Abstract. An ion chromatographic method for determination of fluoride, chloride, nitrate and sulphate in untreated and treated drinking waters was described. An automated 850 IC Professional, Metrohm system equipped with conductivity detector and Metrosep A Supp 7-250 (250 x 4 mm) column was used. The validation of the method was performed for simultaneous determination of all studied analytes and the results have showed that the validated method fits the requirements of the current water legislation. The main analytical characteristics were estimated for each of studied analytes: limits of detection, limits of quantification, working and linear ranges, repeatability and intermediate precision, recovery. The trueness of the method was estimated by analysis of certified reference material for soft drinking water. Recovery test was performed on spiked drinking water samples. An uncertainty was estimated. The method was applied for analysis of drinking waters before and after chlorination.
In this work, the development and optimization of a secondary method for pH measurement using a differential potentiometric cell are described. The method was optimized and validated by measurement of three certified primary buffer solutions (CRMs) with nominal pH values of 4.005, 6.865 and 9.180 at 25 °C. The method was applied to assess homogeneity and stability of phosphate buffer solution with nominal pH of 7.000 at 25 °C which will be used as test item in proficiency testing schemes for pH measurement of testing laboratories. The experiments carried out and described in this article proved that this particular design of secondary differential potentiometric cell requires small volume of solutions, is fast, accurate and precise and is suitable for the characterization of secondary buffer solutions and assessment of homogeneity and stability of buffer solutions.
This paper presents the development of a secondary pH measurement standard and the design of the most critical part of the measurement standard - the secondary cell. The parameters affecting the measurement accuracy are discussed. The validation of the method together with a full uncertainty budget is described. The intended use of the secondary pH measurement standard by the Bulgarian Institute of Metrology (BIM) is also presented.
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