Implementing the Sampling Plan
After a sampling plan has been developed, it is put into action. Implementing a sampling plan normally involves three steps: physically removing the sample from its target population, preserving the sample, and preparing the sample for analysis. Except for in situ sampling, the analysis of a sample occurs after removing it from the target population. Since sampling exposes the target population to potential contamination, the sampling device must be inert and clean.
Once a sample is withdrawn from a target population, there is a danger that it may undergo a chemical or physical change. This is a serious problem since the properties of the sample will no longer be representative of the target population. For this reason, samples are often preserved before transporting them to the labora- tory for analysis. Even when samples are analyzed in the field, preservation may still be necessary.
The initial sample is called the primary, or gross sample and may be a single increment drawn from the target population, or a composite of several increments. In many cases the gross sample cannot be analyzed without further treatment. Pro- cessing the gross sample may be used to reduce the sample’s particle size, to transfer the sample into a more readily analyzable form, or to improve its homogeneity.
In the sections that follow, these three steps are considered for the sampling of liquids (including solutions), gases, and solids.