A selective and sensitive kinetic method for the determination of procaine and benzocaine in pharmaceuticals.

A simple stopped-flow method for the determination of procaine and benzocaine which is suitable for their routine analysis in pharmaceutical samples is reported. The method is based on a condensation reaction between each compound and 4-dimethylaminocinnamaldehyde, which yields coloured compounds and which are monitored spectrophotometrically. The calibration graph generated is linear over the range 0.5-20 micrograms ml-1 (RSD 0.73%) for procaine and 0.5-15 micrograms ml-1 (RSD 0.40%) for benzocaine, and the selectivity is very high in both cases. The proposed methods were satisfactorily applied to the determination of the two drugs in various pharmaceutical samples. A procedure for resolution of procaine-benzocaine mixtures in mass ratios between 15:1 and 1:7 with a precision of ca 1% was developed in order to determine one compound in the presence of the other with no interference.