Fiona Regan

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.

Determination of pesticides in water using ATR-FTIR spectroscopy on PVC/chloroparaffin coatings

The objective of this study is to develop a novel in situ optical sensor for monitoring pesticides in water. The sensor consists of a polymer-coated attenuated total reflection (ATR) element or a silver halide optical fibre. The polymer film, which consists of PVC with a chloroparaffin plasticiser, acts to enrich the chlorinated pesticides and concentrates them within the penetration depth of the evanescent region of the ATR crystal or optical fibre. Measurements were performed by filling the sample cell with the aqueous pesticide solutions and recording a series of spectra over a period of time. Absorbance data were recorded for atrazine at 1577 cm-’ and alachlor at 1104cm-‘. Limits of detection in the region of 2 ppm have been achieved for atrazine and alachlor using a polymer-coated ATR element. Lower limits of detection can be achieved using polymer-coated optical fibres, especially with novel fibre configurations. These data establish the potential for this sensor for the use in pesticide analysis at alarm levels.

Determination of metal ions by capillary electrophoresis using on-column complexation with 4-(2-pyridylazo)resorcinol following trace enrichment by peak stacking

Co2+, Fe2+, Cu2+ and Zn2+ were separated and detected following derivatization with 4-(2-pyridylazo)resorcinol by capillary electrophoresis with UV-Vis detection. Parameters which were examined include both on-column and pre-column complexation, limit of detection, capillary loadability, linear dynamic range and reproducibility. A sample stacking technique was investigated in order to obtain better detection limits and greater sensitivity. Detection limits of 1 x 10(-8) M were achieved for Co2+, Fe2+ and Zn2+ and 4 x 10(-7) M for Cu2+. Mass detection limits were 0.2 fmol for Co2+, Fe2+ and Zn2+ and 7.0 fmol for Cu2+. The use of this method for the determination of metals in vitamin tablets and a pond water sample is presented.

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.

Sensing of chlorinated hydrocarbons and pesticides in water using polymer coated mid-infrared optical fibres

An IR fibre optic sensor which operates in the 4–16 µm wavelength region has been developed for the in-situ monitoring of chlorinated hydrocarbons and pesticides in water. The sensing element consists of a silver halide (AgClxBr1–x) optical fibre, coated with a polymer which both enriches the analyte in the evanescent wave region of the fibre and, when thick polymer coatings are used, minimizes water interference in the IR absorption. Using trichloroethylene and alachlor as representative pollutants, evanescent wave spectrometry in the mid-IR region is shown to provide good performance down to single ppm levels. Furthermore, it is shown that the technique can be applied to multi-analyte samples.

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.

Novel teflon-coated optical fibres for TCE determination using FTIR spectroscopy

The evaluation of a novel Teflon-coated fibre-optic chemical sensor for analysis of chlorinated hydrocarbons in water is described. The sensor which is based on evanescent wave absorption, consists of a Teflon-coated silver halide optical fibre. The Teflon coating is used to enrich the chlorinated hydrocarbon species within the penetration depth of the evanescent field of the fibre-optic sensor. The polymer-coated fibre was mounted in a glass cell containing inlet and outlet ports for the aqueous samples. Trichloroethylene (TCE) was used to calibrate the sensor and absorbance data were recorded at 938 cm- 1. The time constant for 90% saturation of the polymer with TCE was 3 min. The useful calibration range has a correlation coefficient of 0.9990 and relative standard deviation of 0.0002 in the range 5-50 ppm. A limit of detection of 1 ppm was achieved for TCE determination using the Teflon-coated optical fibre.

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.

Development of plasticised PVC sensing films for the determination of BTEX compounds in aqueous samples

A novel plasticised PVC polymer membrane as a sensing film for the determination of BTEX compounds using ATR-FTIR spectroscopy is demonstrated. A range of 10 plasticised PVC phases have been investigated using toluene and tetrachloroethylene as test analytes. Both analyte enrichment rates and infrared absorbance values were considered when choosing a suitable polymer for sensing. An enhancement in analyte absorbance at the characteristic IR absorption bands was noted as the plasticiser concentration in the film was increased. 2% PVC with 75% diisooctyl azelate was found to show promising results for simultaneous determination of the BTEX compounds. All BTEX analytes can be measured in less than 8 min. A study of a multicomponent sample demonstrated that analyte enrichment times were influenced by the presence of even one additional analyte component in the sample.

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.