Determination of Penicillin G in Milk Samples Using Its Effect on Cloud Point Extraction of Triiodide Ion

Abstract

Abstract A cloud point extraction (CPE) method for determination of trace amounts of penicillin G by spectrophotometry based on its effect on the triiodide ion (I3–) has been developed. Penicillin G is converted to the corresponding penicilloic acid by carrying out hydrolysis with sodium hydroxide solution, and treatment with acid yields D-penicillamine that is oxidized quantitatively by iodine to give rise to a disulfide. The I3– remaining in the solution is extracted into the surfactant Triton X-100, and the difference between absorbance of the working solution in the presence and absence of penicillin G is proportional to the amount of penicillin G. The effects of different variables, such as concentrations of sodium hydroxide, hydrochloric acid, surfactant, and I3– and the temperature and incubation time on the CPE were studied. The calibration graph was linear in the range of 50–1250 μg/L, and the LOD was 38 μg/L (n = 10). The RSD for 10 replicate determinations of 1000 μg/L of penicillin G was 1.0%. The method was applied to the determination of penicillin G in milk samples.