Interlaboratory studies organization

This approach corresponds to interlaboratory studies organized on a voluntary basis for specific purposes (e.g., proficiency testing). In this case, the selected laboratories and methods may be very diverse and not necessarily prepared of submitting results aimed at establishing assigned values to a RM. The... 

Nilsson, T, Ferrari, R., and Facchetti, S., Interlaboratory Studies for the Validation of Solid-phase Mieroextraction for the Quantitative Analysis of Volatile Organic Compounds in Aqueous Samples, Anu/yrica Chimica Acta 356, 1997, 113-123. 

Use of Validated Methods In-Home Versus Interlaboratory Validation Wherever possible or practically achievable, a laboratory should use methods which have been fully validated through a collaborative trial, also called interlaboratory study or method performance study. Validation in collaborative studies is required for any new analytical method before it can be published as a standard method (see below). However, single-laboratory validation is a valuable source of data usable to demonstrate the fitness for purpose of an analytical method. In-house validation is of particular interest in cases where it is inconvenient or impossible for a laboratory to enter into or to organize itself a collaborative study [4,5]. 

Figure 5.1. Schematic of the work flow of an interlaboratory study, showing the sequence of actions by each laboratory or organization.

The organizing laboratory performs statistical tests on the results from participating laboratories, and how outliers are treated depends on the nature of the trial. Grubbs s tests for single and paired outliers are recommended (see chapter 2). In interlaboratory studies outliers are usually identified at the 1% level (rejecting H0 at a = 0.01), and values between 0.01 < a < 0.05 are flagged as stragglers. As with the use of any statistics, all data from interlaboratory studies should be scrutinized before an outlier is declared. 

There are two aspects to a report of an interlaboratory study. First the nature, organization, and treatment of results of the trial must be specified,... 

The organizer of an interlaboratory study to assign a quantity value to a reference material is usually a national or international certifying authority, such as the International Atomic Energy Agency (United Nations), the Community Bureau of Reference (European Union), or a national measurement institute. 

An interlaboratory study was organized for the determination of OTC and 4-epi-OTC in pig muscle tissue. Fourteen laboratories from EU member countries agreed to participate. They were... 

A detailed interlaboratory study of arsenic speciation in six different kinds of marine organisms was published (El Moll et al., 1996). Detection of arsenic species in the sample extracts was performed by means of LC-ICP-OES for AB and AC, and by HG-AAS for As111, Asv, MMA and DMA. Many precautions were taken to avoid contamination and losses of analytes, and to improve the accuracy of the results. Data for total As, extractable As, residual As and AB were reported. 

The participants in the interlaboratory study must analyze as indicated and follow the method exactly, including the number of determinations as instructed, and not more Individual values and blanks should be reported, and raw data and graphs should be supplied.The organizer should be called if any problems occur. A complete report should be submitted. 

Asafu-Adjaye, E.B. and Wong, S.K. 2003. Determination of ginsenosides (ginseng saponins) in dry root powder from Panax ginseng, Panax quinquefolius, and selected commercial products by liquid chromatography Interlaboratory study. J. Am. Organ. Analyt. Chemists Inti 86, 1112-1123. 

Phosphorus is not a TE but a major nutrient element. Nevertheless, fractionation of this element is essential for environmental studies, and hence it seems reasonable to highlight here some relevant SEPs. Four different procedures for the fractionation of P in lake sediment samples have been tested in an interlaboratory study in the framework of the SM T program (Ruban et al., 1999). As a result, a novel scheme based on the Williams protocol (Williams et al., 1976) has been developed aimed at the restoration of lake sediments. The scheme comprises three separate assays (1) sequential extraction of NaOH-extractable (Fe- and Al-bound) and HCl-extractable (Ca-bound) fractions, (2) sequential extraction of inorganic and organic phosphorus and (3) single extraction, after calcination, of concentrated HCl-extractable (total P) fraction (see Table 12.3 for further details). Further discrimination of specific compounds is made feasible by the use of chromatographic and capillary separation techniques as reviewed by Spivakov et al. (1999). 

While the amounts of nitrate could be certified in rainwater CRMs [3], their certification in freshwater CRMs was not possible owing to the stabilisation procedure used (involving an addition of nitric acid) [2]. Consequently, it was decided to organize a separate interlaboratory study of which the final aim was to produce artificial freshwater CRMs certified for their contents of nitrate, one with a low nitrate content (CRM 479) and one with a high nitrate content (CRM 480) [4,5]. These CRMs correspond to values below and slightly above the maximum permissible nitrate content (approx. 50 mg L" ) mentioned in the Drinking Water Directive. 

The second interlaboratory study generated detailed discussions one ETAAS technique employed did not include a separation step but the participant stated that EDTA extraction would only extract organic lead compounds this technique was considered to be suitable for the analysis of a simple solution containing only one lead compound but would not be suitable for mixtures of lead species, e.g. the technique would not allow the separation of TriML and TriEL in a natural rainwater sample. In cases where different organolead compounds are to be determined in natural samples or solutions containing different lead compounds, ETAAS should be coupled to a separation technique, e.g. GC or HPLC. 

In the first interlaboratory study, the examination of the raw data (14 sets of results of which 12 involved CVAAS, one RNAA and one MIP-AES) revealed a high spread of results due to two outliers. The mean obtained was 12.6 pg L of Hg with a coefficient of variation (CV) between laboratories of 33%. The two high results were attributed to a laboratory contamination. The accepted values showed a picture which was found more acceptable, i.e. the mean obtained was 10.8 pg L with a CV between laboratories of 6.6"/n [8]. At this stage, the agreement between the laboratories was found to be satisfactory however, the Hg content in this (spiked) sample was considered much too high for being representative of natural samples which justified the organization of a second interlaboratory exercise for which results are described below. 

The organiser of an interlaboratory study must take into account the objective of the exercise. There is a large difference of responsibility and work involved between a simple exercise on major elements in alloys for a method performance study involving some laboratories and the certification of traces of organic contaminants in a matrix material. But in all cases the organiser has to fulfil the following tasks. 

Annexes 5.1 and 12.1 give examples of reporting forms elaborated in BCR (Bureau Communautaire de Reference) for the certification of inorganic and organic parameters in environmental matrices. They may be used as a basis to prepare reporting forms for all type of interlaboratory studies. The elaborate questions listed in the forms are intended to remind the participant of important parameters, which affect the quality of the final result. They can also be used in the technical discussion with the other participants when differences in results are noticed. Finally, they form the basic information for the preparation of certification reports in case certification is considered (see chapter 5). 

Besides the classical interlaboratory studies, improvement schemes enable laboratories to develop and validate all steps of new or existing analytical procedure(s) in adequately organised successive exercises. Improvement schemes may be considered as preliminary studies for laboratory or method performance studies or certification of reference materials [5]. Such programmes are very valuable when the analytical procedures include several complex and critical steps, e.g. for the determination of trace organic compounds or chemical species. They require a long term involvement of the organiser and participants, as well as investment of resources. 

As described in Section 3.2, interlaboratory studies are organized in such a way that several laboratories analyse a common material which is distributed by a central laboratory responsible for the data collection and evaluation. When laboratories participate in an interlaboratory study, different sample pretreatment methods and techniques of separation and final determination are compared and discussed, as well as the performance of these laboratories. If the results of such an intercomparison are in good and statistical agreement, the collaboratively obtained value is likely to be the best approximation of the truth. 

In the lUPAC document Nomenclature for Interlaboratory Studies , Horwitz stresses that at least eight sets of data should be considered as a minimum for a sound statistical treatment to test the performance of a method or a laboratory [62], The organization and interpretation of the data depend on the number of participants. This number may vary from tens to hundreds of laboratories, depending on the objective of the study. 

---