BEER LAMBERT’S LAW
Electromagnetic radiatio :– it is a form of energy whose behavior is described by the properties of particles and wave. Few properties of electromagnetic radiation for eg. Its refraction when it passes from one medium to another are explained best by describing light as a wave. Some other properties such as emission and absorption are better explained by treating light as a particle. The correct or exact nature of electromagnetic radiation is not clearly known, as it has the development of quantum mechanism in the first quarter of twentieth century.
Wave properties of electromagnetic radiation
Electromagnetic radiation consist of oscillating magnetic and electric …show more content…
In many cases calibration curve changes from ideal behavior (shown in figure). Changes from linearity are divided into 3 types i.e. chemical, fundamental and instrumental.
Fundamental limitations of beer Lambert’s law
Beer Lambert’s has a limitation and it is valid only for those analyte which has low concentration. There are 2 contribution to this this limitation of beer Lambert’s law. The individual particles of analyte no longer act independently of each other at higher concentration. The 2nd contribution is that the analyte’s absoptivity rely on the refractive index of sample. As refractive index changes with the analyte’s concentration, the value of ε and a may change. The refractive index is necessarily constant and the caliberation curve is linear, for sufficiently low concentration of analyte.
Chemical limitations to beer’s law
A chemical deviation may occur if the analyte is involved in an equilibrium reaction. suppose , as an example, an analysis for the weak acid, HA. To construct a Beer Lambert’s law calibration curve we prepare a series of standards—each containing a known total concentration of HA—and measure each standard’s absorbance at the same wavelength. Because HA is a weak acid, it is in equilibrium with its conjugate weak base, …show more content…
The 1st limitation is that Beer’s law considers that the radiation reaching the sample is of a single wavelength i.e. that the radiation is purely monochromatic. however, even the best wavelength selector passes radiation with a small, but finite effective bandwidth. Polychromatic radiation always gives a negative deviation from Beer lambert’s law, but the effect is smaller if the value of ε is essentially constant over the wavelength range passed by the wavelength selector. For this reason, it is better to get absorbance measurements at the top of a broad absorption peak. In addition, the deviation from Beer lambert’s law is less serious if the source’s effective bandwidth is less than 1/10th of the natural bandwidth of the absorbing species. When measurements must be made on a slope, linearity is improved by using a narrower effective