USP36-921-WATER-DETERMINATION.doc

水分测定水分测定 WATER DETERMINATION 很多药典物品要么是水合物 要么含有处于吸附状态的水 因此 测定水分含量对于证实 与药典标准的符合性是很重要的 通常 在各论中会根据该物品的性质 要求使用下面若 干方法中的一个 偶尔 会允许在 2 个方法中任选一个 当该物品含有水合状态的水 按 照具体各论中的规定 使用方法 I 滴定法 方法 II 恒沸法 或方法 III 重量分析法 在标题水分项下给出 Many Pharmacopeial articles either are hydrates or contain water in adsorbed form As a result the determination of the water content is important in demonstrating compliance with the Pharmacopeial standards Generally one of the methods given below is called for in the individual monograph depending upon the nature of the article In rare cases a choice is allowed between two methods When the article contains water of hydration the Method I Titrimetric the Method II Azeotropic or the Method III Gravimetric is employed as directed in the individual monograph and the requirement is given under the heading Water 在加热时的失重可能不全是水的情况下 使用标题干燥失重 见干燥失重 The heading Loss on drying see Loss on Drying is used in those cases where the loss sustained on heating may be not entirely water 方法方法 I 滴定测量法 滴定测量法 METHOD I TITRIMETRIC 除各论中另有规定外 使用方法 Ia 来测定水分 Determine the water by Method Ia unless otherwise specified in the individual monograph 方法 Ia 直接滴定 Method Ia Direct Titration 原理 水分的滴定法检测是基于水与二氧化硫及碘的无水溶液在缓冲液中与氢离子之间的 定量反应 Principle The titrimetric determination of water is based upon the quantitative reaction of water with an anhydrous solution of sulfur dioxide and iodine in the presence of a buffer that reacts with hydrogen ions 在原本的滴定测量溶液 即卡尔 费休试剂 中 二氧化硫和碘溶解于嘧啶和甲醇中 供 试样品可以用该试剂直接滴定 或者可以使用剩余滴定程序来进行分析 此反应的化学计 量比不够准确 检测的重现性取决于某些因素 例如该试剂成分的相对浓度 用于溶解供 试样品的惰性溶剂的性质 测定所用的具体方法等 因此 需要使用经验性的标准化方法 以保证必要的准确性 该方法中的精密度很大程度上取决于将大气湿度从该系统中排除的 程度 水分滴定通常使用无水甲醇作为供试样品的溶剂 在有些情况下 特殊或不常见的 供试样品也可以使用其他合适的溶剂 在此种情况下 推荐加入至少 20 的甲醇或者其他 伯醇 USP36 In the original titrimetric solution known as Karl Fischer Reagent the sulfur dioxide and iodine are dissolved in pyridine and methanol The test specimen may be titrated with the Reagent directly or the analysis may be carried out by a residual titration procedure The stoichiometry of the reaction is not exact and the reproducibility of a determination depends upon such factors as the relative concentrations of the Reagent ingredients the nature of the inert solvent used to dissolve the test specimen and the technique used in the particular determination Therefore an empirically standardized technique is used in order to achieve the desired accuracy Precision in the method is governed largely by the extent to which atmospheric moisture is excluded from the system The titration of water is usually carried out with the use of anhydrous methanol as the solvent for the test specimen In some cases other suitable solvents may be used for special or unusual test specimens In these cases the addition of at least 20 of methanol or other primary alcohol is recommended USP36 设备 任何能够充分排除大气湿度 并能确定滴定终点的仪器都可以使用 在直接滴定无 色溶液的情况下 可以通过从金丝雀黄到琥珀色的颜色改变来观察此终点 在向供试样品 作残留滴定的情况下 会观察到与此相反的情况 但是 更常见的情况是 使用仪器依靠 电势确定终点 该向浸没在待滴定溶液中的一对白金电极上施加 200mV 左右的电压 形 成简单电路 在滴定终点 略微过量的该试剂会使电流提高到 50 和 150 微安培 并维持 30 秒到 30 分钟 具体时间取决于被滴定的溶液 可溶解于该试剂中的物质对应的时间是 最短的 在一些自动滴定仪上 在该终点出现的电流或电压的突然变化会使盛装滴定液的 滴定管的电磁阀关闭 市场上销售的仪器通常包含一个封闭系统 由一个或两个自动滴定 管 一个配备了电极和磁力搅拌器的密封的滴定容器组成 系统内空气通过适当的干燥剂 保持干燥 该滴定容器可以通过干燥氮气流或干燥空气流来进行净化 Apparatus Any apparatus may be used that provides for adequate exclusion of atmospheric moisture and determination of the endpoint In the case of a colorless solution that is titrated directly the endpoint may be observed visually as a change in color from canary yellow to amber The reverse is observed in the case of a test specimen that is titrated residually More commonly however the endpoint is determined electrometrically with an apparatus employing a simple electrical circuit that serves to impress about 200 mV of applied potential between a pair of platinum electrodes immersed in the solution to be titrated At the endpoint of the titration a slight excess of the reagent increases the flow of current to between 50 and 150 microamperes for 30 seconds to 30 minutes depending upon the solution being titrated The time is shortest for substances that dissolve in the reagent With some automatic titrators the abrupt change in current or potential at the endpoint serves to close a solenoid operated valve that controls the buret delivering the titrant Commercially available apparatus generally comprises a closed system consisting of one or two automatic burets and a tightly covered titration vessel fitted with the necessary electrodes and a magnetic stirrer The air in the system is kept dry with a suitable desiccant and the titration vessel may be purged by means of a stream of dry nitrogen or current of dry air 试剂 按下面方法配制卡尔 费休试剂 将 125 克碘加入到含有 670mL 甲醇和 170mL 嘧 啶的溶液中 放冷 将 100mL 嘧啶置于一个 250mL 量筒中 冰浴中冷却 送入干燥的二 氧化硫直到体积达到 200mL 边振摇边缓慢将此溶液加入到放冷后的碘混合物中 摇动以 使碘溶解 转移此溶液至设备中 并在标定之前放置过夜 新制的 1mL 此溶液相当于约 5mg 水 但是会逐渐变差 因此 在使用前 1 个小时需对其标定 或在连续使用时每日标 定 使用中需避光 将该试剂的散装存货保存于适当密闭的玻璃塞容器中 完全避光 并 冷藏 测定痕量的水 小于 1 时 最好使用水当量因子不小于 2 0 的试剂 以使滴定 液的消耗量较为明显 USP36 Reagent Prepare the Karl Fischer Reagent as follows Add 125 g of iodine to a solution containing 670 mL of methanol and 170 mL of pyridine and cool Place 100 mL of pyridine in a 250 mL graduated cylinder and keeping the pyridine cold in an ice bath pass in dry sulfur dioxide until the volume reaches 200 mL Slowly add this solution with shaking to the cooled iodine mixture Shake to dissolve the iodine transfer the solution to the apparatus and allow the solution to stand overnight before standardizing One mL of this solution when freshly prepared is equivalent to approximately 5 mg of water but it deteriorates gradually therefore standardize it within 1 h before use or daily if in continuous use Protect from light while in use Store any bulk stock of the reagent in a suitably sealed glass stoppered container fully protected from light and under refrigeration For determination of trace amounts of water less than 1 it is preferable to use a Reagent with a water equivalency factor of not more than 2 0 which will lead to the consumption of a more significant volume of titrant USP36 可以使用市售的卡尔 费休类型试剂的稳定溶液 也可以使用市售的含有除了嘧啶之外的 溶剂或碱 或除了甲醇之外的醇类的试剂 这些试剂可以是单一的溶液 也可以是通过原 位混合两种含有试剂各组分的溶液形成的试剂 如果某些各论中要求使用稀释后的试剂 则应当按照生产商的规定稀释 可以使用甲醇或其他适当溶剂 例如乙二醇一甲醚 作为 稀释剂 A commercially available stabilized solution of Karl Fischer type reagent may be used Commercially available reagents containing solvents or bases other than pyridine or alcohols other than methanol may be used also These may be single solutions or reagents formed in situ by combining the components of the reagents present in two discrete solutions The diluted Reagent called for in some monographs should be diluted as directed by the manufacturer Either methanol or other suitable solvent such as ethylene glycol monomethyl ether may be used as the diluent 供试溶液 除非在各论中另有规定 精密称定或量取一定量的供试样品 其中含水估计在 2 至 250mg 之间 含水的量取决于试剂的水当量因子和终点测定的方法 在大多数情况下 可以使用此公式估计供试样品的最小量 以毫克计算 FCV KF 其中 F 是试剂的水当量因子 单位为毫克每毫升 C 是滴定管容量中所使用的体积的百 分比 V 是滴定管体积 以毫升计 KF 是样品中限度或合理预期的水含量百分比 对于手 动滴定 C 值一般在 30 至 100 之间 而对于仪器方法终点测定 在 10 至 100 之间 注 计算中 FCV 的乘积最好大于等于 200 以保证滴定的最小水量大于等于 2mg Test Preparation Unless otherwise specified in the individual monograph use an accurately weighed or measured amount of the specimen under test estimated to contain 2 to 250 mg of water The amount of water depends on the water equivalency factor of the Reagent and on the method of endpoint determination In most cases the minimum amount of specimen in mg can be estimated using the formula FCV KF in which F is the water equivalency factor of the Reagent in mg per mL C is the used volume in percent of the capacity of the buret V is the buret volume in mL and KF is the limit or reasonable expected water content in the sample in percent C is generally between 30 and 100 for manual titration and between 10 and 100 for the instrumental method endpoint determination Note It is recommended that the product of FCV be greater than or equal to 200 for the calculation to ensure that the minimum amount of water titrated is greater than or equal to 2 mg 如果供试样品是带有推进剂的气雾剂 将其存放于冷冻室中不少于 2 小时 打开容器 并 检验 10 0mL 混合均匀的样品 在滴定该样品过程中 在 10 或更高的温度下确定反应终 点 Where the specimen under test is an aerosol with propellant store it in a freezer for not less than 2 h open the container and test 10 0 mL of the well mixed specimen In titrating the specimen determine the endpoint at a temperature of 10 or higher 如果供试样品为胶囊 使用不少于 4 个胶囊的混合内容物的一部分 Where the specimen under test is capsules use a portion of the mixed contents of not fewer than four capsules 如果供试品为片剂 在已知不会影响检验结果的温度和相对湿度环境中 使用不少于 4 片 磨碎的细粉末 Where the specimen under test is tablets use powder from not fewer than four tablets ground to a fine powder in an atmosphere of temperature and relative humidity known not to influence the results 如果各论中显示供试样品具有吸湿性 精密称取一份该固体制剂转移至滴定容器中 尽快 操作并小心避免其吸收空气中的水汽 如果样品量有限例如冻干制剂或瓶装粉剂 USP36使 用一个干燥注射器 注射经过精确称量的适当体积的甲醇或其他适当溶剂至已去皮的容器 中 摇动以使该样品溶解 使用同一个注射器 从该容器中吸出此溶液并转移至按照测试 方法下规定准备的滴定容器中 使用精确称量的第二份甲醇或其他适当溶剂重复该步骤 将此洗液加入至滴定容器 并立刻滴定 取与用于溶解样品以及洗涤容器和注射器的溶剂 同样体积的一部分溶剂 按照剩余滴定的水溶液的标定项下的规定 测定溶剂中的水分含 量 以 mg 为单位 并从供试样品滴定的水分含量 以 mg 为单位 中减去此数值 在 100 温度条件下将容器及其盖子干燥 3 小时 在干燥器中冷却 称重 根据该容器与其 初始重量的差来确定所测定的样品的重量 Where the monograph specifies that the specimen under test is hygroscopic take an accurately weighed portion of the solid into the titration vessel proceeding as soon as possible and taking care to avoid moisture uptake from the atmosphere If the sample is constituted by a finite amount of solid as a lyophilized product or a powder inside a vial USP36 use a dry syringe to inject an appropriate volume of methanol or other suitable solvent accurately measured into a tared container and shake to dissolve the specimen Using the same syringe remove the solution from the container and transfer it to a titration vessel prepared as directed for Procedure Repeat the procedure with a second portion of methanol or other suitable solvent accurately measured add this washing to the titration vessel and immediately titrate Determine the water content in mg of a portion of solvent of the same total volume as that used to dissolve the specimen and to wash the container and syringe as directed for Standardization of Water Solution for Residual Titration and subtract this value from the water content in mg obtained in the titration of the specimen under test Dry the container and its closure at 100 for 3 h allow to cool in a desiccator and weigh Determine the weight of specimen tested from the difference in weight from the initial weight of the container 如果合适 水可以通过和滴定容器相通的外接炉加热从样品中脱附或释放出来 然后由惰 性的干燥气体例如纯氮气带入滴定容器中 需要注意和计算由载气导致的漂移 需要小心 选择加热条件以避免由于样品成分分解脱水而生成水 这样会使此方法失效 USP36 When appropriate the water may be desorbed or released from the sample by heat in an external oven connected with the vessel to where it is transferred with the aid of an inert and dried gas such as pure nitrogen Any drift due to the transport gas should be considered and corrected Care should be taken in the selection of the heating conditions to avoid the formation of water coming from dehydration due to decomposition of the sample constituents which may invalidate this approach USP36 试剂的标定 在滴定容器中加入足以淹没电极的甲醇或其他适当溶剂 并加入足量的试剂 以产生滴定终点的特征颜色 或者在约 200mV 外加电压下产生 100 50 微安培直流电 Standardization of the Reagent Place enough methanol or other suitable solvent in the titration vessel to cover the electrodes and add sufficient Reagent to give the characteristic endpoint color or 100 50 microamperes of direct current at about 200 mV of applied potential 纯化水 二水合酒石酸钠 USP 标准物质 或者具有可追溯到国家标准的检验合格证明的 市售标准物质可以被用来对试剂进行标定 试剂的当量因子 推荐低定量 滴定管尺寸 以及标准物质用量都是考虑使用何种标准物质和其用量的参数 i 对于纯化水或水标准品 快速加入相当于 2 到 250mg 水的量 计算水当量因子 F 单位为 mg 水每 mL W V 其中 W mg 是标准试样中水分的重量 以 mg 为单位 V mL 是滴定中消耗试剂的体积 对于二水合酒石酸钠 快速加入差量法精密称定的 20 125mg 二水合酒石酸钠 C4H4Na2O6 2H2O 滴定至终点 水当量因子 F 单位为 mg 水每 mL 试剂 由下式给出 W V 36 04 230 08 其中 36 04 是 2 倍的水的摩尔重量 230 08 是二水合酒石酸钠的摩尔重量 W mg 是二水 合酒石酸钠的重量 V mL 是第二次滴定中消耗试剂的体积 注意二水合酒石酸钠在甲醇 中的溶解度 滴定更多的二水合酒石酸钠可能需要加入更多新鲜的甲醇 Purified Water sodium tartrate dihydrate a USP Reference Standard or commercial standards with a certificate of analysis traceable to a national standard may be used to standardize the Reagent The reagent equivalency factor the recommended titration volume buret size and amount of standard to measure are factors to consider when deciding which standard and how much to use 1 For Purified Water or water standards quickly add the equivalent of between 2 and 250 mg of water Calculate the water equivalency factor F in mg of water per mL of reagent W V in which W is the weight in mg of the water contained in the aliquot of standard used and V is the volume in mL of the Reagent used in the titration For sodium tartrate dihydrate quickly add 20 125 mg of sodium tartrate dihydrate C4H4Na2O6 2H2O accurately weighed by difference and titrate to the endpoint The water equivalence factor F in mg of water per mL of reagent is given by the formula W V 36 04 230 08 in which 36 04 is two times the molecular weight of water and 230 08 is the molecular weight of sodium tartrate dihydrate W is the weight in mg of sodium tartrate dihydrate and Vis the volume in mL of the Reagent consumed in the second titration Note that the solubility of sodium tartrate dihydrate in methanol is such that fresh methanol may be needed for additional titrations of the sodium tartrate dihydrate standard 检测方法 除各论中另有规定外 转移足够量的甲醇或其他合适的溶剂入滴定容器中 确 保该体积足够淹没电极 约 30 40mL 以试剂滴定至电化学或目测终点 以消耗掉可能 存在的水蒸气 忽略消耗的体积 因为其不进入计算当中 快速加入供试溶液 混合 再次用试剂滴定至电化学或目测终点 计算被测样品的水分含量 以 mg 为单位 SF 其中 S mL 为第二次滴定中消耗的试剂体积 F 为试剂的水当量因子 Procedure Unless otherwise specified transfer enough methanol or other suitable solvent to the titration vessel ensuring that the volume is sufficient to cover the electrodes approximately 30 40 mL and titrate with the Reagent to the electrometric or visual endpoint to consume any moisture that may be present Disregard the volume consumed because it does not enter into the calculations Quickly add the Test Preparation mix and again titrate with the Reagent to the electrometric or visual endpoint Calculate the water content of the specimen taken in mg SF in which S is the volume in mL of the Reagent consumed in the second titration and F is the water equivalence factor of the Reagent 方法 Ib 剩余滴定 Method Ib Residual Titration 原理 见方法 Ia 部分的原理项下信息 在剩余滴定中 过量的试剂被加入到被测样品中 给予足够的时间使其反应完全 未被消耗的试剂用水在某溶剂 如甲醇 中的标准溶液滴 定 剩余滴定的方法普适 且避免了直接滴定中可能遇到的结合水释放缓慢的问题 Principle See the information given in the section Principle under Method Ia In the residual titration excess Reagent is added to the test specimen sufficient time is allowed for the reaction to reach completion and the unconsumed Reagent is titrated with a standard solution of water in a solvent such as methanol The residual titration procedure is applicable generally and avoids the difficulties that may be encountered in the direct titration of substances from which the bound water is released slowly 设备 试剂 样品溶液 使用方法 Ia Apparatus Reagent and Test Preparation Use Method Ia 剩余滴定中水溶液的标定 将 2mL 水用甲醇或其他合适的溶剂稀释到 1000mL 制成水溶 液 用事先如试剂的标定项下方法标定的试剂滴定 25 0mL 此溶液以标定之 计算所取水 溶液中水的含量 以 mg mL 为单位 V F 25 其中 V 是消耗试剂的体积 F 是试剂的水当量因子 每周测定水溶液的水分含量 并用其 定期按需标定试剂 Standardization of Water Solution for Residual Titration Prepare a Water Solution by diluting 2 mL of water with methanol or other suitable solvent to 1000 mL Standardize this solution by titrating 25 0 mL with the Reagent previously standardized as directed under Standardization of the Reagent Calculate the water content in mg per mL of the Water Solution taken V F 25 in which V is the volume of the Reagent consumed and F is the water equivalence factor of the Reagent Determine the water content of the Water Solution weekly and standardize the Reagent against it periodically as needed 测试方法 如果各论中规定水分测定使用方法 Ib 转移足够的甲醇或其他合适的溶剂至滴 定容器中 确保该体积足够淹没电极 约 30 40mL 以试剂滴定至电化学或目测终点 快速加入样品溶液 混合 加入精确量取的过量的试剂 放置足够长的时间让反应完全 然后使用标定的水溶液滴定未被消耗的试剂至电化学或目测终点 计算所取样品中的水分 含量 mg F X XR 其中 F 是试剂的水当量因子 X mL 是引入样品后加入试剂的体积 X mL 是用于中和 未被消耗的试剂的标定过的水溶液的体积 R 是比例因子 V 25 mL 试剂 mL水溶液 由剩余滴定中水溶液的标定项测得 Procedure Where the individual monograph specifies that the water content is to be determined by Method Ib transfer enough methanol or other suitable solvent to the titration vessel ensuring that the volume is sufficient to cover the electrodes approximately 30 40 mL and titrate with the Reagent to the electrometric or visual endpoint Quickly add theTest Preparation mix and add an accurately measured excess of the Reagent Allow sufficient time for the reaction to reach completion and titrate the unconsumed Reagent with standardized Water Solution to the electrometric or visual endpoint Calculate the water content of the specimen in mg taken F X XR in which F is the water equivalence factor of the Reagent X is the volume in mL of the Reagent added after introduction of the specimen X is the volume in mL of standardized Water Solution required to neutralize the unconsumed Reagent and R is the ratio V 25 mL Reagent mL Water Solution determined from the Standardization of Water Solution for Residual Titration 方法 Ic 库仑滴定 Method Ic Coulometric Titration 原理 库仑滴定法水分测定使用卡尔 费休反应 但是 碘不是由定量试液引入 而是由 含碘离子的溶液在阳极氧化反应中生成 反应池通常包含一个大的阳极池和一个小的阴极 池 由隔膜隔开 其他合适的反应池 例如没有隔膜的 也可以使用 每个电极池都有一 个铂金电极以让电流通过反应池 阳极氧化生成的碘立刻与电极池中的水反应 当所有的 水杯消耗掉以后 过量的碘出现 通常由电位计测量 以指示反应终点 预先电解以除去 系统中的水汽 每次测定后不需要更换卡尔 费休试剂 因为测定可以继续在同样的试剂 溶液中进行 此方法的要求是被测样品的每种成分都互相相容 且测试中不发生副反应 样品溶液通常 通过注射的方法透过隔膜进入到样品池中 气体可以通过可以通过合适的进样管加入样品 池 这个方法的精密度很大程度上取决于系统与大气中水汽的隔绝程度 因此 将固体加 入到电解池中时需要某些预防措施 例如在惰性干燥气氛的手套箱中操作 可以根据基线 漂移的程度监视系统的控制 但是这并不意味着当这样引入样品时可以省略空白校正 USP36 本方法尤其适合于化学惰性物质例如碳氢化合物 醇类 醚类 等等 相比于卡 尔 费休计量滴定 库仑滴定是一种微量方法 Principle The Karl Fischer reaction is used in the coulometric determination of water Iodine however is not added in the form of a volumetric solution but is produced in an iodide containing solution by anodic oxidation The reaction cell usually consists of a large anode compartment and a small cathode compartment that are separated by a diaphragm Other suitable types of reaction cells e g without diaphragms may also be used Each compartment