Promotion of metrological traceability through the provision of a metrologically traceable proficiency testing reference value for the mass fraction of benzoic acid in fish sauce

Abstract

The present paper outlines a joint proficiency testing (PT) programme established between the Asia–Pacific Metrology Programme (APMP) and the Asia Pacific Accreditation Cooperation (APAC). This programme aims to assess the analytical performance and enhance measurement proficiencies in laboratories across various economies, with a focus on the quantification of benzoic acid in fish sauce. This PT programme was organised by the Government Laboratory, the designated institute of metrology in chemistry for Hong Kong, China (GLHK). A comprehensive invitation extended to both APMP and non-APAC members resulted in the participation of 41 laboratories from 19 different economies. The metrological reference value for benzoic acid, provided by GLHK, was determined utilizing isotope-dilution mass spectroscopy (IDMS) with traceability to the International System of Units (SI). This SI-traceable reference value enhances the quality of participants’ measurements and promotes the awareness of traceability among the participants, enabling a more accurate evaluation of their results. Concurrently, this approach facilitates the building of measurement capabilities among participants, fostering more robust connections between metrology institutes and testing laboratories. The programme also revealed a notable deficiency in the understanding of statistical concepts among some participants, including the coverage factor, degrees of freedom, standard uncertainty, and expanded uncertainty. Proper interpretation of zeta-scores or E_n scores based on measurement uncertainties, when analysed alongside z-scores, proves to be indispensable for an accurate assessment of the participants’ measurement competencies and their ability to evaluate measurement uncertainty. The assessment of participants’ performances, taking into account measurement uncertainties, serves as a benchmark for participants to gauge the validity of their measurement uncertainty evaluations.