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7.11: Chapter Summary and Key Terms

  • Page ID
    162890
  • 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