USP-645水电导率.doc

645 WATER CONDUCTIVITY 水电导率 水中的电导率是离子形成电流的一种度量 水分子离解成离子 作为 pH 计和温度 的一个函数 且能产生可预测的电导率 一些气体 尤其是二氧化碳 很容易溶在水 中且与形成的离子相互作用 这些可以用 pH 来预测对电导率的影响 讨论此问题的目 的 这些离子和它们所产生的电导率可以被认为是水本身固有的 水电导率也可以被存在的外来离子影响 在下面所描述模拟电导率标准中所用的 外来离子是氯离子和钠离子 普遍存在的氯离子的电导率 在 USP XXII 或更早期的 修定本中 当它是所必需的一个属性时 理论终点浓度为 0 47 ppm 限度为 0 3 ppm 的氨离子代表绝大部分所允许的水的杂质范围 为保持电中性 阳离子的平衡数量 例 如钠离子 被包括在允许的杂质范围 这些外来离子可能对水的化学纯度和制药应用的 适用性有明显的影响 固有的和外来的离子的混合电导率随 pH 值的变化而变化 是在 进行测试法的第三阶段时附表中所描述和使用的电导率标准的依据 在测试法中包括 两个预备阶段 如果在任何一个预备阶段中 符合测试条件和电导率限度 则认为水 符合检查要求 在此条件下进行第三阶段的实验是没必要的 仅在最后的测试步骤中 出现不合格时 才可以判定供试品不符合测试要求 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 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 represent a major portion of the allowed water impurity level A balancing quantity of cations such as sodium ions 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 procedure described in the section Bulk Water is designed for measuring the conductivity of waters such as Purified Water Water for Injection Water for Hemodialysis and the condensate of Pure Steam produced in bulk For water packaged in bulk but manufactured elsewhere or for Sterile Purified Water Sterile Water for Injection Sterile Water for Inhalation and Sterile Water for Irrigation some additional conductivity tests may be required Such tests are described in the section Packaged Water Online conductivity testing provides real time measurements and opportunities for real time process control decision and intervention Precaution should be taken while collecting water samples for off line conductivity measurements The sample may be affected by the sampling method the sampling container and environmental factors such as ambient carbon dioxide concentration and organic vapors INSTRUMENT SPECIFICATIONS AND OPERATING PARAMETERS Water conductivity must be measured accurately using calibrated instrumentation The conductivity cell constant a factor that represents the geometrical properties of the conductivity sensor must be known within 2 The cell constant can be verified directly by using a solution of known or traceable conductivity or indirectly by comparing the instrument reading taken with the conductivity sensor in question to readings from a conductivity sensor of known or traceable cell constant Meter calibration is accomplished by replacing the conductivity sensor with NIST or equivalent local national authority 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 Excluding the conductivity sensor cell constant accuracy the instrument accuracy must be 0 1 S cm In order to increase the measurement accuracy on the conductivity ranges used which can be large and to ensure a complete equipment calibration it is suggested that periodic verification of the entire equipment be performed This could be done by comparing the conductivity resistivity values displayed by the measuring equipment with those of an external calibrated conductivity measuring device The two nontemperature compensated conductivity or resistivity values must be equivalent to within 20 of each other or at a difference that is acceptable on the basis of product water criticality and or the water conductivity ranges in which the measurements are taken The two conductivity sensors should be positioned close enough together to measure the same water sample in the same environmental conditions In addition to the verification method performed in non temperature compensated mode a similar verification performed in temperature compensated mode could be performed to ensure an appropriate accuracy of the equipment when such a mode is used for trending or other purposes 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 typically done using a temperature sensor embedded in the conductivity sensor 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 Temperature measurement is required for the performance of the Stage 1 test It may be made using the temperature sensor embedded in the conductivity cell sensor An external temperature sensor positioned near the conductivity sensor is also acceptable Accuracy of the temperature measurement must be 2 仪器装置说明与操作参数 水电导率必须使用经校准过的仪器准确测定 电导池常数 常用作仪表刻度读数 的放大器 在已知数的 2 范围内 电导池常数可以通过已知电导率的溶液直接检验 或通过将已知的或经检验过的电导池常数与有问题的仪器电导池读数进行对比而间接 得到 仪表校准通过用可追踪的能斯特精密电阻 精确到标示值的 0 1 或等效的精密调 节的电阻装置 例如惠斯通电桥 给出预期的仪器响应值来完成 再校准的频率是 仪器设计 使用程度等因素的函数 然而 由于一些多刻度仪器有单一的校准调节器 再校准可以在使用不同刻度时进行 仪器必须在最低量程内有 0 1 S cm 的最小分辨 率 除了电导池精确度 仪器精确度必须是 0 1 S cm 在高温和低温下 由于温度对供试品的电导率读数有很大的影响 因此许多仪器 可自动纠正实际读数 以显示在正常温度 25 下观察到的理论值 这可以通过使用在 电导池探针中的温度传感器和仪器线路中的运算来实现 这种温度补偿可能是不准确 的 在这种方法中使用的电导率值是非温度补偿的测量值 温度测量的准确度必须为 2 下面所描述的操作法是用于测量 纯化水与注射用水 的电导率 下面操作法中 的阶段 1 可用在线检测仪器 已经过适当校准 替代 对阶段 1 进行适当的修改 在线仪 器的电导池常数已被精确地测定且温度补偿功能已无效 这样的在线质量控制仪器的 适用性也取决于它在水系统中的位置 所选择的仪器位置必须反映所监测的水的质量 操作法 BULK WATER The procedure below shall be performed using instrumentation that has been calibrated has conductivity sensor cell constants that have been accurately determined and has temperature compensation function that has been disabled For both online and offline measurements the suitability of instrumentation for quality control testing is also dependent on the sampling location s in the water system The selected sampling instrument location s must reflect the quality of the water used 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 Stage 3 pH and Conductivity Requirements 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 Procedure Stage 1 Stage 1 is intended for online measurement or may be performed offline in a suitable container 1 Determine the temperature of the water and the conductivity of the water using a nontemperature compensated conductivity reading 2 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 The corresponding conductivity value on this table is the limit NOTE Do not interpolate 3 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 Stage 1 Temperature and Conductivity Requirements for nontemperature compensated conductivity measurements only Temperature Conductivity Requirement S cm 00 6 50 8 100 9 151 0 201 1 251 3 301 4 351 5 401 7 451 8 Temperature Conductivity Requirement S cm 501 9 552 1 602 2 652 4 702 5 752 7 802 7 852 7 902 7 952 9 1003 1 阶段 1 1 用非温度补偿的电导仪测定水的温度和电导率 可以在适当的容器中测量或在线测 量 2 使用 阶段 1 温度与电导率要求表 找到不高于所测温度的温度值 也就是相邻 的较低的温度 在表中相应的电导率值是限度值 注 不可以内插 3 如果测量的电导率不大于表中的数值 则水符合电导率检查的要求 如果电导率高 于表中的数值 按阶段 2 进行 阶段 1 温度与电导率要求 仅对非温度补偿的电导率测定 温度电导率要求 S cm 温度电导率要求 S cm 00 6552 1 50 8602 2 100 9652 4 151 0702 5 201 1752 7 251 3802 7 301 4852 7 351 5902 7 401 7952 9 451 81003 1 501 9 Stage 2 4 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 S cm per 5 minutes note the conductivity 5 If the conductivity is not greater than 2 1 S cm the water meets the requirements of the test for conductivity If the conductivity is greater than 2 1 S cm proceed with Stage 3 阶段 2 4 将足量的水 100ml 或多于 100ml 转移至一个适宜的容器中 并搅拌供试品 必要 时调节温度 当温度保持在 25 1 开始剧烈的搅拌供试品 并定期观察电导率 当电导率的变化 由于吸收大气中的二氧化碳 小于每 5 分钟 0 1 S cm 的净值 记 录电导率 5 如果电导率不大于 2 1 S cm 水符合电导率检查的要求 如果电导率大于 2 1 S cm 按阶段 3 进行 Stage 3 6 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 791 7 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 Stage 3 pH and Conductivity Requirements for atmosphere and temperature equilibrated samples only pH Conductivity Requirement S cm 5 04 7 5 14 1 5 23 6 5 33 3 5 43 0 5 52 8 5 62 6 5 72 5 5 82 4 5 92 4 6 02 4 6 12 4 6 22 5 6 32 4 6 42 3 6 52 2 6 62 1 6 72 6 6 83 1 6 93 8 7 04 6 阶段 3 6 保持供试品的温度在 25 1 在第 5 步中电导率测定的大约 5 分钟内进行此实验 向相同的水供试品中加入饱和的 KCl 溶液 每 100ml 供试品加入 0 3ml 按 pH 791 项下规定测定 pH 值 读数为 0 1 个 pH 单位 7 参考 阶段 3 pH 值与电导率要求表 在所测量的 pH 值点确定电导率限度 如 果在第 4 步中测定的电导率不大于在第 6 步测得的 pH 值相对应的电导率要求 则 水符合电导率检查的要求 如果任一个测得的电导率大于此值 或 pH 值落在 5 0 7 0 的范围之外 则水不符合电导率检查的要求 阶段 3 pH 值与电导率要求 仅对大气与样品温度相平衡的样品 PH电导率要求 S cm PH电导率要求 S cm 5 04 76 12 4 5 14 16 22 5 5 23 66 32 4 5 33 36 42 3 5 43 06 52 2 5 52 86 62 1 5 62 66 72 6 5 72 56 83 1 5 82 46 93 8 5 92 47 04 6 6 02 4 S cm 微西门子 厘米 mho cm 兆欧姆 cm 的倒数 PACKAGED WATER The procedure and test limits are intended for water packaged in bulk but manufactured elsewhere or for Sterile Purified Water Sterile Water for Injection Sterile Water for Inhalation and Sterile Water for Irrigation All these waters are derived from Purified Water or Water for Injection and therefore have been determined to be compliant with the Bulk Water requirements before being stored in the containe