Title of Invention: COMPOSITION AND METHOD FOR

PREPARATION OF NANOPOROUS PROTECTIVE

MEMBRANE

Technical Field

[1] This invention relates to preparation of porous membrane, and more specifically it relates to composition and preparation of nanoporous membranes to protect electrode surface and allow flow of electrical current.

Background Art

[2] Potentiometric measurement of an ion concentration requires a working electrode having selectivity on the target ion, a reference electrode and a readout circuitry. One of the most widely used electrode is silver-silver chloride electrode built from chlo- rination of silver wire, foil or screen-printed dry paste.

[3] Signal stability in potentiometric device relies on equilibrium of ionic species

involved in reduction-oxidation process involving the cathode and anode, concentration of individual ions and loss of neutral molecules and ionic species from the sensing membrane. While both neutral molecules and ions can leach from the electrode and contaminate the analyte, it is more practical to quantify the amount of lost ions, compared to leaching of neutral molecule. For example leached chloride can be precipitated with silver ion (i.e. from silver nitrate solution) in quantitative manner whereas, leached plasticizer additive cannot be measured in straight forward fashion.

[4] While we should allow transport of ions in potentiometric setup to complete the circuit and thus produce response signal, it is critical to have a minimal loss of ions, in order to maintain a stable signal for a reasonably long period of time. Ion loss and cross contamination will always be part of electroanalytical measurement but it must be designed to accommodate industrial specifications and practical lifetime.

[5] One approach to achieve signal stability is to prevent the loss of ionic and neutral species from the chemical sensors and the reference electrodes.

Disclosure of Invention

Technical Problem

[6]

Technical Solution

[7]

Summary

[8] The present invention provides the use of nanoporous protective membrane for con- trolling the rate of transport of ionic species in the electrode, controlling the rate of loss of sensing membrane components, for maintaining sufficient and linear response signal from chemical sensors, and to achieve low and constant drift rate of chemical sensors.

[9] The present invention is for use in the sensing and the reference electrodes so that the potentiometric system is suitable for long term field deployment.

[10] The present invention provides a nano-porous hybrid solgel protective membrane composition comprises of tetraethylothosilicate, methyltriethoxysilicon, phenyltri- ethosilicon, chloride salt and borate compound.

[11] Accordingly, the protective nano-porous membrane contains 20 to 60% of tetraethy- lorthosilicate, 20 to 60% of methyltriethoxysilicon, 20 to 60% of phenyltri- ethoxy silicon, 1 to 5% of chloride salt and 1 to 5% of borate compound.

[12] Accordingly, the chloride salt is selected from the list of the chloride salt of lithium, sodium or potassium.

[13] Accordingly, the preferred borate compound is trimethyl borate or triethylborate.

[14] Accordingly, the membrane is use for the preparation of leak-free reference

electrode.

[15] Accordingly, the membrane is use for the preparation of ion selective electrode (ISE) chemical sensors.

[16] Accordingly, the membrane is use for the preparation of ISFET chemical sensors.

[17] Accordingly, the membrane is use for preparation of protection membrane for silver- silver chloride electrode.

[18] The present invention also provides a method for preparation of nano-porous glassy materials comprises the steps of:

[19] a) mixing tetraethyl orthosilicate, deionized water, hydrochloric acid,

trimethylborate, lithium chloride, along with desired amount of methyltriethoxysilane and phenyltriethoxysilane

[20] b) stirring vigorously at room temperatur; and

[21] c) aging the mixture in tightly capped vial for 20 hour.

Description of Drawings

[22] Brief description of the drawings

[23] FIG. 1 : illustrates an embodiment of layer composition of screen-printed silver- silver chloride electrode

[24] FTG.2 : illustrates signal stability of chloride response of silver-silver chloride

electrode with protective nano-porous membrane in 10 ³ M KCL

[25] FIG.3 : illustrates the comparison in response signals of chloride ion silver-silver chloride electrode with and witout the nanoporous protective membrane versus double- junction reference electrode.

[26] Detailed description of the preferred embodiment of the present invention [27] Examples

[28] Example 1

[29] Screen-Printed Silver-Silver Chloride electrode

[30] FIGURE 1 illustrates one preferred embodiment of screen-printed silver-silver

chloride electrode 4 of the present invention. Substrate 1 is polymeric material that gives physical strength of the screen-printed electrode and is compatible with the silver paste. Polyester or printed circuit board having thickness of 0.3 to 1mm thickness are most commonly used materials. Layer 2 screen-printed silver materials from commercially available paste mixtures, printed through a mask to give circular shape having 3 to 8mm diameter. The printed silver paste is cured at the temperature of 80 to 150°C to give final dry thickness of 50 to 500 micrometer. Silver chloride layer 3 is grown from the silver material by chlorination process using ferric chloride solution having concentration of 0.1M to 1M for 30 to 120 seconds in the absence of light.

[31 ] Composition of Nano-porous Protective Membrane

[32] Cocktails for protective nano-porous membranes were prepared from the compositions provided in Table 1.

[Table 1]

[Table ]

[33] Table 1: Composition of protective nano-porous membrane

[34]

[35] Example 2

[36] Preparation of Hybrid Solgel Cocktail

[37] Tetraethyl orthosilicate (TEOS, 450uL), 450uL of methyltriethoxysilane (MTES), 280|iL of deionized water (DIW) and 20uL of 0.1 M hydrochloric acid are mixed in a glass vial or round-bottom flask. The mixture was stirred for 4 hours until a clear solution was achieved. Then 200uL of the homogenous mixture was mixed with lithium chloride (LiCl) to get 0.5% LiCl by weight and trimethyl borate (TMB) to get 0.5% TMB by weight and the mixture sonicated for 60 minutes.

[38]

[39] Example 3

[40] Silver-Silver Chloride Electrode with Nanoporous Protective Membrane

[41] Screen printed silver-silver chloride electrode having circular shaped with 4mm

diameter, printed on polyester or FR4 substrate with 0.5mm thickness was dipped into the hybrid solgel cocktail containing 0.5% LiCl and 0.5% TMB, both by weight. The electrode was dried in open air for 10 minutes and the drying process was continued under nitrogen blanket for another 10 minutes. After the ambient temperature drying process, the electrode underwent low-temperature sintering cycles at three different temperatures. First the electrode was heated in the oven at 50°C for 10 minutes and later 70°C for 10 minutes and finally at 100°C for 10 minutes.

[42]

[43] Example 4

[44] Chloride Response from Silver-Silver Chloride Electrodes with and without Nanoporous Protective Membrane

[45] Screen-printed silver-silver chloride electrodes with polyester or FR4 substrate have been prepared using the above procedure. Chloride response signals of this electrode, with and without nano-porous protective membrane, versus conventional double- junction reference electrode have been characterized. The screen-printed Ag-AgCl electrode, with or without nano-porous protective membrane reference electrode were both immersed in 10 ³ M to 10 ¹ M of potassium chloride solutions, and both electrodes were connected to an ion meter. The response signals were recorded after stable readings were achieved.

[46]

[47] The response signal versus chloride ion activity were plotted as shown in FIGURE 3.

The results show that the screen-printed Ag-AgCl electrode, with and without nano- porous protective membranes do not block flow of current in the potentiometric measurement setup, and therefore is suitable to protect the surface of electrodes.

Best Mode

[48]

Mode for Invention

[49]

Industrial Applicability

[50]

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