Serial dilution

A dilution series is the set of solutions that have been made ​​for a specific purpose from a concentrated stock solution by dilution. Here, the solutions known as dilution levels differ in their content ( for example, in the amount of substance concentration, or mass concentration).

In the dilution series, a distinction is those in which the individual dilutions are prepared by dilution of the previous dilution step ( continued dilution, serial dilution ), and those in which all dilutions are prepared directly from the source solution (parallel dilution ).

Applications

• Dilution series frequently for calibration of measuring instruments, eg for use in chemical analysis. These are referred to as the standard series. Occasionally, the term calibration series was used, but the calibration is the competent offices and inspection reserved.

• For categorical detection methods (test with yes or no as a result ), serial dilutions used to determine the limiting dilution ( final dilution above the detection limit ) and to derive the concentration, such as a titer.

• Similarly, serial dilutions are used in microbiology counting of particles such as cells or viruses. Their concentration, so their number in a solution is reduced by the dilution series. Thus they are easier to count at higher dilution levels, the result is then recalculated back to original concentration.

• By dilution series particles are as isolated as cells or viruses. In the course of a limiting dilution cloning, clonal cultures are made possible in a subsequent multiplication.

Dilution series by continued dilution ( Geometric dilution)

Taking for example, 10 milliliters of a stock solution and mixes it with solvent ( eg water), so that there are 100 milliliters, so this first dilution step has only a tenth of the concentration of the starting solution. Taking from the first dilution stage again 10 milliliters out and re-diluted to 100 mL, the second dilution stage has only one hundredth of the concentration of the starting solution. Dilute this solution is the same way, the result is a third dilution step with a thousandth of the concentration of the starting solution. Does the molar concentration of the starting solution, for example, 2 mol / L, then the concentrations of the solutions of the dilution series hereby 0.2 mol / L ( 1 dilution ); 0.02 mol / l ( second dilution step ); 0.002 mol / L ( 3 dilution ). Are there differences between the concentrations of the individual dilution steps as in this case by a factor of 10, so one speaks also of a decimal dilution series. In addition to the commonly encountered decimal dilution series, there are also dilution series with other dilution factors.

Dilution series with uniform distribution of the dilution steps ( Arithmetic dilution)

In this way the contents of the dilution series of the dilutions are distributed uniformly over a level area. To be able to cover evenly example, the levels of a dilution series with a total of five dilution steps the mass concentration range between 0 g / L and 1 g / l. The mass concentrations of the individual dilutions then be 0.2 g / L ( 1 dilution ), 0.4 g / L ( 2 dilution ), 0.6 g / L ( 3 dilution ), 0.8 g / L ( 4 dilution ) and 1.0 g / L ( 5 dilution ). In this type of dilution series all dilutions from the same starting solution can be prepared and not by continued dilution.