Heated in acidic medium, penicillin antibiotics containing an amino group side chain such as amoxicillin (AMO) and ampicilliin (AMP) can be degraded, and the penicillamine and benzyl aminopeniloaldehyde of the degradation products can further react with palladium(II) to form a composition ratio 1∶1∶1 blended ternary complex, which leads to the great enhancement of resonance Rayleigh scattering (RRS) and appearance of new RRS spectra. The spectral characteristics of the reaction products of the two drugs with palladium(II) are similar, and the maximum wavelengths are all at 370 nm. The scattering intensity increments (ΔI) of the products are directly proportional to the concentrations of the antibiotics in certain ranges. The method exhibits higher sensitivity, and the detection limits (3δ) for AMO and AMP are 18.0 and 15.4 ng• mL^－1, respectively. In this case, the other penicillin antibiotics without any amino group in the structure of the side chain have not similar reactions, and certain amounts of some coexisting substances have no interference. Hence, the method has a good selectivity. It can be applied to the determination of amoxicillin and ampicillin in capsule, tablet, human serum and urine samples with satisfactory results.

Key words: ampicillin, amoxicillin, resonance Rayleigh scattering, palladium(II)