COLORIMETRIC ANALYSIS (noun)

 

A specific type of spectroscopic analysis where the wavelength of the radiation being used is in the visible-light region of the electromagnetic spectrum. This type of analysis can be used to determine both the identity and the quantity of chemicals within a liquid sample. For example, performing colorimetric analysis on purple food dye might reveal that it is actually composed of blue and red food-dyes in a 3:1 ratio.

In colorimetric analysis, a beam of polychromatic light is shined through a liquid sample. Various chemicals within the liquid will absorb certain wavelengths of the light and an absorption spectrum is generated by a computer. Comparison of this spectrum to those of known chemicals allows one to identify the chemicals present within the liquid sample. A second colorimetric analysis is then performed, this time at just the one specific wavelength of visible light (monochromatic) that is characteristic of the chemicals that are being examined in the liquid sample.

Using a calibration graph and Beer's Law, the exact concentration of the chemical can then be calculated from the absorbance value. The greater the concentration of the chemical within the liquid sample, the greater will be the absorbance reading.