Determination of cocaine and its metabolites using cation-selective exhaustive injection and sweeping-MEKC

Hsiu L. Su, Lan I. Feng, Hsiu Ping Jen, You-Zung Hsieh*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


We have employed a high-sensitivity on-line preconcentration method, cation-selective exhaustive injection (CSEI) and sweeping MEKC, for the analysis of cocaine, benzoylecgonine, norcocaine, and cocaethylene. We monitored the effects of several of the CSEI-sweeping-MEKC parameters - including the pH, the concentrations of SDS and organic modifier, the injection length of the high-conductivity buffer, and the injection time of the sample - to optimize the separation process. The optimal BGE was 100mM phosphoric acid (pH 1.8) containing 75mM SDS with 10% 2-propanol and 10% tetrahydrofuran as the organic modifier. In addition, electrokinetic injection of the sample at 15 kV for 900 s provided both high separation efficiency and enhanced sweeping sensitivity. The sensitivity enhancements for cocaine, norcocaine, and cocaethylene ranged from 2.06×104 to 3.96×104; for benzoylecgonine it was 1.75×103; the coefficients of determination exceeded 0.9958. The LODs, based on an S/N ratio of 3:1, of sweeping-MEKC ranged from 33.5 to 52.8 ng/mL; in contrast, when using CSEI-sweeping-MEKC the sensitivity increased to range from 29.7 to 236 pg/mL. Under the optimal conditions, we analyzed cocaine in a human urine sample prepared using off-line SPE to minimize the influence of the matrix. The recovery of the SPE efficiency was satisfactory (ca. 74.9-87.6%). Our experimental results suggest that, under the optimal conditions, the CSEI-sweeping-MEKC method can be used to determine cocaine and its metabolites with high sensitivity in human urine.

Original languageEnglish
Pages (from-to)4270-4276
Number of pages7
Issue number20
StatePublished - 3 Dec 2008


  • Cocaine and its metabolites
  • CSEI-sweeping-MEKC
  • On-line preconcentration
  • Sweeping-MEKC

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