美国药典USP31(921)翻译版(下).doc

Method Ib (Residual Titration) 方法Ib（残留滴定）
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.
原理：见方法Ia项下原理部分给出的信息。在残留滴定中，额外的试剂被加入到供试样品中，为反应的完成留下了充分的时间，并且将未消耗掉的试剂与水和某种溶剂（例如，甲醇）的标准溶液一起滴定。残留滴定程序通常是可行的，并避免了可能在直接滴定该物质过程中遇到的困难，这些物质中被束缚水分释放得很缓慢。

Apparatus, Reagent, and Test Preparation— Use Method Ia.
仪器、试剂、供试配制液：同方法Ia。

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 by the formula:
用于残留滴定的水溶液的标准化：以甲醇或其他适当溶剂将2mL水稀释至1000mL，以配制水溶液。使用此前已经按照试剂的标准化项下规定进行过标准化的试剂，对25mL此溶液进行滴定，从而对其进行标准化。按照下面的公式，计算此水溶液中的水分含量（单位mg/mL）：
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.
其中，V¢是消耗掉的试剂，F是试剂的水平衡因子。每周测定水溶液的水分含量，并据此根据需要定期对试剂进行标准化。

Procedure— Where the individual monograph specifies that the water content is to be determined by Method Ib, transfer 35 to 40 mL of methanol or other suitable solvent to the titration vessel, and titrate with the Reagent to the electrometric or visual endpoint. Quickly add the Test 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 by the formula:
步骤：当具体各论中规定用方法Ib测定水分含量时，将35至40mL甲醇或其他适当溶剂转移至该滴定容器，并用试剂滴定至测电法或视觉观察的终点。快速加入供试配制品，混匀，并加入精确称量的额外试剂。留下充分的时间以使该反应完成，使用标准化的水溶液对未消耗的试剂进行滴定至测电法或视觉观察的终点。按照下面的公式，计算样品中的水分含量（单位mg）：
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.
其中，F是试剂的水平衡因子；X¢是在放入样品后加入的试剂体积（单位mL）；X是用于中和未消耗试剂所必需的已标准化水溶液的体积（单位mL）；R是通过用于残留滴定的水溶液的标准化来测定的，V¢/25的比值（mL试剂/mL水溶液）。

Method Ic (Coulometric Titration) 方法Ic（库仑滴定）
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 has a platinum electrode that conducts current through the cell. Iodine, which is produced at the anode electrode, immediately reacts with water present in the compartment. When all the water has been consumed, an excess of iodine occurs, which usually is detected electrometrically, thus indicating the endpoint. Moisture is eliminated from the system by pre-electrolysis. Changing the Karl Fischer solution after each determination is not necessary since individual determinations can be carried out in succession in the same reagent solution. A requirement for this method is that each component of the test specimen is compatible with the other components, and no side reactions take place. Samples are usually transferred into the vessel as solutions by means of injection through a septum. Gases can be introduced into the cell by means of a suitable gas inlet tube. Precision in the method is predominantly governed by the extent to which atmospheric moisture is excluded from the system; thus, the introduction of solids into the cell is not recommended, unless elaborate precautions are taken, such as working in a glove-box in an atmosphere of dry inert gas. Control of the system may be monitored by measuring the amount of baseline drift. This method is particularly suited to chemically inert substances like hydrocarbons, alcohols, and ethers. In comparison with the volumetric Karl Fischer titration, coulometry is a micro-method.
原理：库仑滴定法水分测定应用了卡尔·费休反应的原理。但是，碘不是加入到滴定液中，而是通过阳极氧化在含碘溶液中产生。该反应单元通常由一大、一小两个阳极室构成，二者中间以隔膜分开。也可以使用其他适合的反应单元（例如，没有隔膜）类型。每个阳极室有一个白金电极，会穿过该单元导电。在阳极生成的碘立刻与该阳极室内存在的水发生反应。当所有的水都被消耗之后，多余的碘出现了，这一般通过电势滴定来检测，从而显示终点水分被预电解从该系统中消除。没有必要在每次检测后更换卡尔·费休溶液，因为可以在同一个试剂溶液中连续进行若干单个测定。此方法的一项要求是该供试品的每个阳极室均与其他阳极室兼容，并且不发生副反应。样品通常以溶液形态，穿过隔膜注射至该容器中。其他可以使用适当的气体注入管来引入到该单元。该方法的精密程度主要取决于将大气中水分影响从该系统中排除的程度；因此，除非采取了精心设计的预防措施，例如使用手套箱在有干燥入口气体的环境中工作，否则不建议向该单元中加入固体。可以通过测量基线漂移数量，来监测该系统的控制。此方法特别适合于化学性质迟钝的的物质，例如碳氢化合物、醇类、醚类。与定量测定的卡尔·费休滴定法相比，库仑法是一个小方法。

Apparatus— Any commercially available apparatus consisting of an absolutely tight system fitted with the necessary electrodes and a magnetic stirrer is appropriate. The instrument's microprocessor controls the analytical procedure and displays the results. Calibration of the instrument is not necessary, as the current consumed can be measured absolutely.
仪器：任何市场上销售的仪器，其中包含一个绝对密闭的系统，并装备了必需的电极和磁性搅拌器。该仪器的微处理器控制着分析程序并显示结果。该仪器不必校准，因为消耗的电流绝对可以被测量到。

Reagent— See Reagent under Method Ia.
试剂：见方法Ia项下试剂。

Test Preparation— Where the specimen is a soluble solid, dissolve an appropriate quantity, accurately weighed, in anhydrous methanol or other suitable solvents. Liquids may be used as such or as accurately prepared solutions in appropriate anhydrous solvents.
供试配制品：如果样品为可溶性固体，精密称定若干该样品，溶于无水甲醇或其他适合的溶剂中。这些液体可以这样使用，或者使用在适当的无水溶剂中精密配制溶液。

Where the specimen is an insoluble solid, the water may be extracted using a suitable anhydrous solvent from which an appropriate quantity, accurately weighed, may be injected into the anolyte solution. Alternatively an evaporation technique may be used in which water is released and evaporated by heating the specimen in a tube in a stream of dry inert gas, this gas being then passed into the cell
如果该样品为不溶性样品，其中的水分可以使用适当的无水溶剂提取出来，将一部分精密称定的溶剂注入阳极电解溶液。或者，可以使用蒸发的方法，通过加热该样品将其中的水分释放和蒸发到处于干燥入口气流里的管子中，然后这些气体被传送到该单元中。

Procedure— Using a dry syringe, quickly inject the Test Preparation, accurately measured and estimated to contain 0.5 to 5 mg of water, or as recommended by the instrument manufacturer into the anolyte, mix, and perform the coulometric titration to the electrometric endpoint. Read the water content of the Test Preparation directly from the instrument's display, and calculate the percentage that is present in the substance. Perform a blank determination, and make any necessary corrections.
步骤：使用干燥注射器，将供试配制液，其经过精确称量并估计含有约0.5－5mg水，或按照仪器生产商的建议，快速注射入阳极电解液，混匀，并对电势终点作库仑滴定法。直接从仪器显示中读取该供试配制液的水分含量，并计算该物质中存在水分的百分比。进行空白检测，并作任何适当的校正。

METHOD II (AZEOTROPIC—TOLUENE DISTILLATION)
Apparatus— Use a 500-mL glass flask A connected by means of a trap B to a reflux condenser C by ground glass joints (see Figure).

Toluene Moisture Apparatus
The critical dimensions of the parts of the apparatus are as follows. The connecting tube D is 9 to 11 mm in internal diameter. The trap is 235 to 240 mm in length. The condenser, if of the straight-tube type, is approximately 400 mm in length and not less than 8 mm in bore diameter. The receiving tube E has a 5-mL capacity, and its cylindrical portion, 146 to 156 mm in length, is graduated in 0.1-mL subdivisions, so that the error of reading is not greater than 0.05 mL for any indicated volume. The source of heat is preferably an electric heater with rheostat control or an oil bath. The upper portion of the flask and the connecting tube may be insulated.
Clean the receiving tube and the condenser with chromic acid cleansing mixture, thoroughly rinse with water, and dry in an oven. Prepare the toluene to be used by first shaking with a small quantity of water, separating the excess water, and distilling the toluene.
Procedure— Place in the dry flask a quantity of the substance, weighed accurately to the nearest centigram, which is expected to yield 2 to 4 mL of water. If the substance is of a pasty character, weigh it in a boat of metal foil of a size that will just pass through the neck of the flask. If the substance is likely to cause bumping, add enough dry, washed sand to cover the bottom of the flask, or a number of capillary melting-point tubes, about 100 mm in length, sealed at the upper end. Place about 200 mL of toluene in the flask, connect the apparatus, and fill the receiving tube E with toluene poured through the top of the condenser. Heat the flask gently for 15 minutes and, when the toluene begins to boil, distill at the rate of about 2 drops per second until most of the water has passed over, then increase the rate of distillation to about 4 drops per second. When the water has apparently all distilled over, rinse the inside of the condenser tube with toluene while brushing down the tube with a tube brush attached to a copper wire and saturated with toluene. Continue the distillation for 5 minutes, then remove the heat, and allow the receiving tube to cool to room temperature. If any droplets of water adhere to the walls of the receiving tube, scrub them down with a brush consisting of a rubber band wrapped around a copper wire and wetted with toluene. When the water and toluene have separated completely, read the volume of water, and calculate the percentage that was present in the substance.

METHOD III (GRAVIMETRIC)
Procedure for Chemicals— Proceed as directed in the individual monograph preparing the chemical as directed under Loss on Drying 731.
Procedure for Biologics— Proceed as directed in the individual monograph.
Procedure for Articles of Botanical Origin— Place about 10 g of the drug, prepared as directed (see Methods of Analysis under Articles of Botanical Origin 561) and accurately weighed, in a tared evaporating dish. Dry at 105 for 5 hours, and weigh. Continue the drying and weighing at 1-hour intervals until the difference between two successive weighings corresponds to not more than 0.25%.

Auxiliary Information— Staff Liaison : Gary E. Ritchie, M.Sc., Scientific Fellow
Expert Committee : (GC05) General Chapters 05
USP30–NF25 Page 385
Pharmacopeial Forum : Volume No. 31(2) Page 517
Phone Number : 1-301-816-8353