A dilution is a laboratory procedure in which the concentration of a sample or
solution is reduced by the addition of solvent (diluent). In the laboratory, a dilution is
commonly performed when the concentration of an unknown is greater than the limits of
linearity of a given quantitative procedure or when a working solution must be prepared
from a stock.
Dilutions are expressed as a ratio between the volume of the original solution to
the volume of final solution. The conventional form is to express the dilution as the ratio
of one unit of the original volume to the final volume. Thus, when 2 mL of sample is
added to 8 mL of diluent, the result is a 2:10 dilution, but this is preferably expressed as
a 1:5 dilution. The reciprocal of the dilution is the dilution factor. This is the factor by
which quantitative results are multiplied to give the final concentration for the original,
undiluted sample. For a serum sample diluted 1:10 for a glucose determination, the test
result must be multiplied by the dilution factor, 10, to determine the actual concentration
of the undiluted serum sample. To calculate the concentration of a dilute solution,
multiply the concentration of the original solution by the dilution, expressed as a fraction.
A one to ten dilution may be expressed as 1:10 or equivalently as 1/10.
This, of course, applies to all dilutions.
a. Example 1. A specimen is diluted by combining 3 mL of serum with 21 mL of
saline. What is the dilution of the serum?
Solution. Read the problem carefully and calculate the dilution.
Volume units must be the same when calculating dilutions.
3 mL (parts serum)
+ 21 mL (parts saline)
24 mL (total parts)
Dilution = 3 mL 24 mL