A critical review is given of hydroxyproline analysis. Our procedure published previously—oxidation of the imino acid by chloramine-T in a buffer near neutrality and coupling of the chromogen formed with Ehrlich's aldehyde in strong perchloric acid—is re-evaluated in the light of several modifications of this method applied by different investigators. It was possible to establish a procedure which is faster and more sensitive than the former one and as reliable. The range is from 0.2 up to 6μg hydroxyproline in a 2-ml sample. A certain deviation from the standard procedure will not appreciably influence the results.

For material containing little hydroxyproline (urine, plant or animal tissue) separation from interfering substances by ion exchange is advisable.