Retention Time (tR)
Definition
Time from sample injection to peak maximum at the detector in HPLC or GC. Characteristic of an analyte under a defined column and method. Identification at SFSL level is by retention time match plus spectral or detector response confirmation.
- Field
- HPLC and GC analysis
- Measured from
- Injection to peak maximum
- Depends on
- Column and method conditions
- Identification use
- Matched with spectral confirmation, not alone
Common questions
Why is retention time alone insufficient to identify a compound?+
Different compounds can coelute or show very similar retention times under the same method, so laboratories confirm identity with a second, orthogonal signal such as mass spectral fragmentation or UV/diode-array spectral matching rather than retention time by itself.
What causes retention time to shift between analytical runs?+
Column ageing, temperature or flow rate drift, mobile phase composition changes, and column replacement can all shift retention time, which is why analysts run reference standards alongside casework samples in the same batch.
How close must retention times be to count as a match?+
Laboratories define an acceptance window, often expressed as a percentage or fixed time tolerance around the standard's retention time, established through method validation rather than an arbitrary visual comparison.
Related terms
- Limit of Detection (LOD)
- The lowest concentration of analyte that produces a signal reliably distinguishable from the instrument noise, conventionally three times the standard deviation of...
- Mobile Phase
- The solvent or mixture that flows over the stationary phase and carries analytes along. Polarity, viscosity and volatility set the separation; switching...
- Resolution (Rs)
- Rs = 2(tR2 − tR1) / (W1 + W2). Above 1.5 means baseline separation; below 1.0 means peaks overlap and quantitation is...
- Rf (Retention Factor)
- Distance travelled by the analyte divided by the distance travelled by the solvent front, on a TLC or HPTLC plate. A unit-less...
- Stationary Phase
- The immobile material the mixture flows past. In paper it is water inside cellulose fibres; in classical column work and TLC it...