Provision of proficiency testing for histamine mass fraction in canned tuna to improve the capability of chemical laboratories in the Philippines

In this work, two reference materials (RMs) for mass fraction of histamine in canned tuna were developed to address the need of local testing laboratories for matrix RMs and a PT scheme for histamine. A validated method using HPLC with fluorescence detector (340 nm for excitation and 445 nm for emission) was applied with post-column derivatization for the RM’s homogeneity and stability studies. Acceptable results were obtained after statistical evaluation of homogeneity and stability according to IUPAC Harmonized Protocol and ISO Guide 35, respectively. Two PT exercises for histamine determination based on ISO/IEC 17043 were organized in 2014 and 2015 with the assigned values of 148 and 65 mg/kg, respectively. These reference values were obtained using exact matching liquid chromatography–isotope dilution mass spectrometry (LC–IDMS) with gravimetric sample preparation. The corresponding uncertainty of the reference value was obtained by ISO GUM approach where the characterization of the sample gave the highest contribution (41 %). The satisfactory z-score performance evaluated from the 12 laboratories was 50 % and 58.3 % in the first and second PT round, respectively. Most of the laboratories used AOAC Official Method 977.13 but not all conducted method validation. The 50 % decrease in unsatisfactory results in the second PT round is a significant improvement in the local laboratory performance for histamine analysis. However, the provision of more PT schemes and the increased use of CRMs in the future are still needed by these laboratories for external quality assurance and method validation to enhance the present capability.