Formula Used
| Calculation | Formula | Purpose |
|---|---|---|
| Basic mobility | μ = v/E | Uses measured migration velocity and electric field. |
| Experimental mobility | μ = dL/(tΔV) | Uses distance, field length, time, and voltage. |
| Migration velocity | v = μE | Predicts velocity under an applied field. |
| Migration distance | d = μEt | Predicts displacement during a selected time. |
| Capillary correction | μep = μapp − μEOF | Removes electroosmotic contribution from apparent mobility. |
| Henry equation | μ = 2εζf(κa)/(3η) | Relates mobility and zeta potential. |
Symbols: μ is mobility, v is velocity, E is field strength, d is distance, L is length, t is time, ΔV is potential difference, ε is permittivity, ζ is zeta potential, η is viscosity, and f(κa) is Henry’s function.
How to Use This Calculator
- Select the mode matching your known and required quantities.
- Enter signed values when migration direction is important.
- Select the unit beside every entered measurement.
- Choose result units, precision, and scientific-notation preferences.
- Add relative uncertainties when an uncertainty estimate is needed.
- Use the batch box for replicate experiments and blank correction.
- Review formulas, steps, warnings, and model assumptions before reporting results.
Worked Example Data
| Example | Inputs | Expected approach |
|---|---|---|
| Velocity and field | v = 12.5 µm/s, E = 200 V/cm | Apply μ = v/E after SI conversion. |
| Experimental setup | d = 4.2 cm, L = 10 cm, t = 120 s, ΔV = 200 V | Apply μ = dL/(tΔV). |
| Capillary correction | Leff = 50 cm, Ltot = 60 cm, ΔV = 20 kV, ta = 8.5 min, tEOF = 6.2 min | Subtract EOF mobility from apparent mobility. |
| Zeta estimate | Water, 25°C, μ = −2.5×10⁻⁸ m²/(V·s) | Select Henry, Hückel, or Smoluchowski carefully. |
Understanding Electrophoretic Mobility
Electrophoretic mobility describes charged motion within an applied electric field. It combines migration speed with the field’s driving strength. Signed results preserve useful information about migration direction conventions.
Positive and negative signs require a clearly defined coordinate system. Instrument software may use different polarity and direction conventions. Always document electrode orientation before comparing reported mobility values.
The simplest relationship divides migration velocity by electric-field strength. Both quantities should first use coherent SI base units. Unit conversion errors can otherwise dominate the final calculation result.
Experimental systems often measure distance, voltage, time, and separation length. These measurements produce velocity and field before mobility calculation. Accurate dimensions improve mobility estimates across repeated laboratory measurements.
Capillary electrophoresis includes bulk electroosmotic flow through the capillary. Apparent analyte mobility therefore combines electrophoretic and electroosmotic contributions. A neutral marker helps separate these two transport effects.
Corrected mobility subtracts electroosmotic mobility from apparent analyte mobility. The subtraction may amplify uncertainty when both values are similar. Replicate marker measurements improve confidence in corrected mobility values.
Zeta potential conversion requires viscosity and electrical permittivity data. Henry’s equation also requires a double-layer correction function. These physical properties depend strongly on temperature and medium.
The Smoluchowski approximation suits sufficiently thin electrical double layers. The Hückel approximation suits sufficiently thick double layers instead. Intermediate conditions usually need Henry’s more general treatment model.
The dimensionless parameter κa compares particle radius and Debye length. It helps indicate which approximation may be more appropriate. Real samples can violate ideal assumptions despite suitable κa.
Particle shape, concentration, conductivity, and surface conduction affect measurements. Polydispersity can also broaden observed mobility distributions significantly. Treat calculated zeta potential as a model-based estimate only.
Uncertainty propagation combines independent relative errors through root-sum-square methods. Correlated variables require more detailed covariance analysis than provided. Report assumptions beside every calculated uncertainty value for transparency.
Batch analysis reveals repeatability, spread, blank effects, and controls. Mean values alone cannot describe unstable or heterogeneous samples. Inspect individual measurements before accepting any summary statistic blindly.
Scientific Limitations
Calculated results support planning, education, and preliminary data review. They do not replace instrument calibration, validated laboratory methods, or expert interpretation. Zeta-potential models assume idealized particle and interface behavior.
Temperature presets use approximate property relationships. Custom media should use measured viscosity and permittivity whenever available. Capillary results assume consistent effective length and applied voltage definitions.
Calculation History
Successful calculations are stored locally in this browser only.
| Date | Mode | Primary result | Action |
|---|
Frequently Asked Questions
What is electrophoretic mobility?
It is migration velocity divided by electric-field strength. Its SI unit is square metres per volt-second.
Can mobility be negative?
Yes. A negative result indicates migration opposite the selected positive-field direction.
Why must field length be entered?
Voltage alone is not field strength. Field strength equals potential difference divided by field length.
What is apparent mobility in capillary electrophoresis?
It includes both analyte electrophoresis and electroosmotic bulk flow through the capillary.
How is electroosmotic flow corrected?
The calculator determines neutral-marker mobility and subtracts it from apparent analyte mobility.
Which zeta-potential model should I choose?
Use Hückel for thick layers, Smoluchowski for thin layers, and Henry for intermediate behavior.
What does κa mean?
It compares particle radius with Debye length and helps assess double-layer thickness.
Does the calculator include uncertainty?
Yes. It combines entered independent relative uncertainties using a root-sum-square estimate.
Can I analyse multiple samples?
Yes. Paste CSV-style rows to obtain corrected values, statistics, a chart, and downloadable data.