Enter the retention factor of the second peak and the retention factor of the first peak into the Selectivity Factor Calculator. The calculator will evaluate the Selectivity Factor.

## Selectivity Factor Formula

The following two example problems outline the steps and information needed to calculate the Selectivity Factor.

**a = K2/ K1**

Variables:

- a is the Selectivity Factor ( )
- K2 is the retention factor of the second peak
- K1 is the retention factor of the first peak

## How to Calculate Selectivity Factor?

The following steps outline how to calculate the Selectivity Factor.

- First, determine the retention factor of the second peak.
- Next, determine the retention factor of the first peak.
- Next, gather the formula from above = a = K2/ K1.
- Finally, calculate the Selectivity Factor.
- After inserting the variables and calculating the result, check your answer with the calculator above.

**Example Problem : **

Use the following variables as an example problem to test your knowledge.

retention factor of the second peak = 3

retention factor of the first peak = 2.5

a = K2/ K1** **= ?