First Indonesian proficiency testing using reference value from isotope dilution mass spectrometry method for benzoic acid, methyl paraben, and n-butyl paraben in sweet soy sauce

Research Center for Chemistry-Indonesian Institute of Sciences (RCChem-LIPI) has successfully organized proficiency testing (PT) for the determination of benzoic acid, methyl paraben, and n-butyl paraben in sweet soy sauce. This is the first PT in Indonesia that uses reference values derived from a primary method gas chromatography–isotope dilution mass spectrometry method. Twenty participants from four economies registered in this PT. This paper presents the procedures in the preparation of the PT samples, the homogeneity and stability checks, as well as in the determination of the assigned values. The test samples were a candidate certified reference material prepared in accordance with ISO 17034 and ISO Guide 35. The performance evaluation of participants’ results was conducted in accordance with ISO 13528 by using the PROLab™ software. This paper also discusses the approaches taken in the calculation of the performance’s scores which were set according to the criterion required in homogeneity check, stability check, and limit of uncertainty.