Spectrophotometric Determination of Benzocaine by Azo- Dye Formation Reaction

A spectrophotometric method for the assay of trace amounts of benzocaine was based on the reaction of benzocaine with nitrite ion to form the corresponding diazonium salt followed by coupling reaction with ethyl cyano acetate to form a stable and a soluble yellow azo dye with maximum absorption at 405 nm. Beer’s law was obeyed over the range 5-250g/25ml, i.e, (0.2- 10ppm) of benzocaine and correlation coefficient 0.998 with a molar absorptivity of 3.1 104 L.mol-1.cm-1, a relative error of 0.0 to 0.25 % and a relative standard deviation of  0.03 to  0.38 %, depending on the concentration level. The method has been successfully applied for the assay of benzocaine in one pharmaceutical preparation (Lozenges).