Title of Invention	A PROCESS FOR THE PREPARATION OF A SOLID-STATE METAL BASED PH ELECTRODE
Abstract	A process for the preparation of a solid-state metal based pH electrode: The present invention provides a solid - state metal based pH electrode starting from conducting polymer which has been neutralized/undoped. The neutralized conducting polymer has been combined with polyvinyl chloride resulting enhanced pH sensitivity and range.

Full Text

The present invention relates to a process for the preparation of a solid-state metal based pH electrode, a solid - state pH electrode prepared thereby and a pH meter made therefrom. The present invention particularly relates to a process for the preparation of a solid-state pH electrode based on a conducting polymer such as poly(3-cyclohexyl thiophene). The development of pH electrode based on unblocked (with conventional double barrel configuration) interfaces are known since long. The pH responsive glass membrane electrode continues to be the most widely used Ion Selective Electrode (ISE). Some of the disadvantages associated with these electrodes are: 1) Electrodes have to be always kept in an up-right position 2) Problem of the internal filling solution 3) Due to glass membrane, it needs very care full handling 4) Polarizibility- Glass electrodes are easily polarised even on small current flow in the pH meter in its internal circuits. 5) Acid error- in strong acidic solution (1M H+) glass electrodes shows permanent error. 6) Base error- in high basic solution (> 14 pH) it shows irreversibility. Also shows sensitivity towards Na+ and K+ ions. 7) Its miniaturization is limited 8) Use of the conventional glass pH electrodes for the chemically modified electrodes are very limited because of its glass membrane. Chemical modifications e.g. coating and immobilization of the chemicals/enzymes over the glass electrode itself is very difficult and also it blocks the pores of the glass membrane. In view of above drawbacks several other types of glass membrane electrodes were made but they did not meet the commercial requirements [M.E. Meyerhoff and Y. M. Fraticell; Anal. Chem., 54, 27R-44R, 1982]. Apart from glass membrane electrodes, several other pH electrodes were made using inorganic as well as organic materials. A solid-state pH sensing electrode was developed by using single a- Zirconium hydrogen phosphate crystals [R. Palombari and M. Casciola; J. Electroanal. Chem. Interfacial Electrochem, 216 (1-2), 283, 1987] or palladium hydride [S. Kihara, Z. Yoshida, M. Matsui; Bull. Inst. Chem. Res. Kyoto Unn., 64 (4) 207 , 1986, Chem. Abstr. 106, 226459, 1987]. Some organic material based pH sensors are also known e.g. 3-hydroxy-N-Dodecylpicolinamide in poly(vinyl chloride) mediated electrodes [D. Erne, D. Ammann, W. Chimia, Chem. Abst. 90, 199741 d, 1979] and octaphenyltetrasiloxane and tris(2-ethylhexyl) phosphate based electrode [J.G. Schindler, G. Stork, j.H. Struch, W. Schall, Z. Fresenius; Anal. Chem., 290, 45, 1978]. These electrodes did not meet the commercial sensor requirements due to short pH sensing range ( pH 7 - 8.2) and also showed selectivity towards Li* and other ions. Beside this reproducibility and stability problems were also associated with all these pH electrodes. To the best of our knowledge and belief no solid-state pH electrode has been reported based on conducting polymers. The main object of the present invention is to provide a process for the preparation of a solid-state pH electrode. Another objective of the present invention is to provide a process for the preparation of a solid-state pH electrode based on a conducting polymer such as poly(3-cyclohexyle thiophene). Still another objective present invention is to provide a solid-state pH electrode. Yet another objective of the present invention is to provide a pH meter incorporating the said solid-state pH electrode. Accordingly the present invention provides, a process for the preparation of a solid-state metal based pH electrode which comprises, preparing a saturated solution conducting polymer selected from poly(3-cyclohexyle thiophene) or its copolymers or its derivatives , in organic solvent using 0.1 to 100 weight percent of neutralized/undoped polymer as defined above , blending the obtained solution with 0 to 99 weight percent polyvinyl chloride (PVC), 0 to 10 weight percent plasticizer, coating the said blended solution on to a metallic electrode selected from gold (Au), platinum (Pt), titanium (Ti) and stainless steel by conventional method such as herein described to get a polymer electrode, further incubating the polymer electrode in dilute acid such as herein described , providing an insulating protective outer cover such as herein described to the resultant electrode to get the desired metal based pH electrode. In an embodiment of the present invention, the saturated solution may be prepared using organic solvents such as tetrahydro furan (THF), or chloroform/dichloromethan in the case of 0 % of polyvinyl chloride (PVC). In yet another embodiment of the present invention, the plasticizer used may be such as 2-nitrophenyl octyl ether, dibutyl phthalate, vinyl alcohals. In still another embodiment of the present invention, the metal electrode used may be such as gold (Au), platinum (Pt), titanium (Ti) and stainless steel. In yet another embodiment of the present invention, the coating of the metal electrode with saturated solution of poly(3-cyclohexyle thiophene) may be effected using known methods such as brushing, spin coating or simple solvent evaporation method. In still another embodiment of the present invention, the dilute acid may be used for the incubation of the polymer electrode such as HCI, H2SO4 HCIO4 HNO3 and Organic Acids. In still another embodiment of the present invention, insulating protective outer covering, may be of polyvinyl chloride, acrylates, teflon or any commercially available plastic or metals/allows having perforation. Accordingly, the present invention provides a solid-state pH electrode prepared by the process described above. Accordingly, the present invention provides a pH meter incorporating the solid-state pH electrode as described above, which comprises placing the pH electrode and a reference electrode in a container capable of holding the fluid, the pH for which is to be measured, connecting the out put leads of the said electrode pair through a potential measuring means. In an embodiment of the present invention, the reference electrode used may be such as calomel electrode, Ag/AgCI electrode or any commercially available standard electrode. In another embodiment of the present invention, the means used for measuring the potential difference may be such as multimeter, voltmeter, digital display meter, computer. In the process of the present invention we have used undoped conducting polymer, more specifically poly(3-cyclohexyle thiophene), which we have found to be pH sensitive after incubation in dilute acid for few hours. We have also found that the said conducting polymer may or may not be pH sensitive in its normal form due to its doped sate (having positive charges on the chain and incorporated anions in the matrix). These positive charges in the polymer matrix cases a repulsion to the H+ ions and hence a poor pH sensitivity. Also the anions present in the matrix as the result of the neutralisation for these positive charges occupied the holes/cavity in the polymer matrix and making further inhibition for the H+ ions. So to make the polymer sensitive for the H+ ions (for pH) it is necessary that it should be in its neutralised/undoped sate. Neutralised/undoped poly(3-cyclohexyle thiophene) shows a nice reversible pH response (for acid and base both) but at very high or very low pH a simultaneous doping of the polymers takes place which cases poor sensitivity for the pH. To avoid this type of polymer doping at very high or very low pH, we made a blend/solution of the said neutral/undoped conducting polymer with polyvinyl chloride using some suitable plasticizer in tetra hydro furan and coated over the metal electrode for the preparation of pH electrode. Polymer blend pH electrode shows good reversible pH response even at very low and high pH, which was due to the polyvinyl chloride blend which stop the doping (insertion) of anions to the poly(3-cyclohexyle thiophene). The novelty and inventive steps of the present invention resides in preparing a solid-state pH electrode starting from conducting polymer which has been neutralised/undoped. A further inventive step is the combination of the neutralised conducting polymer with polyvinyl chloride resulting enhanced pH sensitivity and range. The invention is further illustrated with the help of the following examples and therefore should not be construed to limit the scope of the present invention in any manner. Example 1: The polymerisation of 3-cyclohexyle thiophene was carried out by chemical oxidation in chloroform using anhydrous FeCI3 solution in chloroform. Reaction mixture was kept for 24 hrs and then polymer was precipitated by adding methanol in excess. Poly(3-cyclohexyle thiophene) was purified and dried in the vacuum. Neutral/undoped poly(3-cyclohexyle thiophene) was coated over Pt disk electrode (diameter 2mm) from its saturated chloroform solution (30 µl) by solvent evaporation method. After 1 hour drying, the polymer electrode was incubated in the 0.1 M HCI for 10 hours (it is required for only one time just after the construction of polymer electrode) and then properly washed with distilled water and used for pH sensing as follows: The poly(3-cyclohexyle thiophene) coated electrode together with a double junction Ag/AgCI reference electrode (with cell assembly : Reference electrode/test solution/pH electrode) was dipped in the stirred electrochemical cell with a working volume of 20 ml of 1mM tris-HCI buffer (pH 7). The electrode potential was monitored with a Keithley 2000 multimeter interface with computer and recorded on computer using Keithley software. At the steady-state potential, varying concentrations of the HCI solution were injected into the cell and the new steady-state potential was recorded. A calibration curve was made by plotting potential response vs. H+ ion concentration. A nerntian response was observed in the range of pH 5 to pH 3. At the lower pH ( Example 2: Neutral/undoped poly(3-cyclohexyle thiophene) was synthesised as described in example-1 and to avoid the doping of conducting polymer in very low or high pH solution, neutral/undoped poly(3-cyclohexyle thiophene) was blended with polyvinyl chloride (PVC) along with a plasticizer in the following composition: PVC= 28 mg, 2-nitrophenyl octyl ether (plasticizer) = 60µl in 1 ml of neutral/undoped poly(3-cyclohexyle thiophene) saturated tetra hydro furan (THF) solution. Nearly 30 µl of the blend was costed over the Pt- metal electrode and allowed to dry for 12 hours. This electrode was then incubated in 0.1 M HCI for 10 hours for only one time just after the construction. pH electrode was washed in distilled water and finally with tris-HCI buffer (1mM, pH=7) before each use. This modified pH electrode was used for the pH measurements as the same way described in the example 1. The electrode potential was monitored with a Keithley 2000 multimeter interface with computer and recorded on computer using Keithley software. At the steady-state potential, varying concentrations of the HCI solution were injected into the cell and the new steady-state potential was recorded. A calibration curve was made by plotting potential response vs. H+ ion concentration. A nerntian response was observed in the relatively long range of pH 6 to pH 1. Similar experiment was also performed by using NaOH instead of HCI and potential response was recorded and was found to be reversible and reproducible. pH electrode was found to be very stable for several sets of measurements for long time period (more than 6 months). One or two time washing in distilled water was found to be sufficient to reuse the electrode after each use. The main advantages of the present invention are: 1. Solid State pH electrode. 2. Simple configuration of the electrode. 3. Ease in construction of electrode. 4. Cost effective. 5. Occurrence of constant steady-state potential. 6. pH response in the range of 1 to 9. 7. Electrode is stable up to very long time (> 6 months). 207 , 1986, Chem. Abstr. 106, 226459, 1987]. Some organic material based pH sensors are also known e.g. 3-hydroxy-N-Dodecylpicolinamide in poly(vinyl chloride) mediated electrodes [D. Erne, D. Ammann, W. Chimia, Chem. Abst. 90, 199741d, 1979] and octaphenyltetrasiloxane and tris(2-ethylhexyl) phosphate based electrode [J.G. Schindler, G. Stork, j.H. Struch, W. Schall, Z. Fresenius; Anal. Chem., 290, 45, 1978]. These electrodes did not meet the commercial sensor requirements due to short pH sensing range ( pH 7 - 8.2) and also showed selectivity towards Li+ and other ions. Beside this reproducibility and stability problems were also associated with all these pH electrodes. To the best of our knowledge and belief no solid-state pH electrode has been reported based on conducting polymers. The main object of the present invention is to provide a process for the preparation of a solid-state pH electrode. Another objective of the present invention is to provide a process for the preparation of a solid-state pH electrode based on a conducting polymer such as poly(3-cyclohexyle thiophene). Still another objective present invention is to provide a solid-state pH electrode. Yet another objective of the present invention is to provide a pH meter incorporating the said solid-state pH electrode. Accordingly the present invention provides, a process for the preparation of a solid-state metal based pH electrode which comprises, preparing a saturated solution of conducting polymer selected from poly(3-cyclohexyle thiophene) or its copolymers or its derivatives , in organic solvent using 0.1 to 100 weight percent of neutralized/undoped polymer as defined above , blending the obtained solution with 0 to 99 weight percent polyvinyl chloride (PVC), 0 to 10 weight percent plasticizer, coating the said blended solution on to a metallic electrode selected from gold (Au), platinum (Pt), titanium (Ti) and stainless steel by conventional method such as herein described to get a polymer electrode, further incubating the polymer electrode in dilute acid such as herein described , providing an insulating protective outer cover such as herein described to the resultant electrode to get the desired metal based pH electrode. We Claim: 1. A process for the preparation of a solid-state metal based pH electrode which comprises, preparing a saturated solution of conducting polymer selected from poly(3-cyclohexyle thiophene) or its copolymers or its derivatives , in organic solvent using 0.1 to 100 weight percent of neutralized/undoped polymer as defined above , blending the obtained solution with 0 to 99 weight percent polyvinyl chloride (PVC), 0 to 10 weight percent plasticizer, coating the said blended solution on to a metallic electrode selected from gold (Au), platinum (Pt), titanium (Ti) and stainless steel by conventional method such as herein described to get a polymer electrode, further incubating the polymer electrode in dilute acid such as herein described , providing an insulating protective outer cover such as herein described to the resultant electrode to get the desired metal based pH electrode. 2. A process as claimed in claim 1, wherein the organic solvent used is selected from tetra hydro furan (THF), chloroform .dichloromethane . 3. A process as claimed in claims 1 and 2, wherein the plasticizer used selected from 2-nitrophenyl octyl ether, dibutyl phthalate, vinyl alcohols. 4. A process as claimed in claims 1 - 4, wherein the coating of the metal electrode with saturated solution of poly(3-cyclohexyle thiophene) is effected by conventional methods of brushing, spin coating or simple solvent evaporation method. 5. A process as claimed in claims 1 - 5, wherein the dilute acid used for the incubation of the polymer electrode selected from HCI, H2SO4, HCIO4, HNO3. 6. A process as claimed in claims 1 - 6, wherein the insulating protective outer cover used is made of polyvinyl chloride, acrylates, teflon having perforation. 7. A process for the preparation of a solid-state metal based pH electrode substantially as herein described with reference to the example.

Documents:

1279-del-1999-abstract.pdf

1279-del-1999-claims.pdf

1279-DEL-1999-Correspondence-Others.pdf

1279-del-1999-correspondence-po.pdf

1279-del-1999-description (complete).pdf

1279-del-1999-form-1.pdf

1279-del-1999-form-19.pdf

1279-del-1999-form-2.pdf

1279-del-1999-form-3.pdf