Critique on the biological estimation of amino nitrogen

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Abstract
Comparison of titrimetric and Van Slyke methods of estimating amino N in biological extracts has been made. Eight modifications of the formaldehyde and alcohol titration methods are included in an examination of plant leaf extracts. All alcohol (or acetone) methods for amino N are discarded owing to lack of specificity, as in these Mg, which cannot be readily removed, and certain weak acids are also titrated. For colored biological extracts, the Van Slyke method is preferred, but the formaldehyde (phenolphthalein) titration has advantages for lightly colored and colorless extracts. The existing literature is reviewed in a discussion on the general usefulness and accuracy of the several methods. The efficiency of norite and lead acetate as decolorants of leaf extracts is considered with respect to pH. Lead acetate at pH 6 is adopted in preference to norite at pH 1. The coloring matter of the extract migrates as an ampho-lyte during electrodialysis.

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