy metals. According to the second criterion of environmental quality standard for soils, Pb content in all soil samples collected from the orchards of 18 districts were within safe limits, but a few orchards were slightly contaminated with Hg, As, and Cd. Comparison of heavy metal mean concentrations with the safe limits of environmental quality standard for soils, the quality of Ganzhou navel orange orchard soils were in line with the request of the green food production base.     

The role of statistics in quality assurance

Summary The quality of data, which is to say its accuracy, must be known whenever it is to be used for purposes of decision. This is only possible as it is produced by a valid analytical system operating in a state of statistical control. A quality assurance program should be established, consisting of quality control of the analytical system and quality assessment of the data that are produced. Data quality objectives should be established for every measurement situation and the accuracy attained must be within these limits. Ideally, the attained accuracy should exceed the required accuracy by a factor of three, at a minimum. The estimation of attained accuracy is best made using reliable reference materials. When they are not available, spikes may be used with lesser confidence. No matter what estimation techniques are used, decisions must be made on the basis of statistical tests of significance. The evaluation of accuracy is a continuing operation and facilitated by the use of appropriate control charts. The paper discusses the above described concepts and summarizes the techniques most useful for evaluating the accuracy of analytical data.

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Die Rolle der Statistik in der Qualitätssicherung

     

k0-NAA, a valuable tool for reference-material producers.

The main concern of producers of certified reference materials (CRM) is the preparation of high-quality products with demonstrated homogeneity and stability, combined with a well established set of certified characteristics. CRM producers must, furthermore, comply with other constraints imposed by the ISO Guide 34: production processes, production control, and certification analyses should be performed by expert laboratories, using validated protocols documented in their respective quality assurance manuals; laboratory mean values and the corresponding "expanded" uncertainties, must be used for the determination of the certified values, as recommended by the ISO Guide to the Expression of Uncertainties in Measurements (GUM); and when possible, traceability of the certified value to the SI units, using appropriately validated and/or primary methods, must be ensured. k0-NAA, i.e. neutron activation analysis with k0 standardization, is one of the analytical techniques implemented at the Reference Material Unit of IRMM; it meets the first two requirements.     

Certified reference materials (CRM's) for the quality of measurement

Summary A survey of procedures for analytical quality control with emphasis on the use of certified reference materials is given. Requirements for the use and for the preparation of reference materials are presented.     

Analytical quality control program used by the trace elements in foods and diets sub-network of the FAO European cooperative network on trace elements

Summary The analytical quality control program employed by the ongoing FAO study on 14 trace elements in nationally representative staple foods of European countries is presented. The analytical quality control used is based on: 1) precautions taken to avoid trace element contaminations or losses during sampling and sample handling; and, 2) on methods used to guarantee that the actual determinations yield correct results. The precautions are presented. A number of certified biological reference materials (RMs) were used to validate the analytical methods employed. The following staple food RMs were also prepared: wheat flour, potato powder, animal muscle (pork) and milk powder. They were tested for homogeneity and subjected to an interlaboratory comparison study on the basis of which recommended values for trace element concentrations were defined. Further, the mean relative standard deviation for the 95% confidence limits of the medians in all RMs was below 5% for Ca, Mg and Zn; below 10% for Mn; below 15% for Fe, Cu and Se; and below 25% for Mo and Ni. These RMs were used to control the analytical quality of the trace element determinations in the actual samples. It is concluded that important contaminations were avoided in sampling and sample handling and that use of the RMs described was necessary to guarantee the analytical quality of the results.     

Harmonized protocol and certified reference material for the determination of extractable contents of phosphorus in freshwater sediments--a synthesis of recent works.

An analytical protocol for the determination of the extractable phosphorus contents in freshwater sediments has been harmonized through interlaboratory studies in the frame of the Standards Measurements and Testing Program of the European Commission. A homogeneous and stable sediment reference material has been prepared and certified on the basis of this protocol named SMT protocol, and will be available in spring of 2001. The SMT protocol, together with the reference material, are useful tools in the field of water management, especially at a time when quality assurance and data comparability are of paramount importance in laboratory analysis. The knowledge of the bioavailable forms of phosphorus is important not only for sediments but also for sludge and soils. Therefore, the SMT protocol could be extended to these materials and new CRMs could be prepared. The SMT protocol was used in a study of a reservoir, which allowed to calculate the P stock, therefore helping to predict the restoration delay of the lake. The paper describes the protocol and the CRM, and gives a brief outline of the case study.     

Microwave digestion of sediment, soils and urban particulate matter for trace metal analysis

A microwave digestion technique was developed to determine the content of nine heavy metals in sediments and soils. The digests were subsequently analysed by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). The metals determined were Ca, Mg, Fe, Mn, Zn, Cr, Cd, Cu, Pb and V. The digestion was achieved by using an acid mixture of HNO₃, HF and distilled H₂O. The experimental study was conducted using four standard reference materials (SRMs): sewage sludge (LGC6136), marine sediment (PACS-1), urban particulate matter (NIST 1648) and coal carbonisation site soil (LGC6138). Two different programs were examined to determine which was optimal for the digestion of real environmental samples. The accuracy and precision of the two digestion programs for the analysis of the SRMs were compared. From the results obtained, the microwave program providing a maximum of power of 650 W and a cycle time of 51 min resulted in the best analytical performance. The experimental results obtained were in good agreement with the certified values and demonstrated that the proposed method is precise and accurate.