Question

Describe the function of the following chemicals used in protein analysis following the Kjeldahl method: a. Catalyst pellet b. Sulfuric acid c. Sodium hydroxide d. Boric acid e. Hydrochloric acid

Answer 1

Digestion is the decomposition of nitrogen in organic samples utilizing a concentrated acid solution. This is accomplished by boiling a homogeneous sample in concentrated sulfuric acid. Sulfuric acid has been used alone for the digestion of organic samples.

catalysts have been employed by Kjeldahl chemists over the years to increase the rate of organic breakdown during the acid digestion.

Distillation is adding the excess base to the acid digestion mixture to convert NH4+ to NH3, followed by boiling and condensation of the NH3 gas in a receiving solution. This is accomplished by;

1)raising the pH of the mixture using sodium hydroxide (NaOH solution). This has the effect of changing the ammonium (NH4+) ions (which are dissolved in the liquid) to ammonia (NH3)

2) separating the nitrogen away from the digestion mixture by distilling the ammonia (converting it to a volatile gas, by raising the temperature to boiling point) and then trapping the distilled vapors in a special trapping solution of boric acid (H3BO3). The ammonia is bound to the boric acid in the form of ammonium borate complex.

HCl--> Distilled solution is titrated with HCl until the solution has a slight violet color