Question

What are retention indexes? Describe how they are determined

Short answer

Retention indexes is used to convert retention times into system-independent constants.

Step-by-step solution

Retention indexes.

Retention index can be calculated for any solute from it's chromatogram that has to contain the solute as well as at least two normal alkenes that have retention times that bracket that of the solute.

Determining retention indexes.

Scale for the retention index is based on normal alkanes - it equals to $100$times the number of $C$atoms in the compound. Packing of the column doesn't affect it and neither does any other column condition, such as temperature.

retention index $=100\times$number of compound's $C$atoms