Single‑Point Calculator
A = ε × l × cDataset & Linear Regression (A vs c)
Estimate slope m = ε × l and intercept b from multiple points.| # | Concentration c (mol·L⁻¹) | Absorbance A | Action |
|---|---|---|---|
| 1 | |||
| 2 | |||
| 3 | |||
| 4 |
Formula Used
The Beer‑Lambert relation links absorbance to sample properties:
A = ε × l × c
- A — absorbance (unitless)
- ε — molar absorptivity or extinction coefficient (L·mol⁻¹·cm⁻¹)
- l — optical path length (cm)
- c — concentration (mol·L⁻¹)
Rearrangements:
c = A / (ε × l)
l = A / (ε × c)
ε = A / (l × c)
For a set of standards, a linear fit A = m·c + b gives m ≈ ε·l. With a known path length, ε = m / l.
How to Use This Calculator
- Choose Solve for and enter the other three values, then click Compute.
- For calibration, enter multiple c and A pairs in the dataset table.
- Click Run Regression to obtain slope m, intercept b, R², and estimated ε from your specified path length.
- Use CSV to export the table, or PDF to save a report with summary, table, and chart.
- Check linearity (R² close to 1). If non‑linear, reduce concentration or verify wavelength and baseline.
- Record wavelength, temperature, and matrix notes in your own report for traceability.
FAQs
1) What units should I use?
Use cm for path length, mol·L⁻¹ for concentration, and L·mol⁻¹·cm⁻¹ for ε. Absorbance is unitless.
2) Why is my intercept not zero?
Non‑zero intercepts arise from baseline offsets, stray light, or matrix effects. Re‑zero the instrument with a blank and verify cuvette cleanliness.
3) What is a reasonable ε value?
Many organic dyes have ε between 10³–10⁵ L·mol⁻¹·cm⁻¹. Very small values may indicate poor chromophores or wrong wavelength.
4) Can I estimate unknown concentration?
Yes. Run a calibration to get slope m. With measured A and known l, compute c = A / (m) if b ≈ 0, or c = (A − b)/m otherwise.
5) How many calibration points do I need?
At least 5 well‑spaced standards are recommended. Keep absorbance roughly 0.1–1.0 for best accuracy and avoid detector saturation.