Chromatography Resolution Calculator (Rs, Plate Number, Retention Factor)
Resolution between two chromatographic peaks, with the plate number, plate height, retention factor and selectivity, from retention times and base widths.
Results
What this tool does
Resolution is the gap between two peak centres measured in peak widths: Rs = 2Δt ÷ (w₁ + w₂). A value of about 1.5 is usually taken as baseline separation, while 1.0 leaves the peaks touching with a small overlap. The plate number N = 16 (t ÷ w)² uses the width at the base, so measure both on the same time axis; if you only have the width at half height, N = 5.54 (t ÷ w½)². Selectivity α is what the chemistry gives you, while N and the retention factor are what the column and the conditions give you.
Formula
Rs = 2 (t₂ − t₁) ÷ (w₁ + w₂) · N = 16 (t ÷ w)² · k′ = (t − t₀) ÷ t₀ · α = k′₂ ÷ k′₁ · H = L ÷ N
Variables
| Symbol | Meaning | Unit |
|---|---|---|
t0 | Dead time t₀ (unretained peak) | min |
t1 | Retention time of peak 1 | min |
t2 | Retention time of peak 2 | min |
w1 | Base width of peak 1 | min |
w2 | Base width of peak 2 | min |
lc | Column length | mm |
RS | Resolution Rs | — |
SEP | Separation | — |
N | Plate number N (peak 2) | — |
H | Plate height H | µm |
K | Retention factor k′ of peak 2 | — |
AL | Selectivity α | — |
Worked example
- Dead time t₀ (unretained peak)1.2 min
- Retention time of peak 15.4 min
- Retention time of peak 28.1 min
- Base width of peak 10.45 min
- Base width of peak 20.62 min
- Column length150 mm
- Resolution Rs5.05
- SeparationBaseline — fully separated
- Plate number N (peak 2)2731
- Plate height H54.9 µm
- Retention factor k′ of peak 25.75
- Selectivity α1.643
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- The calculation runs at full precision and only the display is rounded. If you copy an intermediate value and retype it, small differences can appear.