The result of any testing method can be no better than the sample on which it is performed. However, it is beyond the scope of Standard Methods for the Examination of Water and Wastewater to specify detailed procedures for the collection of all samples because of varied purposes and analytical procedures. Detailed information may be presented in specific methods and that information is to be followed when available. This section presents general considerations for the collection and preservation of samples applicable primarily to chemical analyses. See appropriate sections for samples to be used in toxicity testing (Section 8020) and microbiological (Sections 9020 and 9060), biological (Part 10 000), and radiological (Section 7010) examinations.
The objective of sampling is to collect a portion of material small enough in volume to be transported conveniently and yet large enough for analytical purposes while still accurately representing the material being sampled. This objective implies that the relative proportions or concentrations of all pertinent components are the same in the samples as in the material being sampled and that the samples are handled in such a way that no significant changes in composition occur before the tests are made.
Frequently, the objective of sampling and testing is to demonstrate whether continuing compliance with specific regulatory requirements has been achieved. Samples are presented to the laboratory for specific determinations, with the sampler being responsible for collecting a valid and representative sample. Because of the increasing importance placed on verifying the accuracy and representativeness of data, greater emphasis is placed on proper sample collection, tracking, and preservation techniques. Often, laboratory personnel help plan a sampling program in consultation with the user of the test results. Such consultation is essential to ensure selected samples and analytical methods provide a sound and valid basis for answering the questions that prompted the sampling and that meet regulatory and project-specific requirements.
This section addresses the collection and preservation of water and wastewater samples; the general principles also apply to the sampling of solid or semisolid matrices.