Page 91 - Analytical Chemistry I E-book

Determination of amino acids
(Sörensen formol titration)

• Amino acids contain both an acidic carboxyl group (-COOH) and a basic
amino group (-NH2), so they cannot be titrated directly.

• Formaldehyde (HCHO) is added to the amino acid sample.

Formaldehyde reacts with the amino group. The remaining
carboxylic acid group can then be titrated with

standard NaOH using phenolphthalein as indicator.

HOOC‒CH2‒NH2 + HCHO → HOOC‒CH2‒N═CH2 + H2O

Glycine