ISO/TC 147/SC 2/WG 48 - QA/QC (Quality assurance/Quality control)

This document specifies representative materials suitable for the determination of the performance characteristics, including uncertainty, during the initial assessment of a quantitative method, used in a laboratory, for physico-chemical water analysis. This document focuses on five main types of water: — waters intended for consumption (5.2); — natural waters (5.3); — waste waters (5.4); — marine waters (5.5); — recreational waters (5.6). NOTE Other more specific or less common types of water can be incorporated in any of the above types provided appropriate justifications. The characteristics of the standard matrix are compatible with the characteristics of the samples handled.

This International Standard specifies methods for the estimation of measurement uncertainty of chemical and physicochemical methods in single laboratories based on validation data and analytical quality control results obtained within the field of water analysis. NOTE 1 The principles of the estimation of uncertainty specified in this International Standard are consistent with the principles described in ISO/IEC Guide 98-3. In this International Standard, the quantification of measurement uncertainty relies on performance characteristics of a measurement procedure obtained from validation and the results of internal and external quality control. NOTE 2 The approaches specified in this International Standard are mainly based on QUAM[11], NEN 7779[8], Nordtest TR 537[10], and Eurolab TR 1[9]. NOTE 3 This International Standard only addresses the evaluation of measurement uncertainty for results obtained from quantitative measurement procedures. The uncertainties associated with results obtained from qualitative procedures are not considered.

ISO/TS 13530:2009 provides comprehensive guidance on within‑laboratory and between‑laboratory quality control for ensuring the production of results with a known level of accuracy in the analysis of waters. ISO/TS 13530:2009 is applicable to the chemical and physicochemical analysis of all types of waters. It is not intended for application to the analysis of sludges and sediments (although many of its general principles are applicable to such analysis) and it does not address the biological or microbiological examination of water. Whilst sampling is an important aspect, this is only briefly considered.

ISO/TS 20612:2007 specifies the criteria related to proficiency testing by interlaboratory comparisons in the field of water, waste water and sludge analysis. In particular, it specifies the requirements in respect to proficiency test providers and to the design, execution and evaluation of laboratory proficiency comparisons. ISO/TS 20612:2007 may be used if the determinands in the interlaboratory test may be regarded as capable of measurement with a certain degree of continuity. This is generally the case for chemical constituents and physicochemical determinands, but continuity does not always exist in the case of biological and/or microbiological determinands.

ISO/TS 16489:2006 describes statistical procedures to test the equivalency of results obtained by two different analytical methods used in the analysis of waters. It is not applicable for establishing whether two methods can be shown to be equivalent. The procedures given in ISO/TS 16489:2006 are only applicable to demonstrating the equivalency of results.

It is not always possible to accurately describe the relationship between a set of calibration points with a rectilinear curve, even by decreasing the working range. Instead of the linear regression analysis, a least-squares fit to a second-order polynomial is applied (see test for linearity in 4.1.3 of ISO 8466-1:1990[1]). Using this fit, it is possible to calculate not only the calibration function but also the confidence interval associated with it. This part of ISO 8466 is intended primarily for use in method development and may not necessarily be applicable to all routine analyses.

Describes the steps to be taken in evaluating the statistical characteristics of this function. It is applicable to methods requiring a calibration. In order to derive comparable analytical results and as a basis for analytical quality control the calibration and evaluation have to be performed uniformly.

Is intended for use in method development and may not necessarily be applicable to all routine analyses. It is not always possible to accurately describe the relationship between a set of calibration points with a rectilinear curve, even by decreasing the working range. Instead of the linear regression analysis, a least squares fit to a second order polynomial is applied. Using this, it is possible to calculate not only the calibration function but also the confidence interval associated with it.