AOAC OMB Final Action Recommendation (December 2019)-2016.14

2016.14 (Jan. 2019) FOS-03 MLT Report FOR ERP USE ONLY DO NOT DISTRIBUTE

a Metrosep Carb 2 column. Some labs (4) used a 4 mm PA1 column instead of the 2 mm mentioned in the protocol and they adapted the main and post-column flow rates accordingly. Several participants also adapted the chromatographic conditions according to their equipment and habits (elution program, injection volume, oven temperature, etc.). Besides all these modifications, 6 participating labs did not use post-column addition of sodium hydroxide. This was clearly not ideal but probably not critical when the sodium hydroxide was in sufficient concentration in the eluent, which was absolutely the case with the Metrosep Carb 2 column (200 mM NaOH). For the 5 other participants, concentrations of NaOH in the mobile phase ranged from 6 mM to 25 mM, whereas it is known that below 15-20 mM NaOH the detector has poor response and linear range. Pictures of representative calibration curves of glucose and fructose were requested from those participants and all showed acceptable fit, except one lab. That lab used PA20 with only 6 mM NaOH which gave unusually convex calibration curves. However, as the sugar contents analysed were probably on acceptable portions of the calibration curves, only 2 results from this lab were identified as outliers by the single Grubb’s test. Which instrument response (area or height) to use for calibration was not clearly defined in the MLT protocol. One lab used height whereas the other 11 participants used area. A summary of the analytical conditions used by all participating laboratories is presented in Table 8 .