Calculator
Example Data Table
| Item | Value | Meaning |
|---|---|---|
| Vo | 8.1 mL | Column void volume from blue dextran or excluded marker. |
| Vt | 24.0 mL | Total bed volume or fully included volume. |
| Unknown Ve | 14.2 mL | Peak elution volume for the unknown protein. |
| Standard | 158 kDa, 13.0 mL | Known marker used in the calibration curve. |
| Output | kDa | Preferred unit for apparent molecular weight. |
Formula Used
Partition coefficient:
Kav = (Ve - Vo) / (Vt - Vo)
Calibration curve:
log10(MW in kDa) = slope × Kav + intercept
Apparent molecular weight:
MW = 10^(slope × Kav + intercept)
Target elution estimate:
Target Ve = Target Kav × (Vt - Vo) + Vo
Oligomer check:
Oligomer ratio = apparent MW / monomer MW
How to Use This Calculator
- Enter the void volume from an excluded marker.
- Enter the total bed volume or fully included volume.
- Enter the unknown sample elution volume.
- Add standard proteins as molecular weight and elution volume pairs.
- Use manual slope and intercept only when standards are unavailable.
- Select the output unit and decimal places.
- Press calculate to view the result above the form.
- Download the CSV or PDF report for lab records.
About the Calculator
Size exclusion chromatography separates proteins by effective size. Large molecules enter fewer pores. They elute earlier. Small molecules enter more pores. They elute later. This calculator turns those elution volumes into a molecular weight estimate. It uses column void volume, total bed volume, sample elution volume, and a standard curve. The curve can be typed directly. It can also be built from protein standards.
Why Kav Matters
The partition coefficient gives a normalized elution position. It reduces column size effects. It also makes results easier to compare. A value near zero means the protein eluted close to the void volume. A value near one means the protein eluted near the total volume. The best range is usually between both limits. Values outside that range should be checked.
Calibration Approach
Standards create the relationship between Kav and log molecular weight. The relation is usually linear across the working range. This page supports regression from multiple standards. It also accepts a known slope and intercept. More standards improve confidence. Standards should cover the sample size range. They should be run on the same column and buffer system.
Interpreting Results
The calculated mass is an apparent molecular weight. It reflects hydrodynamic behavior, not only sequence mass. Shape, glycosylation, aggregation, and buffer conditions can shift elution. A compact globular protein may appear smaller. An elongated protein may appear larger. Use the result with other assays when identity matters.
Good Laboratory Practice
Enter volumes in one consistent unit. Milliliters are common. Confirm that total volume is greater than void volume. Confirm that sample elution volume lies within the useful column range. Remove standards that are overloaded or poorly resolved. Record run temperature, flow rate, column model, and equilibration buffer. These details help explain changes between runs.
Practical Use
The tool is useful for purification monitoring, oligomer checks, method development, and classroom calculations. It can estimate unknown proteins quickly. It can compare monomer and aggregate peaks. It can also document calibration data. Exported CSV and PDF reports make lab notes easier. The example table shows realistic inputs. Use it as a starting point, then replace values with your own chromatogram data. Keep assumptions documented for future review and repeat runs in each report.
FAQs
What does this calculator estimate?
It estimates apparent protein molecular weight from size exclusion chromatography elution data. The value depends on column calibration and protein behavior.
What is Kav?
Kav is the partition coefficient. It normalizes elution volume between void volume and total bed volume.
Should I use standards or manual slope values?
Use standards when possible. They create a curve matched to your column, buffer, and run conditions.
Why is the result called apparent molecular weight?
Size exclusion depends on hydrodynamic size. Protein shape, aggregation, and modifications can change elution behavior.
Can I use any volume unit?
Yes. Use one consistent unit for Vo, Vt, Ve, and standard elution volumes.
What happens if Kav is outside zero to one?
The sample may be outside the useful column range. Check volumes, peak assignment, and column calibration.
How many standards are recommended?
Use at least two standards. Four or more standards usually give a stronger calibration and better diagnostics.
Can this detect protein oligomers?
It can estimate an apparent oligomer ratio when monomer mass is entered. Confirm oligomers with supporting experiments.