ELECTROANALYTICAL INSTRUMENT FOR DETERMINING BY AMPEROMETRY THE PRESENCE OR QUANTITY OF AN ANALYTE IN AN AQUEOUS SAMPLE

Abstract

The present invention relates to an electroanalytical instrument for determining by amperometry (eg chronoamperometry) the presence or quantity (eg concentration) of an analyte in an aqueous sample, comprising a sealed housing, an elongate pivotal arm mounted on the sealed housing, wherein the elongate pivotal arm houses a potentiostat, and a pivotal forearm joined pivotally to the elongate pivotal arm, which is connectable to an electrochemical sensor. By flexing the pivotal forearm, the electrochemical sensor may be electrically connected to the potentiostat. By flexing the elongate pivotal arm, the electrochemical sensor is immersed in the aqueous sample in the sealed housing.

Claims

1. An electroanalytical instrument for determining by amperometry the presence or quantity of an analyte in an aqueous sample comprising: a sealed housing which is compartmentalised, wherein the sealed housing has an exterior compartment defining a receptacle for the aqueous sample and interior compartments; an elongate pivotal arm mounted pivotally at a proximal end on the sealed housing, wherein the elongate pivotal arm houses a potentiostat; a pivotal forearm joined pivotally to or near to a distal end of the elongate pivotal arm, wherein in use an electrochemical sensor is mounted in or on an anterior wall of the pivotal forearm and extends inferiorly to the elongate pivotal arm, wherein on an inferior part of the electrochemical sensor there are a reference electrode, a counter electrode and at least one working electrode which is dosed with a reagent formulation for electroanalysis and on a superior part of the electrochemical sensor each of the reference electrode, counter electrode and at least one working electrode terminates in an electrical contact; and a mounting for electrical contact pins which is mounted sealingly on the distal end of the elongate pivotal arm, wherein in use the electrical contact pins are electrically connected to the potentiostat and apply a potential to the electrochemical sensor, wherein the elongate pivotal arm pivots between a fully extended position and a fully flexed position whereat the inferior part of the electrochemical sensor is immersed in the aqueous sample in the receptacle thereby initiating dissolution of the reagent formulation into the aqueous sample and wherein the pivotal forearm pivots between a fully open position whereat the electrical contact pins are exposed and a fully closed position whereat the electrical contacts on the superior part of the electrochemical sensor are in operative contact with the electrical contact pins whereby when the elongate pivotal arm is in the fully flexed position and the pivotal forearm is in the fully closed position the electrochemical sensor interfaces the electrical contact pins and the aqueous sample.

2. The electroanalytical instrument as claimed in claim 1 wherein the mounting for electrical contact pins is mounted detachably on the distal end of the elongate pivotal arm.

3. The electroanalytical instrument as claimed in claim 1 wherein the mounting for electrical contact pins comprises a flexible polymer body which sealingly encapsulates the electrical contact pins such that the electrical contact pins are protuberant from a front face of the body.

4. The electroanalytical instrument as claimed in claim 1 wherein in use, a slanted part of the front face of the flexible polymer body biassingly abuts the electrochemical sensor.

5. The electroanalytical instrument as claimed in claim 1 wherein when the elongate pivotal arm is in the fully flexed position, the receptacle constrains the pivotal forearm to a partially open position sufficient to permit the electrochemical sensor to dismount from the anterior wall of the pivotal forearm.

6. The electroanalytical instrument as claimed in claim 1 wherein the elongate pivotal arm pivots restrainedly between an extended position and a flexed position.

7. The electroanalytical instrument as claimed in claim 1 wherein the proximal end of the elongate pivotal arm is equipped with a rotary sleeve which is mounted on an elongate shaft extending from the sealed housing, wherein the rotary sleeve and elongate shaft are sealingly spaced apart by a seal.

8. The electroanalytical instrument as claimed in claim 1 wherein the elongate pivotal arm pivots about a first axis between a fully extended position and a fully flexed position and the pivotal forearm pivots about a second axis between a fully open position and a fully closed position, wherein the first axis and second axis are substantially perpendicular.

9. The electroanalytical instrument as claimed in claim 1 further comprising a switch which in response to an operating position of the elongate pivotal arm switches on the potentiostat, wherein the operating position is at or near to the fully flexed position.

10. An electroanalytical instrument for determining by amperometry the presence or quantity of an analyte in an aqueous sample comprising: a sealed housing which is compartmentalised, wherein the sealed housing has an exterior compartment defining a receptacle for the aqueous sample and interior compartments; an elongate pivotal arm mounted pivotally at a proximal end on the sealed housing, wherein the elongate pivotal arm houses a potentiostat; a pivotal forearm joined pivotally to or near to a distal end of the elongate pivotal arm, wherein in use an electrochemical sensor is mounted in or on an anterior wall of the pivotal forearm and extends inferiorly to the elongate pivotal arm, wherein on an inferior part of the electrochemical sensor there are a reference electrode, a counter electrode and at least one working electrode which is dosed with a reagent formulation for electroanalysis and on a superior part of the electrochemical sensor each of the reference electrode, counter electrode and at least one working electrode terminates in an electrical contact; and electrical contact pins on the distal end of the elongate pivotal arm, wherein in use the electrical contact pins are electrically connected to the potentiostat and apply a potential to the electrochemical sensor, wherein the elongate pivotal arm pivots between a fully extended position and a fully flexed position whereat the inferior part of the electrochemical sensor is immersed in the aqueous sample in the receptacle thereby initiating dissolution of the reagent formulation into the aqueous sample and wherein the pivotal forearm pivots between a fully open position whereat the electrical contact pins are exposed and a fully closed position whereat the electrical contacts on the superior part of the electrochemical sensor are in operative contact with the electrical contact pins whereby when the elongate pivotal arm is in the fully flexed position and the pivotal forearm is in the fully closed position the electrochemical sensor interfaces the electrical contact pins and the aqueous sample, wherein when the elongate pivotal arm is in the fully flexed position, the receptacle constrains the pivotal forearm to a partially open position sufficient to permit the electrochemical sensor to dismount from the anterior wall of the pivotal forearm.

11. An electroanalytical instrument for determining by amperometry the presence or quantity of an analyte in an aqueous sample comprising: a sealed housing which is compartmentalised, wherein the sealed housing has an exterior compartment defining a receptacle for the aqueous sample and interior compartments; an elongate pivotal arm mounted pivotally at a proximal end on the sealed housing, wherein the elongate pivotal arm houses a potentiostat; a pivotal forearm joined pivotally to or near to a distal end of the elongate pivotal arm, wherein in use an electrochemical sensor is mounted in or on an anterior wall of the pivotal forearm and extends inferiorly to the elongate pivotal arm, wherein on an inferior part of the electrochemical sensor there are a reference electrode, a counter electrode and at least one working electrode which is dosed with a reagent formulation for electroanalysis and on a superior part of the electrochemical sensor each of the reference electrode, counter electrode and at least one working electrode terminates in an electrical contact; and electrical contact pins on the distal end of the elongate pivotal arm, wherein in use the electrical contact pins are electrically connected to the potentiostat and apply a potential to the electrochemical sensor, wherein the elongate pivotal arm pivots between a fully extended position and a fully flexed position whereat the inferior part of the electrochemical sensor is immersed in the aqueous sample in the receptacle thereby initiating dissolution of the reagent formulation into the aqueous sample and wherein the pivotal forearm pivots between a fully open position whereat the electrical contact pins are exposed and a fully closed position whereat the electrical contacts on the superior part of the electrochemical sensor are in operative contact with the electrical contact pins whereby when the elongate pivotal arm is in the fully flexed position and the pivotal forearm is in the fully closed position the electrochemical sensor interfaces the electrical contact pins and the aqueous sample, wherein the elongate pivotal arm pivots restrainedly between an extended position and a flexed position.

Description

[0079] The present invention will now be described in a non-limitative sense with reference to Examples and the accompanying Figures in which:

[0080] FIG. 1 is a front perspective view of an embodiment of the electroanalytical instrument of the invention;

[0081] FIG. 2 is a rear perspective view of the embodiment of the electroanalytical instrument of the invention;

[0082] FIG. 3 is a front perspective view of the embodiment of the electroanalytical instrument of the invention with the pivotal forearm partially open;

[0083] FIG. 4 is an exploded partial view of the embodiment of the electroanalytical instrument of the invention showing the pivotal mounting of the elongate pivotal arm and the housing;

[0084] FIGS. 5(a) to (c) are views of a mounting for electrical contacts detached from the elongate pivotal arm;

[0085] FIGS. 5(d) and (e) are exploded partial views of the mounting and the pivotal forearm;

[0086] FIGS. 6(a) and (b) are exploded partial views of the pivotal forearm which shows the dismounting of an electrochemical sensor; and

[0087] FIG. 7 shows the results of an experiment carried out to show the impact of immersion rate on the performance of an electrochemical sensor.

[0088] FIGS. 1 and 2 are front and rear perspective views respectively of an embodiment of the electroanalytical instrument of the invention. The electroanalytical instrument may be used to determine the concentration of an analyte of interest in an aqueous sample. Measurements are made by chronoamperometry and for this purpose, the instrument may be used in conjunction with an electrochemical sensor of the type disclosed in WO-A-2007/026152 which is commercially available. Such an electrochemical sensor is planar and consists of an inferior part where there is a reference electrode, a counter electrode and two working electrodes which are dosed with a reagent formulation for electroanalysis and a superior part where each of the reference electrode, counter electrode and working electrodes terminates in an electrical contact. For the sake of simplicity, an electrochemical sensor 100 is shown in the Figures without any detailed structure.

[0089] The electroanalytical instrument comprises a sealed housing 1 which is compartmentalised. An exterior compartment defines a receptacle 2 for the aqueous sample which contains the analyte of interest. An interior compartment of the sealed housing 1 houses a computer which provides a display 9. Other interior compartments of the sealed housing 1 house the electrical and electronic components necessary for electroanalytical measurements.

[0090] The receptacle 2 is equipped with a notched wall 21 which divides the internal chamber into a sample compartment 2b and an overflow compartment 2a. When a threshold volume of aqueous sample is breached in the sample compartment 2b, there is an overflow of the aqueous sample to the overflow compartment 2a.

[0091] An elongate pivotal arm 3 is mounted pivotally at a proximal end on the sealed housing 1. A distal part 7 of the elongate pivotal arm 3 houses a potentiostat. A mounting 6 for four electrical contact pins 18 is mounted sealingly on a distal end of the elongate pivotal arm 3.

[0092] A pivotal forearm 4 is joined pivotally to the distal end of the elongate pivotal arm 3. The electrochemical sensor 100 (not shown in FIGS. 1 and 2) is mounted in a slot 17 in an anterior wall 16 of the pivotal forearm 4 and extends inferiorly to the elongate pivotal arm 3. The inferior part of the electrochemical sensor 100 is outside the slot 17 and the superior part of the electrochemical sensor 100 is inside the slot 17 exposed through a window 15 in the anterior wall 16.

[0093] The elongate pivotal arm 3 pivots between a fully extended position (see FIG. 1) and a fully flexed position (see FIG. 2). In the fully flexed position, the inferior part of the electrochemical sensor 100 is immersed in the aqueous sample in the receptacle 2. The pivotal forearm 4 pivots medially between a fully open position (see FIG. 1) at which the electrical contact pins 18 are exposed and a fully closed position (see FIG. 2) at which the superior part of the electrochemical sensor 100 is in operative contact with the electrical contact pins 18. The axes about which the elongate pivotal arm 3 and pivotal forearm 4 pivot are perpendicular. When the elongate pivotal arm 3 is in the fully flexed position and the pivotal forearm 4 is in the fully closed position as shown in FIG. 2, the electrochemical sensor 100 interfaces the electrical contact pins 18 and the aqueous sample.

[0094] As shown in FIG. 4, the proximal end of the elongate pivotal arm 3 is configured into a rotary sleeve 10 which is mounted on an elongate shaft 11 extending from the sealed housing 1. The rotary sleeve 10 is retained on the elongate shaft 11 by a retaining bracket 40. The rotary sleeve 10 and elongate shaft 11 are sealingly spaced apart by a seal ring. The frictional effect of the seal ring ensures that the elongate pivotal arm 3 pivots restrainedly between the fully extended position and the fully flexed position. This slows the descent of the electrochemical sensor 100 into the receptacle 2 and the immersion of the electrochemical sensor 100 in the aqueous sample is controlled. The benefits of this are demonstrated in the Example hereinafter.

[0095] The mounting 6 for the electrical contact pins 18 is detachable from the elongate pivotal arm 3 and is shown detached in Figures Sa (front view), 5b (rear view) and Sc (side view). The mounting 6 comprises a flexible polymer body 60 which sealingly encapsulates the electrical contact pins 18 such that the electrical contact pins 18 are protuberant from a front face of the body 60 (see Figure Sc). The electrical contact pins 18 are disposed in such a way as to be able to apply a potential to the electrical contacts of the reference electrode, counter electrode and working electrodes of the electrochemical sensor 100. The electrical contact pins 18 are electrically connected at the rear to the potentiostat by a connector 62 (see FIGS. 5(d) and (e)). To enable the mounting 6 to be mounted flush with the distal end of the elongate pivotal arm 3, opposing corners of the flexible polymer body 60 are equipped with a socket 71, 72 to receive a threaded fastener.

[0096] When the pivotal forearm 4 is fully closed, the electrochemical sensor 100 can be forcibly inserted into slot 17 (see FIG. 6a). A slanted part 61 of the front face of the polymer body 60 abuts the electrochemical sensor 100 through the window 15 (see FIGS. 5c and 5d). By virtue of the flexibility of the polymer body 60, the abutment of the slanted part 61 and the electrochemical sensor 100 is biased so as to retain the electrochemical sensor in the slot 17.

[0097] The pivotal forearm 4 is retained in the fully closed position by a magnetic catch. A male part 5a of the magnetic catch is mounted on the anterior wall 16 of the pivotal forearm 4 and is cooperable with a female part 5b of the magnetic catch mounted on the distal end of the elongate pivotal arm 3.

[0098] When the elongate pivotal arm 3 is in the fully flexed position (see FIG. 3), the receptacle 2 constrains the pivotal forearm 4 to a partially open position. To achieve this, a part of the anterior wall 16 extends below the rim of and into the receptacle 2. In the partially open position, the slanted part 61 and the electrochemical sensor 100 are no longer in abutment and the electrochemical sensor 100 dismounts freely from slot 17 into the receptacle 2 without exposing the operator to the electrochemical sensor 100 or the electrical contact pins 18 (see FIG. 6b).

[0099] The electroanalytical instrument further comprises a reed switch or optical switch which in response to an operating position of the elongate pivotal arm 3 switches on the potentiostat. The operating position is at or near to the fully flexed position.

[0100] A temperature probe 8 extends inferiorly from an inferior face 20 of the elongate pivotal arm 3. When the elongate pivotal arm 3 is in the fully flexed position, the temperature probe 8 is immersed in the aqueous sample in the receptacle 2.

EXAMPLE

[0101] An experiment was carried out to determine whether the manner in which electroanalysis was carried out could have an effect on the performance of an electrochemical sensor.

[0102] A 1.1 mg/L free chlorine solution was prepared and tested using a single batch of Chlorosense.sup.R electrochemical sensors. Free chlorine readings were taken at immersion times* of 1 and 3 seconds. (*immersion time is the time taken for the electrochemical sensor to fully immerse into the solution and the instrument to start the reading)

Results

[0103] The results are presented in the Table below and in FIG. 7.

TABLE-US-00001 Reading Immersion Time 1 s Immersion Time 3 s 1 1.07 1.12 2 1.06 1.10 3 1.09 1.07 4 1.10 1.08 5 1.06 1.12 6 1.08 1.10 7 1.12 1.16 8 1.01 1.08 9 1.10 1.15 10 1.03 1.08 11 1.08 1.12 12 1.07 1.14 13 1.03 1.12 14 1.06 1.12 15 1.10 1.15 16 1.02 1.14 17 1.07 1.13 18 1.08 1.15 19 1.13 1.13 20 1.07 1.17 21 1.04 1.12 22 1.08 1.15 23 1.11 1.15 24 1.09 1.14 25 1.04 1.12 26 1.01 1.15 27 1.11 1.12 28 1.18 1.13 29 1.07 1.15 29 1.02 1.16

CONCLUSION

[0104] The results show that the performance of the electrochemical sensor is more consistent at an immersion rate of 3 s than at an immersion rate of 1 s. The electrochemical reagent begins to be released from the moment the electrochemical sensor contacts the free chlorine solution and disperses during the period of measurement. It is evident from this Example that the rate of immersion of the electrochemical sensor and the degree of agitation of the free chlorine solution during this period will affect the rate of dissolution and mixing of the reagent.