How to use & worked examples
Compare the three input conditions
Edit a number or slider for ε, l or c: results and diagrams update immediately. Dilute, Concentrated and Long path are input examples. Reset drawing keeps conditions and pause state while restarting the schematic dots.
Check the defaults
ε=5000 L/(mol·cm), l=1 cm, c=0.1 mmol/L = 0.0001 mol/L. A=5000×1×0.0001=0.5; transmittance is 100×10⁻⁰·⁵=31.6228%, and the half-transmission path is 0.602060 cm.
| Condition | Absorbance A | Transmittance %T |
|---|
| Defaults | 0.5 | 31.6228 |
| Double concentration: 0.2 mmol/L | 1 | 10 |
| Double path length: 2 cm | 1 | 10 |
Doubling concentration or path length doubles A and squares the original fraction T. At fixed concentration, the half-transmission path does not depend on the selected cell length.
Model & applicability
What does the optional stray-light model show?
At 2% stray light (s=0.02), the defaults give apparent absorbance 0.481967 and apparent transmittance 32.9635%. The ideal main-beam values remain A=0.5 and 31.6228%. The assumption is that the same additive Ps bypasses the sample and reaches both sample and blank readings. This does not represent every source of nonlinearity, such as molecular interactions.
Reading very small values
At ε=100, l=0.1 and c=0.001, A=0.00001. At A=2600, the mathematical transmission fraction is 10⁻²⁶⁰⁰, which rounds to zero in ordinary floating point. We retain its logarithm and display 1e-2600 (1×10 to the power −2600). Percent transmittance is 1e-2598%. Absorption shown as ≈100% is a rounded value, not a claim that transmission is physically zero.
Before applying results to measurements
This tool compares principles. Example coefficients are not calibrated material data, and stray light is an assumed constant. There is no universal boundary at which the ideal law must fail outside A=0.1–1.5. Real validity depends on substance, wavelength, solvent and instrument; check standards, blanks and measured calibration curves. The tool does not establish clinical quantities, instrument performance or standards compliance.
Sources and calculation code
The university notes below explain absorbance, transmittance and units; the manufacturer explains negative stray-light deviations. Our normalized constant-stray equation is derived from the stated additive assumption, not a reproduction of the cited instrument performance.
Frequently asked questions
Is the concentration input in mol/L?
The input and calibration x axis use mmol/L. The calculation divides by 1000 to obtain mol/L: A = 0.001 ε l c, with c in mmol/L.
Is the calibration slope equal to ε?
On this mmol/L x axis, the ideal slope is 0.001 ε l. Divide it by 0.001 l to obtain ε. This page does not fit measured calibration data.
Does stray light change absorption by the solution?
Not in this model. Equal additive light at sample and blank raises apparent transmittance and lowers apparent absorbance. Distinguish main-beam absorption from the apparent detector reading.
Do very small transmission values display as zero?
Scientific notation distinguishes them from exact zero. Even below floating-point range, log₁₀T = −A is retained for display.