The Sørensen formol titration(SFT) invented by S. P. L. Sørensen in 1907 Sørensen Biochem Z., 7, 45, 407 1907S. L. Jodidi "Abnormalities In the Formol Titration Method" Journal of American Chemical Society 1918 40 (7), 1031-1035 DOI: 10.1021/ja02240a006 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.Analytical Chemistry of Foods C.S. James Springer Science & Business Media, 2013
In case of tyrosine, the actual results are too high due to the negative hydroxyl group (-OH), which acts as a base. This explanation is supported by the fact that phenylalanine can be accurately titrated.
Method The titration of an amino acid with potassium hydroxide in the presence of formaldehyde.Harry Auterhoff: Lehrbuch der Pharmazeutischen Chemie, 5. Aufl., Wissenschaftliche Verlagsgesellschaft mbH Stuttgart, 1968.
In winemaking Formol titration is used in winemaking to measure yeast assimilable nitrogen needed by wine yeast in order to complete fermentation.B. Zoecklein, K. Fugelsang, B. Gump, F. Nury Wine Analysis and Production pgs 152–163, 340–343, 444–445, 467 Kluwer Academic Publishers, New York (1999) A related analysis method is o-phthaldialdehyde/N-acetyl-L-cysteine spectrophotometric assay (NOPA).
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