Determination and temperature effects of lidocaine (lignocaine) hydrochloride, epinephrine, methylparaben, 2,6-dimethylaniline, and p-hydroxybenzoic acid in USP lidocaine injection by ion-pair reversed-phase high pressure liquid chromatography.

USP Lidocaine injection was assayed using ion-pair high pressure liquid chromatography with an octylsilane (RP-8) reversed-phase column packing and a mobile phase consisting of D-10-camphorsulfonic acid/methanol/acetic acid/water. The effect of temperature was investigated to determine the optimum temperature for separating the drug components and their degradation products. Lidocaine (lignocaine) hydrochloride, epinephrine, methylparaben, and p-hydroxybenzoic acid were separated at 50 degrees C. 2,6-Dimethylaniline was separated from lidocaine at 15 degrees C. An aliquot of the sample was injected directly into the liquid chromatograph, and after separation the compounds were quantitated by their spectrophotometric response at 254 nm (lidocaine) or 280 nm (lidocaine plus epinephrine).