Ira S. Lurie

Separation selectivity in chiral and achiral capillary electrophoresis with mixed cyclodextrins

The use of mixed cyclodextrins (CDs) as run buffer additives for capillary electrophoresis (CE) is reviewed. Mixtures of neutral CDs or neutral and charged CDs are advantageous for both chiral and achiral separations. The unique selectivities offered by these novel combinations allow separations that are often problematic to obtain by other CE techniques.

Simultaneous separation of acidic, basic, and neutral organic compounds, including strong and moderate acids and bases, by capillary electrochromatography.

The separation of strongly basic, moderately basic, weakly basic, strongly acidic, moderately acidic, weakly acidic, and neutral compounds in a single run using capillary electrochromatography (CEC) is presented. This is accomplished using a 3-μm CEC Hypersil C8 capillary with high organic content acetonitrile/phosphate (pH 2.5) mobile phases containing hexylamine. Fifteen basic, acidic, and neutral drugs of forensic interest are resolved using a step gradient. Strong and moderately basic drugs separate before t(o), apparently by a combination of free zone electrophoresis (CZE) and chromatographic phenomena. Weak bases separate after t(o), also by a combination of CZE and chromatographic processes. Due to large selectivity differences between CEC and CZE for bases, there is evidence that the stationary phase is playing a significant role in the separation of these solutes. The CEC approach presented offers unique selectivity, expanded peak capacity, and the ability to solubilize both hydrophilic and hydrophobic solutes in an injection solvent that is compatible with the chromatographic system.

Micellar electrokinetic capillary chromatography of the enantiomers of amphetamine, methamphetamine and their hydroxyphenethylamine precursors

Abstract The separation of the enantiomers of amphetamine, methamphetamine, ephedrine, pseudoephedrine, norephedrine and norpseudoephedrine in a single run via micellar electrokinetic capillary chromatography (MECC) is described. The procedure, which involves preliminary derivatization with 2,3,4,6-tetra-O-acetyl-β- d -glucopyranosyl isothiocyanate (GITC) followed by MECC analysis, is far superior with respect to both resolution and speed of analysis versus similar efforts utilizing high-performance liquid chromatography. The MECC separation was obtained at 20 kV on a 48 cm × 50 ωm I.D. (26 cm length to detector) capillary at 30°C using a run buffer consisting of 20% methanol and 80% sodium dodecyl sulfate (SDS) solution [100 m M SDS, 10 m M phosphate, 10 m M borate (pH 9.0)]. The effects of organic modifier type, organic modifier concentration, voltage, temperature and SDS concentration on the resolution of the GITC derivatives are described. The application of the above methodology to forensic samples is presented.

On-chip chiral and achiral separation of amphetamine and related compounds labeled with 4-fluoro-7-nitrobenzofurazane

Amphetamine and analogous compounds have been labeled with 4‐fluoro‐7‐nitrobenzofurazane and analyzed on a microfabricated chip. Separation of norephedrine, ephedrine, cathinone, pseudoephedrine, methcathinone, amphetamine and methamphetamine is demonstrated using micellar electrokinetic capillary chromatography (MEKC) and laser‐induced fluorescence (LIF) detection. Chiral separations of individual drugs were studied using neutral and negatively charged cyclodextrins (CDs) with and without the addition of an organic modifier and/or sodium dodecyl sulfate (SDS). The best results were obtained using a highly sulfated γ‐CD (HS‐γ‐CD) in combination with a low concentration of SDS. To obtain complete separation of a mixture of (+/−)‐norephedrine, (+/−)ephedrine, (+/−)‐pseudoephedrine, (+/−)‐methcathinone, (+/−)‐amphetamine and (+/−)‐methamphetamine it was necessary to add a small amount (1.5 mM) of SDS to the separation buffer. Optimized chiral separation was achieved within 7 min using an S‐folded separation channel, a separation voltage of 8 kV and a buffer consisting of 50 mM phosphate (pH 7.35), 10 mM HS‐γ‐CD and 1.5 mM SDS.

Capillary electrophoresis in clinical and forensic analysis: Recent advances and breakthrough to routine applications

This paper is a comprehensive review article on capillary electrophoresis (CE) in clinical and forensic analysis. It is based upon the literature of 1997 and 1998, presents CE examples in major fields of application, and provides an overview of the key achievements encountered, including those associated with the analysis of drugs, serum proteins, hemoglobin variants, and nucleic acids. For CE in clinical and forensic analysis, the past two years witnessed a breakthrough to routine applications. As most coauthors of this review are associated with diagnostic or forensic laboratories now using CE on a routine basis, this review also contains data from routine applications in drug, protein, and DNA analysis. With the first‐hand experience of providing analytical service under stringent quality control conditions, aspects of quality assurance, assay specifications for clinical and forensic CE and the pros and cons of this maturing, cost‐ and pollution‐controlled age technology are also discussed.

The use of a highly sulfated cyclodextrin for the simultaneous chiral separation of amphetamine-type stimulants by capillary electrophoresis.

We investigated the simultaneous chiral separation of nine amphetamine type stimulants (dl‐norephedrine, dl‐norpseudoephedrine, dl‐ephedrine, dl‐pseudoephedrine, dl‐amphetamine, dl‐methamphetamine, dl‐methylenedioxyamphetamine (MDA), dl‐methylenedioxymethamphetamine (MDMA), and dl‐methylenedioxyethylamphetamine (MDEA)) by capillary electrophoresis using highly sulfated γ‐cyclodextrin (SU(XIII)‐γ‐CD) as a chiral selector. Three different approaches using SU(XIII)‐γ‐CD with 50 mM phosphate background electrolyte were designed; (I) high CD concentration (10 mM SU(XIII)‐γ‐CD) at neutral pH (pH 7.0) in the normal polarity mode, (II) low CD concentration (1.0 mM) at low pH (pH 2.6) in the normal polarity mode and (III) high CD concentration at low pH (pH 2.6) in the reversed‐polarity mode. In mode (II), the effects of adding three neutral CDs (β‐CD, dimethyl‐β‐CD and hydroxypropyl‐β‐CD) were also investigated. The best separation was obtained after optimizing mode (III) as follows: run buffer of 10 mM SU(XIII)‐γ‐CD with 50 mM phosphate background electrolyte at pH 2.6, applied voltage of –12 kV and capillary temperature of 15°C.

Separation and detection of acidic and neutral impurities in illicit heroin via capillary electrophoresis

The separation and detection of acidic and neutral impurities in illicit heroin using capillary electrophoresis (CE) is described. Separations were achieved using charged cyclodextrin modified micellar electrokinetic capillary chromatography. The use of the anionic beta-cyclodextrin sulfobutyl ether 1V in combination with sodium dodecyl sulfate significantly increased resolution. Improved selectivity and/or sensitivity in detection was obtained using photodiode array ultraviolet and laser-induced fluorescence detection. The phenanthrene-like heroin impurities exhibit high native fluorescence under krypton-fluoride laser excitation (248 nm). The limit of detection by laser-induced fluorescence detection for one of these solutes (acetylthebaol) is 1.8 ng/ml, 500 times more sensitive than UV. This methodology is applicable to analysis of both crude and refined heroin.

Capillary gas chromatographic-electron capture detection of coca-leaf-related impurities in illicit cocaine: 2,4-diphenylcyclobutane-1,3-dicarboxylic acids, 1,4-diphenylcyclobutane-2,3-dicarboxylic acids and their alkaloidal precursors, the truxillines.

A method has been developed that allows for the detection of the eleven stereoisomers of diphenylcyclobutanedicarboxylic acid in illicit cocaine samples, including alpha-, gamma-, and epsilon-truxillic acids and beta- and delta-truxinic acids. These, and other carboxylic acids, were also detected as ester moieties of alkaloidal impurities in illicit cocaine as well as in alkaloids of the South American coca leaf, e.g., alpha- and beta-truxilline. After lithium aluminum hydride reduction of the acidic and basic extracts of a prepared sample, the reduced species were derivatized with heptafluorobutyric anhydride in the presence of pyridine. The heptafluorobutyryl derivatives of the reduced diphenylcyclobutanedicarboxylic compounds were easily detected on-column at low picogram levels using a moderately polar fused-silica capillary column in the splitless mode and interfaced with a 63Ni electron-capture detector.

Use of dynamically coated capillaries with added cyclodextrins for the analysis of opium using capillary electrophoresis.

A rapid, precise, accurate, and robust method using capillary electrophoresis (CE) with dynamically coated capillaries for the analysis of the major opium alkaloids in opium is presented. Dynamic coating of the capillary surface is accomplished using a commercially available reagent kit (polycation coating followed by polyanion coating). The addition of dual cyclodextrins (hydroxypropyl-beta-cyclodextrin and dimethyl-beta-cyclodextrin) to the run buffer imparts excellent selectivity for the opium alkaloids. For the determination of morphine, papaverine, codeine, noscapine and thebaine in opium gum and opium latex samples (using tetracaine as an internal standard) good agreement with values obtained by gradient high-performance liquid chromatography is obtained. Compared to the latter technique, CE affords better resolution with significantly faster analysis time (12 min versus 29 min). Dynamically coated capillaries, which give rise to a relatively high and robust electroosmotic flow (EOF) at the background electrolyte pH of 2.5, allow for rapid analysis and excellent migration time and peak area precision (RSDs < or = 0.12% and < or = 1.2%, respectively). Reproducible separations (relative migration times) for over 500 samples have been obtained on a single capillary. The nature of the injection solvent, the injection time and the contents of the waste vials have a profound effect on the pressure injection precision of the relatively hydrophobic solutes. The CE conditions reported in this study are also applicable to the analysis of lysergic acid diethylamide (LSD) exhibits.

Application of micellar electrokinetic capillary chromatography to the analysis of illicit drug seizures.

The application of micellar electrokinetic capillary chromatography (MECC) to the analysis of illicit drug seizures is presented. Areas investigated include general screening and qualitative and, in some instances, quantitative analysis of various drugs, including heroin, opium, cocaine, amphetamines, LSD and anabolic steroids. Due to its high efficiency, high selectivity and general applicability, MECC is well suited for forensic drug analyses.