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7.S: Collecting and Preparing Samples (Summary)

An analysis requires a sample. 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 the uncertainty in sampling does not limit the precision of our analysis.

A complete sampling plan requires several considerations, including: the type of sample (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 can take advantage of physical properties—such as size, mass or density—or chemical properties. Important examples of chemical separations include masking, distillation, and extractions.

7.9.1 Key Terms

composite sample
coning and quartering
convenience sampling
density gradient centrifugation
distribution ratio
extraction efficiency
grab sample
gross sample
in situ sampling
judgmental sampling
laboratory sample
masking agents
Nyquist theorem
partition coefficient
random sampling
sampling plan
secondary equilibrium reaction
selectivity coefficient
separation factor
size exclusion chromatography
Soxhlet extractor
stratified sampling
supercritical fluid
systematic–judgmental sampling
systematic sampling
target population


  1. Youden, Y. J. J. Assoc. Off. Anal. Chem. 1981, 50, 1007–1013.
  2. Fricke, G. H.; Mischler, P. G.; Staffieri, F. P.; Houmyer, C. L. Anal. Chem. 1987, 59, 1213–1217.
  3. Cohen, R. D. J. Chem. Educ. 1991, 68, 902–903.
  4. Borgman, L. E.; Quimby, W. F. in Keith, L. H., ed. Principles of Environmental Sampling, American Chemical Society: Washington, D. C., 1988, 25–43.
  5. Keith, L. H. Environ. Sci. Technol. 1990, 24, 610–617.
  6. Flatman, G. T.; Englund, E. J.; Yfantis, A. A. in Keith, L. H., ed. Principles of Environmental Sampling, American Chemical Society: Washington, D. C., 1988, 73–84.
  7. Nabulo, G.; Oryem-Origa, H.; Diamond, M. Environ. Res. 2006, 101, 42–52.
  8. Ingamells, C. O.; Switzer, P. Talanta 1973, 20, 547–568.
  9. Blackwood, L. G. Environ. Sci. Technol. 1991, 25, 1366–1367.
  10. Duce, R. A.; Quinn, J. G. Olney, C. E.; Piotrowicz, S. R.; Ray, S. J.; Wade, T. L. Science 1972, 176, 161–163.
  11. Tanner, R. L. in Keith, L. H., ed. Principles of Environmental Sampling, American Chemical Society: Washington, D. C., 1988, 275–286.
  12. (a) Sandell, E. B. Colorimetric Determination of Trace Metals, Interscience Publishers: New York, 1950, pp. 19–20; (b) Sandell, E. B. Anal. Chem. 1968, 40, 834–835.
  13. Glavin, D. P.; Bada, J. L. Anal. Chem. 1998, 70, 3119–3122.
  14. Fresenius. C. R. A System of Instruction in Quantitative Chemical Analysis, John Wiley and Sons: New York, 1881.
  15. Jeannot, M. A.; Cantwell, F. F. Anal. Chem. 1997, 69, 235–239.
  16. Alltech Associates Extract-Clean SPE Sample Preparation Guide, Bulletin 83.
  17. Renoe, B. W. Am. Lab August 1994, 34–40.
  18. McNally, M. E. Anal. Chem. 1995, 67, 308A–315A.
  19. “TPH Extraction by SFE,” ISCO, Inc. Lincoln, NE, Revised Nov. 1992.
  20. “The Analysis of Trihalomethanes in Drinking Water by Liquid Extraction,” EPA Method 501.2 (EPA 500-Series, November 1979).
  21. Aguilar, C.; Borrul, F.; Marcé, R. M. LC•GC 1996, 14, 1048–1054.
  22. Corl, W. E. Spectroscopy 1991, 6(8), 40–43.
  23. Kratochvil, B.; Taylor, J. K. Anal. Chem. 1981, 53, 924A–938A.
  24. Engels, J. C.; Ingamells, C. O. Geochim. Cosmochim. Acta 1970, 34, 1007–1017.
  25. Guy, R. D.; Ramaley, L.; Wentzell, P. D. J. Chem. Educ. 1998, 75, 1028–1033.
  26. Maw, R.; Witry, L.; Emond, T. Spectroscopy 1994, 9, 39–41.
  27. Simpson, S. L.: Apte, S. C.; Batley, G. E. Anal. Chem. 1998, 70, 4202–4205.