645 WATER CONDUCTIVITY

（645）水的电导率

Electrical conductivity in water is a measure of the ion-facilitated electron flow through it. Water molecules dissociate into ions as a function of pH and temperature and result in a very predictable conductivity. Some gases, most /notably carbon dioxide, readily dissolve in water and interact to form ions, which predictably affect conductivity as well as pH. For the purpose of this discussion, these ions and their resulting conductivity can be considered intrinsic to the water.

水的电导率是离子易化电流通过水时的测量值。水分子在pH值和温度的作用下分离成离子，产生一个可预知的电导率。一些气体，尤其是二氧化碳，极易溶解于水中，并相互作用形成离子，从而预先影响电导率以及pH值。针对讨论的目的，这些离子以及它们所导致的电导率可被当作水的固有特性。



Water conductivity is also affected by the presence of extraneous ions. The extraneous ions used in modeling the conductivity specifications described below are the chloride and sodium ions. The conductivity of the ubiquitous chloride ion (at the theoretical endpoint concentration of 0.47 ppm when it was a required attribute test in USP XXII and earlier revisions) and the ammonium ion at the limit of 0.3 ppm represents a major portion of the allowed water impurity level. A balancing quantity of cations, such as sodium ion, is included in this allowed impurity level to maintain electroneutrality. Extraneous ions such as these may have significant impact on the water's chemical purity and suitability for use in pharmaceutical applications. The combined conductivities of the intrinsic and extraneous ions vary as a function of pH and are the basis for the conductivity specifications described in the accompanying table and used when performing Stage 3 of the test method. Two preliminary stages are included in the test method. If the test conditions and conductivity limits are met at either of these preliminary stages, the water meets the requirements of this test. Proceeding to the third stage of the test in these circumstances is unnecessary. Only in the event of failure at the final test stage is the sample judged noncompliant with the requirements of the test.

水的电导率也会受到外部裂化离子的影响。在建立如下所述的电导率规格的模型时外部裂化离子为氯离子与钠离子 。无所不在的氯离子（如果在USP XXII 与初期的修正中必须进行品质测试的话，那么它的理论终点浓度为0.47 ppm）与铵离子的电导率在达到0.3 ppm的限度时呈现出大部分的可允许水杂质层。可允许杂质层必须包含平衡的阳离子数量，例如钠离子，以维持电离平衡。类似的外部裂化离子有可能对水在制药使用上的化学纯度以及适宜性产生极大的影响。内部与外部裂化离子的组合电导率会因pH值的作用而改变，同时它也是附表中所描述的、并在执行测试第3阶段时的电导率基础。测试中包含两个初期阶段，如果测试的条件与水的电导率限度在这两个阶段中任何一个都可以达到话，那么该水符合测试的要求，在这种情况下，则没必要进行第三阶段。但是如果在测试的最后阶段失败的话，则认为是样品不符合测试的要求。



INSTRUMENT SPECIFICATIONS AND OPERATING PARAMETERS

仪器说明与运行参数



Water conductivity must be measured accurately using calibrated instrumentation. The conductivity cell constant, a factor used as a multiplier for the scale reading from the meter, must be known within ±2%. The cell constant can be verified directly by using a solution of known conductivity, or indirectly by comparing the instrument reading taken with the cell in question to readings from a cell of known or certified cell constant.

水的电导率必须使用校准过的仪器准确测量。作为仪表上读取的刻度的乘数，水的细胞传导常数必须在±2%的范围之内。细胞常数可通过对已知传导率的溶液直接进行验证，也可以间接地通过比较不确定的细胞仪器读数与已知或已确认的细胞常数进行验证。



Meter calibration is accomplished by replacing the conductivity cell with NIST-traceable precision resistors (accurate to ±0.1% of the stated value) or an equivalently accurate adjustable resistance device, such as a Wheatstone Bridge, to give a predicted instrument response. Each scale on the meter may require separate calibration prior to use. The frequency of recalibration is a function of instrument design, degree of use, etc. However, because some multiple scale instruments have a single calibration adjustment, recalibration may be required between each use of a different scale. The instrument must have a minimum resolution of 0.1 µS/cm* on the lowest range. Excluding the cell accuracy, the instrument accuracy must be ±0.1 µS/cm.

可通过以下方法完成仪表的校准：使用NIST-traceable精确电阻器（法定值精确至±0.1%）更换传导细胞，或者相同的准确的可调电阻装置，例如惠斯通电桥，引起预先的仪器反应。重新校准的频率可视设计的仪器、使用的程度等而定。但是，由于一些多重标度仪器有一个单一的校准调试，可能还需要在使用不同标度时进行重新校准。 在最低的范围内，仪器必须具备一个最小的分辨率，即0.1 µS/cm。除了细胞的准确性外，仪器的准确性必须为±0.1 µS/cm。



Because temperature has a substantial impact on conductivity readings of specimens at high and low temperatures, many instruments automatically correct the actual reading to display the value that theoretically would be observed at the nominal temperature of 25 . This is done using a temperature sensor in the conductivity cell probe and an algorithm in the instrument's circuitry. This temperature compensation algorithm may not be accurate. Conductivity values used in this method are nontemperature-compensated measurements.

当样品处在高温或低温的情况下，温度会对样品的传导率读数产生极大的影响，许多仪器会自动纠正实际读数，以显示在常温25 的情况下理论上观测的值，

可通过在细胞传感率探测里使用传感器，并在仪器线路上使用十进位计数法而进行。此温度补偿计算法则可能不准确。该方法使用的传导率值为非温度补偿测量。



The procedure described below is designed for measuring the conductivity of Purified Water and Water for Injection. Stage 1 of the procedure below may alternatively be performed (with the appropriate modifications to Step 1) using on-line instrumentation that has been appropriately calibrated, whose cell constants have been accurately determined, and whose temperature compensation function has been disabled. The suitability of such on-line instrumentation for quality control testing is also dependent on its location  in the water system. The selected instrument location  must reflect the quality of the water used.

以下所描述的程序是为测量纯化水与注射用水的电导率而设计的，程序中的阶段1可能会被选择性操作，通过使用已经适当校正过的在线仪器进行，该仪器的细胞常数已被准确测定，同时其的温度补偿功能已经失效。用于质量控制测试的在线仪器的适宜性依赖于它在水系统中所处的位置而定，而所选择的仪器位置则必须反映出所使用水的质量。



Change to read:

阅读如下内容：

PROCEDURE

Stage 1

阶段1

1. Determine the temperature of the water and the conductivity of the water using a nontemperature-compensated conductivity reading. The measurement may be performed in a suitable container or as an on-line measurement.
   
2. 使用非补偿性温度传导率读数测量水的温度与电导率。该测试可在适当的容器中进行，也可在线测试。
   
   
   
3. Using the Stage 1—Temperature and Conductivity Requirements table, find the temperature value that is not greater than the measured temperature, i.e., the next lower temperature. USP28 The corresponding conductivity value on this table is the limit. [NOTE—Do not interpolate.] USP28
   
4. 根据阶段1—温度与传导率要求表，找出小于所测温度的温度值，例如其次的较低温度，表中相应的传导率值为极限。[注释—不得添改]
   
   
   
5. If the measured conductivity is not greater than the table value, the water meets the requirements of the test for conductivity. If the conductivity is higher than the table value, proceed with Stage 2.
   
6. 如果所测的传导率小于表中的值，则该水符合传导率测试的要求。如果传导率值大于表中的值，则进入第2阶段测试。
   
   
   
   Stage 1—Temperature and Conductivity Requirements
   
   (for nontemperature-compensated conductivity measurements only)
   
   阶段1—温度与传导率要求
   
   （只针对非补偿性温度传导率测量）
   
   Temperature  Conductivity Requirement (µS/cm)
   
   0  0.6
   
   5  0.8
   
   10  0.9
   
   15  1.0
   
   20  1.1
   
   25  1.3
   
   30  1.4
   
   35  1.5
   
   40  1.7
   
   45  1.8
   
   50  1.9
   
   55  2.1
   
   60  2.2
   
   65  2.4
   
   70  2.5
   
   75  2.7
   
   80  2.7
   
   85  2.7
   
   90  2.7
   
   95  2.9
   
   100  3.1
   
   
   
   Stage 2
   
7. Transfer a sufficient amount of water (100 mL or more) to a suitable container, and stir the test specimen. Adjust the temperature, if necessary, and, while maintaining it at 25 ± 1 , begin vigorously agitating the test specimen while periodically observing the conductivity. When the change in conductivity (due to uptake of atmospheric carbon dioxide) is less than a net of 0.1 µS/cm per 5 minutes, note the conductivity.
   
8. If the conductivity is not greater than 2.1 µS/cm, the water meets the requirements of the test for conductivity. If the conductivity is greater than 2.1 µS/cm, proceed with Stage 3.
   
   阶段2
   
9. 将足够量的水（100mL或更多）倒入适当的容器中，并搅拌测试液。调节温度，如有必要，将温度保持在25 ± 1 ，充分的搅动测试液，并定时观察传导率。当传导率的改变小于0.1 µS/cm/5mins时，记录传导率。
   
10. 如果传导率小于2.1 µS/cm，那么该水符合传导率测试的要求；如果传导率大于2.1 µS/cm，那么进入第3阶段测试。
    
    
    
    Stage 3
    
11. Perform this test within approximately 5 minutes of the conductivity determination in Step 5, while maintaining the sample temperature at 25 ± 1 . Add a saturated potassium chloride solution to the same water sample (0.3 mL per 100 mL of the test specimen), and determine the pH to the nearest 0.1 pH unit, as directed under pH á791ñ.
    
12. Referring to the Stage 3—pH and Conductivity Requirements table, determine the conductivity limit at the measured pH value. If the measured conductivity in Step 4 is not greater than the conductivity requirements for the pH determined in Step 6, the water meets the requirements of the test for conductivity. If either the measured conductivity is greater than this value or the pH is outside the range of 5.0 to 7.0, the water does not meet the requirements of the test for conductivity.
    
    阶段3
    
    6.　在步骤５测定传导率约５分钟时执行该测试，并将测试液温度维持在25 ± 1 。在同样的测试液中加入饱和的氯化钾溶液（每100 毫升测试液中加入0.3
    
    毫升），根据pH á791ñ测定pH值，并精确至0.1。
    
    7.根据阶段3--pH与传导率要求表，在所测的pH值处测定传导率限度。如果步骤4 所测的传导率小于步骤6所测的pH的传导率要求，那么该水符合传导率测试要求；如果所测的任意传导率大于该值或者pH值不在5.0 至 7.0的范围之中，那么该水不符合传导率测试的要求。
    
    
    
    Stage 3—pH and Conductivity Requirements
    
    (for atmosphere and temperature equilibrated samples only)
    
    阶段3—pH 与传导率要求
    
    (只针对气压与温度平衡的样品)
    
    pH  Conductivity Requirement (µS/cm)
    
    5.0  4.7
    
    5.1  4.1
    
    5.2  3.6
    
    5.3  3.3
    
    5.4  3.0
    
    5.5  2.8
    
    5.6  2.6
    
    5.7  2.5
    
    5.8  2.4
    
    5.9  2.4
    
    6.0  2.4
    
    6.1  2.4
    
    6.2  2.5
    
    6.3  2.4
    
    6.4  2.3
    
    6.5  2.2
    
    6.6  2.1
    
    6.7  2.6
    
    6.8  3.1
    
    6.9  3.8
    
    7.0  4.6