Diffusion-bonded blocks perfect for new analyser

Technology that allows blocks of pre-machined acrylic to be diffusion-bonded together to form complex yet compact manifolds, features in a new range of portable analysis instruments

Technology developed by British company, Carville, that allows blocks of pre-machined acrylic to be diffusion-bonded together to form complex yet compact manifolds, has been central to the development of a new range of portable instruments for real-time field analysis of water quality, industrial effluent, pharmaceutical processes and even blood.

They are due to enter commercial production as soon as strategic partnerships have been established to market the products.

The modular instruments, which are PC-controlled by LabView software running under Windows, are the culmination of the so-called Hisant project, part funded by the Department of Trade and Industry.

Organisations involved are Cardiff and Luton Universities, Ingenion Design and Biotech Instruments, and Thames Water, London Hospital and SmithKline Beecham which have provided test facilities.

Heralding a new era of powerful, on-site monitoring of anything from environmental pollutants to blood sugar, the helium gas-driven, flow injection analysers comprise an array of interconnected modules.

They include an ultrasonic device for separating particles down to below five microns from a pre-filtered, low volume fluid sample, and a bespoke, diffusion-bonded, acrylic manifold produced by Carville.

The latter has built-in miniature solenoid valves supplied by Lee Products in a number of reagent blocks together with incubation, mixing, refrigeration and holding chambers; and finally a flow-through detection cell with a fibre optic link to a spectrophotometer sensitive to the UV or visible spectrum.

By analysing the change in colour of the fluid sample after addition of reagents, the concentration of the analyte under investigation is determined.

The manifold can be configured for each of the main application areas - water, medical, pharmaceutical - and instead of having one channel for analysis, it could be manufactured to sample and test multiple analytes.

Said Peter Dyke, a director of Cambridgeshire-based Ingenion Design, "The advantage with diffusion-bonding is that it gives us the flexibility to configure the manifold for various uses.

We started trying to machine a single plastic block and attach standard Teflon tubing, but there were problems with the fine drilling operations and in any case we could only produce right angle bends.

"The beauty of the Carville system is that it is possible to insert components where they are needed and machine passageways and chambers of any shape before joining the blocks, so curved channels for smooth flow can be created and dead spaces within the manifold are minimised.

"Moreover there is no swarf or debris inside the block, as these are removed before bonding.

The overall result is a more compact and reliable unit that may be reproduced exactly every time during manufacture." As the flowpaths are sealed in diffusion-bonded blocks that are clamped together, reliability is superior to designs that rely on discrete components connected by plastic tubing.

Additionally, by making the passageways very fine, smaller test samples may be taken to minimise the use of expensive reagents.

The other major benefit of diffusion bonding is that there is no adhesive between layers to corrupt the sample.

Owing to its chemical inertness, acrylic is generally chosen for applications like the Hisant project.

The instrument, still at its prototype stage, shows good correlation with results obtained in laboratories.

Key to its performance is the efficiency of the ultrasonic filter at the front end, the best reported clearance (separation efficiency) being 10,000-fold based on a suspension of yeast cells.

Successful clarifications have been made of water and sewage samples; and for the clinical device, 99.98 clearance was achieved with whole blood without significant potassium leakage from the red cells, leaving about 30 per cent by volume of clear plasma for sampling.

In view of these successes, commercial prospects are high as the market for the products in their respective sectors is enormous.

In 1998 there were over two million official water quality determinations in the UK, the majority carried out in analytical laboratories.

Europe-wide, Frost and Sullivan in January 2000 reported the water pollution monitoring instrument market as ?198 million, rising to ?277 million by 2005.

In clinical care, the diabetes market alone accounts for 1.25 million adults in the UK suffering from non-insulin dependent diabetes, with a further 350,000 known dependents.

On-line analysis of fermentation broths in pharmaceutical processes provides another significant marketing opportunity.

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