EP8.0附录2.2.3. pH值电位测定法 中英文.docx

2.2.3. POTENTIOMETRIC DETERMINATION OF pH2.2.3. pH值电位测定法The pH is a number which represents conventionally the hydrogen ion concentration of an aqueous solution.For practical purposes, its definition is an experimental one.The pH of a solution to be examined is related to that of a reference solution (pHs) by the following equation:in which E is the potential, expressed in volts, of the cell containing the solution to be examined and Es is the potential, expressed in volts, of the cell containing the solution of known pH (pHs), k is the change in potential per unit change in pH expressed in volts, and calculated from the Nernst equation.其中，E是待测溶液电势，单位伏特；Es是已知pH溶液的标准电势, 单位伏特；k表示pH每变化一个单位的电势变化，从能斯特方程计算得来，单位伏特。Table 2.2.3.-1. Values of k at different temperatures表2.2.3.-1：不同温度下的k值The potentiometric determination of pH is made by measuring the potential difference between 2 appropriate electrodes immersed in the solution to be examined: 1 of these electrodes is sensitive to hydrogen ions (usually a glass electrode) and the other is the reference electrode (for example, a saturated calomel electrode).pH的电势测定是测定沉浸在待测溶液中的2个适当电极之间的电位差：其中一个是氢离子敏感电极(通常是玻璃电极)，另一个是参比电极(例如饱和甘汞电极)。Apparatus. The measuring apparatus is a voltmeter with an input resistance at least 100 times that of the electrodes used. It is normally graduated in pH units and has a sensitivity such that discrimination of at least 0.05 pH unit or at least 0.003 V may be achieved.仪器：测量仪器是一个电压计，其输入电阻至少是所用电极的100倍。通常标有pH单位刻度，其灵敏度至少0.05pH或0.003V。Method. Unless otherwise prescribed in the monograph, all measurements are made at the same temperature (20-25 C).方法：除非在各论中另有规定，所有测定均在相同温度(2025C)下完成。Table 2.2.3.-2 shows the variation of pH with respect to temperature of a number of reference buffer solutions used for calibration.表2.2.3.-2：校准用参比缓冲液的pH对温度的变化For the temperature correction, when necessary，follow the manufacturers instructions. The apparatus is calibrated with the buffer solution of potassium hydrogen phthalate (primary standard) and 1 other buffer solution of different pH (preferably one shown in Table 2.2.3.-2).如必要，按照制造商的说明进行温度校正。仪器校准用邻苯二甲酸氢钾缓冲液(基准物质)和另一个不同pH值的缓冲液 (最好在表2.2.3.-2中选择)。The pH of a third buffer solution of intermediate pH read off on the scale must not differ by more than 0.05 pH unit from the value corresponding to this solution.pH值为上述两个缓冲液之间的第三个缓冲液pH读数不得超过相应pH值的0.05个单位。Immerse the electrodes in the solution to be examined and take the reading in the same conditions as for the buffer solutions.将电极浸入待测溶液中，在与缓冲液校准相同的条件下，读取待测溶液的读数。When the apparatus is in frequent use, checks must be carried out regularly.如果仪器经常使用，必须定期进行校验。Immerse the electrodes in the solution to be examined and take the reading in the same conditions as for the buffer solutions.将电极浸入待测溶液中，在与缓冲液校准相同的条件下，读取待测溶液的读数。When the apparatus is in frequent use, checks must be carried out regularly.如果仪器经常使用，必须定期进行校验。PREPARATION OF REFERENCE BUFFER SOLUTIONS对照缓冲溶液的配制Potassium tetraoxalate 0.05 M.Dissolve 12.61 g of C4H3KO8,2H2O in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent.0.05mol/L四草酸钾溶液：取C4H3KO8,2H2O 12.61g，用去二氧化碳的水溶解并稀释至1000.0mL。Potassium hydrogen tartrate, saturated at 25 C.Shake an excess of C4H5KO6 vigorously with carbon dioxide-free water R at 25 C. Filter or decant. Prepare immediately before use.25C饱和的酒石酸氢钾溶液：在25C下用去二氧化碳的水溶解过量的酒石酸氢钾，剧烈震摇，之后过滤或轻轻倒出。临用新制。Potassium dihydrogen citrate 0.05 M.Dissolve 11.41 g of C6H7KO7 in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent. Prepare immediately before use.0.05mol/L柠檬酸二氢钾溶液：取柠檬酸二氢钾11.41g，用去二氧化碳的水溶解并稀释至1000.0mL。临用新制。Potassium hydrogen phthalate 0.05 M.Dissolve 10.13 g of C8H5KO4, previously dried for 1 h at 110 2 C, in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent.0.05mol/L邻苯二甲酸氢钾溶液：取事先在1102C干燥1h的邻苯二甲酸氢钾10.13g，用去二氧化碳的水溶解并稀释至1000.0mL。Potassium dihydrogen phosphate 0.025M + disodium hydrogen phosphate 0.025M.Dissolve 3.39 g of KH2PO4 and 3.53 g of Na2HPO4, both previously dried for 2h at 120 2 C, in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent.0.025mol/L磷酸二氢钾 + 0.025mol/L磷酸氢二钠溶液：取事先在1202C干燥2 h的磷酸二氢钾3.39g和磷酸氢二钠3.53g，用去二氧化碳水溶解并稀释至1000.0mL。Potassium dihydrogen phosphate 0.0087M+disodium hydrogen phosphate 0.0303M. Dissolve 1.18 g of KH2PO4 and 4.30 g of Na2HPO4, both previously dried for 2 h at 120 2 C, in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent.0.0087 mol/L磷酸二氢钾+0.0303mol/L磷酸氢二钠溶液：取事先在1202C干燥2 h的磷酸二氢钾1.18 g和磷酸氢二钠4.30 g，用去二氧化碳的水溶解并稀释至1000.0mL。Disodium tetraborate 0.01 M.Dissolve 3.80 g of Na2B4O7,10H2O in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent. Store protected from atmospheric carbon dioxide.0.01mol/L四硼酸二钠溶液：取四硼酸二钠3.80 g，用去二氧化碳的水溶解并稀释至1000.0mL。储存应避免大气中的二氧化碳。Sodium carbonate 0.025 M + sodium hydrogen carbonate 0.025 M.Dissolve 2.64 g of Na2CO3 and 2.09 g of NaHCO3 in carbon dioxide-free water R and dilute to 1000.0 mL with the same solvent. Store protected from atmospheric carbon dioxide.0.025mol/L碳酸钠+0.025mol/L碳酸氢钠:取碳酸钠2.64 g，碳酸氢钠2.09g，用去二氧化碳的水溶解并稀释至1000.0mL。储存应避免大气中的二氧化碳。Calcium hydroxide, saturated at 25 C.Shake an excess of calcium hydroxide R with carbon dioxide-free water R and decant at 25 C. Store protected from atmospheric carbon dioxide.25C饱和的氢氧化钙溶液：在25C下，用去二氧化碳的水溶解过量的氢氧化钙，剧烈震摇，之后过滤或轻轻倒出。储存应避免大气中的二氧化碳。S