Under ISO 17025, what must laboratories establish when sampling substances?

Establishing sampling plans is crucial under ISO 17025 because it ensures that the laboratory has a defined and systematic approach to sampling that reflects the characteristics of the material being sampled. This allows for consistency and reliability in test results, which is essential for maintaining quality management in laboratories. Sampling plans help in determining how samples should be collected, the number of samples needed, and the methodology to be used, thereby ensuring that the samples are representative of the overall population.

By focusing on the quality of sampling practices, laboratories can avoid biases and errors that could compromise the validity of their results. This structured approach is necessary for compliance with ISO 17025, which emphasizes continual improvement and the reliability of testing and calibration results.