The semi-micro determination of water is based upon the quantitative reaction of water with sulfur dioxide and iodine in a suitable anhydrous medium in the presence of a base with sufficient buffering capacity. 水分半微量测定法的原理为在，有足够缓冲能力的无水介质里水与二氧化硫和碘起定量反应。
Apparatus 仪器
The apparatus consists of a titration vessel with: 实验装置由一套滴定容器组成，该滴定容器包含：
— 2 identical platinum electrodes; 2个同样的铂电极
— tight inlets for introduction of solvent and titrant; 严密的溶剂和滴定液引入口
— an inlet for introduction of air via a desiccant; 经干燥剂的空气引入口
— a sample inlet fitted with a stopper or, for liquids, a septum. 具塞进样口，或用于液体的隔膜进样口
Inlet systems for introduction of dry nitrogen or for aspiration of solvents may also be fitted. 还应配备干燥氮气或吸溶剂的引入口系统。
The titration is carried out according to the instrument supplier’s instructions. Care is taken throughout the determination to avoid exposure of reagents and solvents to atmospheric moisture. The end-point is determined using 2 identical indicator electrodes connected to an electrical source that maintains between the electrodes either a constant current or a constant voltage. Where direct titration is used (method A), addition of titrant causes either a decrease in voltage where constant current is maintained or an increase in current where constant voltage is maintained, until the end-point is reached. Instruments with automatic end-point detection are commonly used. 按照仪器供应商说明书进行滴定操作。整个操作过程都应小心避免试液或者溶剂暴露于空气的水分中。通过将两个同样的指示剂电极链接到一个电源上得到恒定的电流和电压来测定终点。直接滴定时（方法A），滴定液的加入使恒定电流状态下的电压下降，或恒定电压状态下电流的增大，直至达到终点。通常使用能自动检测终点的仪器。
Standardisation. To the titration vessel, add methanol R, dried if necessary, or the solvent recommended by the supplier of the titrant. Where applicable for the apparatus used, eliminate residual water from the measurement cell or carry out a pre-titration. Introduce a suitable amount of water in an appropriate form (water R or a certified reference material) and carry out the titration, stirring for the necessary time. The water equivalent is not less than 80 per cent of that indicated by the supplier. Standardise the titrant before the first use and at suitable intervals thereafter. 标定： 将甲醇（必要时，需干燥）或滴定液供应商推荐的溶剂加入滴定容器。当适用于所使用的仪器时，应除去检测池的残留水分或执行预滴定。通过合适的方法加入适量水（水或特定的对照物），滴定，搅拌充足的时间。水当量应不小于供应商规定的80%。第一次使用前标化滴定液，而后间隔合适的时间再标化。
Unless otherwise prescribed, use Method A. 除另有规定外，采用方法A检测
Method A. Introduce into the titration vessel methanol R, or the solvent indicated in the monograph or recommended by the supplier of the titrant. Where applicable for the apparatus used, eliminate residual water from the measurement cell or carry out a pre-titration. Introduce the substance to be examined rapidly and carry out the titration, stirring for the necessary extraction time. 方法A：将甲醇或专论规定的或供应商建议的溶剂加入滴定容器中。适用时，除去测量池内的残留水，或执行预滴定。快速加入供试品，执行滴定，搅拌的足够的时间。
Method B. Introduce into the titration vessel methanol R, or the solvent indicated in the monograph or recommended by the supplier of the titrant. Where applicable for the apparatus used, eliminate residual water from the measurement cell or carry out a pre-titration. Introduce the substance to be examined rapidly and in a suitable state of division. Add an accurately measured volume of the titrant, sufficient to give an excess of about 1 mL or the prescribed volume. Allow to stand protected from light for 1 min or the prescribed time, with stirring. Titrate the excess of reagent using methanol R or the prescribed solvent, containing an accurately known quantity of water. 方法B：将甲醇或专论规定的或供应商建议的溶剂加入滴定容器中。适用时，除去测量池内的残留水，或执行预滴定。将供试品快速加入至一合适的分区。加入精密量取的滴定剂，过量1ml或规定的体积。避光放置1min或规定的时间，并不是搅拌。用甲醇或规定的溶剂（预先精确加入一定量的水）滴定过量的试剂。
Suitability. The accuracy of the determination with the chosen titrant must be verified for each substance to be examined. The following procedure, given as an example, is suitable for samples containing 2.5-25 mg of water. 系统适用性：必须确认每个供试品测定时被选用试剂检测的准确性。举例：下面的操作适合含水量为2.5-25mg的样品。
The water content of the substance to be examined is determined using the reagent/solvent system chosen. Thereafter, sequential known amounts of water R are added in an appropriate form (at least 5 additions) and the cumulative water content determined after each addition. Calculate the percentage recovery (r) at each point using the following expression: 通过选择的试剂/溶剂系统测定供试品的含水量。然后，通过适宜的方式（至少5次）连续加入已知量的水，每次加水后测定累积含水量。根据下面的公式计算每点的回收率（r）：
W1 = amount of water added, in milligrams; W1=加入的水量，mg
W2 = amount of water found, in milligrams. W2=测得的水量，mg
Calculate the regression line of the cumulative water determined against the water added. Calculate the slope (b), the intercept with the y-axis (a) and the intercept of the extrapolated calibration line with the x-axis (d). 根据加入的水量测得累积水量，并得到累积水量的回归曲线。计算斜率（b），y轴的截距（a）及校正线外延在x轴截距（d）
Calculate the percentage mean recovery (). Calculate the percentage errors (e1 and e2) using the following expressions: 计算平均回收率（ ）。根据以下的公式计算误差百分率（e1和e2）
a = the y-axis intercept, in milligrams of water; a= y轴的截距，mg
d = the x-axis intercept, in milligrams of water; d=x轴截距，mg
M = water content of the substance, in milligrams of water. M=样品的含水量，mg
The reagent/solvent system is considered to be acceptable if: 该试剂/溶剂系统的可接受限是：
— and are not greater than 2.5 per cent; |e1| 和 |e2| ≤2.5%
— b is between 0.975 and 1.025 (deviation ± 2.5 per cent); 0.975＜b＜1.025（偏差±2.5）
— is between 97.5 per cent and 102.5 per cent. 平均回收率（ ）为97.5-102.5
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