ISO 13163:2021 pdf download – Water quality — Lead-210 — Test method using liquid scintillation counting.
6 Procedure 6.1? Sample? preparation? for? measurement Filter and acidify the samples and a blank sample prepared with ultrapure water as specified in Clause 5. A minimum of 1 blank sample per batch is required. However, the average of several blanks can be used. Measuring blank samples at regular interval enables to rapidly detect a background issue when measuring the samples (see quality assurance and quality control program in Clause 7). Purify the sample from potential interferents. Examples of purification methods are described in Annex A. Determine the chemical recovery. 6.2? Sample? measurement Measure 210 Pb in the samples by LSC by following the instructions provided by the instrument manufacturer and the steps described in ISO 19361. 7 Quality assurance and quality control program 7.1? General Quality control operations shall meet the requirements of ISO/IEC 17025. Measurement methods shall be performed by suitably skilled staff under a quality assurance program. 7.2? Variables? that? could? influence? the? measurement Special care shall be taken in order to limit as much as possible the influence of parameters that can bias the measurement and lead to a non-representative result. Failure to take sufficient precautions can require corrective factors to be applied to the measured result. Sampling, transportation and storage, reagents, transfer, measurement of stable lead, and the activity measurement of 210 Pb are all subject to potential interference or variability. The presence of chemiluminescence prevents the accurate measurement of the samples. To reduce the chemiluminescence, the samples are left in the dark for a few hours before counting them. This delay can be the same as used for progeny decay as mentioned in Clause 4. If a chemiluminescence peak is observed, wait until the chemiluminescence has decayed and re-count the samples.
Preconcentration step of lead is performed using an Fe(III) co-precipitation, which allows the elimination of Group 1 elements such as K and Na. The chromatographic extraction resin, e.g. an 18C6 crown ether-type resin, has very low affinity for Group 2 elements when choosing appropriate chemical conditions. If these elements are present at high concentrations, the volume of the 18C6 crown ether-type resin column can be revised to cope with their interferences given that the working lead capacity of the 18C6 crown ether-type resin is about 20 mg Pb⋅g -1 of dry resin. If a cation exchange resin is used for the preconcentration step instead of the Fe(III) co-precipitation, the quantity of cation exchange resin should be determined based on its exchange capacity and amount of cationic species in the sample. [26] An excess of resin is usually employed. 7.3? Instrument? quality? control The main instrument parameters such as efficiency and background shall be periodically checked within a quality assurance program established by the laboratory and in accordance with the manufacturer’s instructions.