pH计PH meter

玻璃电极的球泡是特制的薄玻璃膜，膜内外溶液的 H⁺ 活度不同时，膜两侧产生电位差。根据能斯特方程，25 °C 时 pH 每变化 1 个单位，电位变化约 59.16 mV。玻璃膜电阻高达 10⁸ Ω，所以需要高输入阻抗的电子测量电路。温度影响斜率，仪器通常带温度补偿。

The glass bulb is a special thin glass membrane; when the H⁺ activity differs inside and outside, a potential develops across it. By the Nernst equation the potential changes by about 59.16 mV per pH unit at 25 °C. The membrane resistance is around 10⁸ Ω, so a very high-impedance measuring circuit is needed. Temperature changes the slope, so instruments usually compensate for it.

1906 年克雷默尔发现玻璃膜对氢离子有响应。1909 年哈伯和克莱门西维茨研制了玻璃电极。1934 年美国加州理工学院的阿诺德·贝克曼为测量柠檬汁酸度发明了第一台商用 pH 计，并创立了贝克曼仪器公司，这台仪器被认为是现代化学仪器产业的开端。

In 1906 Cremer found that glass membranes respond to hydrogen ions, and in 1909 Haber and Klemensiewicz developed the glass electrode. In 1934 Arnold Beckman at Caltech invented the first commercial pH meter to measure the acidity of lemon juice and founded Beckman Instruments; the instrument is often seen as the start of the modern chemical-instrument industry.

测量前用两种或三种标准缓冲溶液（如 pH 4.00、6.86、9.18）校准；每次测量后用蒸馏水冲洗、用滤纸轻吸，不能擦拭玻璃球泡；电极应保存在 3 mol/L KCl 溶液中，不能干放或泡在纯水中。强碱溶液中 Na⁺ 干扰会导致“碱误差”（读数偏低）。

Calibrate with two or three standard buffers, such as pH 4.00, 6.86 and 9.18, before measuring; rinse with distilled water after each reading and blot, never wipe, the bulb; store the electrode in 3 mol/L KCl, never dry or in pure water. In strongly alkaline solutions sodium ions interfere, causing an 'alkaline error' with low readings.