Chloride in Milk, Milk Powder, Whey Powder, Infant Formula, and Adult Nutritionals Potentiometric Titration: Collaborative Study, Final Action 2016.03

Background: In September 2015, both AOAC Official Methods 2015.07 and 2015.08 single-laboratory validations (SLVs) were reviewed against Standard Method Performance Requirements (R) (SMPR) 2014.015 by the AOAC Stakeholder Panel for Infant Formula and Adult Nutritional (SPIFAN) Expert Review Panel (ERP). Looking at the similarity and uniqueness of the two methods, the authors agreed, as advised by the ERP, to work together to merge the two methods into one. This combined method was assigned Method 2016.03. Objective: In order to determine the repeatability and reproducibility of the AOAC First Action 2016.03 method, a collaborative study was organized. The study was divided in two parts: (Part 1) method set up and qualification of participants and (Part 2) collaborative study participation. During Part 1, each laboratory was asked to analyze two practice samples. The laboratories that provided results within a range of expected levels were qualified for Part 2, during which they analyzed 25 samples in blind duplicates. Results: The results were compared with SMPR 2014.015 established for chloride. The precision results (repeatability and reproducibility) were within the requirements stated in the SMPR. In general, the precision results (repeatability and reproducibility) were well within the limits stated in the SMPR. Repeatability ranged from 0.4 to 1.9%, in accordance with data obtained during SLV, with reported RSD of repeatability from 0.03 to 1.6%. Meanwhile, reproducibility ranged from 0.6 to 4.0%. Finally, the Horwitz ratio values were all below 1, from 0.2 to 0.9%. Conclusions: The ERP determined that the data presented met the SMPR and accordingly recommended the method to be granted Final Action status. In January 2018, the Official Methods Board approved the method as Final Action.