GB2481541A

GB2481541A - Electrochemical test device with rotating stirrer

Info

Publication number: GB2481541A
Application number: GB1110966.7A
Authority: GB
Inventors: Edward Agar
Original assignee: WAGTECH PROJECTS Ltd
Current assignee: WAGTECH PROJECTS Ltd
Priority date: 2010-06-25
Filing date: 2011-06-27
Publication date: 2011-12-28
Anticipated expiration: 2031-06-27
Also published as: GB201110966D0; GB2481541B; GB201010811D0

Abstract

An electrochemical test device for measuring an electrochemical property of a sample solution, especially a water supply, has a probe head 4 for immersion in the sample solution. The probe head comprises one or more electrodes 12 for measuring the electrochemical property and a rotatable stirrer 14 attached to the probe head for stirring the sample solution. The stirrer may comprise a planar disc element 18 and a temperature sensor may also be included as part of the probe. A detachable cell vial 6 may be used to receive the sample solution and this may feature an overflow channel 30 to ensure that the correct amount of sample is maintained in the vial. The device may be portable or hand-held making it suitable for testing water samples at their natural source, such as a river, lake or sea, and can be configured to detect heavy metal ion impurities.

Description

ELECTROCHEMICAL TEST DEVICES

The present invention relates to electrochemical test devices and to water testing methods using them.

Electrochemical test devices or "test cells" are used to test an electrochernical property of a solution.

A sample solution is placed in a cell vial or beaker and a probe with electrodes is immersed in the vial to test a particular sample property, such as ion concentration.

Most samples are tested in laboratories. However it may be desirable in some cases, especially for testing water samples from natural sources such as a lakes, rivers, wells and streams, to test at the location of the natural source i.e. outside the laboratory.

To achieve best results from a probe, the sample should usually be agitated to maintain solution uniformity. A reliable conventional means is a magnetic stirrer bar and plate apparatus.

However this conventional optimised set-up requires extra equipment and in particular is often unavailable outside the laboratory, e.g. by a source of natural water such as a river, lake or well. In this situation the worker must shake the vial instead, and the reliability of the results may be questioned.

The present inventors have sought to address the above issues and to provide an improved electrochemical test device.

At its most general, the present invention provides an electrochemical test device or cell having a rotatable stirrer attached to or comprised in the cell.

Accordingly, in a first aspect the present invention provides an electrochemical test device for measuring an electrochemical property of a sample solution, having: one or more electrochemical probes attached to a probe head for measuring the electrochemical property and a rotatable stirrer attached to the probe head for stirring the sample solution.

The integration of stirrer into the electrochemical test cell allows a compact and easy to use electrochemical test cell. In addition, the sample solution is efficiently stirred and mixed. Furthermore, the solution in the cell may be mixed before and/or during measurements are taken.

Preferably the stirrer has a stirrer shaft connected to a motor and one or more stirrer elements connected to the stirrer shaft to stir the sample solution adjacent to the probes (electrodes). The stirrer shaft is rotatable around its elongate axis. Preferably the stirrer shaft and stirrer element(s) are formed from a single piece of material, such as moulded plastic.

Preferably the stirrer element is planar, in other words, having two elongate axes greater than the third axis. When the stirrer element is planar, it is more preferred that the major plane of the stirrer element is substantially perpendicular to the elongate axis of the stirrer shaft.

In this configuration, the turbulence of the sample solution is minimised to provide a uniform solution that results in an improved repeatability of the electrochemical probe readings compared to turbulent solutions. This is because when a stirrer element has a circular or near-circular outline or cross-section around its rotation axis it rotates with little or no paddling or volume displacement, agitating the liquid rather through surface effects. By avoiding bulk displacement of liquid, cavitation and spillage can be avoided. In particularly preferred embodiments, the planar stirrer element is circular. It may be a disc having an elliptical or circular shape. Or, it may be conical or the like.

The stirrer element may extend substantially perpendicularly to the elongate axis of the stirrer shaft. A region of the element farthest from the shaft travel furthest and fastest through the solution resulting in more effective stirring at that region.

Typically the electrochemical probe has at a first end a probe body or connector connected to the probe head and at a second end an exposed electrode for measuring the electrochemical property of the sample solution. The electrode may have an elongate electrode axis extending from the probe body to an electrode tip, the electrode tip being at a first end of the electrode.

Preferably there is a closest approach (clearance gap) of not more than 10mm between the locus of the stirrer element and the electrode of one or more (and preferably all) of the electrochemical probes. The clearance gap should be at least 0.1mm, preferably at least 0.5mm. Preferably it is not more than 5mm, more preferably not more than 3mm.

Thus, preferably the clearance gap between a surface of the element and the electrode is between 1 -5 mm, still more preferably 2 -3 mm. This may be a gap between an outer edge of the stirrer element and the electrode. If the stirrer element is circular in section, it may be substantially constant during rotation.

The positioning of the stirrer element close to the electrode provides improved sensitivity of the probe reading, particularly when the stirrer is in operation.

An additional benefit is that the stirrer element does not project significantly beyond the electrode(s) so the test device (and the vial) can be compact and portable.

Where, as is preferred, the electrode is an elongate projection (desirably but not essentially parallel to the stirrer axis) the gap may be considered to have first and second components.

Thus, preferably a first minimum clearance gap exists between a first surface of the stirrer element and a first electrode plane, the first electrode plane going through the electrode tip and being perpendicular to the elongate electrode axis.

Preferably the first clearance gap is between 1 and mm and is more preferably around 2 mm. A small first clearance gap between the stirrer element and the electrode tip allows that solution close to the electrode tip to be stirred well. The first clearance gap also ensures that the stirrer is compact in the probe head and does not protrude significantly beyond the electrodes.

Additionally or alternatively, a second minimum clearance gap may exists between a surface of the element and a second electrode plane, the second electrode plane going through the electrode tip and being parallel to the elongate electrode axis.

Preferably the second clearance gap is between 0 and mm and preferably between 0.5 and 1.5 mm. When the second clearance gap is zero, the second surface of the stirrer element lies over the elongate axis of the electrode and the second clearance gap is thus not present. Alternatively and more simply stated, the stirrer element e.g. disc may or may not overlie (as viewed axially of the stirrer) the electrode end(s) . We prefer that it does not fully overlie.

The second clearance gap allows the stirrer element to be close to the electrode to provide suitable stirring of the solution adjacent to the electrodes.

When a first and second clearance gap exists, the first and second surface may be the same or different surfaces of the stirrer element. Preferably the first surface of the stirrer element is a large planar surface.

Preferably the electrochemical test device includes a cell vial to receive the sample solution. Preferably the cell vial is releasably attachable to the probe head.

The cell vial may have an overflow channel to allow excess sample solution to drain from the cell vial. It is often important in electrochemical test devices to have a fixed volume of a sample solution.

The overflow channel is positioned at a height on the cell vial wall so that when the sample solution level reaches the overflow channel, the required volume of sample solution is contained within the cell vial. Any further addition of sample solution brings the level of the sample solution above the overflow channel and the excess sample solution drains away from the cell vial.

Preferably the overflow channel is an aperture in a cell vial wall, the aperture being positioned at a height on the cell vial wall corresponding to the surface level of a fixed volume of the sample solution in the cell vial.

In a particularly preferred embodiment, the cell vial has an overflow channel when the cell vial is releasably attachable to the probe head. In this configuration, the cell vial may be attached to the probe head and both the probe head and cell vial may be submerged in a sample solution source, such as a river.

In the sample solution source, the cell vial fills with sample solution, for example through the overflow channel. When the cell vial and probe head are removed from the sample solution source, any excess sample solution drains from the cell vial through the overflow channel. In this way, the electrochemical test device is filled with sample solution in a quick and easy fashion.

Preferably the probe is a voltammetry electrode.

More preferably the probe is an anodic or cathodic (stripping) voltammetry electrode to measure ion concentration of the sample solution.

Preferably the electrochemical probe is a probe for detecting the concentration of metal ions, in particular heavy metal ions.

In more preferred embodiments, the electrochemical probe is an electrode for detecting the concentration of one or more of the group of arsenic, cadmium, copper, mercury, lead, chromium, nickel, cobalt, manganese and iron ions. These heavy metal ions are frequently tested in samples that originate from a natural water source.

Accordingly it is common for an electrochemical device as described herein to be used at the location of the natural water source.

Preferably the electrochemical probe is a working electrode for measuring an electrochemical property of an aqueous solution. The above described electrochemical test device is particularly useful for testing water samples at their natural water source location, e.g. a river.

Preferably the probe head also has a temperature probe to measure the temperature of the sample solution.

As electrochemical measurements of sample solutions may vary with temperature, a temperature probe may be used to adjust the electrochemical measurement based on the temperature measurement. For example, an automatic correction of 2 of the electrochemical measurement per degree Centigrade change from a standard temperature may be applied. The inclusion of the temperature probe may therefore yield a more accurate electrochemical measurement.

As is conventional per se the device head (probe head or sonde) usually also includes a counter-electrode and a reference electrode for immersion in the sample together with the one or more working electrodes.

Usually the probes/electrodes are provided in a forwardly-directed (forwardly-projecting) array on the front of the probe head. They may project generally parallel to one another. Desirably plural (e.g. 2, 3 or 4) working electrodes are distributed circumferentially in relation to the stirrer element and so as to be similarly spaced from it.

Typically the stirrer is connected to a motor in order to rotate the stirrer. Preferably the motor is located in the probe head. When the motor is contained within the probe head, the electrochemical test device is more compact and so is easier to use, for example outside the laboratory.

Preferably the motor is supplied with power to operate the stirrer at 2000 -6000 revolutions per minute (rpm) when immersed in the sample solution. More preferably the rotation speed of the stirrer is 3000 - 5000 rpm and most preferably is 3600 -4300 rpm during operation.

The above rotation speeds of the stirrer in combination with the shape of the stirrer provides disturbance of the sample solution to efficiently stir the solution and avoids producing a turbulent solution that may affect repeatability of the results from the electrochemical probes.

The power supply required to achieve the above rotation speeds when the probe is immersed in the solution will vary depending on the viscosity of the solution. For example, when the electrochemical probe is used in an aqueous solution, the power supplied required to achieve 3600-4300 rpm will be roughly equivalent to a speed of 5600-6800 rpm when the stirrer is not immersed.

The motor may be linked to operate when the electrochemical probes are operated or may have a separate motor control to select when the motor is operated.

In another aspect, the present invention provides an electrochemical measuring instrument for measuring an electrochemical property of a sample solution, the instrument having an electrochemical test cell as described herein, the electrochemical test device being connected to a control unit for processing data from and controlling the electrochemical test cell.

The control unit may control one or more functions of the electrochemical measuring instrument and/or process one or more types of data received from the electrochemical test device. For example, the control unit may power electrodes, process data from electrodes, process data from a temperature probe, record data from the electrochemical test cell, compute data from the electrochemical cell and display options, functions and results in the form of, for example, ion concentration of the sample.

Preferably the control unit has a motor power source connected to the motor driving the stirrer. More preferably the motor power source also is a power source for electronic components of the control unit. In this way, the control unit may be compact and thus easy to use, for example, outside the laboratory.

Preferably the control unit is 0.Sm or smaller in one dimension. More preferably the control unit is 0.5m or smaller in all dimensions.

Preferably the control unit weighs 2kg or less.

More preferably the control unit weighs 0.6kg or less.

When the control unit is small and/or light, the measuring instrument may be easily transported to testing locations that are outside the laboratory, for example in the hand of a user, a bag or a case. Preferably the control unit is hand-held.

In a further aspect, the present invention provides use of an electrochemjcal test cell as described above to measure an electrochemical property of a sample solution, e.g. a water sample, the electrochemical test device having: one or more electrochemical probes attached to a probe head for measuring the electrochemical property; and a rotatable stirrer attached to the probe head for stirring the sample solution.

The preferred and optional general features of the above aspects are to be combined freely with those of the other aspects above.

?n embodiment of the present invention will be described with reference to the following drawings: Fig. 1 shows a side view of an electrochemical test cell (probe head or sonde, and vial/beaker); Fig.1A is a perspective view of part of the stirrer and electrodes of the test cell; Fig. 2 shows an electrochemical measuring instrument or test device incorporating the cell; Figs. 3, 4 and 5 are respectively a front view, close-up side view and perspective view of the probe head or sonde, without the vial, [reference and counter electrodes being omitted in Fig 4 for clarity] The figures show a probe head 4 and a cell vial 6 for holding a sample solution. The open end of the vial clips onto the front end of the head for dipping into a sample as described below.

Five electrochemical probes 10 are connected to the probe head 4. Each probe 10 has an electrode for measuring an electrochemical property of the sample solution. Specifically (see Fig 3) these may be a counter-electrode 111, a reference electrode 112, and one, two or three reaction-specific working electrodes 12. The electrodes are preferably removable by unplugging from the head 4. The device may then be used with any one, two or three working electrodes 12 in place, e.g. for different ionic impurities which are of concern, and the control software may control it accordingly.

The electrode probes 10 are clustered on one face of the probe head 4 so that the probes 10 can be inserted together into the cell vial 6 for immersion. The probes extend along an elongate axis 32 from the probe head 4 to an electrode tip 34.

In addition, a temperature probe 36 is attached to the probe head 4 for measuring the temperature of the sample solution before, during or after the electrochemical property of the solution is measured.

The probes 10 containing the electrodes 12 are anodic and cathodic stripping voltammetry probes for detecting the concentration of one or more heavy metal ions in the sample solution. In particular, the electrodes 12 are operable according to known principles to detect the concentration of e.g. arsenic, mercury, cadmium, lead and/or copper ions, at concentrations of parts per billion (ppb).

A rotatable stirrer 14 is also attached to the probe head 4. The stirrer 14 has a stirrer shaft 16 extending from the probe head 4 alongside the probes 10. A stirrer element 18 formed in one piece with the shaft 16 is connected to the end of the shaft 16. The element 18 extends substantially perpendicular to the elongate axis of the shaft 16 to give a stirrer 14 that is T-shaped in axial cross-section. In this way, the stirrer element 18 spins around the elongate axis of the stirrer shaft 16 as the stirrer 14 rotates.

The element 18 is a flat circular disc and is shown in more detail in Fig 1A. The major plane of the disc is perpendicular to the elongate axis of the shaft 16 so that the disc spins within this plane, and essentially within its own shape envelope, when the stirrer 14 rotates. The disc is connected to the shaft 16 in the centre.

Referring back to Fig.l, the stirrer element 18 is located adjacent to the electrodes 12. A large planar surface 34 of the disc-shaped element 18 is around 2 mm from the tip and radially overlaps the electrode A. The stirrer is around 3 mm from the tip and around 1 mm from the elongate axis of electrode B. Therefore, the disc-shaped stirrer element 18 lies over some, but not all, of the electrode tips 34.

Figs 3 to 5 show an electrode array more particularly. Sites are provided for up to three working electrodes 12 (WE1, WE2, WE3), each of which will be similarly spaced with respect to the spinning edge 38 of the stirrer disc 18. In this embodiment, radial overlap of disc 18 with electrode tips 12 is about 0.5mm. This could vary, e.g. from non-overlapping radial spacing of about 1mm to overlap to 50 of the radius of the electrode. Trial and error can optimise the positions.

The axial clearance -here representing the closest approach -is 2 to 2.5mm, but could be from 1mm to 5mm.

The electrodes are plug-in and therefore freely exchangeable.

The reference and counter electrodes 111,112 are spaced a little further away from the stirrer, agitation being less critical for them.

When the element 18 is close to the electrodes 12, the stirrer 14 does not significantly project beyond the electrode probes 10 resulting in a compact electrochemical test device 2. In addition, the solution is stirred a large amount around the element 18, so positioning the element 18 adjacent to the electrodes 12 allows the solution around the electrodes 12 to have an improved homogeneity.

In operation, the stirrer 14 rotates about the elongate axis of the shaft 16 resulting in the element 18 stirring the sample solution. The stirrer 14 revolves at around 3600-43 00 rpm when in the sample solution. The disc-shaped element produces low turbulence of the sample solution. The low turbulence provides a uniform solution which affords improved repeatability (reduced result variance) from the electrodes 12 than high turbulence solutions.

The motor 20 for the stirrer 14 is accommodated in the probe head 4 and receives power from a power source through a cable 24. The cable 24 also carries wiring from the probes 10 to a control unit (not shown).

In this embodiment, the probe head 4 has locking lugs 26 to slot into locking slots 28 of the cell vial 6 in order to lock the cell vial 6 and probe head 4 together. Once the locking lugs 26 are positioned in the locking slots 28, the cell vial 6 is rotated to achieve locking. Counter-rotating the cell vial 6 achieves unlocking of the cell vial 6 and probe head 4.

The cell vial 6 also has an overflow channel 30 for draining excess sample solution, such as water, from the cell vial 6. This allows the cell vial 6 to conveniently have the correct volume of sample solution by overfilling the cell vial 6 and allowing excess solution to escape through the overflow channel 30.

In operation, the probe head 4 is connected to the cell vial 6 and then both the probe head 4 and the cell vial 6 are placed into a sample solution source, such as a river. The cell vial 6 fills with sample solution from the sample solution source (which may be natural body of water) and the probes 10 and stirrer 14 become immersed in the sample solution. Any excess water discharges through the overflow slots 30 so that the cell vial 6 holds a fixed volume of the sample solution.

In this embodiment the total length of the probe head with electrodes (not vial) is 135mm. The working electrode probes 10 are about 45mm long, including the projecting electrodes 12 whose diameter is about 4mm.

The stirrer (shaft and disc) is about 48mm long, and the disc 20mm in diameter.

Fig. 2 shows a measuring instrument 50 or complete test device with the electrochemical test cell 2 of Fig. 1 attached to a control unit 52. The cell 2 is connected via the cable 24 to a connector 54 so that the electrochemical test cell 2 may be disconnected for storage, servicing or replacement.

Data from the electrochemical test cell head 2 are transmitted up the cable 24 to the control unit 52 and recorded by the control unit 52. The control unit 52 also computes the data to show the relevant metal ion concentration(s) found in the sample solution tested in the electrochemical test device 2. The metal ion concentration(s) are shown on a display 56.

The display 56 also shows options available to a user which are controlled by function buttons 58. A battery power source is contained within the device casing 62 to power the motor of the electrochernical test device 2 and other electronic components in the control unit 52.

The control unit 52 is around 0.23 m long, 0.10 m wide and 0.06 m deep. The control unit 52 is around 0.6 kg in weight. The weight and dimensions of the control unit 52 allow the control unit 52 to be hand-held and easily transported. In this way, the measuring instrument 50 is very useful for measuring the electrochemical property of a water sample at the location of its source, e.g. a river.

Claims

CLJIMs: 1. An electrochemical test device for measuring an electrochemical property of a sample solution, having a probe head for immersion in the sample solution and comprising: one or more electrochemical probes attached to the probe head, for measuring the electrochemical property; and a rotatable stirrer attached to the probe head for stirring the sample solution.
2. electrochemical test device according to claim 1 wherein the stirrer has a stirrer shaft connected to a motor and a stirrer element connected to the shaft for stirring the sample solution.
3. An electrochemical test device according to claim 2, wherein the stirrer shaft is rotatable around its elongate axis and the element extends substantially perpendicular to the elongate axis of the shaft.
4. An electrochemical test device according to claim 2 or claim 3, wherein the stirrer element is circular in shape.
5. An electrochemica]. test device according to claim 4, wherein the element is a planar disc and connected to the shaft to rotate in the plane of the disc.
6. An electrochemical test device according to any one of claims 2 to 5, wherein the electrochemical test device has a clearance gap of 0.1 -10 mm between the stirrer element and an electrode of one or more of the probes.
7. An electrochetnical test device according to claim 6 in which said clearance is from 1 to 3mm.
8. An electrochemical test device according to any one of claims 1 to 7 in which an edge of the stirrer is the closest part thereof to the electrode(s)
9. An electrochemical test device according to any one of claims 1 to 8, wherein the electrochemical test device further includes a temperature probe to measure the temperature of the sample solution.
10. An electrochemical test device according to any one of claims 1 to 9, wherein the cell includes a cell vial to receive the sample solution.
11. An electrochentical test device according to claim 10, wherein the cell vial has an overflow channel to allow excess sample solution to escape from the cell vial.
12. An electrochemical test device according to claim 11, wherein the overflow channel is an aperture in a cell vial wall, the aperture being positioned at a height on the cell vial wall corresponding to the surface level of a fixed volume of the sample solution in the cell vial.
13. An electrochemical test device according to any one of claims 10 to 12, wherein the cell vial is releasably attachable to the probe head.
14. An electrochemical test device according to any one of claims 2 to 13, wherein the motor is located in the probe head.
15. An electrochemical measuring instrument for measuring an electrochemical property of a sample solution, the instrument having an electrochemical test device probe head according to any one of claims 1 to 14, the electrochemical test device being connected to a control unit for recording information from the electrochemical test device.
16. The electrochemical measuring instrument according to claim 15, wherein the control unit has a power source connected to a motor connected to the stirrer.
17. The electrochemical measuring instrument according to claim 15 or claim 16, wherein the control unit is hand-held.
18. Use of an electrochemical test device according to any one of the preceding claims for measuring the level of one or more metallic contaminants in a water supply.
19. An electrochemical test device or measuring instrument, or method of use thereof, substantially as described herein with reference to the accompanying drawings.*::r: INTELLECTUAL . ... PROPERTY OFFICE Application No: GB1110966.7 Examiner: Dr Stephen Otter Claims searched: 1-18 Date of search: 30 September 2011 Patents Act 1977: Search Report under Section 17 Documents considered to be relevant: Category Relevant Identity of document and passage or figure of particular relevance to claims X 1-18 EP0672908A2 (SOLOMAT) see whole document especially Figures 4-7 and column line 1 to column 17 line 43 X 1-9,14-16 EP1941272A1 & 18 (INTELLITECT WATER) see whole document especially Figure 1 and page 5 lines 4-22 and page 9 line 13 to page 10 line 2 X 1-4, 8-10 GB 1431537 A & 13-17 (NEW COSMOS ELECTRIC) see whole document especially Figure 1 and page 1 line 42 to page 2 line 54 X,P 1-5 at CN 101949879 A least (UNIVERSITY SOUTHEAST) see especially Figure 1 and EPODOC and WPI abstracts Categories: X Document indicating lack of novelty or inventive A Document indicating technological background and/or state step of the art.Y Document indicating lack of inventive step if P Document published on or after the declared priority date but combined with one or more other documents of before the filing date of this invention.same category.& Member of the same patent family E Patent document published on or after. but with priority date earlier than, the filing date of this application.Field of Search:Search of GB, EP, WO & US patent ijoctiments classified in the following areas of the UKCX Worldwide search of patent documents classified in the following areas of the IPC BO1F; GO1N The following online and other databases have been used in the preparation of this search report EPODOC, WPI International Classification: Subclass Subgroup Valid From GO1N 0027/28 01/01/2006 GOIN 0027/403 01/01/2006 GO1N 0033/18 01/01/2006 Intellectual Property Office is an operating name of the Patent Office www.ipo.gov.uk