Indonesian proficiency testing for electrolytic conductivity measurement of synthetic wastewater: a comparison of performance evaluation based on four standardized performance statistics

Electrolytic conductivity is recognized as one of the parameters to determine water quality. An accurate measurement of electrolytic conductivity of wastewater before dumping it into the environment is crucial to prevent water pollution. Therefore, the ability of laboratories in conducting accurate and comparable measurements of electrolytic conductivity is important to guarantee the measurement results. The measurement quality of the laboratories can be determined by participating in a proficiency testing (PT) conducted by accredited PT provider. In 2018, Chemical Metrology Laboratory, Indonesian Institute of Sciences (LIPI), as a PT provider, conducted a PT for electrolytic conductivity measurement with synthetic wastewater as the PT test item. It was prepared from cations and anions commonly found in natural wastewater. A total of 25 participants from Indonesian testing laboratories reported their electrolytic conductivity measurements. These results were then evaluated using a standardized performance statistic of z score, z′ score, E_n score and ζ (zeta) score. There were 20 laboratories having satisfactory results evaluated using both z score and z′ score, while only 14 laboratories were considered having a successful performance evaluated using E_n score and ζ score. The evaluation results show that the participants already have the ability to measure the electrolytic conductivity value but some of them still need improvement in estimating the uncertainty.