Spectrophotometric Titrations with Nitrous Acid I.**Control Laboratories, Winthrop Laboratories, Rensselaer, N. Y.

Principles in the Spectrophotometric Determination of Propoxycaine in the Presence of Procaine**Division of Chemistry, American Dental Association, Chicago, Ill.

“…Propoxycaine hydrochloride can be conveniently assayed alone by simple ultraviolet methods (2) or by spectrophotometric titration with nitrous acid (3). The presence of procaine hydrochloride will, however, interfere with both of these methods, as well as most classical methods such as modified acid-base titrations which are employed in the U. S. P. assay for procaine hydrochloride (4), and the N. F. assay for lidocaine hydrochloride (5).…”