Incorporation of high performance liquid chromatography with resonance Rayleigh scattering detection for determination of procaine and lidocaine in human plasma

A reliable and novel high performance liquid chromatography (HPLC) incorporating resonance Rayleigh scattering (RRS) detection was developed for the determination of procaine (Pro) and lidocaine (Lid). This method was based on the weak intensity of RRS of procaine and lidocaine, which can be enhanced by the addition of Erythrosin Yellowish (E-Y) in pH 4.4 acidic medium. The RRS signal was detected at lambda(ex) = lambda(em) = 370 nm. The conditions of separation and detection were optimized (pH, proportion of organic phase, flow rate, reaction temperature, concentration of E-Y and the length of reaction tube). The shape of ion-association complexes was observed by scanning electron microscopy. The reasons for RRS enhancement and the nature of the ion-association complexes were discussed by quantum chemistry calculation, scanning electron microscopy and absorption spectroscopy. The calibration curves of procaine and lidocaine were linear in the range from 0.005 to 15.375 mu g mL(-1) and the limit of detection (S/N 3) was 2.3 ng mL(-1) for procaine and 15 ng mL(-1) for lidocaine. The developed method was validated for the assay of procaine and lidocaine in human plasma samples. The recoveries were between 97.8% and 105.9% which is within acceptable limits.