Bernard J. Treves Brown

The development of a metal clad leaky waveguide sensor for the detection of particles

A novel leaky waveguide device for the detection of particles has been developed and shown to be more sensitive than the currently used waveguide sensors. These metal clad leaky waveguide (MCLW) devices have been used as preliminary study on the feasibility for the detection of soluble proteins but can also be used for the detection of large particles such as bacteria, bacterial spores, yeasts and latex beads. A MCLW device has been fabricated to increase the overlap of the evanescent field extension from the sensor surface with the particles in the bulk solution of a flowing system, to place most of the entire volume of the particles within the evanescent field. Increasing the overlap of the evanescent field with the particles and permitting mode propagation along the direction of a flow for a few millimetres provides an effective interrogation approach for multi-particle detection in a single flow channel.

Bidirectional isotachophoresis on a planar chip with integrated conductivity detection.

The use of a miniaturised planar separation device with integrated conductivity detection for performing bidirectional isotachophoresis (ITP) is described. The chips were produced in poly(methyl methacrylate) (PMMA) using a milling procedure. To enable bidirectional ITP the devices were designed to inject samples into the centre of the section channel and incorporated two integrated on-column conductivity detectors, positioned at opposite ends of this channel. When used with a hydrodynamic sample transport system the devices were used for the analysis of a range of small ions: NH4+; Na+; Mg2+; Ca2+; Li+; NO3-; ClO4-; SO4(2-); F-. Results sucessfully achieved included the simultaneous separation of three anions and three cations.

Determination of metal cations on miniaturised planar polymeric separation devices using isotachophoresis with integrated conductivity detection

The feasibility of using miniaturised planar polymeric separation devices for the isotachophoretic separation of metal cations was demonstrated. Devices were produced in silicone rubber using a cast moulding fabrication technique. Detection was performed using an integrated single electrode conductivity detector, a design which offers simple fabrication and high resolution. The electrical characteristics of the devices were found to be suitable for performing electroseparations with a power dissipation of up to 1.5 W m-1 being achieved. The separation of a sample containing a mixture of the four metal ions lithium, lanthanum, dysprosium and ytterbium was reproducibly achieved using miniaturised devices. A comparison with a capillary scale separation of the same mixture was made. The miniaturised separations were achieved in under 600 s, which is less than half the time taken for the capillary scale separations.

Miniaturised isotachophoretic analysis of inorganic arsenic speciation using a planar polymer chip with integrated conductivity detection

A new method allowing the analysis of inorganic arsenic species using isotachophoresis has been developed. This method has been shown to be suitable for use on both miniaturised planar polymer separation devices and capillary scale devices. A poly(methyl methacrylate) chip with integrated conductivity electrodes has been successfully used for the rapid analysis of inorganic arsenic species in under 600 s. Limits of detection of 1.8 mg l(-1) and 4.8 mg l(-1) for arsenic(V) and arsenic(II), respectively, have been achieved with the miniaturised device. The device has also been used to perform the simultaneous separation of arsenic(III), arsenic(V), antimony(III), molybdenum(VI) and tellurium(IV).

Single electrode conductivity detection for electrophoretic separation systems

Various types of detectors have been utilised in electrophoretic separation systems, but conductivity detection provides the obvious choice for detecting ionic substances. This paper describes a new design of conductivity detector utilising a single, on column, sensing electrode. This new design is seen as offering the twin advantages of much higher resolution, than has previously been possible, and simple construction. The detector has been evaluated using separations of sodium and potassium in capillary isotachophoretic and miniaturised planar polymer isotachophoretic separation systems. Good linearity has been found and the limit of detection of sodium calculated to be 0.43 mM.

Miniaturised free flow isotachophoresis of bacteria using an injection moulded separation device

A new design of miniaturised free flow electrophoresis device has been produced. The design contains a separation chamber that is 45 mm long by 31.7 mm wide with a depth of 50 μm and has nine inlet and nine outlet holes to allow for fraction collection. The devices were formed of polystyrene with carbon fibre loaded polystyrene drive electrodes and produced using injection moulding. This means that the devices are low cost and can potentially be mass produced. The devices were used for free flow isotachophoresis (FFITP), a technique that can be used for focussing and concentrating analytes contained within complex sample matrices. The operation of the devices was demonstrated by performing separations of dyes and bacterial samples. Analysis of the output from FFITP separations of samples containing the bacterium Erwinia herbicola, a biological pathogen, by cell culturing and counting showed that fractionation of the output was achieved.

Determination of chlorine containing species in explosive residues using chip-based isotachophoresis

A new method has been developed to allow the determination of the chlorate, chloride and perchlorate anions in inorganic explosive residues to be made using isotachophoresis (ITP). To enable a good separation of these species to be achieved the method involves the use of two complexing agents. Indium(III) is used to allow the determination of chloride whilst using nitrate as the leading ion and alpha-cyclodextrin is used to allow the separation of chlorate and perchlorate. Separations were carried out using a miniaturised poly(methyl methacrylate) (PMMA) separation device. The method was applied to analysing both model samples and actual inorganic explosive containing residue samples. Successful determinations of these samples were achieved with no interference from other anions typically found in inorganic explosive residues. Limits of detection (LOD) for the species of interest were calculated to be 0.80 mg l(-1) for chloride, 1.75 mg l(-1) for chlorate and 1.40 mg l(-1) for perchlorate.

Isotachophoresis on Planar Polymeric Substrates

The work presented here describes the design, fabrication, evaluation and use of miniaturised polymeric devices, for performing capillary isotachophoresis (CITP). CITP is an electrophoretic separation method that provides a simple technique for the analysis of ionic substances. The two principal advantages of CITP over capillary zone electrophoresis (CZE) are that it allows larger volumes of dilute sample solutions to be loaded into the separation channel and the electrolyte system can be chosen to eliminate sample matrix constituents which are not of interest. In addition CITP can be used as a preconcentration technique to provide a narrow sample band for subsequent on-line CZE separation. The devices are fabricated from silicone elastomer with on-chip conductivity detection. The resulting system has been used to separate simple mixtures of ions.

Thiocyanate and nitrite analysis using miniaturised isotachophoresis on a planar polymer chip

A new method has been developed to improve the determination of thiocyanate using isotachophoresis. This method uses complexation with copper(II) as a mechanism for improving the separation of thiocyanate from chlorate and perchlorate. By using a pH of 3.25 the method can also be used to analyse nitrite. Separations were carried out using a miniaturised poly(methyl methacrylate) (PMMA) separation device. Linearity was observed from 1.25 to 75 mg dm(-3) with a correlation coefficient of 0.998 for both thiocyanate and nitrite. Limits of detection for these two species were calculated to be 0.8 mg dm(-3) and 0.9 mg dm(-3) respectively. The method was successfully applied to the analysis of these anions in a range of samples including explosive residues.

A capacitively coupled conductivity detector for electroseparations

A conductivity detector providing high-voltage isolation for electroseparations is described. It is based on an oscillator which is capacitively coupled to the measurement electrodes; the conductance between the electrodes determines the output frequency. The detector was evaluated using a small-volume (500 nl) conductivity cell (cell constant 5.1 ? 103 m-1 ) which is described. It was then characterized using a factorial method and optimized to maximize the sensitivity (absolute change in frequency) to changes in conductivity. A novel method was used to determine the cell constant for a pair of microband electrodes (100 ?m across on 200 ?m centres) with electrolyte confined in a fine channel above them - this was 2615?86 m-1 and the detector has been used with this cell for isotachophoretic separations reported elsewhere.