AOAC SPIFAN Nutrients ERP (December 7, 2022)

For ERP/Working Group Use Only DO NOT DISTRIBUTE Fluor-04 (SLV) Resubmission FOR ERP USE ONLY DO NOT DISTRIBUTE

2. To troubleshoot electrode performance, proceed as follows: a) Immerse the fluoride and reference electrode into 50 mL of the 1ppm intermediate standard b) Equilibrate for 5 minutes and record mV reading. c) Pipette 50 mL of laboratory water into test solution. d) Equilibrate for 5 minutes and record mV reading. The difference between the second and first readings will be 18mV ± 1mV if the electrodes are operating properly. Differences greater than this indicate poor performance that could be due to a dirty electrode (buildup of residue on the sensing surface) or an electrode that has reached the end of its useful life. Polish the electrode according to the manufacturer’s recommendations. Alternatively, it can be polished using a Kimwipe (or equivalent wiper) and a small amount of regular fluoride toothpaste. Rinse the electrode thoroughly with laboratory water, flush the electrode fill solution, and refill with fresh solution. Soak the electrode in 100 ppm fluoride standard for 2 hours. After cleaning, the equilibration time for the first measurement might be longer than 5 minutes before a stable reading is obtained. Follow the electrode manufacturer’s suggestions for storage.

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