Method Validation for Determination of Total Acid in Vinegar Based on Potentiometric Titration by Interlaboratory Study

Abstract

An interlaboratory study was performed to evaluate a method for determining total acid in Jozo-su (vinegar), for revision of the Japanese Agricultural Standard (JAS). Methods using titration with a pH meter or a potentiometric titrator were optimized based on the JAS analysis method. The optimum conditions were sampling a test portion after putting 100 mL of water into a 200 mL beaker, and titrating with 0.5 mol/L NaOH until pH 8.2, using a pH meter or a potentiometric titrator. Then, fourteen laboratories (pH meter, 9 labs ; potentiometric titrator, 5 labs) participated and analyzed 6 test materials as blind duplicates with this method. After removing outliers statistically, the repeatability (RSD_r) and the reproducibility (RSD_R) of this method were 0.10∼0.17% and 0.32∼0.48%, respectively. HorRat (RSD_R/predicted RSD_R) for the reproducibility showed 0.11 to 0.15. This method was shown to have an acceptable precision by the present study.