Physical Principle
Spectroscopic analysis relies on the beer lambert law to relate the attenuation of light to the properties of the material through which it travels. The law defines the linear relationship between the absorbance of a medium and the concentration of the absorbing species and the light path.
Absorption Relation
Light intensity decreases exponentially as it passes through a sample according to the product of molar absorptivity and the concentration of the sample. Detectors measure the ratio of transmitted light to the initial source intensity. This ratio is converted into an absorbance value for analysis.
Logarithmic scaling allows the concentration to be read as a linear function.
Path Length
Optical cells provide a fixed distance for the light to travel through the gas or liquid sample. Gold plated mirrors often reflect the beam multiple times to increase the effective distance inside a small footprint. Longer paths improve the detection of trace contaminants.
Short paths prevent signal saturation in high concentration environments.
Concentration Limit
Deviations from the law occur when the chemical density becomes so high that molecules interact with each other. This effect changes the charge distribution and shifts the absorption peak. Scattering from particles in the path also introduces non linear errors.
Calibration curves must be established within the linear range to ensure accuracy.
