Other physicochemical parameter detection

This part of GB/T 13025 specifies the determination method for iodine in iodized edible salt. The direct titration method in this section is applicable to the determination of iodine in iodized edible salt with added iodate; The oxidation-reduction titration method is suitable for the determination of iodine in iodized edible salt containing iodide or reducing substances; Photometric method is suitable for rapid determination of iodine. The following normative references are essential for the application of this document. For dated references, only the dated version applies to this document. For undated references, the latest version (including all modification orders) applies to this document. GB/T 6682-2008 Specification and Test Methods for Analytical Laboratory Water 3. Volumetric Method 3.1. Direct Titration Method 3.1.1. Principle: In an acidic medium, the iodate ion in the sample oxidizes potassium iodide to precipitate elemental iodine. Titrate with a sodium thiosulfate standard titration solution to determine the iodine content. IO+ 5T -+6HI+-31.+3H, O2S: O+l -... -21-+S, O3.1.2 Reagent 3.1.2.1 Reagent specifications Unless otherwise specified, only reagents confirmed as analytical pure and Grade III water specified in GB/T 66822-2008 shall be used in the analysis. 3.1.2.2 Phosphoric acid solution (1 mol/L) Measure 17 mL of 85% phosphoric acid and dilute with water to 250 mL. 3.1.2.3 Potassium Iodide Solution (50 z/L) Weigh 25.0g of potassium iodide, dissolve and dilute with water to 500 mI, store in a brown bottle, and prepare as needed. 3.1.2.4 Potassium Iodate Standard Solution Accurately weigh 1.427 g of potassium iodate reference reagent dried to constant weight at 110 ℃± 2 ℃, place in a 150 ml beaker, dissolve with water, transfer to a 1000 mL volumetric flask, dilute with water to the mark, shake well, and the concentration of this solution is c (- KIO,)=4.000 × Dilute the above solution accurately by 20 times to obtain a concentration of c (KIO,)=2.000 × 10- * mol/L. Potassium iodate standard solution

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