Use this retention index calculator to determine Kovats retention index (RI) or predict retention time under isothermal or temperature-programmed GC conditions using n-paraffin reference compounds.
Retention Index Calculator Interface
Reference Formula
For isothermal condition:
\[ RI_i = 100 \left( n_1 + \frac{\log t_i – \log t_1} {\log t_2 – \log t_1} (n_2 – n_1) \right) \]For temperature programmed condition:
\[ RI_i = 100 \left( n_1 + \frac{t_i – t_1} {t_2 – t_1} (n_2 – n_1) \right) \]Before You Go
Ensure that the n-paraffin reference compounds bracket the analyte of interest. The unknown compound must elute between n₁ and n₂ for accurate interpolation.
For isothermal conditions, retention times must be converted consistently and logarithmic interpolation is required. For temperature-programmed GC, linear interpolation is used.
The article explaining how this calculator works is available at GC Retention Index Explained Simply in Gas Chromatography Columns series.
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