Determination of the Molecular Mass of Modified Citrus Pectin Using High-Performance Size Exclusion Chromatography

Liquid-liquid-liquid phase microextraction (LLLME) coupled with high performance liquid chromatography was developed for the determination of amphetamine and ketamine in human urines. The effects of the extraction solvent, the pH value of the donor solution, the stirring rate, the extraction time and HCl concentration in the acceptor phase on the enrichment factors of analytes were investigated. The optimal experimental conditions, 300 microL of toluene as the organic phase, pH 11 of the donor phase, 1.0 microL of 0.1 mol/L HCl as the acceptor phase, 600 r/min of the stirring rate, and 50 min of the extraction time, were obtained. Under the above conditions, high enrichment factors were reached. The linear ranges were from 0.01 to 10 microg/mL for amphetamine, and 0.01 to 5 microg/mL for ketamine. The relative standard deviations were lower than 2%. The limits of detection were 5 ng/mL for the two target compounds at signal-to-noise ratio of 3. The method with little solvent consumption may provide high analyte pre-concentration and excellent sample clean-up, and it is a sensitive and suitable method for the simultaneous determination of above two analytes in human urines.