LAUSR

Reference materials for proficiency testing (PT) were prepared for 6 years. The target analytes were food additives, sorbic acid, benzoic acid, and propyl p-hydroxybenzoate, in two kinds of commercial beverages. To enhance the stability of PT reference materials, a sterilization step was employed in the procedure of preparation. However, when beverage reference materials were irradiated with gamma rays (γ-rays), the irradiation affected sorbic acid and benzoic acid, and the mass fractions of the analytes changed. In addition, the target analytes in a beverage containing many ingredients were less affected by irradiation than those in a beverage containing simple ingredients. To avoid the changes and the variation of the mass fraction of target analytes, propionic acid was used as an antibacterial agent instead of irradiation. The result was that the reference materials remained stable. The propionic acid preserved the matrices of the beverage reference materials and did not affect the mass fraction of the target analytes by the end of the PT program.