本文件规定了通过液体闪烁计数（LSC）测量所有类型水中99Tc的方法。 该方法适用于供应/饮用水、雨水、地表水和地下水以及冷却水、工业用水、生活和工业废水的测试样品，经过适当的取样和处理，以及测试样品制备。测试样品的过滤是必要的。 检测限取决于样品体积和所用仪器。本文件中描述的方法使用目前可用的LSC仪器，其检测限约为5 Bq·kg？1至20 Bq·kg？1，低于世卫组织饮用水安全饮用标准（100 Bq l？1）[3]。对于在14mL至40mL之间变化的样品体积，可以用30分钟的计数时间获得这些值。本文件中提供的方法不适用于超痕量99Tc的测定。 本文件中的活度浓度值以样品质量单位表示，而不是类似标准品中通常采用的样品体积单位。原因是99Tc是在各种基质类型如淡水或海水中测量的，这些基质类型具有显著的密度差异。通过测量样品体积，可以容易地将活性浓度值转换为样品体积单位。然而，它增加了活性浓度结果的不确定性。 本文件中描述的方法适用于紧急情况，但如果99mTc的含量可能会引起干扰，并且如果99mTc用作回收示踪剂，则不适用。 吸附在悬浮物上的Tc的分析不包括在该方法中。 用户有责任确保本测试方法对所测试水样的有效性。

This document specifies a method for the measurement of ⁹⁹Tc in all types of waters by liquid scintillation counting (LSC). The method is applicable to test samples of supply/drinking water, rainwater, surface and ground water, as well as cooling water, industrial water, domestic, and industrial wastewater after proper sampling and handling, and test sample preparation. A filtration of the test sample is necessary. The detection limit depends on the sample volume and the instrument used. The method described in this document, using currently available LSC instruments, has a detection limit of approximately 5 Bq·kg^？1 to 20 Bq·kg^？1, which is lower than the WHO criteria for safe consumption of drinking water (100 Bq l^？1)^[3]. These values can be achieved with a counting time of 30 min for a sample volume varying between 14 ml to 40 ml. The method presented in this document is not intended for the determination of ultra-trace amount of ⁹⁹Tc. The activity concentration values in this document are expressed by sample mass unit instead of sample volume unit as it is usually the case in similar standards. The reason is that ⁹⁹Tc is measured in various matrix types such as fresh water or sea water, which have significant differences in density. The activity concentration values can be easily converted to sample volume unit by measuring the sample volume. However, it increases the uncertainty on the activity concentration result. The method described in this document is applicable in the event of an emergency situation, but not if ^99mTc is present at quantities that could cause interference and not if ^99mTc is used as a recovery tracer. The analysis of Tc adsorbed to suspended matter is not covered by this method. It is the user's responsibility to ensure the validity of this test method for the water samples tested.