Beverages and beverage testing

5.3 Instruments and equipment: Scattering deep turbidity meter. 5.4 The analysis steps should be carried out according to the instrument user manual. When the turbidity exceeds 40 NTU, it can be diluted with water and measured. The expression of analysis results is calculated by multiplying the turbidity reading displayed during instrument measurement by the dilution factor. Principle 6.1: pH is the logarithmic value of the reciprocal hydrogen ion activity in water, and is an important parameter for evaluating water quality. When water is polluted, it can cause significant changes in pH; When water contains a large amount of free carbon dioxide, it can significantly reduce the pH of the water. The pH of water is measured using the glass electrode method. Using a glass electrode as the indicator electrode and a saturated calomel electrode as the reference electrode, insert it into the solution to form a primary battery. When the concentration of hydrogen ions changes, the electromotive force between the glass electrode and the calomel electrode also changes. At 25 ℃, each unit of pH scale is equivalent to a 59.1 mV change in electromotive force, which is directly represented by the pH reading on the instrument. There is a compensation device for temperature difference on the instrument. 6.2 Reagents and Materials Unless otherwise specified, all reagents used in this method are analytical pure, and the water is Grade III water according to GB/T6682. 6.2.1 Potassium hydrogen phthalate standard buffer solution: Weigh 10.21 g of potassium hydrogen phthalate (KHC, H, O) dried at 105 ℃ for 2 hours, dissolve it in water, and dilute to 1000 ml. The pH of this solution is 4.00 at 20 ℃, and the pH at different temperatures is shown in Table 2. 6.2.2 Mixed phosphate standard buffer solution: Weigh 3.40 g of potassium dihydrogen phosphate (KH, PO,) and 3.55 g of disodium hydrogen phosphate (NagHPO,) dried at 105 ℃ for 2 hours, dissolve them in water, and dilute to 1000 mL. The pH of this solution is 6.88 at 20 ℃, and the pH at different temperatures is shown in Table 2. 6.2.3. Sodium tetraborate standard buffer solution; Weigh 3.8l g of sodium tetraborate (NaB, O · 10HO), dissolve in water, and dilute to 1000 mL. The pH of this solution is 9.22 at 20 ℃. The pH at different temperatures is shown in Table 2

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