The Sørensen formol titration(SFT) invented by S. P. L. Sørensen in 1907  is a titration of an amino acid with potassium hydroxide in the presence of formaldehyde. It is used in the determination of protein content in samples.
If instead of an amino acid an ammonium salt is used the reaction product with formaldehyde is hexamethylenetetramine:
The liberated hydrochloric acid is then titrated with the base and the amount of ammonium salt used can be determined.
With an amino acid the formaldehyde reacts with the amino group to form a methylene amino (R-N=CH) group. The remaining acidic carboxylic acid group can then again be titrated with base.