David E. Wells

Design and evaluation of the QUASIMEME inter-laboratory performance studies: A test case for robust statistics☆

The QUASIMEME laboratory performance studies have been designed according to the recent IUPAC/ISO protocol. An overview of the design is given and, in addition to the Z-score for ranking the bias of laboratories, a term called ‘P score’ is introduced as an aid to the assessment of the precision of the laboratories. The data have been evaluated using robust statistics. Little information is available on practical applications of robust statistics for the evaluation of inter-laboratory studies, therefore, part of the data have been used to compare two different algorithms for robust statistics and the conventional ISO 5725 procedure. The data obtained from these intercomparison studies are heterogeneous in nature, and it is concluded that robust statistics have distinct advantages in assessing the data, but should not be used without a critical examination of the dataset.

A new model for the inference of population characteristics from experimental data using uncertainties. Application to interlaboratory studies

Abstract A new model to make inferences about population characteristics from experimental datasets is presented. It derives concepts and procedures from quantum chemistry. The model uses the observed values and the uncertainty estimates thereof. It provides the different modes of the distribution and for each mode the expectation value, the standard deviation and a percentage indicating the fraction of observations encompassed. An implementation of the model that does not require uncertainty estimates is provided too. In this paper, the model is elaborated and applied to the evaluation of interlaboratory studies. It has, however, a much wider generic application. It is demonstrated that the model can cope with asymmetric, strongly tailing and multimodal distributions and that it is superior to existing techniques (e.g. ISO 5725, robust statistics).

The assessment of the QUASIMEME laboratory performance studies data: Techniques and approach

Abstract A detailed assessment programme has been developed by the QUASIMEME Scientific Assessment Group to evaluate the results of the five rounds of the interlaboratory studies for the main mandatory chemical determinands in European Marine Monitoring Programmes. Two robust statistical algorithms were evaluated and one applied systematically to the study data. The established method of evaluation dealt with zero values, ‘less than’ values, skewed distributions, bimodal distributions from methodologically defined measurements and extreme values differing by factors of 2 to 1000 from the assigned value. Data from reference laboratories and declared concentrations from the sample preparation were, in the main, used to establish the assigned values. Z Scores were used to assess the laboratory performance. The sum of the number of satisfactory Z scores was used as an indicator of performance for successive inter-laboratory studies.

Determination of chlorobiphenyls, with the separation of non-ortho, mono-ortho and di-ortho chloro congeners in fish and sea mammals

A method for the preparation, clean-up and separation of chlorobiphenyls (CBs) into fractions containing non-ortho CBs, mono-ortho CBs and di-tri-ortho CBs is given. Methods of clean-up by gel permeation, saponification and sulphuric acid impregnated silica gel are compared. Highly chlorinated CBs were shown to decompose under alkaline hydrolytic conditions. The cleaned-up samples were fractionated using a 250 mm pyrenyl liquid chromatographic column and determined by GC-ECD and GC-NICIMS. The limit of determination was 10–50 pg kg−1 (wet weight) for a 10-g sample and the overall long-term variance for the method was ⩽ 15%.

Extraction and pre-concentration of organometallic species from environmental samples

Methods of extraction, clean-up and preconcentration normally reserved for organic trace analysis are considered with a view to applying such techniques to the developing field of organometallic speciation. The overview covers the main compartments of the natural environment; water, soil and sediment, plant and animal tissue.

Developments in quality assurance in marine environmental monitoring. The QUASIMEME II Laboratory Performance Studies and EU quality assurance of sample handling (QUASH) project

Abstract The EU project QUASIMEME 1993–1996 has now developed in two directions. The inter-laboratory studies have been extended to incorporate the UK National Marine AQC test requirement by extending the range of determinands to include aqueous samples for trace metals and organic contaminants as well as the nutrients. The Laboratory Performance Studies (LPS) are based on six-monthly series with two test materials at two levels on each occasion. The LPS is now a subscription based study which is available to laboratories worldwide and has a current membership of some 120 institutes. A second project entitled QUASH 1996–2000 which is funded by the EU, is focusing on the quality assurance of sampling and sample handling. The QUASH studies are divided onto six key areas. These cover (i) the sampling and preservation of nutrients, (ii) sample preparation of sediments and the measurement of co-factors for trace metal and organic contaminant analysis, (ii) sampling and sample handling of fish and shellfish, (iii) measurement of the co-factors for trace metal and organic contaminant analysis of biological tissue and (iv and v) the preparation of test materials and associated inter-laboratory studies. The project will be co-ordinated on a two-tier system with national centres for each European country forming one level and national laboratories forming the second.

Polychlorobiphenyls and persistent organochlorine pesticides in sea water at the pg 1−1 level. Sampling apparatus and analytical methodology

Abstract A sampling apparatus has been constructed for the collection and filtration of up to 28 1 of water at sea. The apparatus has been designed to minimise possible contamination from both the sampling equipment and the ships environment. The apparatus has been utilised in the analysis of chlorinated biphenyls (CBs), persistent organochlorine pesticides (OCs), and pentachlorophenol (PCP), in both the aqueous and particulate phases. The apparatus is suitable for collection of estuarine and coastal waters where the levels of dissolved CBs, OCs and PCP are above the limit of determination of 15 pg l−1. The efficiency of the recovery of these compounds and variance of the extraction and analysis have been estimated by analysis of filtered sea water spiked at a range of concentrations from pg l−1 ng l−1. Recoveries ranged from 66.5 to 97.3% with coefficients of variation for the complete method from 7.2 to 29.9%. The contribution of the extraction to the variance of the complete method has been estimated utilising on-going laboratory quality control data.

The isolation and identification of polychloro-2-(chloro-methylsulphonamide) diphenyl ether isomers and their metabolites from eulan wa new and fish tissue by gas chromatography—mass spectrometry

Abstract The active ingredients of Eulan WA New have been isolated and identified by nuclear magnetic resonance and mass spectrometry. The gas chromatography thermal decomposition products of the polychloro-2-(chloromethylsulphonamide) diphenyl ether isomers have been monitored and the chromatogram of Eulan WA New has been characterized. A method for the extraction, clean-up, and analysis of the isomers and their metabolites in fish tissue by g.c.—m.s. has been developed.

Progress in the quality assurance of environmental trace organic analysis

An overview is given on the stepwise learning programmes undertaken to identify the main sources of error associated with the determination of the mandatory organic contaminants in the marine monitoring programmes. Details are given on the preparation and use of LRMs and CRMs to maintain analytical control and quantify the laboratory errors in relation to the measurement of changes in the environment.

QUASIMEME: a preliminary study on the effects of sample handling on the measurement of trace metals and organochlorine residues in mussels

Abstract As part of the development of quality measurement of trace metals and organochlorine residues in marine biota, the QUASIMEME Project undertook an interlaboratory study to determine the magnitude of the errors associated with the sample handling of mussels ( Mytilus edulis ) prior to analysis. Mussels were distributed to participating laboratories which homogenized and freeze-dried five pools of 10 mussels. Each pool was analysed both by the participants and by a reference laboratory. Systematic errors resulting from the freeze drying and from contamination during analysis for the trace metals, particularly lead and organochlorines, were identified. In general, the errors associated with the sample preparation were of similar magnitude to the final measurement of the trace metals, whereas the errors for the measurement of the chlorobiphenyls and the organochlorine pesticides still dominated the overall variance and bias for the analysis.