1.1 本试验方法包括电导率低于100的水样pH值的精确在线测定 μS/cm（见 表1 和 表2 )在3至11的pH范围内（参见 图1 )，在现场操作条件下。低电导率水的pH测量对于常规pH电极、方法和相关测量设备是有问题的。 图1 电导率-pH关系的限制 1.2 本试验方法包括连续测量低电导率水样流pH值所需的程序和设备，包括控制样品流压力、流速和温度的要求。对于低电导率样品的离线pH测量，请参考测试方法 D5464型 . 1.3 以国际单位制表示的值应视为标准值。本标准不包括其他测量单位。 1.4 本标准并不旨在解决与其使用相关的所有安全问题（如有）。 本标准的使用者有责任在使用前建立适当的安全、健康和环境实践，并确定监管限制的适用性。 1.5 本国际标准是根据世界贸易组织技术性贸易壁垒（TBT）委员会发布的《国际标准、指南和建议制定原则决定》中确立的国际公认标准化原则制定的。 =====意义和用途====== 5.1 在使用多程反渗透工艺的纯水处理中，有时需要在低电导率样品中连续测量pH值。几种污染物的膜截留效率取决于pH值测量和传导率低的通道之间的控制。 5.2 连续pH测量用于监测电厂循环化学，其中添加少量氨或胺或两者，以最大限度地减少高温纯水和蒸汽的腐蚀。 5.3 传统的pH测量是在含有相对大量酸、碱或溶解盐的溶液中进行的。在这些条件下，可以快速准确地进行pH测定。低电导率水样的连续在线pH测量更为困难 ( 4. , 5. ) 这些低离子强度溶液容易受到大气、样品流硬件和pH电极的污染。低电导率水成分浓度的变化会导致液体结电位的变化（参见 3.2.1 )导致pH测量误差。需要采取特殊预防措施。

1.1 This test method covers the precise on-line determination of pH in water samples of conductivity lower than 100 μS/cm (see Table 1 and Table 2 ) over the pH range of 3 to 11 (see Fig. 1 ), under field operating conditions. pH measurements of water of low conductivity are problematic for conventional pH electrodes, methods, and related measurement apparatus. FIG. 1 Restrictions Imposed by the Conductivity pH Relationship 1.2 This test method includes the procedures and equipment required for the continuous pH measurement of low conductivity water sample streams including the requirements for the control of sample stream pressure, flow rate, and temperature. For off-line pH measurements in low conductivity samples, refer to Test Method D5464 . 1.3 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard. 1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. 1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee. ====== Significance And Use ====== 5.1 Continuous pH measurements in low conductivity samples are sometimes required in pure water treatment using multiple pass reverse osmosis processes. Membrane rejection efficiency for several contaminants depends on pH measurement and control between passes where the conductivity is low. 5.2 Continuous pH measurement is used to monitor power plant cycle chemistry where small amounts of ammonia or amines or both are added to minimize corrosion by high temperature pure water and steam. 5.3 Conventional pH measurements are made in solutions that contain relatively large amounts of acid, base, or dissolved salts. Under these conditions, pH determinations may be made quickly and precisely. Continuous on-line pH measurements in water samples of low conductivity are more difficult ( 4 , 5 ) . These low ionic strength solutions are susceptible to contamination from the atmosphere, sample stream hardware, and the pH electrodes. Variations in the constituent concentration of low conductivity waters cause liquid junction potential shifts (see 3.2.1 ) resulting in pH measurement errors. Special precautions are required.