WO2013081443A1

WO2013081443A1 - Ammonium selective electrode and method of preparing it

Info

Publication number: WO2013081443A1
Application number: PCT/MY2012/000182
Authority: WO
Inventors: Alva Sagir; Ahmad Mohd Rais
Original assignee: Mimos Bhd
Current assignee: Mimos Bhd
Priority date: 2011-12-02
Filing date: 2012-06-29
Publication date: 2013-06-06
Anticipated expiration: 2014-06-02

Abstract

There is disclosed a sub-ppm ammonium ion sensor with cast doped polythiophene nanocomposite transducer comprising: a substrate; for providing mechanical strength for the sensor tip; at least one silver layer as conducting layer and wire trace; at least one carbon layer; to provide adhesion to cast polythiophene nanocomposite; at least one polythiophene transducer layer for converting chemical potential to electrical signal; and at least one ammonium sensing membrane for recognizing ammonium ion and transport it to the surface of the transducer layer.

Description

AMMONIUM SELECTIVE ELECTRODE AND METHOD OF PREPARING IT

FIELD OF INVENTION

The present invention relates generally to compound detection device and methods, and more particularly to ammonia detection device and methods.

BACKGROUND Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that this prior art forms part of the common general knowledge in Malaysia or any other country. Chemical sensing has become a significant aspect in resolving serious environmental challenges facing humankind aside from detection of useful compounds and much have been written about them. Gradually recognizing its potential to radically modify the living conditions of future generations has put forward various efforts to provide improved systems and methods for detecting the concentration of selected compounds within a sample.

In many attempts to provide effective detection methods, a great majority are highly complex and rather cumbersome for users. In other cases, the methods lack precision. Typically, methods use to determine the ammonium ion concentration is purge and trap ion chromatography, and spectrometry. Ion chromatography technique is capable of doing separation, identification and quantification of ammonium ion at ug/L level. Because of the complexity in this method, a development of ion selective electrode based on potentiometric is done to overcome the complicated and time- consuming measurement. Other alternatives include using an electrode with a presence of bacteria that consume oxygen during its respiratory which later a decrease in current from oxygen electrode is proportional to the concentration of ammonium sensor. Another example is the known Nessler method, which is also capable to detect ammonium ion but with spectrometry method, few sample pre-treatment steps need to be done before it and it will bring disadvantage in term of time consuming. Nessler method also has limitation over the level of turbidity of sample, since cloudy sample might not be able to analyze accurately. Moreover, the quick measurement needs to be done since the sample might easily change color.

In view of potentiometric chemical sensor, polymer has become a useful element as it has capability of conducting electricity and at the same time able to function as transducer too. The common polymers use for this particular purpose includes polyaniline, polythiophene, polypyrrole and polyacetylene . Nevertheless, an apparent problem related to using polymer is the potential of chemical reactions which leads to prohibition of electron transfer and thus the electrode become unstable.

Considering the limitations of current methodologies, there is a need to identify a new method in detecting ammonium concentration so as to accommodate rapidly increasing demands.

Therefore this proposed sub-ppm ammonium ion sensor will overcome this indirect measurement because it provides a sensing element which can straight forward measure the ammonium concentration in liquid form. The proposed ammonium sensor comprises of ammonium membrane on novel polythiophene transducer, which gives good accuracy at sub-ppm for aquaculture, environmental monitoring and medical applications. This proposed sub-ppm ammonium ion sensor also has a simple measurement method because this sensor element is only need to be couple with a reference electrode and connect to a high impedance potential measuring device.

Further objects and advantages of the present invention may become apparent upon referring to the preferred embodiments of the present invention as shown in the accompanying drawings and as described in the following description.

SUMMARY OF INVENTION

In one aspect there is provided an ammonium ion sensor with cast doped polythiophene nanocomposite transducer comprising: a substrate; for providing mechanical strength for the sensor tip; at least one silver layer as conducting layer and wire trace; at least one carbon layer; to provide adhesion to cast polythiophene nanocomposite; at least one polythiophene transducer layer for converting chemical potential to electrical signal; and at least one ammonium sensing membrane for recognizing ammonium ion and transport it to the surface of the transducer layer.

In another aspect of the present invention there is disclosed a method of preparing the sub-ppm ammonium ion sensor with cast doped polythiophene nanocomposite transducer comprising the steps of: depositing carbon electrode, preferably via screen printing method; preparing CNT-polythiophenes conducting layer by chemical; drop coat polythiophenes on carbon electrode surface as transducer layer to allow electron transfer; characterizing CNT-polythiopene transducer; depositing ammonium ion membrane on polythiophenes transducer layer; and characterizing the ammonium ion sensor.

BRIEF DESCRIPTION OF DRAWINGS

Some figures contain color representations or entities. This invention will be described based on experimental results by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which: FIG 1 shows the sensor in accordance with one embodiment of the present invention;

FIG 2 shows the steps involved in preparing a component in accordance with one embodiment of the present invention;

FIG 3 shows an example of the sensor in accordance with an embodiment of the present invention;

FIG 4 shows the results obtained based on the sensor in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION

Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or integer or group of elements or integers but not the exclusion of any other element or integer or group of elements or integers.

The present invention provides an ammonium sensor, which capable of doing trace level measurement in sub-ppm value. · This proposed ammonium sensor comprises of ammonium membrane on novel polythiophene transducer, which gives good accuracy at sub-ppm for aquaculture, environmental monitoring and medical applications. This proposed ammonium ion sensors have a recognition element (ammonium selective membrane layer) which selectively picks the wanted chemical ion/ species and transducer (polythiophene layer) will convert the signal into an electronic signal and later the concentration of ion/species will be known.

A schematic view of the ammonium ion sensor in accordance with the preferred embodiments of the present invention is shown in FIG 1.

The sub-ppm ammonium ion sensor with cast doped polythiophene nanocomposite transducer in accordance with the preferred embodiments of the present invention comprises: a substrate; for providing mechanical strength for the sensor tip; at least one silver layer as conducting layer and wire trace; at least one carbon layer; to provide adhesion to cast polythiophene nanocomposite; at least one polythiophene transducer layer for converting chemical potential to electrical signal; and at least one ammonium sensing membrane for recognizing ammonium ion and transport it to the surface of the transducer layer.

Referring now to FIG 2, the steps involved in preparing the ammonium selective material with polythiophenes transducer membrane in accordance with one embodiment of the present invention includes: preparation of carbon electrode, preferably via screen printing method; preparation of CNT-polythiophenes conducting layer by chemical; coating polythiophenes on carbon electrode surface as transducer layer to allow electron transfer; characterizing CNT- polythiophene transducer; depositing an amount of, preferably 30μ1 ammonium ion membrane of polythiophenes transducer layer; and characterization of ammonium ion sensor.

In accordance with the embodiments of the present invention, the ammonia presence on the as toxic (un-ionized) ammonia (NH₃) and nontoxic (ionized) ammonia (NH₄ ⁺) as in equation below:

H⁺ + (NH₃ -» NH+₄)

This portion of toxic and non toxic ammonia depends on water's temperature and pH condition. If the pH of water increases, the ammonia is converted to the un-ionized form of NH3. The non toxic form of NH4+ normally formed in the low pH or acidic conditions.

As shown in FIG 3, this proposed sub-ppm ammonium ion sensor also has a simple measurement method because this sensor element is adapted to be coupled only with a reference electrode and connect to high impedance potential measuring device. The potentiometric sensor will have a potential variation depend on the concentration of ammonium ions in the solution. This potential measuring device will measure a differential potential between sensing membrane surface with the potential generated by reference electrode. The potential different is measured as a voltage (mV) and plotted as a function of logarithmic ammonium concentration.

Based on this measurement method, good responses and good linearity on miniaturized planar electrode can be obtained. The results indicate that the disclosed invention can be deployed for detecting a trace level of ammonium species in the fields. This sub-ppm ammonium ion selective sensor with polythiophenes layer can be packaged into a small wireless system and deployed for in-situ measurement of the analytes.

In accordance with one embodiment, the doped polythiophene transducer of the sensor comprises 0.1 to 20% polythiophene', 0.1 to 20% dopant, 40 to 90% binder and 0.1 to 20% carbon nanotubes, all by weight.

It is preferred that the conducting polythiophene of the sensor in accordance with the preferred embodiments of the present invention has the following structure:

= H, methyl, ethyl, butyl, pentyl, hexyl, heptyl, octyl

R₂ = H, methyl, methoxy, thiomethyl

R₃ = H, methyl, ethyl, butyl, pentyl, hexyl, heptyl, octyl

Further in accordance with the preferred embodiments of the present invention, the dopant of the sensor is at least one or combination of the following dopants; chloride, tetrafluoroborate, iodide, para-toluene sulfonate, trifluoromethane sulfonate, camphor sulfonate, poly styrene sulfonate, nafion, hexafluorophosphate . Below are examples on how the device of the present invention can be prepared. It shall be apparent to one skilled in the art that the exemplifications are provided to better elucidate the embodiments of the present invention and therefore should not be construed as limiting the scope of protection. All methods described as exemplifications herein may be performed in any suitable order unless otherwise indicated herein.

EXAMPLE 1

Preparation of sub-ppm Ammonium Electrode .

Silver and carbon was screen printed on the printed circuit board substrate. This SPE (screen printed electrode) was cleaned by sonication method with DI water to remove any dirt particle on the carbon surface which might affect the sensing performance later on. After a minute of cleaning in sonicator, the carbon printed electrode was cleaned and dried. In order to prepare the electrode as a sensing element, 10 microL polythiophene solution was carefully deposited on the carbon printed electrode by mean of drop casting. During this preparation, the polythiophene solution should be evenly spread on to the carbon surface area. Then, the electrode was allowed to dry for 30-45 minutes under a continuous flow of Nitrogen gas. The polythiophene layer should be dried before deposit another layer called membrane layer .

Example 2 Preparation of Sub-ppm Ammonium Sensing Membrane

A cocktail for ammonium membrane layer was prepared by mixing of lmg potassium tetrakis p-chlorophenyl borate (KTpCIPB) , 3mg Ammonium Ionophore 1, 30mg high molecular weight of polyvinyl chloride (PVC) , and 3mg dioctyl sebacate (DOS) in a lOmL glass bottle. The cocktail mixture was dissolved in lmL tetrahydrofuran (THF) and mixed homogeneously. Then, 30microL of cocktail membrane was drop-casting on the polythiophene layer and allowed to dry at room temperature for overnight. The electrode was rinsed with DI water and conditioned in 10^"3M of NH₄C1 before characterization process.

Example 3

Characterization of sub-ppm Ammonium Sensor.

The sub-ppm Ammonium Sensor prepared as above example is used as ammonium sensing electrode and paired with standard Ag/AgCl reference electrode, which were set-up with Orion Ion Meter. The Ag/AgCl reference electrode was prepared 0.1M LiOAc (lithium acetate) as external electrolyte. After conditioning with 10^"3M of NH₄C1, the sensor electrode was rinsed with DI water and dried. The characterization was carried out in temperature of 25°C.

The standard test solution was prepared from a stock solution of 10^" ³M NH₄CI. The NH4⁺ solution with concentration of 10^~5, 10^"6 and 10^"M for this experiment was prepared by dilution of stock solution with DI water. In the other words, for this purposed of experiment, the NH4+ solution is prepared in 0.18, 0.018 and 0.0018ppm value. This range of sub-ppm value of ammonium ion is applicable for environmental monitoring application.

Both sub-ppm ammonium sensor electrode and reference electrode were immersed in the test solution. The potential value of sensing electrode against the Ag/AgCl reference electrode, which measured in mV was recorded in each concentration as mentioned earlier. The potential value was recorded when the display value on Orion Ion Meter was non-flashing and stable.

Based on Table 1 and Figure 2, this proposed sub-ppm ammonium sensor electrode shows Nernstian response of 58.03mV/decade over a range of

10⁵ to 10^"7M. The response also has a good linear regression value of 0.991. This showed that the proposed sensor can worked in lower range of NH4⁺ concentration.

Table 1 : Results of sub-ppm ammonium sensor

slope 58.03

intercept 516

R² 0.991

FIG 4 shows the results obtained based on the sensor of the present invention . It is understood by a person skilled in the art that- the methods for experiments and studies are described as exemplifications herein and thus the results are not intended, however, to limit or restrict the scope of the invention in any way and should not be construed as providing conditions, parameters, agents or starting materials which must be utilized exclusively in order to practice the present invention. It is therefore understood that the invention may be practiced, within the scope of the appended claims, with equivalent methods for the experiments than as specifically described and stated in claims.

Claims

1. An ammonium ion sensor with cast doped polythiophene

nanocomposite transducer comprising: a substrate; for providing mechanical strength for the sensor tip; at least one silver layer as conducting layer and wire trace;

at least one carbon layer; to provide adhesion to cast polythiophene nanocomposite;

at least one polythiophene transducer layer for converting chemical potential to electrical signal; and

at least one ammonium sensing membrane for recognizing ammonium ion and transport it to the surface of the transducer layer.

2. The sensor as claimed in Claim 1 wherein the sensor is sub-ppm sensor .

3. The sensor as claimed in Claim 1 wherein the doped

polythiophene transducer comprises 0.1 to 20% polythiophene, 0.1 to 20% dopant, 40 to 90% binder and 0.1 to 20% carbon nanotubes, all by weight.

4. The sensor as claimed in claim 1 wherein the conducting

polythiophene having the following structure:

R-i = H, methyl, ethyl, butyl, pentyl, hexyl, heptyl, octyl

R₂ = H, methyl, methoxy, thiomethyl

R₃ = H, methyl, ethyl, butyl, pentyl, hexyl, heptyl, octyl

The sensor as claimed in claim 1 wherein the dopant is at least one or combination of the following dopants; chloride,

tetrafluoroborate, iodide, para-toluene sulfonate,

trifluoromethane sulfonate, camphor sulfonate, poly styrene sulfonate, nafion, hexafluorophosphate .

The sensor as claimed in claim 1 wherein the ammonium sensing membrane comprising; acrylic copolymer adhesive; forms

homogenous blend with high molecular weight polymer and functions as adhesion promoter to solid electrode surface; high molecular weight polymer; functions as lipophilic polymeric matrix to allow transport of ionic species to electrochemical transducer surface;plasticizer; to soften the high molecular weight polymer; lipophilic additive; to create ionic sites within the polymer matrix; ammonium-recognizing molecule; to selectively bind with the analyte and to transport it across the membrane; and solvent for dissolving the mixture of ammonium cocktail.

7. The sensor as claimed in claim 6 wherein the copolymer comprises one part of methyl methacrylate monomer and at least one part of tetrahydrofurfuryl acrylate monomer by volume.

8. A method of preparing the sub-ppm ammonium ion sensor with cast doped polythiophene nanocomposite transducer comprising the steps of: depositing carbon electrode, preferably via screen printing method; preparing CNT-polythiophenes conducting layer by chemical; drop coat polythiophenes on carbon electrode surface as transducer layer to allow electron transfer; characterizing CNT-polythiopene transducer; depositing ammonium ion membrane on polythiophenes transducer layer; and characterizing the ammonium ion sensor.

9. The sensor as claimed in Claim 1 used in aquaculture, medical and environmental monitoring applications.