| CLAIMS What is claimed is: 1. The measurement and use of the zeta potential of a substrate in the presence of isotopes for the detection of the isotopes or for measuring the isotope ratios comprising: a substrate; a surface ionic layer covering at least part of the substrate; and isotope adsorbates binded to the substrate. 2. The substrate according to claim 1 , wherein the material of the substrate is formed from a material selected from the group consisting of polymers, glasses, ceramics, carbon, metals, composites and combinations thereof. 3. The substrate according to claim 1 , wherein the substrate is bulk material. 4. The substrate according to claim 1 , wherein the substrate is flexible. 5. The substrate according to claim 1 , wherein the substrate is rigid. 6. The substrate according to claim 1, wherein the material of the substrate comprises colloidal material. 7. The substrate according to claim 1, wherein the material of the substrate comprises nano- particulate material. 8. The substrate according to claim 1 , wherein the material of the substrate comprises colloidal silica, alumina, gold, silver and combinations thereof. 9. The substrate according to claim I, wherein at least part of the surface adsorbing layer comprises surface ionic groups. 10. The substrate according to claim 1 , wherein at least part the surface adsorbing layer comprises surface ionic groups capable of binding the isotopes to the surface of the colloid wherein the zeta potential effect is effective. 11. The substrate according to claim 1 , wherein the isotopes comprise atoms, molecules or ions. 12. The substrate according to claim 1 , wherein the isotopes comprise metals, non-metals and metalloids and combinations thereof. 13. The substrate according to claim 1, wherein the isotopes comprise 6Li+, 7Li+, and 14NH4+, l 5NH4+ ions. 14. The substrate according to claim 1, wherein the isotopes comprise a single layer. 15. The substrate according to claim 1, wherein the isotopes comprises double and multiple layers. 16. The substrate according to claim 1, wherein the zeta potential effect is exhibited. 17. A method for using a substrate for the detection of isotopes and isotope ratios comprising the steps of: a) providing a substrate, a material suitable for binding isotopes to the substrate; b) contacting the substrate with the isotopes under conditions effective for at least partial binding of the isotopes to the substrate; and c) measuring and using the zeta potential of the substrate comprising the at least partially bound isotopes for the detection of the isotopes or the isotope ratios. 18. The method according to claim 17, wherein the material of the substrate is formed from a material selected from the group consisting of polymers, glasses, ceramics, carbon, metals, composites and combinations thereof. 19. The method according to claim 17, wherein the material of the substrate comprises colloidal material. 20. The method according to claim 17, wherein the material of the substrate comprises nano- particulate material. 21. The method according to claim 17, wherein the material of the substrate comprises colloidal silica, alumina, gold, silver and combinations thereof. 22. The method according to claim 17, wherein at least part of the surface adsorbing layer comprises surface ionic groups. 23. The method according to claim 17, wherein at least part the surface adsorbing layer comprises surface ionic groups capable of binding the isotopes to the surface of the colloid wherein the zeta potential effect is effective. 24. The method according to claim 17, wherein the isotopes comprise atoms, molecules or ions. 25. The method according to claim 17, wherein the isotopes comprise metals, non-metals and metalloids and combinations thereof. 26. The method according to claim 17, wherein the isotopes comprise 6Li+, 7Li+, and 14NH4+, 15NH4+ ions. 27. The method according to claim 17, wherein the surface adsorbed isotopes comprise a single layer. 28. The method according to claim 17, wherein the surface adsorbed isotopes comprises double and multiple layers. 29. The method according to claim 17, wherein the zeta potential effect is exhibited. |
Novel method to measure isotope ratios
BACKGROUND OF THE INVENTION
The present invention relates to a novel zeta potential effect observed on substrate materials in the presence of isotopes, to methods of making them and to uses therefor. In particular the invention concerns such materials, methods and uses for the application of this zeta potential effect for isotope detection or isotope ratio analysis.
The zeta potential of materials are influenced by their external environment, both chemical and physical. Understanding interactions which take place between a material and its environment is important in connection with such fields as ion-exchange chromatography, detergents, soil chemistry and water purification. One material characteristic which has been shown to influence the zeta potential behaviour is the surface charge and many studies have been done to investigate this influence. A review of such investigations may be found in; Electrokinetic Phenomena by Anurag S. Rathore and Andras Guttman (Marcel Dekker, Inc. New York, 2004).
The zeta potential is the electrical potential that exists at some small distance from the surface of a particle called its shear plane. Some colloids dispersed in a solvent (usually water) bear a surface charge due to the presence of adsorbed ions or terminal ionised groups. In an electrolyte solution, this charge affects the distribution of solvated ions in the immediate neighbourhood of the particle resulting in a fixed layer of ions of opposite charge (counter ions) to that of the particles. Outside the fixed layer, there is an increased concentration of solvated ions (relative to the bulk solution) on both charges, forming a cloud-like area. These two regions together form an electrical double-layer around the particle.
The ions in the fixed layer are bound fairly strongly to the surface of the particles, whilst those in the diffuse region are held more weakly. The balance and concentration of ions in this region are determined by a combination of electrostatic forces and random thermal motion. The potential in this region, therefore, decays with distance from the surface until at some point it becomes zero.
When a voltage is applied to the solution in which the particles are dispersed, they move towards the electrode of opposite polarity, accompanied by the fixed layer and part of the diffuse double- layer. The potential at the boundary between this unit, i.e., the shear plane, and the surrounding medium is called the zeta potential (ζ). The ζ is a function of the surface charge of a particle, any adsorbed layer(s) at the surface and the type and composition of the surrounding medium in which the particle is dispersed.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a use of zeta potential to detect isotopes or measure isotope ratios of adsorbed isotopes onto substrate materials. It is a further object of the invention to provide such a system which is sufficiently robust to be useful in commercial applications. Another object of the invention is to provide a system which can be manufactured reproducibly, conveniently and without excessive expense.
According to the present invention there is provided a novel zeta potential effect exhibited on a substrate in the presence of isotopes comprising:
a substrate;
an ionic surface layer covering at least part of the substrate; and
isotopes capable of binding to the substrate surface ionic layer. The substrate in the presence of isotopes has been shown to exhibit different zeta potentials between pairs of isotope ions as adsorbate. The method of the invention therefore provides a novel technique which may find application in a wide variety of circumstances. For example, the method according to the invention may be used to provide a means for detecting isotope ratios in binary isotope systems. Equipment for use in environmental research, dating techniques, quality control, separation technologies may be manufactured from method according to the invention. Furthermore, existing technologies used in these areas could easily be replaced by the present invention. To our knowledge, there are no prior art methods or other techniques using zeta potential analysis for the means described above. Many methods used for isotope ratio analysis, mainly mass spectroscopy, tend to be non-ideal for many commercial applications as they are expensive, not sufficiently versatile to measure high enrichments of isotopes and entail large waiting times for analysis.
In the context of this document, "adsorbate" is used to refer to the surface layer of isotopes adsorbed, for example 6 Li + and 7 Li + .
The adsorbate may form a layer upto any depth on the substrate. Such an layer may comprise, for example, a partial, single, double or diffuse adsorbate layer around the substrate.
The examples described later show zeta potential dependence of 6 Li + , 7 Li + and , NH 4 + , 15 NH 4 + isotope pairs on the substrate.
The surface layer of isotopes is preferably provided by means of controlled deposition onto the surface of the substrate.
The substrates, methods and uses of the invention have advantages over conventional engineering, scientific approaches used in isotope ratio analysis and detection. For isotope ratio analysis, the overall apparatus embodying the invention would be quite small in dimension, allowing transportation from site to site, thus allowing large numbers of data to be acquired on site. The invention would also greatly reduce costs of obtaining results, waiting times and maintenance of instruments.
The analysis of different isotopes according to the invention can be achieved by selecting different substrates, as isotopes interact differently to different substrates. The invention therefore provides a valuable tool for use in analysing many different types of isotopes. The invention may be applied to, or incorporated into a wide variety of uses. For example, the invention may be used in the following list (which is by no means exhaustive) of products and services:
Isotope mapping in the atmosphere for studies on climate change;
Studies of sources and sinks of artificially introduced chemicals to the environment, e.g., fertilizers in cultivated land use;
Quality control for use in isotope production or separation facilities;
An alternative to mass spectroscopy for isotope ratio analysis.
It will be apparent to the skilled person, that the method of the invention can be carried out using materials which are non-toxic to human health. For example, the use of amorphous colloidal silica (S1O2 - silicon dioxide) is known to be non-toxic to humans. Other non-toxic materials may also be employed, such alumina, gold or silver.
The substrate may be any dimension. These methods are particularly suited to substrates having having at least one dimension which is measurable at the nanometre level, for example a feature which measures from about 1 to about 200 nm, preferably from about 1 to about 150 nm, even more preferably from about 1 to about 100 nm, and most preferably less than about 50 nm in at least one dimension.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
The invention will now be more particularly described with reference to the following Figures and Examples in which:
TABLE. 1 shows the change in zeta potential with substrate-isotope interactions in accordance with the invention; the data being generated by a zeta plus analyser;
FIGS. 1 & 2 show graphically the change in zeta potential with substrate- isotope interactions from Table. 1 in accordance with the invention;
DETAILED DESCRIPTION OF THE INVENTION
Substrates in accordance with the present invention may be rigid or flexible. Further, substrates in accordance with the present invention may be any dimension. Substrates in accordance with the present invention are generally colloidal. The substrate provides support as well as a suitable surface area for the binding of the isotopes to the surface layer of the substrate. Typically, the substrate is selected with characteristics appropriate for the isotopes used, for example, positively charged substrates for the adsorption of isotope anions or negatively charged substrates for the adsorption of isotope cations.
A preferred substrate is colloidal. More preferably a substrate is colloidal silica or alumina which are inorganic polymers comprised of Si-O or Al-0 network macro-structures and advantageously can be in colloidal form, finely ground powder or rigid bulk material whichever is desired for the substrate. Both silica and alumina are readily available materials common in many materials and uses and are one of the most abundant minerals in the earth's crust. Advantageously, the substrate of the present invention may utilize silica or alumina thus imparting these virtues on the substrate.
Preferably, the substrate is a clean, purified, well characterised support.
The isotopes may be applied to the substrate through either immersion of the substrate in a solution of the isotopes or through other application techniques known in the art for applying adsorbates to adsorbents. Furthermore, the isotope concentrations used in the invention are determined by isotope type and concentration/surface area of the substrate. Preferably, the isotopic concentrations which are chosen should result in the formation of an ionically bound monolayer.
A substrate in the presence of isotopes according to the aforementioned steps may initiate a distinct set of characteristics affecting the magnitude of the zeta potential of the substrate thus allowing for a method of isotope detection or isotope ratio measurement. In order to further illustrate the principles and operation of the present invention, the following examples are provided. However, these examples should not be taken as li iting in any regard.
EXAMPLE 1
An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 10% w/w silica in a 100 cm3 volumetric flask. The pH of 10 ml of this dispersion was then noted. 1.5 ml of this mixture was then transferred to a Brookhaven Instruments Ltd zeta potential analyser and the ζ measured over 10 runs of 5 cycles and the average ζ obtained. TABLE.1 shows the results of this experiment and clearly show a ZP of -19.36 mV as a result of substrate contact or interaction. In this case the adsorbate ions are Na + which are present due to NaOH in the Ludox which as as a stabilizer.
EXAMPLE 2
In a variant of Example 1, the isotope 6 Li was investigated using lithium chloride as the source of 6 Li + . An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 10% w/w silica in a 100 cm3 volumetric flask. To 10 ml of this dispersion, 0.5312 g of 6 LiCl (Sigma-Aldrich) was added with gentle mixing for 1 minute and the pH noted. 1.5 ml of this mixture was then transferred to a Brookhaven Instruments Ltd zeta potential analyser and the ζ measured over 10 runs of 5 cycles and the average ζ obtained. TABLE.1 shows the results of this experiment and clearly show a decrease in the ZP from -19.36 to -6.83 mV as a result of substrate contact or interaction. In this case the adsorbate ions are 6 Li + .
In a variant of Example 1, the isotope 7 Li was investigated using lithium chloride as the source of 7 Li + .An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 10% w/w silica in a 100 cm3 volumetric flask. To 10 ml of this dispersion, 0.5440 g of 7 LiCl (Sigma-Aldrich) was added with gentle mixing for 1 minute and the pH noted. 1.5 ml of this mixture was then transferred to a Brookhaven Instruments Ltd zeta potential analyser and the ζ measured over 10 runs of 5 cycles and the average ζ obtained. TABLE.1 shows the results of this experiment and clearly show a decrease in the ZP from -19.36 to -13.71 mV as a result of substrate contact or interaction. In this case the adsorbate ions are 7 Li + .
EXAMPLE 3
In a variant of Example 1, the isotope 14 N was investigated using ammonium chloride as the source of ammonium ions, NH 4 " . An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 10% w/w silica in a 100 cm3 volumetric flask. To 10 ml of this dispersion, 0.4046 g of 14 H 4 C1 (Cambridge Isotopes) was added with gentle mixing for 1 minute and the pH noted. 1 .5 ml of this mixture was then transferred to a Brookhaven Instruments Ltd zeta potential analyser and the ζ measured over 10 runs of 5 cycles and the average ζ obtained. TABLE.1 shows the results of this experiment and clearly show a decrease in the ZP from -19.36 to -7.02 mV as a result of substrate contact or interaction. In this case the adsorbate ions are 14 NHj + .
In a variant of Example 1, the isotope ,5 N was investigated using ammonium chloride as the source of ammonium ions, 5 NH 4 + . An aqueous dispersion of silica sol, (Ludox TM-50, Sigma-Aldrich), containing approximately 50% w/w silica particles of approximately 21 nm diameter was diluted with water to 10% w/w silica in a 100 cm3 volumetric flask. To 10 ml of this dispersion, 0.4122 g of 15 NH4C1 (Cambridge Isotopes) was added with gentle mixing for 1 minute and the pH noted. 1.5 ml of this mixture was then transferred to a Brookhaven Instruments Ltd zeta potential analyser and the ζ measured over 10 runs of 5 cycles and the average ζ obtained. TABLE.1 shows the results of this experiment and clearly show a decrease in the ZP from -19.36 to - 16.61 mV as a result of substrate contact or interaction. In this case the adsorbate ions are 15 NH4 + .
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