Collaborative study of methods for the determination of chloride, citrate, and phosphate in processed cheese.

A collaborative study was conducted to compare the International Dairy Federation (IDF)/International Organization for Standardization (ISO)/Association of Official Analytical Chemists (AOAC) proposed methods for the determination of chloride and citrate in processed cheese with the corresponding current AOAC methods. Since there is no current AOAC method for phosphate, only the IDF/ISO/AOAC method was used. Five samples of processed cheese were prepared with varying added amounts of the anions of interest. The samples were analyzed in duplicate by 7 collaborating laboratories. For chloride, both methods are comparable, but since the IDF/ISO/AOAC method is simpler and faster it has been adopted as official first action to replace the current AOAC method, 16.224. For citrate, the colorimetric IDF/ISO/AOAC method is more rapid and simpler than the current AOAC gravimetric method. However, the AOAC method is more precise. Therefore, the proposed method has been adopted as official first action as an alternative to 16.237. For phosphate, 2 of the 7 laboratories were outliers by the Youden ranking test but the results by the remaining laboratories appear satisfactory. The phosphate method should receive further study to reduce the between-laboratory error component.