Accreditation of sampling activities

Since the introduction of ISO/IEC 17025 it is a requirement for all accredited laboratories to include sampling in their quality statements. It is well understood that sampling and handling of the sample are key factors in the validity of a result. The fact that many laboratories worldwide are not involved in sampling poses a challenge to accreditors liability. This article describes the Israel Laboratory Accreditation Authoritys (ISRAC) and other accreditors approaches to sampling.Presented at the Second International Conference on Metrology—Trends and Applications in Calibration and Testing Laboratories, 4–6 November 2003, Eilat, Israel.     

Influence of buffer quality on pH measurement uncertainty: prediction and experimental evaluation

Dependence of the uncertainty of a pH measurement result on the quality of buffers (i.e. the uncertainty of their certified pH values) at different levels of instrumental uncertainty (pH-meter, etc.) was simulated using the Monte Carlo method and regression analysis. The contribution of the instrumental standard uncertainty (in the studied range from 0.1 to 1 mV) to the uncertainty of the pH measurement result is negligible, if the standard uncertainties of the pH buffers exceed 0.04 pH (e. g. for in-house buffers). It is shown how the choice of pH-meter and buffers should be correlated in order to meet the required uncertainty of a pH measurement result in a sample under analysis. The results of the simulation were compared with experimental data obtained from calibrations of a pH/ion-meter with a hydrogen working electrode (Radiometer PHM-240) and with a glass electrode (Metrohm 744). Buffers of different quality (National Institute for Standards and Technology standard reference materials, certified Radiometer buffers and Merck CertiPUR buffers) were used for the calibrations. The uncertainties of the experimental results are close to the predicted ones obtained by the simulation. Received: 16 June 2002 Accepted: 19 July 2002 Presented at the 14^th International Conference of the Israel Society for Quality, 18–21 November 2002, Jerusalem, Israel Correspondence to I. Kuselman     

Current best practice for traceability in testing laboratories,when certified reference materials are unavailable

Since the implementation of ISO/IEC 17025 in 2002, all accredited laboratories (at the least) need to establish traceability in all their tests and calibration methods. Traceabilty, though well understood in the calibration field (through an unbroken chain of comparisons to the International System of Units —SI), is less straight forward and not so well understood in the testing laboratories. Traceability in analytical and biological testing is found through the use of reference materials, and the validated steps of a test method. This article describes the possibilities to comply with the traceability requirement of ISO/IEC 17025 in testing laboratories , when certified reference materials are unavailable.Presented at the Second International Conference on Metrology—Trends and Applications in Calibration and Testing Laboratories, 4–6 November, 2003, Eilat, Israel