3. PREAMBLE TO THE DESCRIPTION

a. Background of invention:

The electrochemical system normally consists of an electrochemical cell with three electrodes. The first is current-injecting probe, called the counter electrode and the second is the reference electrode, typically it is non-responsive to the changes in the composition of the test solution and the third electrode responsive to the analyte is called as the working electrode.

The reference electrode often causes difficulties in electrochemical measurements, especially used for a longer time. There is a continual interest in developing alternatives to the reference electrodes which are currently being used. It is difficult to find a stable reference electrode that can be used for both organic and aqueous solutions. Most popular reference electrodes are of the type, calomel and silver-silver chloride. These conventional reference electrodes used for electrochemical measurements, have a limited range of applicability. The liquid junction is problematic with these electrodes, and they cannot be used with completely solid-state electrochemical cells. The reference electrode is obviously an essential component of electrochemical cells, especially for the purpose of electrochemical analysis. Thus many conventional reference electrodes have been developed and some are commercially available. However, smaller and simpler reference electrodes are increasingly required for recent electroanalytical applications.

One of the reasons is the emerging demand in the electrochemical systems of micro-total-analysis-systems, which lay a few serious restraints on reference electrodes therein. First of all, no internal filling solution is allowed in most of the cases and their size should be limited to integrate other components on a microchip. Moreover, the performance as a reference electrode must resist harsh conditions during chip fabrication and post treatment procedure. A micro-machined liquid-junction Ag/AgCl electrode is based on thin film of silver deposited on glass wafers using photolithography [H. Suzuki et al, Actuators B 46(1998) 146]. Unfortunately, Ag/AgCl thin film is unstable even in very common conditions. Furthermore, Ag/AgCl obviously demands an invariable and high chloride concentration to maintain a stable potential, which is a less common condition than a constant pH.

Electrochemical solid-state electrodes based on metal oxides have been addressed over the last few decades with the aim of developing practical alternatives to Ag/AgCl, especially for miniaturized systems because metal oxides are favorable for conventional patterning processes. The ideal reference electrode must have a non-polarizable interface, on which any particular current does not produce further overpotential. Bockris et al. described that the equilibrium exchange current density is a quantitative criterion of polarizability [J. 0. M. Bockris, A. K. N. Reddy, Modern Electrochemistry, Vol. 2, Plenum, New York 1973]. The electrode/solution interface becomes proportionally less polarizable as it grows.

Today there is a great need for rapid and accurate methods of assaying electroactive organic compounds and the metal ions (which may be at low concentration). It is well known to provide reference electrode as an electrical reference point in addition to working and auxiliary electrodes in an electrolytic medium to be investigated. Reference electrodes are non-polarizable reversible half-cells which form almost possible constant potential which is independent of the composition of the medium to be analyzed. Recently, the electrochemical treatment of carbon-based electrodes has received rather extensive interest from analytical chemists. There are several types of carbon materials available that are suitable for electrochemical applications, among them glassy carbon, graphite and recently, the carbon nanotubes. U.S. Pat. No. 4,431,508 describes a graphite reference electrode with a hydrophilic coating containing a redox couple manufactured with non-planar conventional technology. U.S. Pat No.3,926,764 describes the ion-sensitive membrane electrode such as graphite hydrophobised with polymeric material used as inner reference electrode. However, surprisingly, it has been found that a reference electrode will still be operative with conventional reference electrodes.

In light of the above background, in order to fill the requirements of the electrochemical industries and research institutions, the present invention enables one to have pre-prepared electrodes which are ready for analysis in aqueous and non-aqueous solutions thereby providing an instant test without the need of any pre-calibration tests and without concern for the stability and condition of the calibration fluid. Thus the electrodes can be made disposable. Alternatively, they can be made re-useable after removing the previous history of the test solution either by simple polishing of the electrode surface or voltammetric cycling.

b. Object of the Invention:

The object of the present invention is to provide an improved and simple Absolute Graphite Electrode System for the analysis of metal ions and electroactive organic compounds present in aqueous and non-aqueous solutions of interest. The proposed electrode system minimizes the most of the aforesaid disadvantages of conventional reference electrodes and provides the common user with a useful choice.

c. Statement of the Invention:

The present invention provides a device for the qualitative and quantitative determination of an ion in a fluid, the receptacle comprising three electrodes - counter electrode, working electrode and reference electrode. In a particularly preferred embodiment, all the three electrodes are made up of the same material, for example, graphite leads to provide absolute combined electrode system. One of the graphite leads acts as a working electrode, a second lead as reference electrode which provides a potential difference and third lead forms a counter electrode to which a potential difference is applied. Accordingly, the invention provides an Absolute Graphite Electrode System in electro-analytical methods for detecting the presence of one or more metal ions and electroactive organic molecules of interest in a given sample.

The present invention does not involve the conventional reference electrodes and, thereby, avoids the contamination of the analyte with the reference solutions. It is devoid of liquid junction potential, which is a major problem in case of conventional reference electrodes. It involves the use of solid-state absolute combined electrode systems, which facilitates easy regeneration of the electrode surface. It can be used for online analysis of the samples such as water samples, industrial wastes etc. The proposed method is free from pre-calibration procedures and is made available for all or part of diagnostic and analytical purposes.

d. Summary of the Invention:

Present invention provides an Absolute Graphite Electrode System to solve the problems encountered in systems described in prior art. The 'Absolute Graphite Electrode System' consists of three graphite cylindrical rods (electrodes), encapsulated in a cylindrical plastic shell, upper ends of graphite electrodes connected to copper wire for electrical measurement, lower ends submerged in the analyte under study and is used for voltammetric determination of metal ions and electroactive compounds present in aqueous and non-aqueous solutions of interest (analyte). Cylindrical graphite rods are of size about 0.5 mm in dia and 50 mm long and of commercial grade (graphite leads in pencils used for writing). Plastic shell is a thin walled plastic tube of about 10 mm external dia and 50 mm long; cylindrical graphite rods being arranged, one by the side of the other in a line, parallel to each other along the axis of the plastic tube such that the rods are mutually at a distance of about 1 mm throughout their length. The upper ends of graphite rods are connected to copper wire so that they can be used for measurement of voltage / current. In the plastic shell, the graphite rods are sealed by filling it with epoxy resin and further curing it and, after curing, lower end the shell is polished with emery and fine grade alumina. For the purpose of voltammetric study, using Absolute Graphite Electrode System, the central electrode is used as reference electrode and the other two electrodes on either side are used as working and auxiliary electrodes; and, using a suitable electrochemical workstation (for measuring current / voltage), the voltage is applied across reference electrode and working electrode, the resultant current (in the analyte) is measured between auxiliary electrode and working electrode. The graphite rods, used in the Absolute Graphite Electrode System being chemically neutral, overcome the error in the measurement of potential, normally observed in conventional 3-electrode system (due to oxidation / reduction of analyte) and hence the potential (voltage) measurements are very stable and accurate, as evidenced by voltammetric study of different analytes under various experimental variables. This Absolute Graphite Electrode System can also be extended to other chemical neutral electrodes like gold and platinum, just by replacement of electrodes by gold and platinum wires of suitable length and diameter, as evidenced by the studies shown in this specification. The Absolute Graphite Electrode System can also be extended by just modified the surface properties of graphite lead by electrodeposition of gold. The absolute graphite electrode system for voltammetric applications is substantially described herein with reference to the examples and drawings accompanying this specification.

In this invention, electrochemical behavior of potassium ferricyanide at the new absolute electrode system has been described and also a comparison with the conventional electrode system has been made. Further, potential measurements for few selected metal ions and organic compounds have been undertaken. Also the stability of the absolute electrode systems has been studied.

The present invention encourages the design of low-cost, more sophisticated and easily portable instrumentation system by which the researchers can carry out electrochemical investigations comfortably.

4. DESCRIPTION

The invention will be further described with reference to the following example read in conjunction with the accompanying drawings.

A. Description of the accompanied drawings:

To assist the understanding of the present invention, reference will now be made to the accompanying drawings which are as follows:

Fig. 1 shows the schematic diagram illustrating the structure of the Absolute Graphite Electrode System.

Fig. 2 shows the schematic diagram of the experimental set up for the analysis of an analyte solution on Absolute Graphite Electrode System.

Fig. 3 shows the cyclicvoltammetric response of 25 mM K3[Fe(CN)6] in 0.1 M KC1 at conventional (a) and Absolute Graphite Electrode System (b); scan rate 50 mV s"1.

Fig. 4 shows the cyclicvoltammetric response of (A) 50 mM CUSO4.5H2O, (B) 50 mM C0CI2.6H2O, (C) 50 mM CdCl2.H20, and (D) 50 mM ZnS04.7H20 in 0.1 M KCl at conventional (a) and Absolute Graphite Electrode System (b); scan rate 50 mV s'1.

Fig. 5 shows the cyclicvoltammetric response of 25 mM K.3[Fe(CN)6] in 0.1 M KCl at conventional (a) and absolute gold electrode system (b); scan rate 50 mV s"1.

Fig. 6 shows the cyclicvoltammetric response of 40 mM K.3[Fe(CN)6] in 0.1 M KCl at conventional (a) and absolute platinum electrode system (b); scan rate 50 mV s"1.

Fig. 7 shows the cyclicvoltammetric response of 25 mM K3[Fe(CN)6] in 0.1 M KCl at conventional (a) and gold coated absolute graphite electrode system (b); scan rate 50 mV s' .

Fig. 8 shows the cyclicvoltammetric response of (A) 1 mM AA, (B) 100 uM DA in 0.1 M phosphate buffer solution of pH 7.0 at conventional (a) and gold coated absolute graphite electrode system (b); scan rate: 50 mV s'1.

B. Detailed description

1. Construction of Absolute Graphite Electrode System:

The construction of absolute graphite electrode system is shown in Fig. 1. The commercial pencil graphite leads (2B, 0.5 mm x 50 mm) were procured from the market. Three such graphite leads (1, 2 & 3) were used for preparing the electrode system. These leads were inserted in a plastic shell (4). Plastic shell is a thin walled plastic tube of about 10 mm external dia and 50 mm long; cylindrical graphite rods being arranged, one by the side of the other in a line, parallel to each other along the axis of the plastic tube such that the rods are mutually at a distance of about 1 mm throughout their length (as shown in Fig. 1). The upper end of the graphite leads were individually connected to copper wires (5, 6, 7) for electrical contact through a plastic cork (8). Then the plastic shell was filled with epoxy resin (9) without disturbing the graphite leads and allowed for 24 hours for setting up of epoxy resin. After 24 hours, the lower end of the cylindrical tube was scraped with a knife so as to expose the graphite leads (as shown in Fig. 1). The exposed end of the tube containing graphite leads was polished using different grade emery papers and finally with 0.5 urn alumina. Further, the electrode was subjected to sonication followed by water wash.

2. Experimental

The experimental set up consists of an absolute graphite electrode system, analyte solution of which electrochemical behavior is to be studied and an electrochemical workstation with the help of which oxidation / reduction potential of analyte is measured.

In Fig. 2, (1) represents absolute electrode system. The analyte solution (2), quantity - 10 niL, was taken in a glass cell (3) of suitable capacity. The pre-cleaned absolute graphite electrode system (1) was immersed into the analyte solution. All the chemicals were of analytical-reagent grade and used as received without any further purification. All the solutions were freshly prepared with double distilled water. The three leads of the absolute graphite electrode system were connected to the electrochemical workstation (4) (Model: CHI660D) as shown. The central lead was connected to the reference terminal (RE) and other two leads were connected to the working (WE) and auxiliary (AE) terminals of the workstation. A small variable voltage ( -1.0 V to +1.0 V) was applied between RE and WE and resultant current (in mA or uA) was measured between AE and WE. For any given analyte, current has been measured at different applied potentials (in mV). By plotting the current vs. potential (voltammogram), the nature of electrochemical behavior of the analyte can be obtained. This method, referred to as cyclicvoltammetric method, using the Absolute Graphite Electrode System.

The following studies describe the electrochemical behaviors of newly developed absolute electrode systems:

(a) Electrochemical behavior of [Fe(CN)6]3'/4' redox couple at conventional and Absolute Graphite Electrode System (Fig. 3).

(b) Electrochemical behaviour of various metal ions at conventional and Absolute Graphite Electrode System (Fig. 4).

(c) Determination of open circuit potential for few supporting electrolytes.

(d) Cyclic voltammetric analysis of single drop of K3[Fe(CN)6].

(e) Voltammetric studies using Absolute Graphite Electrode System by increasing the resistance (length) of the connecting wires.

(f) Determination of stability of the Absolute Graphite Electrode System.

(g) Electrochemical behaviour of Absolute Gold and Platinum Electrode Systems (Figs. 5 and 6).

(h) Electrodeposition of gold onto the Absolute Graphite Electrode System and their electrochemical behaviour (Fig. 7). (i) Catalytic activity of Gold Coated Absolute Graphite Electrode System (Fig. 8).

Experiments (a) and (b) depict the behavior of the absolute electrodes system, (c), (d),(e) and (f) depict the behavioral stability with experimental variables and (g) and (h) show how this system can be extended to other absolute electrode systems.

The potentials measured by new electrode systems were compared with the conventional electrode systems. These studies revealed that the developed absolute electrode systems can be used as an alternative to the existing conventional electrode systems. These absolute electrode systems could be used for all type of voltammetric analyses without sacrificing the reproducibility or accuracy.

The following examples are given by way of illustrations of the present invention and should not be construed to limit the scope of the present invention. On the other hand, the common structures or steps that are known to everyone are not depicted in detail. Some preferred embodiments of the invention are described in detail in the following examples. However, it should be recognized that the present invention can be practiced in a wide range of other applications besides those explicitly described here and the scope of the present invention is expressly not limited except as specified in the accompanying claims.

(a) Electrochemical behavior of [Fe(CN)6]3/4" redox couple at conventional and Absolute Graphite Electrode Systems

Conventional electrode system:

• Reference electrode: Saturated Calomel electrode

• Working electrode: Graphite lead

• Counter electrode: Graphite lead

Absolute Graphite Electrode System:

• Reference electrode: Graphite lead

• Working electrode: Graphite lead

• Counter electrode: Graphite lead

The [Fe(CN)6]3"/4' redox couple is the most valuable and convenient probe to characterize the electrochemical performance of the electrode systems. Voltammetric measurements were performed using an electrochemical workstation (Model: CHI 660D, USA) using Absolute Graphite Electrode System. In conventional electrode system the Saturated Calomel electrode acts as reference, other two graphite leads acts as working and counter electrode. Fig. 3 depicts cyclic voltammograms (CV) obtained at absolute graphite electrode system and conventional electrode system in 25 mM K.3[Fe(CN)6]. The Em of the mediator (taken as the average of the cathodic peak potential (Epc) and anodic peak potential (Epa)) was 52 mV at both the electrode systems. Only a parallel shift of both Epc and Epa without affecting the change in peak potential value and nature of peak current was observed. The fact that the absolute graphite electrode system shows a consistent behaviour regardless of the reference electrode used indicates that the results are attributable to the redox system and not to the type of reference electrode. It can be seen that the newly developed Absolute Graphite Electrode System has the desirable reversibility characteristics when compared to conventional electrode system.

(b) Electrochemical behaviour of various metal ions at conventional and Absolute Graphite Electrode Systems

Conventional electrode system:

• Reference electrode: Saturated Calomel electrode

• Working electrode: Graphite lead

• Counter electrode: Graphite lead

Absolute Graphite Electrode System:

• Reference electrode: Graphite lead

• Working electrode: Graphite lead

• Counter electrode: Graphite lead

Fig. 4 shows cyclic voltammograms (CV) of Co2+, Cd2*, Cu+, Cu2+ and Zn2+metal ions in 0.1 M KC1 solution at absolute graphite electrode system and conventional electrode system comprising saturated calomel electrode. Fig. 4A shows the CV curves for the redox reaction of Cu2+ and Cu+ ions. The nature of CV curves and peak currents at Absolute Graphite Electrode System and conventional electrode system are found to be exactly same but with a parallel shift of peak potentials (Table 1). Similarly, Figs. 4B, 4C and 4D show the CV curves of 50 mM solutions of C0CI2, CdS04 and ZnSC<4 in 0.1 M KCl solution, respectively, at Absolute Graphite Electrode System and conventional electrode system. The nature of CV curves obtained for all the metal ions at both the electrode systems are found to identical but with a parallel shift of peak potentials towards more negative values (Table 1). The shift in peak potential is attributed to the characteristic property (over potential) of the electrode material being used as reference electrode. The above results indicated that Absolute Graphite Electrode System could be used as the absolute combined electrode system for voltammetric analysis of metal ions without the aid of any conventional reference electrodes.

Table - 1: Stability of the Absolute Graphite Electrode System as determined by the cyclicvoltammetric studies of metal ions in 0.1M KG solution (Fig. 4).

(c) Determination of open circuit potential in presence of different supporting electrolytes

The open circuit potentials (OCPs) in presence of different supporting electrolytes were measured at conventional and absolute graphite electrode systems in aqueous solutions. OCPs were measured using an electrochemical workstation (Model: CHI 660D, USA) using Absolute Graphite Electrode System. The pre-treated electrode systems were kept in 0.1 M solutions of different supporting electrolytes. The OCPs values at Absolute Graphite Electrode System and conventional electrode systems were recorded after attainment of constant potential values (Table 2). The experiments were repeated five times in respective solutions and found that the value of OCP remained within the deviation of ± 5mV.

Conventional electrode system:

• Reference electrode: Saturated Calomel Electrode

• Working electrode: Graphite lead

• Counter electrode: Graphite lead

Absolute graphite electrode system:

• Reference electrode: Graphite lead

• Working electrode: Graphite lead

• Counter electrode: Graphite lead

Table - 2: Open Circuit Potentials (OCPs) in presence of different supporting electrolytes at Absolute Graphite Electrode and conventional electrode systems in aqueous solutions.

(No figure attached to depict the results)

(d) Cyclic voltammetric analysis of single drop of K3[Fe(CN)6]

The graphite electrode system was clamped to a stand in vertical position and a drop (50 uL) of the analyte (25 raM K.3[Fe(CN)6] in 0.1 M KC1) was place on the top of the Absolute Graphite Electrode using micropipette. The obtained voltammogram is exactly identical in peak currents and peak potentials as that of voltammogram obtained at the Absolute Graphite Electrode in a conventional manner using 10 mL of the analyte in a glass cell. These results revealed that the proposed voltammetric method at absolute graphite electrode system could be used for the analysis of 50 uL sample solution. This method is more advantageous in cases, where there is a scarcity for the sample availability. Also the method is less time consuming and does not require any additional accessories, including the cylindrical glass cell, to carry out the experiments.

(e) Voltammetric studies using Absolute Graphite Electrode System by increasing the resistance (length) of the connecting wires

The cyclic voltammetric studies were carried out by connecting the Absolute Graphite Electrode System to the electrochemical workstation with copper wires of 7 m length. The voltammograms obtained are exactly identical in peak currents and peak potentials as that of the curves obtained in the conventional analysis using normal length of connecting wires supplied with the instrument. The above results clearly indicated that the proposed voltammetric method using connecting wires of longer lengths could be used for online analysis of underground water, water in a reservoir, metal ion concentrations in industrial reactors and pollution level at different locations etc.

(f) Determination of stability of the Absolute Graphite Electrode System

The stability of the proposed electrode system was studied by using [Fe(CN)6]3/4 redox couple in presence of 0.1 M KC1. The first CV scan was performed at the beginning and second scan was made after retaining the electrode in the same cell for 24 hours. The two curves are very close to each other, and the peak potentials were stable within the average deviation of 2 to 3 mV. The absolute graphite electrode system was washed with distilled water and kept at room temperature without any protection for a period of 15 days and then the CV studies were carried out. It was found that there was a small shift of the peak potential (± 5mV) of [Fe(CN)6]3/4 redox couple. These observations clearly indicated that the stability and uniqueness of absolute graphite electrode system.

(g) Electrochemical behaviour of Absolute Gold Electrode and Absolute Platinum

Electrode Systems

The same procedure, which was adopted for the construction Absolute Graphite Electrode System, was used for the construction of Absolute Gold Electrode and Absolute Platinum Electrode Systems. The three identical gold or platinum wires (0.5 mm x 50 mm) were used for the fabrication of absolute electrode systems.

For Absolute Gold Electrode System

Conventional electrode system:

• Reference electrode: Saturated Calomel electrode

• Working electrode: Gold wire

• Counter electrode: Gold wire

Absolute gold electrode system:

• Reference electrode: Gold wire

• Working electrode: Gold wire

• Counter electrode: Gold wire

Figure 5 shows a typical CV curves of [Fe(CN)6]3/4 redox couple in 0.1 M KC1 solution at Absolute Gold Electrode System and conventional electrode system. The E1/2 of the mediator (taken as the average of Epc and Epa) was found to be 123 mV at absolute gold electrode system and it was 103 mV at conventional electrode system.

For Absolute Platinum Electrode System

Conventional electrode system:

• Reference electrode: Saturated Calomel electrode

• Working electrode: Platinum wire

• Counter electrode: Platinum wire

Absolute platinum electrode system:

• Reference electrode: Platinum wire

• Working electrode: Platinum wire

• Counter electrode: Platinum wire

Figure 6 shows typical cyclic voltammograms of [Fe(CN)6]3/4 redox couple in 0.1 M KC1 solution at Absolute Platinum Electrode System. The E1/2 of the mediator was found to be 141 mV at absolute platinum electrode system and it was 163 mV at conventional electrode system.

The fact that the absolute gold and platinum electrode systems show a consistent behaviour regardless of the reference electrode used, which indicates that the results are attributable to the redox system and not to the type of reference electrodes. Similar to Absolute Graphite Electrode System the newly developed Absolute Gold Electrode and Absolute Platinum Electrode Systems also have the desirable reversibility characteristics when compared to conventional electrode systems. But the desirable reversibility and sensitivity of Absolute Gold Electrode and Absolute Platinum Electrode Systems are found to be lower than that of the Absolute Graphite Electrode System.

(h) Electrodeposition of gold onto the Absolute Graphite Electrode System

The absolute graphite electrode system was polished, sonicated and finally washed with double distilled water. All the three leads of Absolute Graphite Electrode System were subjected to electrodeposition using 1 raM chloroauric acid at the applied potential of-1.0 V for 5 minutes. After electrodeposition the Gold Coated Absolute Graphite Electrode System was washed with double distilled water and used for the electrochemical experiments.
The formation of gold nanostructures not only enlarges the surface area of the electrode, but also improves the electron transfer rate between the electrode surface and the bulk solution, which has been confirmed by the performance of Gold Coated Absolute Graphite Electrode System in the electrochemical investigation of the mixture of ascorbic acid (AA) and Dopamine (DA).

Conventional electrode system:

• Reference electrode: Saturated Calomel electrode

• Working electrode: Gold coated graphite lead

• Counter electrode: Gold coated graphite lead

Gold Coated Absolute Graphite Electrode System:

• Reference electrode: Gold coated graphite lead

• Working electrode: Gold coated graphite lead

• Counter electrode: Gold coated graphite lead

Electrochemical behaviour of gold coated graphite electrode system - Figure 7 shows a typical CV curves of [Fe(CN)6]3"/4' redox couple at Gold Coated Absolute Graphite Electrode System in 0.1 M KC1 solution. The E\n of the mediator (taken as the average of Epc and Epa) was found to be 41 mV at both Gold Coated Absolute Graphite Electrode System and conventional electrode system.

(j) Catalytic activity of gold coated Absolute Graphite Electrode System
To test the catalytic activity of Gold Coated Absolute Graphite Electrode System towards the oxidation of AA and DA, cyclic voltammograms were recorded for ascorbic acid (AA) and dopamine (DA) in 0.1 M phosphate buffer (As shown in Fig 8A & 8B). From Fig. 8A, it can be seen that a broad oxidation peak for AA was appeared around 23 mV and 141 mV at conventional electrode system and Gold Coated Absolute Graphite Electrode System, respectively. Figure 8B shows similar oxidation peak for DA around 150 mV and 227 mV at conventional and gold coated graphite electrode systems, respectively. Both the electrode systems show the same electrochemical response towards the oxidation of AA and DA. Also the peak currents for both AA and DA at these systems are found to be same indicating the suitability of gold coated Absolute Graphite Electrode System for the estimation of AA and DA without the aid of any conventional reference electrodes. The shift in the oxidation potential of AA and DA towards more positive value could be explained on the basis of the characteristic property (over potential) of Gold Coated Absolute Graphite Electrode System. Due to the improved selectivity and sensitivity, the Gold Coated Absolute Graphite Electrode System could be used as a potential candidate for the simultaneous estimation of biologically important compounds.

5. Claims

We claim,

1. The 'Absolute Graphite Electrode System' consists of three cylindrical graphite rods (electrodes), encapsulated in a cylindrical plastic shell, upper ends of graphite electrodes connected to copper wire for electrical measurement, lower ends submerged in the analyte under study and is used for voltammetric determination of metal ions and electroactive compounds present in aqueous and non-aqueous solutions of interest (analyte).

2. Cylindrical graphite rods, referred in claim (1), are of size about 0.5 mm in dia and 50 mm long and of commercial grade (graphite leads in pencils used for writing).

3. Plastic shell, referred in claim (1), is a thin walled plastic tube of about 10 mm external dia and 50 mm long; cylindrical graphite rods being arranged, one by the side of the other in a line, parallel to each other along the axis of the plastic tube such that the rods are mutually at a distance of about 1 mm throughout their length (as clearly shown in Fig-1).

4. Further upper ends of graphite rods, referred in claim (1), are connected to copper wire so that they can be used for measurement of voltage / current.

5. Further in the plastic shell, referred in claim (1), the location of graphite rods are sealed by filling it with epoxy resin and further curing it and, after curing, lower end the shell is polished with emery and fine grade alumina.

6. Further for the purpose of voltammetric study, using Absolute Graphite Electrode System, referred in claim (1), the central electrode is used as reference electrode and the other two electrodes on either side are used as working and auxiliary electrodes; and, using a suitable electrochemical workstation (for measuring current / voltage), the voltage is applied across reference electrode and working electrode, the resultant current (in the analyte) is measured between auxiliary electrode and working electrode (as clearly shown in Fig. 2).

7. The graphite rods, used in Absolute Graphite Electrode System, referred in claim (1), being chemically neutral, overcome the error in the measurement of potential, normally observed in conventional three-electrode system (due to oxidation / reduction of the internal reference solution) and hence the potential (voltage) measurements are very stable and accurate, as evidenced by voltammetric study of different analytes under various experimental variables (as shown by the examples in this specification).

8. This Absolute Graphite Electrode System, referred in claim (1), can also be extended to other noble electrodes like gold and platinum, just by replacement of graphite electrodes by gold and platinum wires of suitable length and diameter, as evidenced by the studies shown in this specification.

9. The Absolute Graphite Electrode System, referred in claimed in (1), can also be extended to electrodeposited electrodes just by electrodeposition of gold on graphite leads, as evidenced by the voltammetric studies shown in this specification.

10. The absolute graphite electrode system for voltammetric applications, referred in claim (1), is substantially described herein with reference to the examples and drawings accompanying this specification.