Nitrogen determination has a long history in the area of analytical Chemistry. Johan Kjeldahl first introduced Kjeldahl Nitrogen method in 1883 at meeting of the Danish Chemical Society. As a Chairman of Chemistry department of the Carlsberg laboratorium near Copenhagen, Kjeldahl was assigned, to scientifically observe the processes involved in beer making. While studying proteins during production he developed a method of determining Nitrogen content that was faster and more accurate than any method available at that time.
An Italian Scientist by name Dumas developed a method in 1830 which dealt with the Pyrolytic distruction of sample with the Nitrogen being reduced to Nitrogen gas. From the volume of Nitrogen gas produced the Nitrogen content of the sample is calculated. But Dumas method was too slow and gave incomplete results too. There are number of secondary methods for determination of protein or nitrogen. But all have to be caliberated against a standard method and with no other option the standard method is Kjeldahl.
EVOLUTION OF KJELDHAL METHOD
The Kjeldhal method is a means of determining the Nitrogen content of organic and inorganic substances. Although the technique and apparatus have been altered considerably over the past 125 years, the basic principles introduced by John Kjeldhal endure even today. From 1889 onwards several Chemists have made improvements in the method. These include the use of metalic Catalyst which produced a faster and greater recovery of Nitrogen, addition of pottasium Sulphate which raised the digestion temperature and shortened the digestion time, etc.
Later another Scientist – a Scandinavian agricultural Chemist by name Rozen Mosseberg’s invented the block digestor for more economical, accurate, safe, efficient and speedy way of Analysis, based on Kjeldahl Chemistry.
THE KJELDHAL CHEMISTRY
The Kjeldhal method may be broken down into three main steps.
DIGESTION:- The decomposition of Nitrogen in organic samples utilizing a concentrated Acid Solution.This is accomplished by boiling a homogenous sample in concentrated sulphuric acid and digestion catalyst.The end result is an ammonium Sulphate solution.
DISTILLATION:- Distillation involves adding base to the acid digestion mixture to convert NH4+ to NH3.This is followed by boiling.Finally NH3 gas is condensed and trapped in a receiving solution (H3BO3)
TITRATION:- Quantifying the amount of Ammonia ions in the receiving solution the percentage of Nitrogen can be calculated.