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Heated in a boiling water bath, penicillin antibiotics such as amoxicillin, ampicillin, sodium cloxacillin, sodium carbenicillin and sodium benzylpenicillin could react with K 3 [Fe(CN) 6 ] to form combined products in a dilute HCl medium. As a result, resonance Rayleigh scattering (RRS) intensity was enhanced greatly and new RRS spectra appeared. The maximum scattering wavelengths of the five combined products are all located at 330 nm. The scattered intensity increments (∆I) of the combined products are directly proportional to the concentrations of the antibiotics in a certain range. The methods exhibit high sensitivity, and the detection limits for the five penicillin antibiotics are between 4.61 and 5.62 ng•mL -1 . The spectral characteristics of RRS and the optimum reaction conditions were investigated. The mechanism of reaction and the reasons for the enhancement of resonance light scattering were discussed. The effects of coexisting substances have been examined, and the results indicated that the method had a good selectivity. It can be applied to the determination of penicillin antibiotics in capsule, tablet, human serum and urine samples.

In pH 4.9 Britton-Robinson buffer solution, methotrexate (MTX) reacted with thallium(III) to form a 3∶1 chelate. This resulted in great enhancement of second-order scattering (SOS) spectra and frequency doubling scattering (FDS) spectra and appearance of new SOS and FDS spectra. Their maximum wavelengths were located at 520 and 390 nm, respectively. The increments of scattering intensities (∆I) were directly proportional to the concentrations of MTX in the ranges of 0.022-2.0 µg•mL -1 (SOS method) and 0.008-2.5 µg•mL -1 (FDS method). The methods exhibited high sensitivities. The detection limits for MTX were 7.4 ng•mL -1 (SOS method) and 2.3 ng•mL -1 (FDS method), respectively. The optimum conditions of the reaction, the influencing factors and the effects of coexisting substances were investigated. A highly sensitive, simple and fast method for the determination of MTX has been developed. The method can be applied satisfactorily to the determination of MTX in human serum samples. In this work, the charge distribution of MTX was calculated by a CNDO quantum chemistry method. In addition, the reaction mechanism was discussed.