Barbara A. Fogarty

Carbon paste-based electrochemical detectors for microchip capillary electrophoresis/electrochemistry

The first reported use of a carbon paste electrochemical detector for microchip capillary electrophoresis (CE) is described. Poly(dimethylsiloxane) (PDMS)-based microchip CE devices were constructed by reversibly sealing a PDMS layer containing separation and injection channels to a separate PDMS layer that contained carbon paste working electrodes. End-channel amperometric detection with a single electrode was used to detect amino acids derivatized with naphthalene dicarboxaldehyde. Two electrodes were placed in series for dual electrode detection. This approach was demonstrated for the detection of copper(II) peptide complexes. A major advantage of carbon paste is that catalysts can be easily incorporated into the electrode. Carbon paste that was chemically modified with cobalt phthalocyanine was used for the detection of thiols following a CE separation. These devices illustrate the potential for an easily constructed microchip CE system with a carbon-based detector that exhibits adjustable selectivity.

Development of comparative methods using gas chromatography-mass spectrometry and capillary electrophoresis for determination of endocrine disrupting chemicals in bio-solids.

Two analytical separation techniques are being investigated for their potential in determining a wide range of endocrine disrupting chemicals (EDCs) in the environment. Capillary electrophoresis (CE) in the micellar mode in conjunction with a cyclodextrin (CD) modifier is shown to have potential for determination of alkylphenol breakdown products. Gas chromatography with mass spectrometric (GC-MS) detection is being utilised for validation of the CE method development and in addition as a separation technique to optimise preconcentration using solid-phase extraction. GC has demonstrated potential for the separation of 26 priority chemicals suspected as being endocrine disrupting compounds. The challenge of the method development process lies in the fact that these compounds are of differing polarities, size and charge and therefore are difficult to separate in a single run. Capillary electrophoresis in the CD-MEKC (micellar electrokinetic chromatography) mode is showing potential in this regard. Limits of determination are in the low mg/l range for CE and GC, however, using preconcentration it is possible to improve detection sensitivity with >80% recovery for some analytes and up to 100% recovery for most target species.

Novel modes of capillary electrophoresis for the determination of endocrine disrupting chemicals

The synthesis and usage of a wide range of organic chemicals has increased dramatically over the last five decades. These compounds sometimes termed endocrine disrupting chemicals include agricultural pesticides, industrial solvents, dyes, plasticisers, detergents and heat exchangers. Concerns have been raised about the potential adverse effects of these compounds on humans and wildlife species. Our objectives are to develop a method to identify, using novel capillary electrophoretic techniques, the endocrine disrupting compounds that are reported to be present in environmental samples. The CE modes, capillary zone electrophoresis, micellar electrokinetic chromatography (MEKC), cyclodextrin-modified MEKC (CD-MEKC) and electroosmotic flow-suppressed CD-MEKC were investigated for the determination of a range of endocrine disrupting chemical compounds. This paper shows some initial results obtained.

Potential of microemulsion electrokinetic chromatography for the separation of priority endocrine disrupting compounds

This work examines the potential of microemulsion electrokinetic chromatography for the separation of several priority endocrine disrupting compounds (EDCs). The optimised microemulsion system comprised 25 mM phosphate buffer pH 2, 80 mM octane, 900 mM butanol, 200 mM sodium dodecyl sulphate and was further modified with 20% propanol. The use of a low pH buffer resulted in the suppression of electroosmotic flow within the capillary. Reversal of the conventional electrode polarity resulted in faster migration of hydrophobic compounds. Test analytes included the octylphenol, nonylphenol and nonylphenol diethoxylate, which are breakdown products of the alkylphenolic detergents. The synthetic oestrogens diethylstilbestrol and ethynyloestradiol were also included in the separation along with the plastic monomer bisphenol-A. Test analytes were selected due to their reported presence in environmental samples namely industrial and domestic wastewater treatment effluents and sludges. Using the optimised method a separation of six EDCs was achieved within 15 min. The optimised method was then applied to the analysis of a spiked wastewater influent sample with UV detection of all six compounds at 214 nm.

Microchip capillary electrophoresis: application to peptide analysis.

The development of analytical methodologies to elucidate mechanisms of peptide transport and metabolism is important for the understanding of disease states and the design of effective drug therapies. Interest in the use of microchip capillary electrophoresis (CE) devices for peptide analysis stems from the ability to perform fast, highly efficient separations combined with small sample volume requirements. Many of the separation modes developed on conventional systems, including electrochromatography, isoelectric focusing, and electrophoretic bioaffinity assays, have been demonstrated on microchip devices. Steps that include sample preparation and labeling can also be integrated onto the microchip platform. This chapter will discuss considerations for peptide analysis using microchip CE and will focus on different approaches to sample preparation, separation, and detection.

Separation of two groups of oestrogen mimicking compounds using micellar electrokinetic chromatography.

Two groups of compounds are being investigated due to their reported oestrogen mimicking characteristics in the environment. Separation of phenolic compounds and synthetic oestrogens using micellar electrokinetic chromatography is reported. Photodiode array detection is used for both separations. A standard separation buffer can be used for both groups of compounds including zwitterionic buffer cyclohexylamino-1-propanesulfonic acid, 20 mM at pH 11.5. It was found necessary to include 15% acetonitrile and 25 mM sodium dodecyl sulfate to aid separation and maintain analytes in solution. Optimum separations are achieved using 20 kV with hydrodynamic injection for 5 s. The relative standard deviation (RSD) for reproducibility was investigated for a mixture of phenols and synthetic oestrogens. For these compounds RSD was found to be <0.6% in all cases. Peak efficiencies ranged from 76,000 to 150,000 theoretical plates for different analytes. Application to environmental samples is discussed.