A serial dilution is the step-wise dilution of a substance in solution, either by using a constant dilution ratio, or by using a variable factor between dilutions. If the dilution factor at each step is constant, this results in a geometric progression of the concentration in a fashion. A ten-fold serial dilution could be 1 M, 0.1 M, 0.01 M, 0.001 M ... Serial dilutions are used to accurately create highly diluted solutions as well as solutions for resulting in concentration curves with a logarithmic scale. A tenfold dilution for each step is called a logarithmic dilution or log-dilution, a 3.16-fold (100.5-fold) dilution is called a half-logarithmic dilution or half-log dilution, and a 1.78-fold (100.25-fold) dilution is called a quarter-logarithmic dilution or quarter-log dilution. Serial dilutions are widely used in experimental sciences, including biochemistry, pharmacology, microbiology, and physics.
In biology and medicine
In
biology and
medicine, besides the more conventional uses described above, serial dilution may also be used to reduce the concentration of microscopic organisms or cells in a sample. As, for instance, the number and size of
bacterial colony that grow on an
agar plate in a given time is concentration-dependent, and since many other diagnostic techniques involve physically counting the number of micro-organisms or cells on specials printed with grids (for comparing concentrations of two organisms or cell types in the sample) or wells of a given volume (for absolute concentrations), dilution can be useful for getting more manageable results.
[K. R. Aneja. Experiments in Microbiology, Plant Pathology and Biotechnology. New Age Publishers, 2005, p. 69. ] Serial dilution is also a cheaper and simpler method for preparing
axenic than
optical tweezers and
.
In homeopathy
Serial dilution is one of the core foundational practices of
homeopathy, with "succussion", or shaking, occurring between each dilution. In homeopathy, serial dilutions (called potentisation) are often taken so far that by the time the last dilution is completed, no molecules of the original substance are likely to remain.
See also
-
Michael L. Bishop, Edward P. Fody, Larry E. Schoeff. Clinical Chemistry: Principles, Procedures, Correlations. Lippincott Williams & Wilkins, 2004, p. 24. .
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