Quality parameter testing of dairy products

This standard specifies the determination method for urease in infant and young child food and dairy products. This standard is applicable to the qualitative testing of urease in infant and young child food and dairy products. Principle 2: Urease catalyzes the conversion of urea to ammonium carbonate under appropriate pH and temperature conditions. Ammonium carbonate generates ammonium hydroxide under alkaline conditions, and reacts with the potassium mercuric iodide complex salt in Nessler's reagent to produce a brown color of mercuric ammonium iodide. 3 Reagents and Material Notes: Unless otherwise specified, all reagents used in this standard are analytical pure, and water is Grade III water as specified in GB/T 6682. 3.1 Reagent 3.1.1 Urea (H: NCONH:). 3.1.2 Sodium tungstate (Naz wo. -2H: O. 3.1.3 Potassium sodium tartrate (CA H.O. KNa 4HO). 3.1.4 Sulfuric acid (H: SO,) 3.1.5 Disodium hydrogen phosphate (Naz HPO,) 3.1.6 Potassium dihydrogen phosphate (KH, PO,) 3.1.7 Mercury iodide (HgI). 3.1.8 Potassium iodide (KD). 3.1.9 Sodium hydroxide (NaOH). 3.2 Reagent Preparation 3.2.1 Urea Solution (10 g/L): Weigh 5g of urea and dissolve it in 500 mL of water. Store in a brown reagent bottle and refrigerate in the refrigerator, with a validity period of 1 month. 3.2.2 Sodium tungstate solution (100 g/L); Weigh 50 g of sodium tungstate and dissolve it in 500 ml. of water. 3.2.3 Potassium sodium tartrate solution (20 g/L); Weigh 10 g of potassium sodium tartrate and dissolve it in 500 ml of water. 3.2.4 Sulfuric acid solution (50 mL/L): Take 25 mL of sulfuric acid and dissolve it in 500 ml of water. 3.2.5: Disodium hydrogen phosphate solution; Weigh 9.47 g of anhydrous disodium hydrogen phosphate and dissolve it in 1000 mL of water. 3.2.6 Potassium dihydrogen phosphate solution; Weigh 9.07 g of potassium dihydrogen phosphate and dissolve it in 1000 mL of water. 3.2.7 Neutral buffer solution; Take 611 mL of disodium hydrogen phosphate solution and 389 mL of potassium dihydrogen phosphate solution, and mix the two solutions evenly. 3.2.8 Mercury iodide potassium iodide mixed solution; Weigh 55 g of red mercury iodide and 41.25 g of potassium iodide, and dissolve them in 250 mL of water. 3.2.9 Nessler's reagent: Weigh 144 g of sodium hydroxide and dissolve it in 500 ml of water. After fully dissolving and cooling, slowly transfer it into 1000 mL

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