Aim: Estimation of amino acids by formal titration
Principle
The method is based on the reaction between amino
acids and formaldehyde, which results in the formation of a methylol
derivative. This reaction is quantitative, allowing for the estimation of amino
acid content.
Materials
Sample containing amino acids
(glycine)
Formaldehyde solution (37-40%)
0.1N Sodium hydroxide (NaOH) solution
0.1 N Hydrochloric acid (HCl)
solution
Phenolphthalein indicator
Procedure
1.
Preparation
of sample: Prepare a solution of the sample containing amino acids glycine
(10ml)
2.
Addition
of formaldehyde: Add a known excess of formaldehyde solution to the sample
solution.
3.
Neutralization:
Neutralize the solution to a faint pink color using phenolphthalein indicator,
by adding a strong base sodium hydroxide (NaOH).
4.
Back
titration: Add a strong acid like hydrochloric acid (HCl) to the solution until
the pink color disappears.
Observation Table:
|
Sr.No. |
Volume of NaOH added to get pink
colour (ml) |
Volume of HCl added To disappear Colour (ml) |
|
1 |
13 |
20 |
|
2 |
14 |
20 |
|
3 |
13 |
21 |
|
Mean |
13 |
20 |
Calculation: Calculate the amount of
amino acid present in the sample using the following formula:
Amino acid content (%) = (Volume of HCl used x
Normality of HCl x Molecular weight of amino acid) / (Volume of sample x 100)
Example
Suppose we want to estimate the amount of glycine
(molecular weight = 75.07 g/mol) in a sample.
Volume of HCl used = 20 mL
Normality of HCl = 0.1 N
Volume of sample = 10 mL
Amino acid content (%) = (20 mL x 0.1 N x 75.07 g/mol)
/ (10 mL x 100) = 1.5%
Result:
The result indicates that the sample contains 1.5% glycine.
