1．原理 通过测量两个浸液电极的电位差来测量样品溶液的PH值。 2．仪器 (1). pH计，玻璃电极，甘汞电极。 (2). 标准缓冲溶液pH4和7。 3．测定步骤 将电极与pH计连接好，打开电源预热一定时间，并将温度补偿开关旋至被测溶液温度相同的数值，调节仪器的零点，用标准液进行定位后，移去缓冲溶液，用蒸馏水冲洗电极并用滤纸吸干电极上的水待用。 称取 6g（士0.1g）样品，放入 400ml烧杯中加入 194ml纯水，搅拌使样品分散，并把烧杯置于沸水浴中，水浴液面应高于样品液面，搅拌淀粉乳直至淀粉糊化（大约5min），在冷水浴中立即冷却到室温（大约 25℃），从水浴中取出并搅拌淀粉糊以破坏任何已形成的凝胶。 用磁力搅拌器以足够的速度搅拌淀粉糊，使其在溶液表面产生小的旋涡。在淀粉糊中插入已标定好的电极，待读数稳定后，记录PH值至0.1个pH单位。
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