Retention Index Calculator
Calculate Kováts retention indices for plant volatile organic compounds (PVOCs) using n-alkane standards. Automatically match calculated RIs against a curated library of 505 essential oil compounds.
Retention Index Formula
Adjusted retention time of unknown compound (RT − void time)
Carbon number of the n-alkane eluting just before the unknown
Adjusted RT of n-alkane with n carbons
Adjusted RT of n-alkane with n+1 carbons
Workflow Overview
Column Void Time (t₀)
Enter the void time (dead time) of unretained analytes on your GC column.
Instructions: Enter retention times for n-alkane standards (C₇-C₂₅). You may enter values in minutes or seconds. Enter at least 5 consecutive alkanes for reliable calibration. Verify R² value > 0.99 before analyzing samples.
| Alkane | Carbon # (n) | RT (minutes) | RT (seconds) | Typical RT (min) | Status |
|---|
Calibration Curve (RT vs Carbon Number)
Calibration Statistics
Sample Retention Times
Enter retention times for unknown compounds. Enter up to 30 compounds.
| # | RT (minutes) | RT (seconds) | Adjusted RT (sec) | Compound Name (optional) |
|---|
Note: Enter retention times in either minutes or seconds. The other column will be calculated automatically. Adjusted RT = RT - void time. Make sure alkane standards are entered and R² > 0.99 before proceeding to Results.
Calculated Retention Indices & Library Matches
| # | RT (min) | Adj RT (sec) | Calculated RI | Library RI | Δ RI | Library Compound | Plant Source | Reference |
|---|
Enter alkane standards and sample data to view results
Go to tab 2 (Alkane Standards) to begin
RI Library Browser
| RI | Compound | Plant Source | Reference |
|---|
Plant Source Codes:
How to Use This Calculator
Determine Column Void Time
Inject an unretained compound (e.g., methane, butane for solvent delay) or use the solvent front peak to determine t₀. Enter this value on the Alkane Standards tab.
Run n-Alkane Standard Mix
Separate a standard mixture of n-alkanes (C₇-C₂₅ or similar range covering your compounds) using the exact same GC method you will use for samples.
Enter Alkane Retention Times
Enter the retention times for each alkane in either minutes or seconds. Check the calibration curve and verify that R² > 0.99. R² values below 0.99 indicate chromatographic problems.
Enter Sample Data
Enter retention times for unknown peaks from your sample chromatogram. You may enter times in either minutes or seconds.
View Results & Match Compounds
Go to the Results tab to see calculated RIs and nearest matches from the library. A Δ RI ≤ 5 units combined with a good mass spectral match (≥ 950) typically indicates positive identification.
Important Notes
- • Compounds with RIs < 850 or > 1900 may show greater variability. A tolerance of ± 10 units may be appropriate for early- or late-eluting compounds.
- • This calculator uses the van den Dool & Kratz formula for temperature-programmed GC. For isothermal separations, use the original Kováts formula based on adjusted retention volumes.
- • Retention indices are column-specific. Library values were determined on DB-5 (5% phenyl methyl siloxane) columns.
- • Always confirm identifications with mass spectral matching and/or authentic standards when possible.
Reference
Lucero, M., Estell, R., Tellez, M., & Fredrickson, E. (2009). A Retention Index Calculator Simplifies Identification of Plant Volatile Organic Compounds. Phytochemical Analysis, 20(5), 378-384. DOI: 10.1002/pca.1137