AOAC SPIFAN Nutrients ERP Method Reviews (September 7, 2019)

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RSD IR values ranged from 3.1 – 11.3%. These values met the SMPR requirements, as their concentrations were in (or below) the lower concentration range of the SMPR. • System suitability: The correlation coefficient for the standard curve before must be greater than 0.995; calibration must be checked every 2 hours and is considered stable if within 2% of the initial mV reading. Recommendation: There appear to be several variables which can influence the response of the electrode to standard / sample solutions, including: o The amount of time the electrode is exposed to the solution before the response observation is made; o The rate at which the solution is stirred:  Incorporating oxygen into the sample can make the response unstable;  The heat produced by the spin plate can change the temperature of the solution, and affect the electrode response; o The way in which acid is added to samples, causing clumping (probably localized protein denaturation); o The degree to which the sample preparation (reconstitution or RTF aliquot) is homogenized: whether further treatment is needed. Lastly, it was noted that Adult Nutritional High Protein and High Fat liquid matrices were diluted 1:3 with water prior to analysis: however it was not explained on what basis this was necessary, or how it would be known for other matrices whether or not this treatment was needed. The nuance of each of these characteristics is likely well understood by the method authors, and when new analysts are trained or the method is set up in a new laboratory the details are conveyed. These points notwithstanding, the method met the SMPR requirements for LoQ, analytical range, precision, and accuracy, and the analytical community would benefit from its publication:

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