Sørensen formol titration
The Sørensen formol titration invented by S. P. L. Sørensen in 1907 is a largely archaic method that was once used to determine the amino acid content of a sample. It is used in the determination of protein content in samples.
In case of tyrosine, the actual results are too high due to the negative hydroxyl group, which acts as a base. This explanation is supported by the fact that phenylalanine can be accurately titrated.