Serial dilution

This technique is used when a high degree of dilution is required.

For example, you may need to dilute a solution by a factor of one million. This would be quite difficult to do in one go. You could start with 1 cm³, but if you dilute this by a million you would end up with 1,000,000 cm³ of solution. This is 1000 litres, or a lot of solution! Alternatively if you wanted to end up with a litre of solution, you would need to start with 0.001 cm³ of original solution. This is very small and would be difficult to measure out accurately.

The solution to the problem is to use serial dilution. We start by taking 1 cm³ of original solution and dilute it to 100 cm³ in a volumetric flask. This is now 100 times more dilute. We now take 1 cm³ of this diluted solution and dilute it to 100 cm³ in a volumetric flask. This is diluted by a further 100 times. Finally we take 1 cm³ of the twice diluted solution and dilute it to 100 cm³ in a volumetric flask. Our total dilution is 100 × 100 × 100 = 1,000,000. An alternative would have been to do two 1 cm³ to 1000cm³ dilutions - 1000 × 1000 = 1,000,000.

A 1000-fold serial dilution achieved by diluting 10 ml to 100ml three times