Mass spectroscopy and microfluidic technology, when combined, offer significant advantages in radiochemical analysis sample volume and cost reduction. A microfluidic device designed for efficiency has been developed. This device separates uranium from key trace elements by utilising UTEVA® chromatographic resins and nitric acid solutions of different concentrations for adsorption and recovery. The eluates from this microdevice are then diluted and directed to an inductively coupled plasma mass spectrometry system, enabling direct analysis of trace elements and uranium with minimal operator-sample interaction. This efficient approach greatly reduces the volume of sample required for trace elemental analysis in actinide materials, thereby reducing costs and satisfying the As Low As Reasonably Achievable (ALARA) principle.

Accurate identification of isotopes and elements of uranium (U) and plutonium (Pu) in environmental samples from the nuclear fuel cycle is essential for environmental monitoring and safeguarding. A novel microfluidic system coupled with a multi-collecting inductively coupled plasma mass spectrometer (MC-ICP-MS) allows the measurement Pu and U isotope ratios in real time. The application reduces the sample volume required to less than 80 µL with required quantities of analytes being reduced from the conventional micrograms to less than nanograms. This reduction in sample and reagent volume makes the analytical process less resource-intensive and generates less waste; a significant benefit for safer and more efficient analysis operations.

Particle concentration and filtration is a key stage in a wide range of processing industries and also one that can be present challenges for high throughput, continuous operation. Here we demonstrate some features which increase the efficiency of ultrasound enhanced sedimentation and could enable the technology the potential to be scaled up. In this work, 20 mm piezoelectric plates were used to drive 100 mm high chambers formed from single structural elements. The coherent structural resonances were able to drive particles (yeast cells) in the water to nodes throughout the chamber. Ultrasound enhanced sedimentation was used to demonstrate the efficiency of the system (>99% particle clearance). Sub-wavelength pin protrusions were used for the contacts between the resonant chamber and other elements. The pins provided support and transferred power, replacing glue which is inefficient for power transfer. Filtration energies of ∼4 J/ml of suspension were measured. A calculation of thermal convection indicates that the circulation could disrupt cell alignment in ducts >35 mm high when a 1K temperature gradient is present; we predict higher efficiencies when this maximum height is observed. For the acoustic design, although modelling was minimal before construction, the very simple construction allowed us to form 3D models of the nodal patterns in the fluid and the duct structure. The models were compared with visual observations of particle movement, Chladni figures and scanning laser vibrometer mapping. This demonstrates that nodal planes in the fluid can be controlled by the position of clamping points and that the contacts could be positioned to increase the efficiency and reliability of particle manipulations in standing waves.

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.

The primary requirement for a mixing operation in droplet-based microfluidic devices is an accurate pairing of droplets of reaction fluids over an extended period of time. In this paper, a novel device for self-synchronous production of droplets has been demonstrated. The device uses a change in impedance across a pair of electrodes introduced due to the passage of a pre-formed droplet to generate a second droplet at a second pair of electrodes. The device was characterised using image analysis. Droplets with a volume of ~23.5 ± 3.1 nl (i.e.~93% of the volume of pre-formed droplets) were produced on applying a voltage of 500 V. The synchronisation efficiency of the device was 83%. As the device enables self-synchronised production of droplets, it has a potential to increase the reliability and robustness of mixing operations in droplet-based microfluidic devices.

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 new method has been developed to allow the determination of potassium in post-explosion residues to be made using miniaturised isotachophoresis. The method is based on the use of a caesium leading ion with 4.5 mM 18-crown-6 ether added to retard the potassium to allow reliable determinations to be made. With the conditions selected no interference was noted from other small inorganic cations, such as ammonium, barium, calcium, magnesium, sodium or strontium. The method was successfully applied to the analysis of seven samples containing explosive residues obtained from the unconfined burning of several flash powders. The procedure was found to offer good linearity for potassium determinations over the concentration range of 1.25-150 mu g/mL with a coefficient of determination of 0.999 achieved.

This paper presents a mathematical and experimental study of the effect of inlet concentration (and therefore viscosity) of glycerol solutions on the performance of a microfluidic network. This was achieved with analytical modelling, implemented in MATLAB, and optical measurement of the entire concentration distribution of the network. A mathematical proposal to improve the linearity of the outlet profile is also implemented and successfully verified experimentally. The concentration gradients of a two inlet–six outlet (2–6) microfluidic network device were obtained with inlet solutions of 10–40 wt% glycerol and flow rates of up to 5 μl/s per inlet. The mathematical model developed gave a good agreement with the experimental results obtained. ‘S’ shaped outlet profiles were obtained for the four glycerol cases studied and the closest results to the model were achieved at an optimised flow rate of 1μl/s for 10 wt% glycerol, 5 μl/s for both 20 and 30 wt% glycerol and 1.5 μl/s for 40 wt% glycerol. The linearity of the outlet profiles for the 20, 30 and 40 wt% inlet glycerol experiments were improved from R 2 of 0.977, 0.946 and 0.966, respectively (before linearisation) to their new values of 0.997, 0.995 and 0.974, respectively (after the linearisation). This was performed by application of the mathematical model, at controlled inlet flow rate ratios of 0.77, 0.63 and 0.52 with respect to the viscous inlet, for 20, 30 and 40 wt% glycerol experiments, again with very good agreement of the outlet performance between the experimental and the mathematical results.

The use of malonic acid as a complexing agent has enabled a new method to be devised to allow the determination of magnesium to be made using miniaturised isotachophoresis. Using a leading electrolyte of 10 mmol L(-1) caesium hydroxide and 2 mmol L(-1) malonic acid at pH 5.1 gave the method a high specificity towards magnesium. Investigations using a poly(methyl methacrylate) chip device with an integrated conductivity detector showed that no interference from calcium, strontium, barium and sodium should occur. The method was found to be linear over the range of magnesium concentrations from 0.625 to 75 mg L(-1) and the limit of detection was calculated to be 0.45 mg L(-1). Separations were demonstrated with water samples but the procedure should also be applicable to more complex sample matrices such as inorganic explosive residues, blood or urine.

This paper presents and fully characterises a novel simplification approach for the development of microsystem based concentration gradient generators with significantly reduced microfluidic networks. Three microreactors are presented; a pair of two-inlet six-outlet (2-6) networks and a two-inlet eleven-outlet (2-11) network design. The mathematical approach has been validated experimentally using a purpose built optical detection system. The experimental results are shown to be in very good agreement with the theoretical predictions from the model. The developed networks are proven to deliver precise linear concentration gradients (R(2) = 0.9973 and 0.9991 for the (2-6) designs) and the simplified networks are shown to provide enhanced performance over conventional designs, overcoming some of the practical issues associated with traditional networks. The optical measurements were precise enough to validate the linearity in each level of the conventional (2-6) networks (R(2) ranged from 0.9999 to 0.9973) compared to R(2) = 1 for the theoretical model. CFD results show that there is an effective upper limit on the operating flow rate. The new simplified (2-11) design was able to maintain a linear outlet profile up to 0.8 microl/s per inlet (R(2) = 0.9992). The proposed approach is widely applicable for the production of linear and arbitrary concentration profiles, with the potential for high throughput applications that span a wide range of chemical and biological studies.

This article describes work into a prototype system for the assay of amylase, using microfludic technologies. The new system has a significantly shorter cycle time than the current laboratory methods, which generally use microtitre plates, yet is capable of generating significantly superior results. As such, we have shown that sensitivity is enhanced by a factor of 10 in the standard assay trials, and by a factor of 2 in the real-sample lab trials. In both assays, the use of a microreactor system reduced the reaction time by a factor of 6.2, from 20 min incubation to 3.2 min. Basing the conclusion on the Megazyme Cerealpha Standard Method, and using the Cerealpha units as a measure of assay efficiency, the typical response for the microfluidic assay was shown to be 1.0 x 10(-3) CU/mL (standard deviation [SD] 2.5 x 10(-4) CU/mL), compared to 2.56 x 10(-4) CU/mL (SD 5.94 x 10(-5) CU/mL) for the standard macroassay. It is believed that this improvement in the reaction schematics is due to the inherent advantages of microfluidic devices such as superior mixing, higher thermal efficiency, and enhanced reaction kinetics.

An integrated microfluidic/electrochemical sensor with a dual working electrode configuration was fabricated for voltammetric and electrochemiluminescence (ECL) applications. The fabrication method integrates the two techniques of injection molding and screen printing for the first time. Injection molding is used to fabricate the flow cell with integrated electrical and fluidic connectors. Screen printing was used to print the electrodes directly onto the injection molded base plate. An over molding procedure followed by ultrasonic welding was used to form the complete sensor. The electrochemical and ECL performance of the sensors was assessed by applying different electrochemical methods such as cyclic voltammetry (CV), anodic stripping voltammetry (ASV) and chronoamperometry. The attractive analytical performance demonstrates good capability of the disposable sensors for routine online electrochemical and ECL measurements.

The design and operation of a gradient network is particularly critical when mixing solutions of different viscosities, which is common with real samples, especially in life science applications. The dynamic concentration gradient formed from mixing equal inlet flow rates of (0.01-1.5mol/kg) sucrose solution with deionized water in a network was analytically modelled and experimentally investigated. The generation of a stable profile was highly dependent on both the inlet flow rate and the inlet viscosity ratio of the mixed solutions for each case study. The optimum flow rate per inlet for a stable profile was also determined. The experimental investigations show that optimizing the diffusion rate and providing sufficient mixing are key parameters to validate the analytical model. An inlet viscosity ratio of >1.009:1 (with respect to water inlet) was sufficient to perturb the outlet concentration profile. The linearity of the outlet concentration profile decreased and tended towards a sigmoidal profile with increasing sucrose concentration. Enhanced linearity of the outlet concentration profile, through optimizing the inlet flow rate ratio for each case study was also performed.