Determination of procaine, benzocaine and tetracaine by sequential injection analysis with permanganate-induced chemiluminescence detection

Local anaesthetics procaine hydrochloride (I), benzocaine (II), and tetracaine hydrochloride (III) were determined by the technique of sequential injection analysis (SIA) with chemiluminescence (CL) detection. The CL was emitted during the oxidation of the analytes by permanganate in aqueous sulphuric acid in the presence of various CL enhancers (4-hydroxybiphenyl, Rhodamine B, glycolaldehyde, glutaraldehyde and formic acid). The optimum enhancer or reagent concentrations, order and volumes of the injected zones were: 0.37 M formic acid (40, 23 or 28 μl for I–III, respectively), sample (40 μl), 2.3 M H2SO4 (20, 16 or 18 μl for I–III, respectively), and 0.5 mM KMnO4 (19, 13 or 15 μl for I–III, respectively). After a double (or single for III) reversal of the flow the mixed zone was pushed into the detector at a flow rate of 100 μl s−1. The transient CL signal was recorded at ≥390 nm. The calibration graphs relating the intensity of the emission (peak heights) to the concentration of the analytes were curvilinear (a second order polynomial showed the best fit) and they were suitable for determining I–III in the ranges 0.5–50, 0.5–25 and 0.2–25 μg ml−1, respectively. The limits of detection (3σ) were 0.3 μg ml−1 for I and II and 0.1 μg ml−1 for III. The sample throughput was 120 h−1. The relative standard deviations were ≤3.8% (n=10) when determining 5 μg ml−1 of I–III in prepared pure test solutions. The I and II were assayed in pharmaceutical dosage forms by the proposed method and the SIA results did not show any statistically significant difference from those obtained by standard titrimetry with sodium nitrite.