COLORIMETRY AND SPECTROPHOTOMETRY

COLORIMETRY is a technique used to determine the concentration of colored compounds in solution.


   A colorimeter is a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light.

 

 

 

 

digital photo colorimeter

  
A SPECTROPHOTOMETER primarily differs from the colorimeter by also covering the ultraviolet region of the electromagnetic spectrum.Further other devices make the spectrophotometer more sensitive
than the colorimeter.

PRINCIPLE BEHIND THE WORKING OF A SPECTROPHOTOMETER

 
 Firsly a beam of light is provided by source.
This light source then strikes adiffraction grating which acts like a prism and splits the beam of light into its component colours.
The grating is then rotated so that only a specific wavelength of light reaches the exit slit.
Then the specific wavelenth of light interacts with the sample.
A detector placed after the sample measures the transmittance and absorbance of the sample.
The transmitted light is then sensed by the detector and then converted into a digital display.
The following video makes the principle of working very clear.
http://www.youtube.com/watch?v=pxC6F7bK8CU&feature=related

BEER LAMBERT LAW

Coloured solutions have the property of absobing light of different waveletgths.
The amont of light absorbed or transmitted by a coloured solution is in accordance with the Beer-Lambert law.

BEER'S LAW
The intensity of the colour is directly proportional to the concentration of coloured particles in the solution.

LAMBERT'S LAW
The amount of light  absorbed by a coloured solution depends on the length of the column or depth of the liquid(in other words called pathlength) of the liquid through which the liquid passes.

BEER-LAMBERT law combines both these laws.

                   Here,   Io= intensity of incident light
                               I=intensity of emergent light

 The ABSORBANCE so calculated or determined is the OPTICAL DENSITY(OD) of the solution.

BEER-LAMBERT LAW

The following two videos make the Beer-Lambert law very clear and easy to understand.
http://www.youtube.com/watch?v=Y-BcIDKMSzE&feature=related 
http://www.youtube.com/watch?v=5GdXyDpR1pw&feature=relmfu

SOME INTERESTING DAY TO DAY APPLICATIONS SPECTROPHOTOMETRY AND COLORIMETRY

Used in scientific research for measuring the concentration of solid material.

Used for measuring phosphorus content of soils.

Used domestically in food preparation. In fact, the advanced CR-410 colorimeter can precisely calculate the colour of cooked french fries.Until the introduction of colorimeters in the food industry, the colour of cooked french fries was measured visibly!!!

So in conclusion I would like to say that both colorimetry and spectrophotometry are fields which provide us a wide range of benefits for our day to day life.
Also further reseach in these fields may even lead to the improvement of our lifestyle,that is, if  we visualize and come up with more applications for the betterment of mankind!!!