7.11: Chapter Summary and Key Terms

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Chapter Summary

An analysis requires a sample and how we acquire that sample is critical. The samples we collect must accurately represent their target population, and our sampling plan must provide a sufficient number of samples of appropriate size so that uncertainty in sampling does not limit the precision of our analysis.

A complete sampling plan requires several considerations, including the type of sample to collect (random, judgmental, systematic, systematic–judgmental, stratified, or convenience); whether to collect grab samples, composite samples, or in situ samples; whether the population is homogeneous or heterogeneous; the appropriate size for each sample; and the number of samples to collect.

Removing a sample from its population may induce a change in its composition due to a chemical or physical process. For this reason, we collect samples in inert containers and we often preserve them at the time of collection.

When an analytical method’s selectivity is insufficient, we may need to separate the analyte from potential interferents. Such separations take advantage of physical properties—such as size, mass or density—or chemical properties. Important examples of chemical separations include masking, distillation, and extractions.

Key Terms

 centrifugation convenience sampling distillation extraction efficiency grab sample homogeneous laboratory sample Nyquist theorem purge-and-trap recrystallization secondary equilibrium reaction size exclusion chromatography sublimation systematic–judgmental sampling composite sample density gradient centrifugation distribution ratio filtrate gross sample in situ sampling masking partition coefficient random sampling retentate selectivity coefficient Soxhlet extractor subsamples systematic sampling coning and quartering dialysis extraction filtration heterogeneous judgmental sampling masking agents preconcentration recovery sampling plan separation factor stratified sampling supercritical fluid target population

This page titled 7.11: Chapter Summary and Key Terms is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by David Harvey.