Low sodium sulfite detection

This standard specifies the limit test method for heavy metals in food additives. This standard is applicable to the limit test of heavy metals in food additives. Under weakly acidic conditions (pH 3-4), the heavy metal ions in the sample react with hydrogen sulfide to produce black lead. Compare it with the lead standard solution treated by the same method and conduct a limit test. 3 Reagents and Materials Note: Unless otherwise specified, all reagents used in this standard are analytical pure, and water is Grade 1 water as specified in GB/T 6682. 3.1 Reagent 3.1.1 Nitric acid (HNO,). 3.1.2 Sulfuric acid (H, SO), 3.1.3.3 Hydrochloric acid (HCD. 3.1.4 Ammonia water (NH-HO), 3.1.5 Ammonium acetate (CH, NOz), 3.1.6 Phenolphthalein (C, OH, O.), 3.1.7 Hydrogen peroxide (H, O:), 3.1.8 Hydrogen sulfide (HaS). 3.1.9 Perchlorate acid (HCIO) 3.2 Reagent preparation 3.2.1 Hydrochloric acid solution (6 mol/L): Measure 50 mI of hydrochloric acid and dilute with water to 100 ml. 3.2.2: Hydrochloric acid solution (1 mol/L); Measure 8.3 mL of hydrochloric acid and dilute with water to 100 ml. 3.2.3 Ammonia solution (6 mol/L): Measure 40 mL of ammonia water and dilute with water to 100 mL. 3.2.4 Ammonia solution (1 mol/L): Take 6.7 ml of ammonia water and dilute it with water to 100 ml. 3.2.5 pH 3.5 acetate buffer solution; Weigh 25.0 g of ammonium acetate and dissolve it in 25 mL of water, add 45 mL of 6 mol/L hydrochloric acid solution, adjust the pH to 3.5 with dilute hydrochloric acid or ammonia water, and dilute with water to 100 mL. 3.2.6 Phenolphthalein ethanol solution (1%): Weigh 1.0 g of phenolphthalein and dissolve it in 100 mL of ethanol solution. 3.2.7: Hydrogen sulfide saturated solution; Hydrogen sulfide gas is introduced into water without carbon dioxide (such as at a flow rate of about 80 mL/min, ventilated for 1 hour. This solution is prepared before use). 3.2.8- Nitric acid solution (1%): Dilute 1 mL of nitric acid with water to 100 mL

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