Interlaboratory exercises

Martin-Esteban a, Fernandez P, Camara C, Kramer GN, Maier EA 1997) Preparation, homogeneity and stability of polar pesticides in freeze-dried water interlaboratory exercise. Int. J Environ Anal Chem 67 125-141. 

Quantification is usually achieved by a standard addition method, use of labeled internal standards, and/or external calibration curves. In order to allow for matrix interferences the most reliable method for a correct quantitation of the analytes is the isotope dilution method, which takes into account intrinsic matrix responses, using a deuterated internal standard or carbon-13-labeled internal standard with the same chemistry as the pesticide being analyzed (i.e., d-5 atrazine for atrazine analysis). Quality analytical parameters are usually achieved by participation in interlaboratory exercises and/or the analysis of certified reference materials [21]. 

The present chapter discusses the results of a series of three small-scale interlaboratory exercises performed within the framework of the European Union-funded PRISTINE project (ENV4-CT97-0494), employing HPLC-fluorescence (FL) and LC-MS techniques for the determination of ionic and non-ionic surfactants. 

The results of the interlaboratory exercises involving LC-APCI-MS, LC-ESI-MS, FIA-MS and LC-FL show that in general repeatability (as reflected by within-laboratory RSD) is at a satisfactory level (i.e. RSD around 10%) for LAS and NPEO. 

Interlaboratory exercises have to be a part of the measurement program in order to ensure, as far as possible, a consistent data set. CRMs of artificial precipitation samples and solid samples are available from various organizations, for example, BCR, NIST, and IAEA. In addition, laboratory intercomparisons are arranged annually by, for example, WMO/GAW and EMEP. Artificial precipitation samples are distributed to different laboratories. EMEP laboratory comparisons of the main components in precipitation have been conducted for 25 years, and they have provided important documentary evidence for the evolution of data quality in EMEP during this period. The results show that laboratory performance has improved during this period, so that at present most laboratories manage to be within the 10% relative standard deviation (RSD) for all the major ions (Table 17.4). 

Quantitative results for Se-Met (59 and 68% of total Se in wheat Bour and in yeast) in good agreement with the mean values obtained in collaborative interlaboratory exercise... 

One of the most critical points in organometallic chemistry analysis is the availability of calibrants of suitable purity and verified stoichiometry. This aspect was recognised at an early stage of the project and the purity of alkyllead compounds used in the feasibility study was carefully verified [10]. Additional experiments were performed on calibrants in the frame of the first interlaboratory exercise as described below. 

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. 

All the selected laboratories for the certification exercise had already been involved in an earlier interlaboratory exercise in order to validate the analytical methods used [44]. An estimation of the recovery of the pesticides from one liter of water was requested by adding a known amount of each pesticide or by reextraction. For chromatographic analysis at least the use of one internal standard was necessary. The reconstitution process had to be strictly followed by all laboratories. 

Poorer extraction recoveries for TBT in CRM 462 were often observed in comparison to recoveries obtained from other sediment materials. Some laboratories found lower recoveries if the spike was allowed to equilibrate longer. The previous interlaboratory exercise on TBT-spiked sediment had identified the need to allow spikes to equilibrate at least overnight to get a realistic assessment of extraction recoveries. 

RESULTS OF THE FIRST AND SECOND INTERLABORATORY EXERCISES (STEPS 1, 2 AND 3). THE TABLE LISTS THE MEAN OF THE LABORATORY MEANS ALONG WITH THE STANDARD DEVIATION (SD) AND THE COEFFICIENT OF VARIATION (CV) OBTAINED. THE TRACE METAL CONTENTS ARE GIVEN IN... 

The second interlaboratory exercise on extractable trace metals in sediment showed a consequent improvement in comparison with the results of the first exercise. 

The interlaboratory study should px)ssibly lead to conclusions useful to the participants. Therefore, the results of the exercise have to be made available to them. To arrive at clear conclusions it is not sufficient to know only the performance of other participants, the mean value of the means and the between laboratory standard deviation. In fact the conclusions which can be drawn may be subject to ambiguity, especially with regards to trueness. If one biased method is used by a majority of participants of a group one individual laboratory using a more accurate method may have an outlying value. Figure 12.1 shows the results of an interlaboratory exercise on the determination of Sn in brass laboratories which applied wet methods with an acidic dissolution were all confronted to losses due to precipitation (the mean is far from the target value calculated from the preparation procedure). 

An interlaboratory exercise is organised with a defined task. The minimum information, which has to be given in the protocol accompanying the test samples, is the specification of the task of the study. 

RESULTS OF THE FIRST AND SECOND INTERLABORATORY EXERCISES (STEPS 1, 2 AND 3) ON EXTRACTABLE ELEMENTS FROM SOILS... 

Techniques used in the interlaboratory exercises and certification campaigns are described below. Discussions of the sources of discrepancies detected in the various exercises are reported in the section related to the technical evaluation of the results. 

The results of Ni determination in this exercise demonstrated a considerable inprovement in comparison with the first interlaboratory exercise (Table 11.1). 

In the case of step 3, similar problems as in step 2 were found. The accepted results ranged from 596 to 735 mg kg with a CK between laboratories below 10% (with techniques covering 1 ETAAS, 9 FAAS, 4 ICP and 1 ICP-MS), which was considered to be acceptable for possible certification. As observed for the other metals, the type of shaking could be an important cause of the spread of results. The agreement between laboratories was found to be similar or slightly better than in the first interlaboratory exercise. However, the range of techniques should be enlarged in order to avoid a possible method effect . 

The second interlaboratory exercise on extractable trace metals in sediment showed a consequent improvement in comparison with the results of the first exercise. Furthermore, these collaborative efforts allowed the sequential extraction procedure to be slightly improved by minor amendments. The general noticeable trend was the important decrease in the number of total and accepted sets of values for concentrations in the extract below 10 pgL , which illustrated the difficulties experienced by a number of laboratories in the determination of such concentration levels in these matrices. 

In 2006, an interlaboratory exercise was organized by the Community Reference Laboratory for Marine Biotoxins (CRLMB) to evaluate its fitness for purpose for the Official Control of PSP toxins in the EU laboratories [41]. Eighteen European Union (EU) laboratories took part in the study. The participants had to analyze six bivalve mollusks samples with various PSP toxic profiles. The performance of the participant laboratories in the application of the 2005.06 AOAC Official... 

Leger P, Bengtson DA, Sorgeloos P (1989) Analytical variation in the determination of the fatty acid composition of standard preparations of brine shrimp Artemia an interlaboratory exercise. In CowgiU UM, Williams LR (eds) Hazard assessment, vol 12, ASTM STP 1027, American Society Testing Materials, Philadelphia, p 413 Latasa M, Bidigare RR, Ondrusek ME, Kennicutt MC II (1996) Mar Chem 51 315 Poisson A, Culkin F, Ridout P (1990) Deep Sea Res 37 1647... 

Stability of Bromate Speeies Immobilized on Alumina Microcolumns Interlaboratory Exercise for Bromate Determination... 

Interlaboratory exercises focusing on nuclear forensics have been initiated by the Joint Research Centre (JRC) of the European Community. The two most recent exercises were called NUSIMEP-6 (Aregbe et al. 2008) and NUSIMEP-7 (Truyens et al. 2013) (NUSIMEP—Nuclear Signatures Inter-laboratory Measurement Evaluation Programme). In these exercises, identical samples were sent to the participating laboratories and the predefined analytes (content and isotopic ratios) were measured and reported to the coordinators, who then compiled the results, compared them with the target value, and produced a report. The remainder of the samples that were not consumed in the measurements can subsequently serve as standards for future measurements. One other benefit of these intercomparisons is that the accuracy and effectiveness of the different analytical procedures and the instrumentation can be assessed. In addition, corrective measures can be implemented in order to improve the performance. Finally, the cooperation between the scientists and the laboratories can lead to the development of standard procedures and recommended methods. This is essential for nuclear forensics where the implications of the analytical results, as mentioned earlier, may evoke political and even military actions in some cases. 

Aregbe, Y., Trnytens, J., Kips, R. et al. (2008). NUSIMEP, P-6 Uranium isotope amount ratios in nraninm particles. Geel, Belgium Interlaboratory Exercise, Joint Research Commission. 

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