美国药典USP31(921)翻译版(下)

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。