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Interlaboratory validation of PrEN 12673: Water quality - Gas Chromatographic determination of some selected chlorophenols in water

Interlaboratorium vergelijkingsonderzoek ten behoeve van de validatie van PrEN 12673: Water kwaliteit - bepaling van sommige geselecteerde chloorfenolen in water door gas chromatografie

Synopsis

An interlaboratory study was organised to validate the preliminary CEN method PrEN 12673: Water Quality - Gas Chromatographic determination of some selected chlorophenols in water. This intercomparison study on three types of water - drinking water, surface water and waste water - comprised a total of nine samples: a high-level, low-level and blank for each of the three types of water. The level of sample was based on the water quality objectives. The variation of the samples with respect to homogeneity and stability of the components appeared after extensive testing to be negligible in comparison with the variation between the results of the participants. In this data set about 7% of the data were detected as statistical outliers and subsequently rejected. For the remaining data set the relative standard deviations for repeatability varied between 5% and 25% and reproducibility between 25% and 55%. Both these ranges comply with the general variation in interlaboratory studies as found by Horwitz. The recovery of the spikes found by the participants generally varied between 60 and 140%. These differences do not exceed the combined uncertainty between the two values. The data set was also evaluated for differences in results due to the degrees of freedom in the standard method. The largest difference was found between participants performing internal versus external calibration. The latter obtained results that are on average up to 50% lower than the results of the participants applying internal standards. Another degree of freedom in the standard method that should be evaluated was the use of a mass spectrometer (MS) instead of an electron capture detector (ECD). The MS results varied among the components from minus 25% to plus 20% compared to the ECD results.
 

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