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Abstract -
A comparison between ISO standards - ISO 21748:2010 and ISO 11352:2012 for the measurement uncertainty estimation in the field of water analysis is presented. Several Certified reference materials (CRMs) with certified values for several water quality parameters were measured and measurement uncertainties were evaluated for each of them according to the above mentioned ISO standards. Results show excellent agreement for chemical oxygen demand (COD), total organic carbon (TOC), ammonium nitrogen (NH^sub 4^^sup +^ - N), nitrate nitrogen (NO^sub 3^^sup -^-N), total phosphorus (PO^sub 4^^sup 3-^-P) and chloride (Cl-). Based on the experiment design and the comparison results, ISO 11352:2012 is recommended for measurement uncertainty estimation in the field of water analysis during method validation.
Keywords - ISO 21748, ISO 11352, measurement uncertainty, uncertainty estimation, method validation
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1. INTRODUCTION
Chemical analysis of a set of water quality indicators is the most powerful tool for the determination of water suitability for human consumption or to be released back into nature after treatment. Numerous analytical methods exist for measuring COD, total organic carbon (TOC), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3"-N), total phosphorus (P043'-P) and chloride (Cl-) at laboratory scale. They are usually carried out according to the national and international standard methods. These methods are well studied and documented, but they are often too sophisticated and time consuming for operational control and require considerable practical experience and skill to get reproducible results. Furthermore, most of them require the use of toxic substances, which can be harmful to the analyst and their subsequent utilization can be dangerous to environment. Spectrophotometric methods for water analysis, based on ready-to-use cuvette tests, can be an alternative to the time-consuming reference methods. Practically all compounds and indicators of water environment could be measured directly or after suitable preliminary treatment using contemporary spectrophotometers and portable photometers. The cuvette tests quality is demonstrated by the fact that for the first time a COD cuvette test has been accepted as a reference method [1].
The aim of this study was to compare the measurement uncertainty estimation according to two different ISO standards - ISO 21748 : "Guidance for the use of repeatability, reproducibility and trueness estimates in measurement uncertainty estimation" [2], and ISO 11352: "Water quality - Estimation...