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

Fluoride Determination in Milk, Soy, and Water-Based Products Using Ion-Selective Electrode and Direct Measurement Technique

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A. SAFETY CONCENTRATED HYDROCHLORIC ACID IS AN EXTREMELY CORROSIVE LIQUID THAT MAY BE FATAL IF SWALLOWED OR INHALED. INHALATION MAY CAUSE CHOKING, INFLAMMATION OF THE NOSE, THROAT AND UPPER RESPIRATORY TRACT, AND IN SEVERE CASES, PULMONARY EDEMA, AND CIRCULATORY FAILURE. SKIN CONTACT CAUSES REDNESS, PAIN, AND SEVERE SKIN BURNS. VAPORS ARE IRRITATING TO THE EYES AND MAY CAUSE PERMANENT EYE DAMAGE. ALWAYS USE PROTECTIVE LABORATORY EQUIPMENT WHEN HANDLING THIS CHEMICAL. IF CONTACT OCCURS, IMMEDIATELY FLUSH WITH WATER FOR AT LEAST 15 MINUTES. SODIUM CITRATE MAY CAUSE IRRITATION TO THE SKIN, EYES AND RESPIRATORY TRACT. USE THE PROPER LABORATORY EQUIPMENT WHEN HANDLING THIS CHEMICAL. IF CONTACT OCCURS, WASH THE EXPOSED AREA WITH WATER. SODIUM FLUORIDE IS POISONOUS, AND MAY BE FATAL IF SWALLOWED. SOLUTIONS ARE CORROSIVE. EFFECTS OF EXPOSURE MAY NOT APPEAR IMMEDIATELY. IF INGESTED, ADMINISTER MILK OR CALCIUM CARBONATE. WASH AREA WITH SOAP AND WATER IF SKIN CONTACT OCCURS. B. THEORY Ion-selective electrodes are used in this method to determine fluoride concentrations in products and ingredients. The fluoride ion-selective electrode is a solid-state electrode in which a single lanthanum fluoride crystal is sealed into a plastic electrode body. One face of the crystal is in contact with the internal reference solution and the other face is in contact with the sample. The crystal allows fluoride ions to pass through; this movement of ions sets up an electrical potential, which is proportional to the activity of fluoride ions in the sample. The fluoride concentration of the sample is measured by comparing its potential to the potential of standards of known fluoride concentration. Standards and samples are prepared in the same manner. Concentrated hydrochloric acid is added to help solubilize suspended inorganic material in the sample. Sodium citrate buffer is added to adjust the pH and ionic strength. The fluoride concentration is determined using a direct measurement technique.

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