An interlaboratory study to improve the quality of chemical and biological measurements in waste water

 Analyses of waste water are routinely performed to monitor the level of contamination. To verify the quality of such determinations the National Institute of Chemistry, with the support of the Ministry of Environment and Spatial Planning and the Slovenian Accreditation Agency, organizes interlaboratory comparisons. Over the last 3 years, five interlaboratory trials named "MPP-Waste Water" were organized. Each round attracted around 50 participants, mostly from Slovenia and some from abroad, which enabled the testing of SIST ISO methods or alternative methods. We prepared samples for determination of harmful substances that are important for the characterization of waste water; physico-chemical parameters (pH), global parameters – chemical oxygen demand (COD), biochemical oxygen demand (BOD₅), metals (mercury, cadmium, copper, nickel, lead and chromium (VI)), nutrients (ammonia and total phosphorus), anions (chloride, nitrite, nitrate, sulphate) and toxicity to Daphnia magna. For the analysis of each parameter we prepared two samples at two different concentration levels. The materials used in the proficiency testing were carefully prepared and their homogeneity and stability were verified. The purpose of this scheme was to enable participants to check their day-to-day analytical performance. The results should enable the participants to improve the quality of their analyses.

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Received: 24 October 2002 Accepted: 2 January 2003

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Acknowledgments We would like to thank the Ministry of Environment and Spatial Planning and the Ministry for Education, Science and Sport for providing financial support. We would like to thank members of the Technical Committee: Mrs. Marjana Kovacˇicˇ, Dr. Katja Otrin-Debevc, Prof. Dr. Marjan Veber and Mrs. Boža Gregorc for their valuable support. Special thanks are due to Dr. Adrian Van der Veen who helped us in running the first PT.

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Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia

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Correspondence to M. Cotman     

Endogenous and synthetic steroids in bovine urine – Preparation of in-house reference material,stability studies and results of a proficiency test

Within the framework of the German National Residue Control Plan a specific number of samples of animal origin have to be analysed for natural and synthetic steroids each year. As a measure of external quality control of the methods applied in routine analysis a proficiency test was carried out. To this end, in-house reference material containing incurred residues of 17α- and 17β-nortestosterone and 17α- and 17β-estradiol as well as fortified residues of 17α-methyltestosterone and 17α-trenbolone in bovine urine were produced. Before sending the proficiency test material to the participants, the homogeneity of all samples was tested and confirmed. Furthermore extensive short- and long-term stability studies were carried out.     

Proficiency testing as a tool for implementing internal quality control: the case of ochratoxin A in cocoa powder

This paper describes the interlaboratory study aimed at assessing the performance of 18 laboratories (14 national and 4 European) for Ochratoxin A (OTA) determination in cocoa powder samples. The study was tested at three levels of OTA covering the range in which presumably European regulatory limits could fall in the near future. For the extraction step, almost all laboratories used an aqueous solution of sodium hydrogen carbonate with the exception of one laboratory using dichloromethane consistently with the ELISA procedure adopted in the study. The clean-up step was performed by utilizing the immunoaffinity columns by the two main manufacturers (R-Biopharm Rhone and VICAM) and for the quantitative analysis, HPLC was used by all the participants except one using ELISA. From the output of the study, it can be concluded that at low level (0.19 μg/kg) 10 out of 18 (56%), at medium level (0.45 μg/kg) 11 out of 18 (61%), and at high level (1.45 μg/kg) 12 out of 18 (67%) results fell within the satisfactory ranges. This interlaboratory study provides an estimate of the performance of national and European laboratories involved in OTA determination in cocoa powder samples, which sounds extremely valuable in view of potential future legislation by the European Commission.     

Preparation and characterization of a proficiency test material “Polish mushrooms” supported by the International Atomic Energy Agency (IAEA), Vienna

Mushroom reference material has been prepared and characterized for use in proficiency test exercises within the frame of an IAEA Interregional Technical Cooperation Project. Laboratories from 14 countries provided results for homogeneity testing and the assignment of property values. The contents of 11 elements have been assigned. The material was used for conducting a proficiency test in Poland and the results obtained by Polish laboratories are presented and discussed.     

Comparability and compatibility of proficiency testing results in schemes with a limited number of participants

Comparability and compatibility of proficiency testing (PT) results are discussed for schemes with a limited number of participants (less than 20–30) based on the use of reference materials (RMs) as test items. Since PT results are a kind of measurement/analysis/test result, their comparability is a property conditioned by traceability to measurement standards applied in the measurement process. At the same time, metrological traceability of the certified value of the RM (sent to PT participants as test items) is also important, since the PT results are compared with the RM certified value. The RM position in the calibration hierarchy of measurement standards sets the degree of comparability for PT results, which can be assessed in the scheme. However, this assessment is influenced by commutability (adequacy or match) of the matrix RM used for PT and routine samples. Compatibility of PT results is a characteristic of the collective (group) performance of the laboratories participating in PT that can be expressed as closeness of the distribution of the PT results to the distribution of the RM data. Achieving quality-of-measurement/analysis/test results in the framework of the concept “tested once, accepted everywhere” requires both comparability and compatibility of the test results.     

Local comparability of proficiency testing results: determination of concrete slump and compressive strength values

A proficiency testing (PT) scheme is developed for comparability assessment of results of concrete slump and compressive strength determination. The scheme is based on preparing of a test portion/sample of a concrete in-house reference material (IHRM) at a reference laboratory (RL) in the same conditions for every PT participant. Therefore, in this scheme IHRM instability is not relevant as a source of measurement/test uncertainty, while intra- and between-samples inhomogeneity parameters are evaluated using the results of RL testing of the samples taken at the beginning, the middle and the end of the PT experiment. The IHRM assigned slump and compressive strength values are calculated as averaged RL results. Their uncertainties include the measurement/test uncertainty components and the components arising from the material inhomogeneity. The test results of 25 PT participants were compared with the IHRM assigned values taking into account both the uncertainties of the assigned values and the measurement/test uncertainties of the participants. Since traceability of the IHRM assigned values to the international measurement standards and SI units cannot be stated, local comparability of the results is assessed. It is shown, that comparability of the slump and compressive strength determination results is satisfactory, while uncertainty evaluation for slump results requires additional efforts.     

An interlaboratory study as useful tool for proficiency testing of chemical oxygen demand measurements using solid substrates and liquid samples with high suspended solid content

In 2008, the first Proficiency Testing Scheme of Chemical Oxygen Demand (1^stCOD-PT^ADG) was conducted to assess the results obtained for different research groups whose field work is mainly anaerobic digestion. This study was performed using four samples, two solid samples as raw materials and two solid samples to prepare high concentration suspended solid solutions. Invitations were sent to a large number of laboratories, mainly to anaerobic digestion research groups. Finally, thirty labs from sixteen countries agreed to participate, but for different reasons four participants could not send any data. In total, twenty-six results were reported to the COD-PT coordinator.This study showed the importance of continuous participation in proficiency testing (PT) schemes in order to compare the results obtained. Taking into account the lack of a general standard method and high quality certified reference materials (CRMs), the traceability of COD determination is not currently easy to check. In addition, the spread of participants’ results obtained was high and pointed to the advisability of using consensus values due to their unreliability. Therefore, the theoretical oxygen demand (ThOD) values were considered as assigned values for all the samples analysed. On the other hand, in this PT the established standard deviation (ESD) has been determined by the Horwitz modified function.Participants of this 1^stCOD-PT^ADG were asked to give a short report on the analytical method used. Although all the participants used potassium dichromate as their oxidant reagent, their experimental procedures were very different. With the purpose of comparing the results obtained, the different experimental conditions used were classified into five methods, corresponding to two main categories, open and closed reflux. The performance of laboratories was expressed by the z-score, whose value is considered satisfactory when z-score ≤±2. The overall analytical data evaluation showed that 64% of z-scores obtained were outside the accepted limits.     

Practical uses of proficiency testing as valuable tools for validation and performance assessment in environmental analysis

Besides their role as an external quality control tool, PT results or samples could be used as an alternative to fulfil some of the quality assurance requirements such as analytical precision, uncertainty assessment, and internal quality control. This additional use of proficiency testing could help laboratories to reduce the financial impact of their quality assurance process. The purpose of this paper is to highlight some practical uses of PT results or samples in the environmental analytical field, which have been implemented at ISSeP (Institut Scientifique de Service Public), either for method validation or for internal quality control.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Influence of sampling to the homogeneity of Cu-Ti-Zn alloy samples for the analyses with glow discharge optical emission spectroscopy

 Using Plackett-Burman experimental design the parameters of different ways of sampling (design and materials of the sampling mold, conditions of solidification of samples) that influence on the homogeneity of copper-titanium-zinc alloy samples in the production of titanium zinc were determined. Based on these results, the homogeneity of samples taken with two different sampling molds was investigated with GD-OES technique regarding alloyed elements (Cu and Ti) and impurities (Fe, Pb, Cd, Sn, Al) and was evaluated with analysis of variance (ANOVA). For Cu, Ti and Fe an overall (combined) uncertainty for different sampling approaches were estimated and compared to the expanded uncertainty evaluated without including the uncertainty due to sampling. Received: 28 October 2002 Accepted: 2 January 2003 Presented at CERMM-3, Central European Reference Materials and Measurements Conference: The function of reference materials in the measurement process, May 30–June 1, 2002, Rogaška Slatina, Slovenia Correspondence to B. Kokliˇc     

Use of uncertainty estimates as reported by participants in proficiency testing for the evaluation of their results: pros and cons

The aim of this paper is to study the measurement uncertainties reported in proficiency tests (PTs) using examples from PTs in the environmental sector and to compare the obtained measurement uncertainty estimates using different approaches. In addition, the paper focusses on the differences between the z-score and the zeta score. Since the year 2000, the Finnish Environment Institute has asked participants to report analytical methods as well as measurement uncertainties in connection with PT results. The measurement uncertainties of the assigned value have also been evaluated. On the basis of the results, the measurement uncertainties reported by the participants varied greatly. Participants often reported underestimated measurement uncertainties, but overestimated uncertainties were also reported. At the moment, it seems as if performance assessment should be based on the z-score because of a number of significant over- and underestimated measurement uncertainties. The zeta score should be used for information and educational purposes mainly.     

QUASIMEME results of laboratories involved in the German Marine Monitoring Programme for the North and Baltic Seas

This case study is written for laboratories in the German Marine Monitoring Program (GMMP) for the North and Baltic Seas in order to give support to the assessment of proficiency testing results for their external quality assurance. A second issue is to provide a practical, understandable and common way for the calculation of laboratory performance parameters, so-called combination scores. In this paper, the GMMP laboratory proficiency testing results of QUASIMEME (Quality Assurance of Information for Marine Environmental Monitoring in Europe) Laboratory Performance Studies for the last 5 years were reviewed. Combination scores for organochlorine pesticides and chlorinated biphenyls in marine sediment are presented and explained. However, the assessment approach is very general and should be applicable to most testing laboratories in the chemical field.Presented at the Eurachem PT Workshop September 2005, Portorož, Slovenia     

Anionic microemulsion to solvent stacking for on‐line sample concentration of cationic analytes in capillary electrophoresis

The common SDS microemulsion (i.e. 3.3% SDS, 0.8% octane, and 6.6% butanol) and organic solvents were investigated for the stacking of cationic drugs in capillary zone electrophoresis using a low pH separation electrolyte. The sample was prepared in the acidic microemulsion and a high percentage of organic solvent was included in the electrolyte at anodic end of capillary. The stacking mechanism was similar to micelle to solvent stacking where the micelles were replaced by the microemulsion for the transport of analytes to the organic solvent rich boundary. This boundary is found between the microemulsion and anodic electrolyte. The effective electrophoretic mobility of the cations reversed from the direction of the anode in the microemulsion to the cathode in the boundary. Microemulsion to solvent stacking was successfully achieved with 40% ACN in the anodic electrolyte and hydrodynamic sample injection of 21 s at 1000 mbar (equivalent to 30% of the effective length). The sensitivity enhancement factors in terms of peak height and corrected peak area were 15 to 35 and 21 to 47, respectively. The linearity R² in terms of corrected peak area were >0.999. Interday precisions (%RSD, n = 6) were 3.3–4.0% for corrected peak area and 2.0–3.0% for migration time. Application to spiked real sample is also presented.     

It is never too early to introduce measurement and quality concepts: a proficiency test competition for schools and colleges

 This paper describes how the LGC and the Nuffield Curriculum Projects Centre set up an analysis competition for 16- to 19-year-old students. The competition was based on the procedure for proficiency testing. The results and reports give some insight into current standards of teaching and learning about analytical procedures and the treatment of uncertainty in courses at this level. The outcomes justify the production of a good-practice guide for teachers so that they can introduce concepts of valid analytical measurement into pre-university courses.     

A definitive RNAA method for determination of selenium in biological samples: uncertainty evaluation and assessment of degree of accuracy

This article describes work on the development of a highly accurate RNAA method for determination of selenium in biological samples. The analytical post-irradiation procedure is based on a combination of cation-exchange and extraction chromatography with final selective and quantitative fixation of selenium on a column packed with 3,3′-diaminobenzidine (DAB) supported on Amberlite XAD4, followed by gamma-ray spectrometric measurement. The suitability and accuracy of the method was demonstrated by analysing CRMs with certified selenium content. The uncertainty budget for Se determination in standard reference material Peach Leaves NBS 1547 was estimated; the combined standard uncertainty was calculated as 1.7%. The described method fulfils all the criteria for definitive methods. It was subsequently used for determination of selenium in biological materials intended as new CRMs and proficiency test samples.     

Principal component analysis and hierarchical cluster analysis for homogeneity evaluation during the preparation of a wheat flour laboratory reference material for inorganic analysis

The development of a homogeneity study during the preparation of a wheat flour laboratory reference material (LRM) for use in the quantification of metals and metalloids is reported. Inductively coupled plasma optical emission spectrometry (ICP OES) was used with validation performed using a certified reference material of wheat flour furnished by the National Institute of Standards and Technology (NIST). Copper, iron, manganese, phosphor, strontium and zinc were studied in a within-bottle homogeneity test whereas barium, copper, iron, zinc, manganese, strontium, phosphor and calcium were included in a between batch homogeneity study. Standard univariate analysis of variance (ANOVA) was performed for all analytes. Furthermore an alternative multivariate analysis for homogeneity is proposed by performing ANOVA of principal component scores and by inspection of principal component score graphs and hierarchical cluster analysis dendrograms. The ANOVA F-tests performed on both, the univariate and multivariate parameters, were not significant at the 95% confidence level and indicated homogeneous wheat flour samples. A 10 kg amount of material was processed, which was distributed in 100 bottles, each containing 100 g. For the between-bottle homogeneity test, three replicates were taken from each of 10 bottles selected of the 100 bottles obtained. The results were evaluated using an F-test, which demonstrated no significant difference for the between-bottle results. It is indicative that this material is homogeneous. Afterwards, the influence of the sample mass on the homogeneity of the material was also evaluated by quantification of the elements for 100, 300, 500, 700 and 1000 mg sample masses with all the experiments being performed in triplicate. The F-test was also used for evaluation of these results and demonstrated that the material is homogeneous for masses taken in the 100 to 1000 mg range. All these results were further evaluated employing the principal component analysis (PCA) and hierarchical cluster analysis (HCA) multivariate techniques. Both techniques also demonstrated that the material is perfectly homogeneous for use as laboratory reference material.     

The development of gas standards and calibration techniques for measurements of vehicle, aircraft and industrial emissions, natural gas, occupational exposure and air quality

 The National Physical Laboratory (NPL) is involved in the dissemination of nationally traceable standards to which measurements of air quality, occupational exposure and air pollution source emissions, and natural gas analyses, can be referenced. This has required the development of national primary gas standards using absolute gravimetric and other techniques, and the development of dynamic calibration techniques for gaseous species which would be unstable in high-pressure cylinders. The methodology used for preparing gas standards gravimetrically is described, together with the rigorous quality assurance measurements and consistency checks which are used to demonstrate their accuracy and stability. The uncertainty budget assigned to these standards will also be summarised. NPL primary standards are used to certify traceable 'secondary' gas standards which are disseminated so as to ensure the accuracy of gas analysis measurements. Examples of the applications of these secondary standards are presented. The gas standards are employed in proficiency testing of industrial stack-testing organisations, and results of the initial rounds are presented. NPL gas standards are also now being used as the basis of the United Kingdom Environment Agency's new type-approval and certification scheme for continuous industrial stack-emission analysers. A recent important international initiative, in the field of gas analyses, is the agreement by national standards laboratories across the world to demonstrate the equivalence of their calibrations, by means of key comparisons between them. These worldwide key comparisons are complemented in Europe through the EUROMET initiative which seeks to establish the equivalence and comparability of calibration standards held at national standards laboratories across Europe. Examples of these intercomparisons are presented. Received: 23 March 2000 / Accepted: 18 August 2000     

A liquid chromatography/tandem mass spectrometric multi-mycotoxin method for the quantification of 87 analytes and its application to semi-quantitative screening of moldy food samples

This paper describes the extension of a previously published method based on liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI-MS/MS) from 39 to currently 87 analytes. Besides the mycotoxins for which regulated concentrations exist, the method now comprises not only almost all mycotoxins for which standards are commercially available, but also a number of other important metabolites produced by fungi involved in food spoilage. The method is based on a single extraction step using an acidified acetonitrile/water mixture followed by analysis of the diluted crude extract. Method performance characteristics were determined after spiking breadcrumbs as model matrix at multiple concentration levels. With very few exceptions, coefficients of variation of the whole procedure of <5% and repeatabilities at the highest spiking level of <7% were obtained. Limits of detection ranged between 0.02 and 225 μg kg⁻¹. The quantitative determination of ergopeptides was disturbed by epimerization due to the acidic conditions. From the remaining 77 analytes, the apparent recoveries of nine substances deviated significantly from the CEN target range of 70–110% due to incomplete extraction and/or matrix effects. In principle, the latter can be compensated for by the application of matrix-matched calibration. The developed method was applied to 18 moldy samples (including bread, fruits, vegetables, jam, cheese, chestnuts and red wine) from private households. This study revealed the great value of the described method: 37 different fungal metabolites were identified at concentrations of up to 33 mg kg⁻¹, and some of these have never been reported before in the context of moldy food products. Figure ESI (+) MS/MS chromatogram (total ion current of all MRMs) of a sample of moldy dark bread