THEORY

The instrumental technique of atomic absorption spectrometry (AAS) uses the Beer–Lambert Law (Beer's Law), which relates the concentration of an analyte in a sample to the sample's absorption of electromagnetic radiation. Beer's Law states that the optical absorbance of a chromophore in a transparent solvent is linearly proportional to the chromophore's concentration and also to the sample cell path length. Beer's Law is applicable only if the spectral bandwidth of the light is narrow compared to the spectral line widths in the spectrum and is expressed as follows: A = εbc A = absorbance ε = molar absorptivity [L/(mol·cm)] b = path length of the sample cell (cm) c = concentration (mol/L) In addition: A = log₁₀(P₀/P) = log₁₀(1/T) = log₁₀(100/%T) = 2 − log₁₀%T P₀ = intensity of light passing through a sample P = intensity of light leaving the sample T = transmittance %T = 100 × T