title: Head-column field-amplified sample stacking in binary system capillary electrophoresis. Preparation of extracts for determination of opioids in microliter amounts of body fluids.
abstract: Head-column field-amplified sample stacking (head-column FASS) is an efficient, on-line sample concentration technique that can easily provide a sensitivity enhancement of three orders of magnitude. Application of head-column FASS to the capillary electrophoretic analysis of opioid extracts prepared from 20 to 100 microliters of human plasma, serum or urine is reported. In the described approach, efficient concentration of cationic opiates from low conductivity extracts of body fluids is effected across a water plug, with separation taking place in a binary buffer comprising 60% (v/v) ethylene glycol, 75 mM Na2HPO4 and 25 mM NaH2PO4 (pH 7.9), and detection is effected at 210 nm. Sample extracts are prepared in 55% (v/v) ethylene glycol containing 100 microM H3PO4. Application of mixed-mode polymer solid-phase resins is shown to provide extracts that are either too salty or contain quite a large number of endogenous substances that could interfere with certain opioids. Liquid-liquid extraction with hexane, dichloromethane, ethyl acetate and dichloromethane-isopropanol is shown to provide extracts that are sufficiently clean. At a given pH, however, only closely related opioids can be extracted. Using ethyl acetate at alkaline pH, dihydrocodeine and nordihydrocodeine can reproducibly be recovered from 20-100 microliters of plasma, serum and urine. Application of head-column FASS and UV absorption detection thereby leads to the determination of ppb concentrations (> or = 1 ng/ml) of these compounds, an approach that only requires microliter amounts of sample and organic solvents.
authors.affiliation: Department of Clinical Pharmacology, University of Berne, Switzerland.
authors.forename: A B
authors.initials: AB
authors.lastname: Wey
authors.forename: C X
authors.initials: CX
authors.lastname: Zhang
authors.forename: W
authors.initials: W
authors.lastname: Thormann
mesh_terms: D001826:Body Fluids / Q000737:chemistry*; D003061:Codeine / Q000031:analogs & derivatives / Q000032:analysis / Q000097:blood; D019075:Electrophoresis, Capillary / Q000379:methods*; D019855:Ethylene Glycol / Q000737:chemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009294:Narcotics / Q000032:analysis* / Q000097:blood / Q000652:urine
chemical_list: D009294:Narcotics; C109998:nordihydrocodeine; D019855:Ethylene Glycol; C014481:dihydrocodeine; D003061:Codeine