Adsorption of penicillin-berberine ion associates at a water/tetrachloromethane interface and determination of penicillin based on total internal-reflected resonance light scattering measurements

In aqueous medium of pH 5.33, penicillin, such as ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO), interacts with berberine (BB), forming ion associates through electrostatic attraction of the polar head groups of penicillin and BB. The formed ion associates are then adsorbed into the amphiphilic H2O/CCl4 interfaces, displaying greatly enhanced total internal-reflected resonance light scattering (TIR-RLS) signals with the maximum peak at 370 nm. With the enhanced TIR-RLS data, thermodynamic parameters of adsorption of penicillin-BB ion associates into interfaces were measured. Mechanism studies show that the ion associates of penicillin with BB at H2O/CCl4 interfaces have 1:1 binding molar ratio, and the formation constants are in the range of 3.67 × 104 to 5.48 × 104 mol−1 dm4. It was found that the enhanced TIR-RLS intensity was directly proportional to the concentration of penicillin in the range of 0.98 × 10−7 to 10.0 × 10−7 mol l−1 for BP, 0.87 × 10−7 to 10.0 × 10−7 mol l−1 for OA, 1.1 × 10−7 to 12.0 × 10−7 mol l−1 for AmP and 1.2 × 10−7 to 12.0 × 10−7 mol l−1 for AmO with the corresponding limits of determination (3σ) being 3.48 × 10−8, 3.85 × 10−8, 4.22 × 10−8 and 4.86 × 10−8 mol l−1, respectively.