Measuring and testing – Liquid analysis or analysis of the suspension of solids in a...
Patent
1996-02-12
1998-11-10
Williams, Hezron E.
Measuring and testing
Liquid analysis or analysis of the suspension of solids in a...
73 6141, 73 6456, 7386323, 7386451, 210638, 210653, 210688, 210490, G01N 140, G01N 3000, G01N 3318
Patent
active
058346333
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a probe for use in measuring amounts of a component in a liquid environment, e.g. for use in measuring trace metal concentrations. The invention relates more particularly but not exclusively to such a device for use in an aqueous environment (e.g. river, lake, sea etc).
The idea of using a passive in situ sampling device to provide an integrated record of trace metal concentrations in natural waters has long appealed to regulatory authorities. To date, this role has been partly filled by analysis of the metal content of shellfish such as mussels.
It has been proposed to use Chelex resin in situ to concentrate a wide range of metal ions from natural waters. For example the resin has been suspended in a bag but the mass transport of ions to the resin has been ill defined resulting in at best semi-quantitative data. To overcome this problem, water has been mechanically pumped over the resin but such procedures are inevitably complicated, expensive and cumbersome.
Recently polyacrylamide gels have been used to provide measurements of metal ion concentrations in pore waters by the technique of diffusive equilibration in thin films (DET)--see Nature, Vol 352, pages 323-325 (Jul. 25, 1991). In this technique, ions are simply allowed to diffuse into the gel until equilibrium with the pore waters is established. The gel can then be analysed by techniques such as a proton microprobe or MeV-proton-induced X-ray emission (PIXE) to determine trace metal amounts at submillimetre resolution. The article in Nature states that detection limits could possibly be lowered by incorporating chemical concentration steps within the gel but there is no further disclosure as to this possibility.
According to a first aspect of the present invention there is provided a probe device for use in measuring quantities of a component in a liquid environment, the device comprising means providing a diffusion pathway which is or which contains a liquid, and along which said component may diffuse, and a layer of a material in contact with the diffusion pathway and arranged to receive component which has diffused along said pathway from a face of the device juxtaposed, in use of the device, to said liquid environment, said diffusion pathway having a length of at least 0.1 mm.
In use, the device is located in the liquid environment and the component to be measured diffuses along the diffusion pathway until it reaches the material which is capable of binding the component. It can be shown (see infra) that this results in a large concentration enhancement of the component in the material as compared to that in the liquid environment. After a suitable period of immersion, the device (which will generally be used only once) may be retrieved and the material analysed to determine the amount of the component present therein. This may be related to the amount of the component present in the liquid environment as described more fully below.
Therefore according to a second aspect of the present invention there is provided a method of determining the amount of a component present in a liquid environment comprising providing the device of the first aspect of the invention in the liquid environment and subsequently analysing said material to determine the amount, or a representation of the amount, of said component therein.
The device is particularly useful for determining amounts of components (e.g. metal ions) in aqueous environments. The liquid which is, or which is contained within, the diffusion pathway is preferably water.
When a device in accordance with the invention is immersed in a liquid environment a diffusive boundary layer (DBL) is established at the device/liquid environment interface. It is an important feature of the invention that, as explained later, the length of the diffusion pathway is greater (preferably by a factor of at least 10, more preferably at least 20) than the thickness of the DBL. This thickness does depend on the liquid environment in which the device is located and is greater, for example,
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Audunsson, "Aqueous/Aqueous Extraction by Means of a Liquid Membrane For Sample Cleanup and Preconcentration of Amines in a Flow System", Analytical Chemistry, vol. 58, No. 13, Nov. 1986, pp. 2714-2723.
Benes, "Semicontinuous Monitoring of Truly Dissolved Forms of Trace Elements in Streams Using Dialysis In Situ--I. Principles and Conditions", Water Research, vol. 14, 1986, pp. 511-513.
Davison et al., "Distribution of Dissolved Iron in Sediment Pere Waters at Submillimetre Resolution", Nature, vol. 352, 25 Jul. 1991, pp. 323-325.
Davison et al., "In Situ Speciation Measurements of Trace Components in Natural Waters Using Thin-Film Gels", Nature, vol. 367, 10 Feb. 1994, pp. 546-548.
Larkin Daniel S.
University of Lancaster
Williams Hezron E.
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