WO2015122330A1 - イオンセンサ用触媒およびこれを用いたイオンセンサならびに定量法 - Google Patents
イオンセンサ用触媒およびこれを用いたイオンセンサならびに定量法 Download PDFInfo
- Publication number
- WO2015122330A1 WO2015122330A1 PCT/JP2015/053112 JP2015053112W WO2015122330A1 WO 2015122330 A1 WO2015122330 A1 WO 2015122330A1 JP 2015053112 W JP2015053112 W JP 2015053112W WO 2015122330 A1 WO2015122330 A1 WO 2015122330A1
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- WIPO (PCT)
- Prior art keywords
- hydrogen phosphate
- phosphate ions
- concentration
- ion sensor
- catalyst
- Prior art date
Links
- 239000003054 catalyst Substances 0.000 title claims abstract description 119
- 238000000034 method Methods 0.000 title claims abstract description 86
- 238000011002 quantification Methods 0.000 title abstract description 17
- NBIIXXVUZAFLBC-UHFFFAOYSA-L Phosphate ion(2-) Chemical compound OP([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-L 0.000 claims abstract description 210
- 238000001514 detection method Methods 0.000 claims abstract description 184
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 134
- 230000003647 oxidation Effects 0.000 claims abstract description 129
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 107
- 150000002500 ions Chemical class 0.000 claims abstract description 90
- WOCIAKWEIIZHES-UHFFFAOYSA-N ruthenium(iv) oxide Chemical compound O=[Ru]=O WOCIAKWEIIZHES-UHFFFAOYSA-N 0.000 claims abstract description 34
- 229910001925 ruthenium oxide Inorganic materials 0.000 claims abstract description 33
- BPUBBGLMJRNUCC-UHFFFAOYSA-N oxygen(2-);tantalum(5+) Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ta+5].[Ta+5] BPUBBGLMJRNUCC-UHFFFAOYSA-N 0.000 claims abstract description 22
- 229910001936 tantalum oxide Inorganic materials 0.000 claims abstract description 21
- 229910052698 phosphorus Inorganic materials 0.000 claims description 70
- 239000011574 phosphorus Substances 0.000 claims description 70
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 68
- 238000005259 measurement Methods 0.000 claims description 34
- 239000000758 substrate Substances 0.000 claims description 29
- KJTLSVCANCCWHF-UHFFFAOYSA-N Ruthenium Chemical compound [Ru] KJTLSVCANCCWHF-UHFFFAOYSA-N 0.000 claims description 19
- 229910052707 ruthenium Inorganic materials 0.000 claims description 19
- 229910052715 tantalum Inorganic materials 0.000 claims description 17
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 claims description 17
- 238000004445 quantitative analysis Methods 0.000 claims description 9
- 238000004364 calculation method Methods 0.000 claims description 3
- 230000035945 sensitivity Effects 0.000 abstract description 42
- 239000000523 sample Substances 0.000 description 72
- 239000000243 solution Substances 0.000 description 29
- 230000000694 effects Effects 0.000 description 27
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 23
- RTAQQCXQSZGOHL-UHFFFAOYSA-N Titanium Chemical compound [Ti] RTAQQCXQSZGOHL-UHFFFAOYSA-N 0.000 description 19
- 239000010936 titanium Substances 0.000 description 19
- 229910052719 titanium Inorganic materials 0.000 description 19
- HTXDPTMKBJXEOW-UHFFFAOYSA-N dioxoiridium Chemical compound O=[Ir]=O HTXDPTMKBJXEOW-UHFFFAOYSA-N 0.000 description 18
- 230000007613 environmental effect Effects 0.000 description 17
- 238000006722 reduction reaction Methods 0.000 description 12
- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 10
- 230000001590 oxidative effect Effects 0.000 description 10
- -1 phosphorus compound Chemical class 0.000 description 10
- 230000009467 reduction Effects 0.000 description 10
- 229910052751 metal Inorganic materials 0.000 description 9
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 8
- 239000002184 metal Substances 0.000 description 8
- 229910052760 oxygen Inorganic materials 0.000 description 8
- 239000001301 oxygen Substances 0.000 description 8
- 239000003637 basic solution Substances 0.000 description 7
- 239000011248 coating agent Substances 0.000 description 7
- 238000000576 coating method Methods 0.000 description 7
- 230000007423 decrease Effects 0.000 description 7
- NBIIXXVUZAFLBC-UHFFFAOYSA-M dihydrogenphosphate Chemical compound OP(O)([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-M 0.000 description 7
- 239000000203 mixture Substances 0.000 description 7
- 238000005979 thermal decomposition reaction Methods 0.000 description 7
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 6
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 6
- 239000003153 chemical reaction reagent Substances 0.000 description 6
- 150000001875 compounds Chemical group 0.000 description 6
- 238000002484 cyclic voltammetry Methods 0.000 description 6
- BHEPBYXIRTUNPN-UHFFFAOYSA-N hydridophosphorus(.) (triplet) Chemical compound [PH] BHEPBYXIRTUNPN-UHFFFAOYSA-N 0.000 description 6
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Chemical compound [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 6
- 239000000126 substance Substances 0.000 description 6
- 239000002351 wastewater Substances 0.000 description 6
- 238000002441 X-ray diffraction Methods 0.000 description 5
- 230000009471 action Effects 0.000 description 5
- 239000007864 aqueous solution Substances 0.000 description 5
- 238000004040 coloring Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
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- 229920003023 plastic Polymers 0.000 description 5
- 229910052709 silver Inorganic materials 0.000 description 5
- 239000004332 silver Substances 0.000 description 5
- VEXZGXHMUGYJMC-UHFFFAOYSA-M Chloride anion Chemical compound [Cl-] VEXZGXHMUGYJMC-UHFFFAOYSA-M 0.000 description 4
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 4
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 4
- 150000001450 anions Chemical class 0.000 description 4
- 239000002585 base Substances 0.000 description 4
- 239000012482 calibration solution Substances 0.000 description 4
- 230000003197 catalytic effect Effects 0.000 description 4
- 150000001768 cations Chemical class 0.000 description 4
- 229910003460 diamond Inorganic materials 0.000 description 4
- 239000010432 diamond Substances 0.000 description 4
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 4
- 239000007772 electrode material Substances 0.000 description 4
- 239000007788 liquid Substances 0.000 description 4
- 239000001103 potassium chloride Substances 0.000 description 4
- 235000011164 potassium chloride Nutrition 0.000 description 4
- 239000002243 precursor Substances 0.000 description 4
- 229910019142 PO4 Inorganic materials 0.000 description 3
- 238000002835 absorbance Methods 0.000 description 3
- 238000011088 calibration curve Methods 0.000 description 3
- 238000006243 chemical reaction Methods 0.000 description 3
- GTKRFUAGOKINCA-UHFFFAOYSA-M chlorosilver;silver Chemical compound [Ag].[Ag]Cl GTKRFUAGOKINCA-UHFFFAOYSA-M 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
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- 150000002739 metals Chemical class 0.000 description 3
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- 125000005461 organic phosphorous group Chemical group 0.000 description 3
- 239000010452 phosphate Substances 0.000 description 3
- 229940085991 phosphate ion Drugs 0.000 description 3
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- 239000010865 sewage Substances 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 description 2
- XMWRBQBLMFGWIX-UHFFFAOYSA-N C60 fullerene Chemical compound C12=C3C(C4=C56)=C7C8=C5C5=C9C%10=C6C6=C4C1=C1C4=C6C6=C%10C%10=C9C9=C%11C5=C8C5=C8C7=C3C3=C7C2=C1C1=C2C4=C6C4=C%10C6=C9C9=C%11C5=C5C8=C3C3=C7C1=C1C2=C4C6=C2C9=C5C3=C12 XMWRBQBLMFGWIX-UHFFFAOYSA-N 0.000 description 2
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- ZOKXTWBITQBERF-UHFFFAOYSA-N Molybdenum Chemical compound [Mo] ZOKXTWBITQBERF-UHFFFAOYSA-N 0.000 description 2
- 238000005481 NMR spectroscopy Methods 0.000 description 2
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 2
- 238000004833 X-ray photoelectron spectroscopy Methods 0.000 description 2
- 238000010521 absorption reaction Methods 0.000 description 2
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- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 2
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 2
- 238000004458 analytical method Methods 0.000 description 2
- 238000003491 array Methods 0.000 description 2
- 125000003118 aryl group Chemical group 0.000 description 2
- WPYMKLBDIGXBTP-UHFFFAOYSA-N benzoic acid Chemical compound OC(=O)C1=CC=CC=C1 WPYMKLBDIGXBTP-UHFFFAOYSA-N 0.000 description 2
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- 239000001257 hydrogen Substances 0.000 description 2
- 229910052739 hydrogen Inorganic materials 0.000 description 2
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- 238000004255 ion exchange chromatography Methods 0.000 description 2
- 229910052741 iridium Inorganic materials 0.000 description 2
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- 244000144972 livestock Species 0.000 description 2
- RPZHFKHTXCZXQV-UHFFFAOYSA-N mercury(i) oxide Chemical compound O1[Hg][Hg]1 RPZHFKHTXCZXQV-UHFFFAOYSA-N 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
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- 235000006408 oxalic acid Nutrition 0.000 description 2
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- QVLTXCYWHPZMCA-UHFFFAOYSA-N po4-po4 Chemical compound OP(O)(O)=O.OP(O)(O)=O QVLTXCYWHPZMCA-UHFFFAOYSA-N 0.000 description 2
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- OEIMLTQPLAGXMX-UHFFFAOYSA-I tantalum(v) chloride Chemical compound Cl[Ta](Cl)(Cl)(Cl)Cl OEIMLTQPLAGXMX-UHFFFAOYSA-I 0.000 description 2
- 239000003643 water by type Substances 0.000 description 2
- 238000003911 water pollution Methods 0.000 description 2
- NWUYHJFMYQTDRP-UHFFFAOYSA-N 1,2-bis(ethenyl)benzene;1-ethenyl-2-ethylbenzene;styrene Chemical compound C=CC1=CC=CC=C1.CCC1=CC=CC=C1C=C.C=CC1=CC=CC=C1C=C NWUYHJFMYQTDRP-UHFFFAOYSA-N 0.000 description 1
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- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- MNXRHPOFECQNIX-UHFFFAOYSA-K O.O.O.O.O.O.Cl(=O)(=O)[O-].[Ir+3].Cl(=O)(=O)[O-].Cl(=O)(=O)[O-] Chemical compound O.O.O.O.O.O.Cl(=O)(=O)[O-].[Ir+3].Cl(=O)(=O)[O-].Cl(=O)(=O)[O-] MNXRHPOFECQNIX-UHFFFAOYSA-K 0.000 description 1
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- XPPKVPWEQAFLFU-UHFFFAOYSA-N diphosphoric acid Chemical compound OP(O)(=O)OP(O)(O)=O XPPKVPWEQAFLFU-UHFFFAOYSA-N 0.000 description 1
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- 150000002222 fluorine compounds Chemical class 0.000 description 1
- 238000010438 heat treatment Methods 0.000 description 1
- GPRLSGONYQIRFK-UHFFFAOYSA-N hydron Chemical compound [H+] GPRLSGONYQIRFK-UHFFFAOYSA-N 0.000 description 1
- 201000005991 hyperphosphatemia Diseases 0.000 description 1
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- 229910010272 inorganic material Inorganic materials 0.000 description 1
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- 229920003303 ion-exchange polymer Polymers 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 1
- VLAPMBHFAWRUQP-UHFFFAOYSA-L molybdic acid Chemical compound O[Mo](O)(=O)=O VLAPMBHFAWRUQP-UHFFFAOYSA-L 0.000 description 1
- 230000007935 neutral effect Effects 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 238000001225 nuclear magnetic resonance method Methods 0.000 description 1
- 239000002773 nucleotide Substances 0.000 description 1
- 125000003729 nucleotide group Chemical group 0.000 description 1
- 235000015097 nutrients Nutrition 0.000 description 1
- 239000011368 organic material Substances 0.000 description 1
- 150000002903 organophosphorus compounds Chemical class 0.000 description 1
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- 238000009304 pastoral farming Methods 0.000 description 1
- 239000000575 pesticide Substances 0.000 description 1
- 239000008055 phosphate buffer solution Substances 0.000 description 1
- 150000003904 phospholipids Chemical class 0.000 description 1
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- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- USHAGKDGDHPEEY-UHFFFAOYSA-L potassium persulfate Chemical compound [K+].[K+].[O-]S(=O)(=O)OOS([O-])(=O)=O USHAGKDGDHPEEY-UHFFFAOYSA-L 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 229940005657 pyrophosphoric acid Drugs 0.000 description 1
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- BIXNGBXQRRXPLM-UHFFFAOYSA-K ruthenium(3+);trichloride;hydrate Chemical compound O.Cl[Ru](Cl)Cl BIXNGBXQRRXPLM-UHFFFAOYSA-K 0.000 description 1
- 229920006395 saturated elastomer Polymers 0.000 description 1
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- ISIJQEHRDSCQIU-UHFFFAOYSA-N tert-butyl 2,7-diazaspiro[4.5]decane-7-carboxylate Chemical compound C1N(C(=O)OC(C)(C)C)CCCC11CNCC1 ISIJQEHRDSCQIU-UHFFFAOYSA-N 0.000 description 1
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- ZTWIEIFKPFJRLV-UHFFFAOYSA-K trichlororuthenium;trihydrate Chemical compound O.O.O.Cl[Ru](Cl)Cl ZTWIEIFKPFJRLV-UHFFFAOYSA-K 0.000 description 1
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Images
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4166—Systems measuring a particular property of an electrolyte
- G01N27/4168—Oxidation-reduction potential, e.g. for chlorination of water
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/28—Electrolytic cell components
- G01N27/30—Electrodes, e.g. test electrodes; Half-cells
- G01N27/333—Ion-selective electrodes or membranes
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4166—Systems measuring a particular property of an electrolyte
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
- G01N27/416—Systems
- G01N27/4166—Systems measuring a particular property of an electrolyte
- G01N27/4167—Systems measuring a particular property of an electrolyte pH
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
- G01N33/18—Water
- G01N33/182—Specific anions in water
Definitions
- the present invention relates to an ion sensor catalyst for quantifying hydrogen phosphate ions in water, an ion sensor for quantifying hydrogen phosphate ions using the ion sensor catalyst, and phosphoric acid using the ion sensor catalyst.
- the present invention relates to a quantitative method for quantifying hydrogen ion concentration and / or total phosphorus concentration.
- Phosphorus is present in rocks and is also found in all animals and plants and their excreta. Phosphorus is also contained in fertilizers, pesticides, synthetic detergents, etc.
- the increase in phosphorus in environmental water is due to household wastewater, human waste, domestic wastewater, factory wastewater, agricultural wastewater, It is often derived from contamination of livestock wastewater.
- phosphorus is hardly removed, and discharged water from human waste treatment plants and sewage treatment plants may cause an increase in phosphorus in environmental water.
- Phosphorus is one of the nutrients of living organisms, but if the concentration of phosphorus increases, it promotes eutrophication of rivers, lakes, marine areas, fishery water, etc., resulting in environmental problems such as large quantities of plankton and red tides . Therefore, the concentration of phosphorus contained in environmental water, factory effluent, agricultural effluent, domestic effluent, domestic effluent, livestock effluent, wastewater treatment water, aquaculture water, human waste, effluent from sewage treatment plants, etc. It is important and necessary in terms of environmental conservation. On the other hand, phosphorus exists as various phosphate esters including phosphate ions, DNA, and RNA. Phosphorus compounds are important regulators of biological systems.
- ATP and DNA essential for biological energy metabolism are made up of nucleotides that contain phosphate as part of the molecule.
- the amount of phosphoric acid obtained from is greatly restricted.
- the phosphorus concentration in the blood is also important, and the reference range of adult plasma inorganic PO 4 concentration is 2.5-4.5 mg / dL, below which is called hypophosphatemia, It may cause muscle weakness, respiratory failure, heart failure, convulsions and coma, and when it is high, it is called hyperphosphatemia, which is caused by chronic renal failure, hypoparathyroidism, and the like.
- the form of the phosphorus compound is classified into an inorganic state and an organic state, and the inorganic phosphorus is further classified into orthophosphoric phosphorus and polymerized phosphorous phosphorus.
- the presence of orthophosphoric phosphorus present in water changes depending on the pH, phosphorous acid H 3 PO 3 (pH is 2 or less), dihydrogen phosphate ion H 2 PO 4 ⁇ (pH is 2 to 7), Hydrogen phosphate ions HPO 4 2 ⁇ (pH is 7 to 12) and phosphate ions PO 4 3 ⁇ (pH is 12 or more) are the main forms in each pH region.
- Polymerized phosphorous phosphorus includes pyrophosphoric acid (P 2 O 7 4 ⁇ ) and the like, and these are changed to hydrogen phosphate ions by hydrolysis or the like.
- organic phosphorus includes various phosphorus-containing organic compounds such as esters and phospholipids.
- tripolyphosphates and sewage treatment agents contained in synthetic detergents are also examples of organic phosphorus.
- the phosphorus concentration here is a phosphorus concentration generally defined as “total phosphorus”, which is a strong acid or other oxidizing agent, hydrolysis, etc. Is the weight of phosphorus contained in 1 L of sample water obtained by a predetermined method after all are decomposed to orthophosphoric phosphorus, and is usually displayed in units of mg / L.
- organic phosphorous or polymerized phosphorous phosphorus in the sample water is decomposed with potassium peroxodisulfate or nitric acid and sulfuric acid, and all are converted to orthophosphoric phosphorus.
- a step of reacting phosphate ions and molybdic acid, adding a reducing agent such as ascorbic acid to produce molybdenum blue and coloring, and using an absorptiometer A step of measuring absorbance is required.
- the determination of the concentration of orthophosphoric phosphorus alone is not the chemical treatment as described above, but the pH of the sample water is adjusted to the pH range in which phosphate ions are present, and the molybdenum blue method and the absorptiometric method are combined.
- the quantification of total phosphorus and phosphate ions described above is also defined in JIS K 0102.
- Patent Document 1 and (Patent Document 2) disclose methods for measuring the concentration of phosphate ions.
- phosphate ions in a sample water are reacted with a plurality of reagents.
- This is a method similar to that defined in the above-mentioned JIS, in which the absorbance or transmittance is measured after coloring or coloring.
- the environmental standards and drainage standards set the concentration of “total phosphorus”, and there are no environmental standards and drainage standards for orthophosphoric phosphorus.
- orthophosphoric phosphorus is present as PO 4 3 ⁇ by adjusting the pH of the sample water, and all of organic phosphorous and orthophosphoric phosphorus (inorganic phosphorous) are PO 4. It is measured in the form of 3- . Therefore, the concentration of orthophosphoric phosphorus in the environment is not determined for each existing form, and a method for determining the concentration for each existing form has not been developed.
- organic phosphorus compounds are listed as harmful items of the wastewater standards of the Water Pollution Control Law, and the allowable limit is 1 mg / L, and the specific underground seepage water contains harmful substances.
- the concentration of phosphorus is set at 0.1 mg / L, and the specific underground seepage water corresponding to this is not allowed to penetrate underground.
- the concentration limit of the total phosphorus concentration of 16 mg / L (daily average of 8 mg / L) is set as the allowable limit.
- the standard in the living environment item is applied to the effluent discharged into the lakes and marshes and the public waters into which these inflows are established.
- the environmental standard is “a standard that is desirable to maintain in order to protect health and preserve the living environment”, and is set to a value lower than the drainage standard.
- the current total phosphorus and phosphate ions are quantified by chemical treatment of the sample water, changing all the phosphorus to the form of phosphate ions, and then coloring and spectroscopic analysis of the phosphate ions. Or, after separating phosphate ions by ion chromatography, it is a method to measure the electrical conductivity of a solution containing phosphate ions or to measure ultraviolet absorption, and the work is complicated and the treatment of sample water It took time until the final concentration was determined. In addition, in these methods, since all phosphorus is changed to PO 4 3 ⁇ , there is no means for separately measuring the concentration of other orthophosphoric phosphorus.
- Patent Document 3 a solution containing at least one compound selected from an aromatic acid and / or an aromatic derivative and hydrogen phosphate ion is brought into contact with the solution.
- This hydrogen phosphate ion sensor and its quantification method are used not only for the concentration of phosphorus in the environment as described above, but also for in vivo signal transduction systems through various phosphorylated proteins and phospholipid phosphate groups.
- Patent Document 3 Since transmission is controlled, it is also intended to be applied to a sensing system for detecting such hydrogen phosphate ions in a living body.
- Patent Document 3 also requires a large analytical instrument such as a spectroscopic method or a nuclear magnetic resonance method, takes time to measure, and uses an analytical reagent such as an aromatic acid or aromatic derivative. It was what I needed. That is, the conventional techniques described so far are not methods that can directly detect only the target ions in either case of phosphate ions (PO 4 3 ⁇ ) or hydrogen phosphate ions (HPO 4 2 ⁇ ). It was.
- Patent Document 5 when the phosphate ion is reacted with the phosphate ion in the presence of an oxidoreductase that catalyzes the reaction for producing the oxide with a substrate that becomes an oxide, There has been disclosed a qualitative and quantitative method for phosphate ions, characterized by measuring a current generated by further oxidizing a reduced mediator produced by the coexistence of an oxidized mediator. Furthermore, (Non-Patent Document 1) describes indirect from the current that flows by oxidizing the hydrogen peroxide (H 2 O 2 ) generated on the electrode by reacting phosphate ions in a multistage enzymatic reaction. Discloses a method for quantifying the concentration of phosphate ions.
- H 2 O 2 hydrogen peroxide
- Non-patent Document 2 In addition to phosphate ions, methods for electrochemically detecting hydrogen phosphate ion concentrations are disclosed in (Non-patent Document 2) to (Non-patent Document 4). In these methods, hydrogen phosphate ions are quantified from the obtained oxidation current or impedance by measuring the oxidation current or impedance of the electrode that varies depending on the concentration of hydrogen phosphate ions in the sample water.
- a catalyst for a detection electrode for electrochemically detecting hydrogen phosphate ions As a catalyst for a detection electrode for electrochemically detecting hydrogen phosphate ions, a perovskite oxide, a spinel oxide, a pyrochlore oxide, etc.
- the inventor of the present invention studied the electrochemical reaction in the sample water containing hydrogen phosphate ions using iridium dioxide (IrO 2 ) as a sensing electrode material. As a result, oxidation of hydrogen phosphate ions on this oxide was performed. It has already been clarified that an electric current is generated and that the concentration of hydrogen phosphate ions and the oxidation current are proportional, and the oxidation current density (current per unit area of the detection electrode) at this time is (Non-Patent Document 2) to (Non-Patent Document) It has been clarified that the time (detection time) until a stable oxidation current is obtained is shorter than the value disclosed in the literature 4) by about 100 to 1000 times in the same concentration range. In the detection electrode using iridium as a catalyst, the concentration range proportional to the oxidation current is narrow (1 mmol / L to 10 mmol / L), and the quantifiable concentration is limited.
- IrO 2 iridium dioxide
- JP 2006-84451 A Japanese Patent Laid-Open No. 2005-99014 Japanese Patent Laid-Open No. 2007-40760 JP 2005-265501 A Republished patent WO2005 / 73399
- any phosphate phosphate ion can be directly quantified electrochemically using a catalyst.
- This method can be applied to cases.
- hydrogen phosphate ions not only hydrogen phosphate ions but also organic phosphorous and inorganic phosphorous, both directly and electrodelessly via an oxidized or reduced mediator, etc. Sensors and quantitative methods based on reaction have not been put into practical use. If hydrogen phosphate ions can be electrochemically quantified, the total phosphorus concentration can be converted to hydrogen phosphate ions by only oxidizing the sample water and adjusting the pH, and then electrochemically oxidized on the catalyst. Thus, it can be obtained directly from the current value.
- the phosphorous concentration of a biological sample can be determined by a similar method without using a large device such as a spectroscopic device or a nuclear magnetic resonance device.
- an ion sensor equipped with a detection electrode using such a catalyst can be miniaturized to the extent that it can be carried, and in a wide range of application fields such as environmental measurement, medical work, various analytical work, etc. Measurement and continuous monitoring can be performed easily.
- the present invention solves the above-mentioned problems, and in an ion sensor catalyst capable of detecting hydrogen phosphate ions in water and determining the hydrogen phosphate ion concentration from the oxidation current density, the detection sensitivity is higher than before, and High detection sensitivity can be maintained in a wide concentration range of hydrogen phosphate ions, and since the proportional relationship holds between the concentration and the oxidation current density, the concentration can be accurately determined regardless of the concentration range, and the oxidation current can be reduced.
- the time to reach a steady value in a short time and the time to determine the current density is short. Therefore, the time for quantifying hydrogen phosphate ions is short, and it is inexpensive to repeatedly and stably respond to the oxidation of hydrogen phosphate ions.
- An ion sensor for measuring hydrogen phosphate ions that can be quantified, is portable and can be mass-produced at low cost, and has excellent measurement stability and reproducibility, and all phosphorus and hydrogen phosphate ions using this ion sensor It is to provide a highly sensitive and highly reproducible quantitative method.
- the catalyst for an ion sensor of the present invention is a catalyst that electrochemically oxidizes hydrogen phosphate ions in water, and includes a mixed oxide of ruthenium oxide and tantalum oxide.
- a mixed oxide of ruthenium oxide and tantalum oxide shows high catalytic activity selectively in a wide concentration range of hydrogen phosphate ions with respect to electrochemical oxidation of hydrogen phosphate ions in water, and is high It has the effect of producing an oxidation current density.
- the ion sensor catalyst of the present invention can detect hydrogen phosphate ions with higher detection sensitivity than other catalysts, and determine the concentration thereof.
- the time to determine the density is short, so the time for quantifying hydrogen phosphate ions is short, and it is possible to repeatedly and stably respond to the oxidation of hydrogen phosphate ions, and the stability and reproducibility of the measurement. It has the effect of being excellent in.
- the catalyst for ion sensors of the present invention has high detection sensitivity, and the concentration range that can be quantified is very wide compared to iridium dioxide. It has the effect of being excellent in accuracy and reliability.
- Ruthenium is about 1/10 the price of iridium, and tantalum is about 1/10 the price of ruthenium. Sensitivity and quantification of hydrogen phosphate ions in a wide concentration range can be made possible, and the effects of resource saving, practicality, and measurement stability are excellent.
- the catalyst of the present invention does not cause oxidation of other anions and cations such as dihydrogen phosphate ions and chloride ions, only hydrogen phosphate ions are selectively detected and The concentration can be determined, and it has the effect of having excellent measurement reliability and reliability.
- the catalyst for an ion sensor of the present invention (hereinafter referred to as the catalyst of the present invention) can be synthesized and used by the following method.
- the catalyst of the present invention is for oxidizing hydrogen phosphate ions and detecting the oxidation current, and needs to be connected to a conductive part for outputting the detected current to the outside. If the catalyst of the present invention is formed on a conductive substrate, it can be used as a detection electrode having the conductive substrate as a conductive portion for external output of current.
- a conductive part may be formed on a part of the insulating substrate, and the catalyst of the present invention may be formed on a part of the conductive part, and this may be used as a detection electrode.
- At least another electrode that causes some reduction is required in addition to the above-described detection electrode on which the catalyst of the present invention is formed.
- a reference electrode is required to control the detection electrode potential.
- the detection electrode and the counter electrode, or the detection electrode, the counter electrode, and the reference electrode must be structured so that the electrodes do not conduct each other on the same conductive substrate.
- the conductive part and the counter electrode, or the counter electrode and the reference electrode, in which the catalyst of the present invention is formed are electrically insulated, so that the detection electrode and the counter electrode or the detection electrode on the same insulating substrate. It is possible to form a pole, a counter electrode, and a reference electrode.
- various materials having conductivity such as metals, alloys, various carbon materials (including conductive diamond, graphene, fullerene, etc.), conductive plastics, conductive oxides, etc.
- a metal paste containing a compound, silver or the like can be used, but is not limited thereto.
- various insulating oxides such as alumina, carbides, nitrides, and organic materials such as diamond, DLC (diamond-like carbon), silicon, plastics and resins can be used. It is not limited to.
- These conductive parts, conductive bases, and insulating bases are plate-like, net-like, rod-like, sheet-like, tubular, wire-like, spiral-like, perforated-plate-like, porous-like, true-spherical, cage-like, or bonded particles.
- Various shapes such as a three-dimensional porous body can be taken.
- Carbon fibers, carbon nanotubes, carbon fiber arrays in which these are regularly arranged, carbon nanotube arrays, and the like can also be used as the conductive portion and the conductive substrate.
- the catalyst unit of the present invention may be obtained by supporting or mixing the catalyst of the present invention or the catalyst carrier carrying the catalyst of the present invention on the conductive part or conductive substrate of various shapes as described above. You may devise so that the surface area per mass may increase.
- a precursor solution containing ruthenium and tantalum is applied on the conductive substrate or conductive portion, and then a predetermined temperature is applied.
- the catalyst of the present invention is synthesized in advance by various physical vapor deposition methods such as sputtering method and CVD method and methods directly formed by chemical vapor deposition method, sol-gel method and other precursor firing methods, It is possible to use various methods such as coating, baking, bonding, welding, and adsorption on the conductive substrate or conductive portion.
- a method of forming the catalyst of the present invention on a titanium plate which is an example of a conductive substrate by a thermal decomposition method will be described.
- various forms such as an inorganic compound, an organic compound, an ion, and a complex may be used.
- a precursor solution in which ruthenium and tantalum are dissolved is applied onto a titanium plate and thermally decomposed at 200 to 600 ° C., the titanium plate A mixed oxide composed of ruthenium oxide and tantalum oxide is formed thereon.
- a butanol solution in which ruthenium trichloride hydrate and tantalum pentachloride are dissolved is used as a precursor solution, which is applied to a titanium plate and thermally decomposed.
- the range of a suitable molar ratio of ruthenium and tantalum can be appropriately selected depending on the thermal decomposition temperature or the like.
- the conductivity of the catalyst itself of the present invention tends to decrease, and the detected oxidation current tends to decrease.
- the ratio of tantalum to the total amount of tantalum is smaller than 1%, the high catalytic activity for hydrogen phosphate ions exhibited by mixing ruthenium oxide with tantalum oxide tends to be lost, both of which are preferable. Absent.
- tantalum oxide is amorphous, but ruthenium oxide is amorphous, crystalline, or amorphous depending on the pyrolysis temperature. It will be in a crystalline mixed state.
- the ruthenium oxide may have any crystal structure. Such a difference in crystal structure can be relatively determined from the intensity of the ruthenium oxide diffraction line obtained by the X-ray diffraction method. When the ruthenium oxide crystallinity decreases, the intensity of the diffraction line decreases. When completely amorphous, the diffraction line disappears.
- the tantalum oxide is amorphous.
- the tantalum oxide may be crystalline.
- the examples of the thermal decomposition method described above are not limited to the use of butanol solvent, the molar ratio of ruthenium and tantalum and the range of the thermal decomposition temperature related thereto, the above conditions are only examples,
- the method for obtaining the catalyst of the present invention is not particularly limited as long as a mixed oxide of ruthenium oxide and tantalum oxide can be obtained by any method other than those described above.
- the molar ratio of ruthenium to tantalum in the mixed oxide is preferably 30:70 to 80:20. With this configuration, the following effects can be further obtained. (1) Since the molar ratio of ruthenium and tantalum in the mixed oxide is 30:70 to 80:20, it has an effect that a particularly high catalytic activity can be obtained in a wide concentration range for hydrogen phosphate ions.
- the proportion of ruthenium becomes smaller than 30%, the conductivity of the mixed oxide tends to decrease, and the oxidation current density with respect to hydrogen phosphate ions tends to decrease, and the proportion of ruthenium becomes larger than 80%. As a result, the effect of mixing with tantalum oxide becomes difficult to obtain, and the oxidation current density with respect to hydrogen phosphate ions tends to be small.
- the mixed oxide further contains amorphous ruthenium oxide.
- the reaction surface area of the catalyst is increased as compared with the case where the ruthenium oxide is all crystalline, thereby oxidizing the hydrogen phosphate ions at the same concentration.
- the detection sensitivity increases, and the concentration range that can be quantified becomes wider.
- such a difference in crystal structure can be relatively judged from the intensity of the ruthenium oxide diffraction line obtained by the X-ray diffraction method.
- the intensity of the diffraction line with respect to ruthenium oxide decreases.
- the ruthenium oxide contained in the mixed oxide is all amorphous or the mixed oxide is composed of amorphous ruthenium oxide and tantalum oxide, the diffraction line for ruthenium oxide disappears.
- the ion sensor of the present invention is an ion sensor for quantifying hydrogen phosphate ions in water, and includes a detection electrode using the ion sensor catalyst.
- a catalyst for an ion sensor containing a mixed oxide of ruthenium oxide and tantalum oxide as a detection electrode, the concentration of hydrogen phosphate ions is determined by determining the concentration of hydrogen phosphate ions from the current flowing when oxidizing the hydrogen phosphate ions. It has the effect that it becomes possible to quantify hydrogen phosphate ions selectively and accurately in a short time with a detection sensitivity and over a wide concentration range.
- the operation of the ion sensor of the present invention does not require a large device or high power, and the ion sensor can be downsized to a portable size, and is excellent in energy saving, compactness, and practicality. Has an effect.
- the catalyst for the ion sensor and other parts necessary for the ion sensor of the present invention can be manufactured at low cost, has excellent resource saving and mass productivity, and is stable against the measurement of hydrogen phosphate ion concentration. In addition, it has the effect of allowing quantification with excellent reproducibility.
- the ion sensor of the present invention selectively detects only hydrogen phosphate ions because it does not oxidize other anions and cations such as dihydrogen phosphate ions and chloride ions on the detection pole. In addition, the concentration can be determined, and the reliability and reliability of measurement are excellent.
- the ion sensor detects a detection unit that detects an oxidation current of hydrogen phosphate ions, and a detection electrode and a counter electrode arranged in the detection unit, or a detection electrode, a counter electrode, and a reference electrode. Apply a predetermined voltage between the counter electrode and the counter electrode, or apply a predetermined potential to the detection electrode with respect to the reference electrode at the detection electrode, the counter electrode, and the reference electrode, and measure the oxidation current generated at the detection electrode, and then calculate A control unit for finally calculating the hydrogen phosphate ion concentration and displaying the calculation result is provided.
- control unit applies a predetermined voltage between the detection electrode and the counter electrode, or a function of applying a predetermined potential to the detection electrode with respect to the reference electrode in the detection electrode, the counter electrode, and the reference electrode, and a current generated in the detection electrode. At least it is necessary to have a function to measure, but as described above, it is possible to add various configurations and functions used in existing chemical sensors and electrochemical sensors as described above. . Therefore, here, the configuration and function of the detection unit in the ion sensor of the present invention will be further described.
- the detection unit has either a detection electrode and a counter electrode, or a detection electrode, a counter electrode, and a reference electrode.
- the electrodes may be individually disposed, or may be integrally disposed on the same insulating substrate without electrical contact.
- the detection electrode has the material and configuration as described above together with the catalyst of the present invention, oxidizes hydrogen phosphate ions, and causes the generated oxidation current to flow to the control unit. Although some reduction reaction occurs at the counter electrode, the reduction of water is generally known as the reduction reaction occurring in the sample water.
- the counter electrode material includes platinum, silver, other metals, conductive compounds such as conductive oxides, various materials used as electrochemical sensors and other electrode materials such as conductive plastics, and the present invention.
- a material capable of causing an electrode reaction such that the reduction product does not react rapidly with hydrogen phosphate ions for example, when platinum or silver is used, the reduction of water as described above occurs.
- a voltage suitable for causing an oxidation reaction of hydrogen phosphate ions at the detection electrode is applied between the detection electrode and the counter electrode by the control unit.
- the waveform of the voltage to be applied may be a constant voltage or a voltage waveform that changes over time.
- Such a voltage waveform may be, for example, a rectangular voltage pulse or a voltage voltage that changes stepwise.
- it is desirable that the oxidation current of hydrogen phosphate ions is measured in a state in which a voltage that maximizes the oxidation current is applied.
- the polarity of the voltage applied between the detection electrode and the counter electrode is reversed.
- a voltage waveform that prevents such an inhibitory effect may be applied by setting the voltage so that hydrogen phosphate ions are not oxidized temporarily at the detection electrode.
- Such a method of periodically inverting the voltage and necessary circuits are generally known in the electrochemical field such as electrochemical sensors, electroplating, industrial electrolysis, and batteries.
- a potential suitable for causing an oxidation reaction of hydrogen phosphate ions at the detection electrode is applied to the reference electrode by the control unit.
- the in electrochemical terms the potential difference between two electrodes is generally called a voltage, but when the potential difference from the target electrode is defined using a reference electrode that does not change its own potential, such as a reference electrode. Is expressed as a potential rather than a voltage.
- the reference electrode generally known reference electrodes such as a silver-silver chloride electrode and a mercury-mercury oxide electrode can be used.
- the waveform of the applied potential may be a constant potential or a potential waveform that changes with time.
- a potential waveform may be, for example, a rectangular potential pulse or a waveform that changes the potential stepwise.
- it is desirable that the oxidation current of hydrogen phosphate ions is measured in a state where a potential that maximizes the oxidation current is applied.
- the potential of the detection electrode relative to the reference electrode is changed to the natural potential ( It is also possible to apply a potential waveform that prevents such an inhibitory effect by making the value lower than the immersion potential and temporarily preventing oxidation of hydrogen phosphate ions at the detection electrode.
- Such a method of periodically changing the potential and necessary circuits are generally known in the electrochemical field such as electrochemical sensors, electroplating, industrial electrolysis, and batteries.
- the flow injection method can be used to generate an oxidation current under the condition that the sample water is sent to the detector, or the detector can be immersed in the sample water while flowing the sample water in a fixed volume container with stirring. Alternatively, a method of generating an oxidation current in such a state may be used.
- a basic solution containing a component that does not interfere with the oxidation of hydrogen phosphate ions and having a conductivity sufficient to measure the oxidation current is prepared, and a predetermined amount of sample water is added thereto. May be the target for measurement. Before measuring the sample water, obtain the relationship between the hydrogen phosphate ion concentration and the detected oxidation current using two or three calibration solutions with known concentrations in advance.
- the hydrogen phosphate ion concentration can be determined by a standard addition method for obtaining the ion concentration.
- the ion sensor of the present invention further has a function of measuring the pH and / or temperature of sample water containing hydrogen phosphate ions.
- the pH and / or temperature of sample water containing hydrogen phosphate ions as well as hydrogen phosphate ions can be measured simultaneously.
- characteristic values of sample water such as pH and temperature can be obtained simultaneously with the hydrogen phosphate ion concentration.
- the quantification method of the present invention is a quantification method for determining the concentration of hydrogen phosphate ions or total phosphorus in water, and using the ion sensor catalyst as a detection electrode, the hydrogen phosphate ions in the water
- (1) By using a catalyst for an ion sensor containing a mixed oxide of ruthenium oxide and tantalum oxide, the concentration of hydrogen phosphate ions can be selectively determined from the current that flows when oxidizing the hydrogen phosphate ions.
- the concentration of hydrogen ions or total phosphorus can be quantified with high detection sensitivity and over a wide concentration range in a short time with high accuracy.
- the ion sensor used in the quantification method of the present invention does not require a large device or electric power to operate, it can be downsized to a portable size, and when used on the spot or at the time of measurement It can be quantified in various situations such as when movement is required, and has the effect of being excellent in versatility, handleability, functionality, and mass productivity.
- the ion sensor catalyst and other components necessary for the ion sensor used in the quantification method of the present invention are inexpensive, and it is not necessary to use a specific solvent or reagent as in the prior art.
- Quantification with excellent reproducibility is possible, and it has the effects of excellent resource saving and practicality.
- oxidation of other anions and cations such as dihydrogen phosphate ions and chloride ions does not occur on the detection pole, so that only hydrogen phosphate ions are selectively detected. Therefore, the concentration can be determined, and the reliability and reliability of measurement are excellent.
- the pH of the sample water is first adjusted to a pH at which hydrogen phosphate ions are present, or if the sample water itself is in such a pH range, Using water as it is, hydrogen phosphate ions are oxidized at the detection electrode using the catalyst of the present invention, and the hydrogen phosphate ion concentration is determined from the current.
- the configuration of the detection electrode necessary at this time and the ion sensor including the same and the method for determining the hydrogen phosphate ion concentration using the same are the same as those described above.
- the pH can be easily adjusted by adding an alkaline compound or a solution thereof, or using a buffer solution. However, the phosphate buffer solution itself contains hydrogen phosphate ions. It is better not to use it.
- the pH is adjusted and all phosphorus is converted to hydrogen phosphate ions.
- the hydrogen phosphate ion concentration can be determined by the method described above, and this can be used as the total phosphorus concentration. According to the quantification method of the present invention, the concentration of hydrogen phosphate ions or total phosphorus can be determined only by the difference in whether or not the sample water is pretreated.
- a solution containing hydrogen phosphate ions flows around the detection electrode or is sent to the detection electrode.
- the following effects can be further obtained.
- (1) When a solution containing hydrogen phosphate ions flows around the detection electrode or is sent to the detection electrode, convection and diffusion are promoted, and these are not performed for the same concentration of hydrogen phosphate ions. Compared to this, the oxidation current density is increased, so that the detection sensitivity is further improved.
- the oxidation reaction at the detection electrode is promoted, the time until a stable current is observed is shortened, and the time required for measurement is further shortened.
- the solution containing hydrogen phosphate ions is not only sample water itself such as environmental water and biological fluid, but also a test solution in which these are added to a basic solution suitable for measurement.
- a basic solution is usually an aqueous solution, and examples thereof include, but are not limited to, an aqueous potassium chloride solution.
- hydrogen phosphate ions have a buffering action with dihydrogen phosphate ions or phosphate ions
- an aqueous solution containing dihydrogen phosphate ions or phosphate ions is not preferable as a basic solution.
- a solution containing hydrogen phosphate ions from the direction perpendicular to the detection electrode.
- the following effects can be further obtained. (1) Compared with the case where a solution containing hydrogen phosphate ions flows around the detection electrode and the case where the solution is fed in the horizontal direction with respect to the detection electrode, convection and diffusion are further promoted, and hydrogen phosphate having the same concentration This has the effect of increasing the oxidation current density with respect to ions and thus further improving the detection sensitivity.
- the present invention it is possible to accurately determine hydrogen phosphate ions or total phosphorus at a low concentration, or total phosphorus at a high concentration exceeding the discharge standard, in a short time compared to the conventional case. It has the effect. 4) Further, the same ion sensor has an effect that the concentration of both hydrogen phosphate ions and total phosphorus can be easily measured. 5) In addition, the sensitivity to hydrogen phosphate ions is higher than in the past, and the accuracy of quantification is high even in a wide concentration range. In addition, the concentration of hydrogen phosphate ions or total phosphorus can be accurately measured.
- the schematic diagram which shows an example of the ion sensor using the catalyst for ion sensors of this invention
- FIG. 1 is a schematic view showing an ion sensor using an ion sensor catalyst of the present invention.
- 1 is an ion sensor using the catalyst for an ion sensor of the present invention
- 2 is various insulating oxides such as alumina, carbide, nitride, diamond, DLC (diamond-like carbon), silicon, etc.
- the formed insulating substrate 3 is a conductive metal, alloy, various carbon materials (including conductive diamond, graphene, fullerene, etc.), conductive plastic, conductive oxide, etc. on the insulating substrate 2.
- Three conductive portions formed linearly with a metal paste containing a compound, silver, etc., 4 forms an ion sensor catalyst containing a mixed oxide of ruthenium oxide and tantalum oxide at one end of the central conductive portion 3
- the detection electrode 5 is made of platinum, silver, other metals, conductive compounds such as conductive oxides, conductive plastics, etc. at one end of the other conductive part 3.
- Various materials used as electrochemical sensors and other electrode materials, as well as counter electrodes formed using the catalyst of the present invention, 6 is silver-silver chloride at one end of another conductive portion 3
- a reference electrode 7 formed by using an electrode, a mercury-mercury oxide electrode, and the like, is a detection unit including a detection electrode 4, a counter electrode 5, and a reference electrode 6.
- the ion sensor 1 applies a predetermined potential to the detection electrode 4 with respect to the reference electrode 6, measures the oxidation current generated at the detection electrode 4, and finally calculates the hydrogen phosphate ion concentration through arithmetic processing or the like.
- a control unit 8 for calculating and displaying the calculation result is provided.
- the usage method of the ion sensor 1 comprised as mentioned above is demonstrated.
- the detection electrode 4 oxidizes hydrogen phosphate ions and causes the generated oxidation current to flow to the control unit 8 through the conductive unit 3.
- the control unit 8 applies a potential suitable for causing an oxidation reaction of hydrogen phosphate ions at the detection electrode 4 to the reference electrode 6.
- the waveform of the applied potential may be a constant potential or a potential waveform that changes with time.
- Such a potential waveform may be, for example, a rectangular potential pulse or a waveform that changes the potential stepwise.
- the oxidation current of hydrogen phosphate ions is measured in a state where a potential that maximizes the oxidation current is applied.
- the potential of the detection electrode 4 with respect to the reference electrode 6 is set in the sample water.
- the potential potential is lower than the natural potential (also referred to as the immersion potential) of the electrode, and a potential waveform is applied so as to prevent the hydrogen phosphate ion from being oxidized temporarily at the detection electrode 4 so as to prevent such an inhibitory action. May be.
- a predetermined amount of sample water is dropped on the detection unit 7 so that the detection unit 7 is immersed in the sample water and the sample water contacts the detection unit 7.
- the above voltage or potential is applied to generate an oxidation current of hydrogen phosphate ions.
- the sample water is sent to the detection unit 7 by the flow injection method to generate an oxidation current under the condition that the sample water is flowing, or the detection unit 7 is stirred while stirring the sample water in a fixed volume container.
- a method of generating an oxidation current while immersed in sample water may be used.
- a basic solution containing a component that does not interfere with the oxidation of hydrogen phosphate ions and having a conductivity sufficient to measure the oxidation current is prepared, and a predetermined amount of sample water is added thereto. May be the target for measurement. Before measuring the sample water, obtain the relationship between the hydrogen phosphate ion concentration and the detected oxidation current using two or three calibration solutions with known concentrations in advance.
- the hydrogen phosphate ion concentration can be determined by a standard addition method for obtaining the ion concentration.
- each electrode is individually on an insulating substrate or conductive. You may arrange
- the catalyst of the present invention is formed on a conductive substrate, it can be used as a detection electrode having the conductive substrate as a conductive part for external output of current.
- the detection unit 7 may be configured by a detection electrode 4 and a counter electrode 5. In this case, a voltage suitable for causing an oxidation reaction of hydrogen phosphate ions at the detection electrode 4 is applied between the detection electrode 4 and the counter electrode 5 by the control unit 8.
- the concentration of hydrogen phosphate ions is determined by determining the concentration of hydrogen phosphate ions from the current flowing when oxidizing the hydrogen phosphate ions. It has the effect that it becomes possible to quantify hydrogen phosphate ions selectively and accurately in a short time with a detection sensitivity and over a wide concentration range.
- the operation of the ion sensor of the present invention does not require a large device or electric power, and the ion sensor can be miniaturized to a portable size, and is excellent in energy saving, compactness, and practicality.
- the catalyst for the ion sensor and other parts necessary for the ion sensor of the present invention can be manufactured at low cost, excellent in resource saving and mass productivity, and for electrochemical oxidation of hydrogen phosphate ion in water.
- it shows high catalytic activity selectively in a wide concentration range of hydrogen phosphate ions and generates a high oxidation current density, so the concentration can be determined accurately regardless of the concentration range. It has the effect
- the ion sensor of the present invention selectively detects only hydrogen phosphate ions because it does not oxidize other anions and cations such as dihydrogen phosphate ions and chloride ions on the detection pole.
- the concentration can be determined, and the reliability and reliability of measurement are excellent.
- Example 1 A commercially available titanium plate (length 5 cm, width 1 cm, thickness 1 mm) was immersed in a 10% oxalic acid solution at 90 ° C. for 60 minutes for etching treatment, washed with water, and dried. Next, in a butanol (nC 4 H 9 OH) solution containing 6 vol% concentrated hydrochloric acid, the molar ratio of ruthenium and tantalum is 80:20, and the total of ruthenium and tantalum is 70 g / L in terms of metal.
- a butanol (nC 4 H 9 OH) solution containing 6 vol% concentrated hydrochloric acid
- a coating solution was prepared by dissolving ruthenium trichloride trihydrate (RuCl 3 .3H 2 O) and tantalum pentachloride (TaCl 5 ). This coating solution was applied to the dried titanium plate, dried at 120 ° C. for 10 minutes, and then thermally decomposed in an electric furnace maintained at 500 ° C. for 20 minutes. This application, drying, and thermal decomposition were repeated a total of 7 times, and the catalyst of Example 1 was formed on a titanium plate as a conductive substrate to produce a detection electrode.
- RuCl 3 .3H 2 O ruthenium trichloride trihydrate
- TaCl 5 tantalum pentachloride
- Example 1 a mixed oxide catalyst composed of crystalline ruthenium oxide and amorphous tantalum oxide was formed on the titanium plate.
- a commercially available potassium chloride (KCl) reagent is dissolved in distilled water to prepare a solution having a KCl concentration of 0.05 mmol / L, and a disodium hydrogen phosphate (Na 2 HPO 4 ) reagent is dissolved in distilled water.
- the detection electrode is embedded in a holder made of polytetrafluoroethylene and the electrode area in contact with the sample water placed in the beaker is regulated to 1 cm 2 . Arranged. Further, a saturated potassium chloride aqueous solution was put in a container different from the sample water, and a commercially available silver-silver chloride electrode was immersed in the container as a reference electrode. This saturated aqueous potassium chloride solution and sample water were connected using a salt bridge and a Lugin tube to produce a three-electrode electrochemical measurement cell. During the measurement, the sample water was stirred with a stirrer.
- the detection electrode in which the catalyst of Example 1 was formed was obtained.
- an oxidation wave having a peak oxidation current around 0.95 V was observed, and it was found that hydrogen phosphate ions were oxidized.
- an electric current increased due to oxygen generation caused by electrolysis of water (decomposition of the whole sample water) was observed at a potential higher than this peak, but no other current indicating oxidation or reduction was observed. It was found that hydrogen phosphate ions were selectively oxidized on one catalyst.
- the potential of the detection electrode was set to 1.05 V with respect to the reference electrode, and the oxidation current density was measured for each concentration of sample water.
- the oxidation current density (mA / cm 2 ) is a value obtained by dividing the oxidation current (mA) flowing through the detection electrode by the electrode area.
- the electrode area in Example 1 is 1 cm 2 . Therefore, the values of the oxidation current and the oxidation current density are actually the same.
- the oxidation current was determined by subtracting the residual current that flows in the absence of hydrogen phosphate ions. A substantially constant current density was exhibited 10 to 20 seconds after the potential was applied to the detection electrode.
- the relationship between the oxidation current density thus obtained and the hydrogen phosphate ion concentration is shown in FIGS.
- a proportional relationship was observed in a wide concentration range from a low concentration to a high concentration.
- the detection sensitivity obtained from the slope of the straight line between the concentration and the oxidation current density was 209 A ⁇ cm / mol.
- Example 2 The catalyst of Example 2 is the same as Example 1 except that the molar ratio of ruthenium and tantalum in the coating solution is 30:70 in the method for forming the catalyst described in Example 1. To form a sensing electrode. As a result of analyzing this catalyst, it was found to be composed of a mixture of RuO 2 and Ta 2 O 5 as in Example 1. That is, in Example 2, a mixed oxide catalyst composed of crystalline ruthenium oxide and amorphous tantalum oxide was formed on the titanium plate.
- Example 2 As a result of performing cyclic voltammetry using this detection electrode in the same manner as in Example 1, a peak of the oxidation current of hydrogen phosphate ions was observed at substantially the same potential as in Example 1, and in addition to the oxygen generation current, Since neither an oxidation current nor a reduction current was observed, it was found that hydrogen phosphate ions were selectively oxidized on the catalyst of Example 2.
- the detection electrode was held at a constant potential, and the oxidation current density in the sample water in which various concentrations of hydrogen phosphate ions were dissolved was measured. As a result, the potential was applied to the detection electrode. After 10 to 20 seconds, a substantially constant current density was exhibited.
- the relationship between the oxidation current density thus obtained and the hydrogen phosphate ion concentration is shown in FIGS.
- the detection sensitivity obtained from the slope of the straight line between the concentration and the oxidation current density was 182 A ⁇ cm / mol.
- iridium dioxide was formed on a titanium plate as a conductive substrate to produce a detection electrode.
- the formed iridium dioxide was identified by an X-ray diffraction method.
- a peak of the oxidation current of hydrogen phosphate ions was observed at substantially the same potential as in Example 1, and in addition to the oxygen generation current, Since neither an oxidation current nor a reduction current was observed, it was found that hydrogen phosphate ions were selectively oxidized on the iridium dioxide catalyst of Comparative Example 1.
- the detection electrode was held at a constant potential, and the oxidation current density in the sample water in which various concentrations of hydrogen phosphate ions were dissolved was measured. As a result, the potential was applied to the detection electrode. After 10 to 20 seconds, a substantially constant current density was exhibited. As a result of calculating the detection sensitivity from the relationship between the oxidation current density thus obtained and the hydrogen phosphate ion concentration, the detection sensitivity was 0.30 times higher when the catalyst of Example 1 was used. It was 0.36 times the detection sensitivity when using.
- the detection sensitivity is 2.8 times to 3.3 times in the same concentration range and the same measurement conditions as compared with the case of using iridium dioxide which is the prior art. It was found that it improved twice. Further, when the detection sensitivity obtained with the catalyst of the present invention was compared with the value (2.5 A ⁇ cm / mol to 85 A ⁇ cm / mol) described in (Non-patent Document 4), the catalyst of the present invention was used. It was found that the detection sensitivity was 83 times higher at the maximum.
- Example 3 The catalyst of Example 3 was the same as Example 1 except that a titanium disk (diameter 4 mm, thickness 4 mm) was used in place of the titanium plate in the method of forming the catalyst described in Example 1. To form a sensing electrode. As a result of analyzing this catalyst, it was found to be a mixture of crystalline RuO 2 and amorphous Ta 2 O 5 as in Example 1. That is, in Example 3, a mixed oxide catalyst composed of crystalline ruthenium oxide and amorphous tantalum oxide was formed on the titanium disk as in Example 1.
- Example 1 As a result of performing cyclic voltammetry using this detection electrode in the same manner as in Example 1, a peak of the oxidation current of hydrogen phosphate ions was observed at substantially the same potential as in Example 1, and in addition to the oxygen generation current, Since neither an oxidation current nor a reduction current was observed, it was found that hydrogen phosphate ions were selectively oxidized on the catalyst of Example 3. Further, as in Example 1, the detection electrode was held at a constant potential, and the oxidation current density in sample water in which various concentrations of hydrogen phosphate ions were dissolved was measured. In Example 1, during the measurement, While the sample water in the beaker was stirred with a stirrer, in Example 3, the measurement was performed using the rotating disk electrode device with the detection electrode rotated.
- the configuration of the electrochemical measurement cell was the same as in Example 1 except that the detection electrode was rotated using a rotating disk electrode device. As a result, the sample water flows in the direction parallel to the detection electrode in Example 1, but in Example 3, the sample water is sent from the direction perpendicular to the detection electrode toward the detection electrode by the rotation of the detection electrode. It was. In addition to the method of rotating the detection electrode, such liquid feeding is a device used in the flow injection method or the like, and allows sample water to flow from the direction perpendicular to the stationary detection electrode toward the detection electrode. It is also possible to carry out similarly. The relationship between the oxidation current density thus obtained and the hydrogen phosphate ion concentration is shown in FIG. 6 and FIG.
- Example 4 In the method of forming the catalyst described in Example 1, a titanium disk (diameter 4 mm, thickness 4 mm) was used instead of the titanium plate, except that it was thermally decomposed in an electric furnace maintained at 260 ° C. for 20 minutes, Others were the same as in Example 1, and the catalyst of Example 4 was formed to produce a sensing electrode. As a result of analyzing this catalyst, it was a mixture of crystalline RuO 2 and amorphous Ta 2 O 5 in Example 1, but in Example 4, it was amorphous RuO 2 and amorphous Ta 2 O. It was found to consist of 5 mixtures.
- Example 4 a mixed oxide catalyst composed of amorphous ruthenium oxide and amorphous tantalum oxide was formed on a titanium disk.
- a peak of the oxidation current of hydrogen phosphate ions was observed at substantially the same potential as in Example 1, and in addition to the oxygen generation current, Since neither an oxidation current nor a reduction current was observed, it was found that hydrogen phosphate ions were selectively oxidized on the catalyst of Example 4. Further, as in Example 3, the detection electrode was held at a constant potential, and the oxidation current density was measured in sample water in which various concentrations of hydrogen phosphate ions were dissolved.
- Example 4 since the ruthenium oxide of the catalyst was amorphous, the detection sensitivity was 1.3 times that of Example 3 in which the composition ratio of ruthenium and tantalum of the catalyst was the same.
- Example 4 the detection sensitivity was tripled by making the ruthenium oxide amorphous and making the liquid feeding direction perpendicular to the detection electrode. Furthermore, in Example 4, both the linear scale (FIG. 8) and the logarithmic scale (FIG. 9) are linear, and the detection sensitivity varies in a wide concentration range from 10 ⁇ 2 mmol / L to 10 mmol / L. I found that there was no. That is, compared with Example 3, the ruthenium oxide of the catalyst becomes amorphous, so that the detection sensitivity is increased, and the concentration range that can be quantified is expanded, and the phosphoric acid phosphate has high detection sensitivity in any concentration range. It was shown that hydrogen ions can be quantified.
- Example 5 In the catalyst formation method described in Example 4, the catalyst of Example 5 was the same as Example 4 except that the molar ratio of ruthenium and tantalum in the coating solution was 50:50. To form a sensing electrode. As a result of analyzing this catalyst, it was found that it was composed of a mixture of amorphous RuO 2 and amorphous Ta 2 O 5 as in Example 4. That is, also in Example 5, a mixed oxide catalyst composed of amorphous ruthenium oxide and amorphous tantalum oxide was formed on the titanium disk.
- Example 4 As a result of performing cyclic voltammetry using this detection electrode in the same manner as in Example 1, a peak of the oxidation current of hydrogen phosphate ions was observed at substantially the same potential as in Example 1, and in addition to the oxygen generation current, Since neither an oxidation current nor a reduction current was observed, it was found that hydrogen phosphate ions were selectively oxidized on the catalyst of Example 5. Further, as in Example 4, the detection electrode was held at a constant potential, and the oxidation current density in the sample water in which various concentrations of hydrogen phosphate ions were dissolved was measured. As a result, the potential was applied to the detection electrode. After 10 to 20 seconds, a substantially constant current density was exhibited.
- Example 6 In the same manner as the catalyst formation method described in Example 4, the catalyst of Example 6 was formed to produce a detection electrode. Further, in the same manner as in Example 4, the detection electrode was held at a constant potential, and the oxidation current density in sample water in which various concentrations of hydrogen phosphate ions were dissolved was measured. However, in this measurement, disodium hydrogen phosphate was added in a state where the potential was applied for 5 minutes in advance and the residual current was sufficiently attenuated. After the addition of disodium hydrogen phosphate, the oxidation current density became a substantially constant value in about 20 seconds. The relationship between the oxidation current density thus obtained and the hydrogen phosphate ion concentration is shown in FIGS.
- the present invention is a catalyst for an ion sensor that can detect hydrogen phosphate ions in water and determine the hydrogen phosphate ion concentration from the oxidation current density. It can be maintained in the ion concentration range, and since the proportional relationship holds between the concentration and the oxidation current density, the concentration can be determined accurately regardless of the concentration range, and the oxidation current reaches a steady value in a short time. Providing an inexpensive catalyst for an ion sensor that has a short time to determine the current density, and therefore has a short time for quantifying hydrogen phosphate ions, and that repeatedly and stably responds to oxidation of hydrogen phosphate ions.
- hydrogen phosphate ions can be quantified in a wide range of concentrations, with high detection sensitivity, and in a short time, with a portable size.
- the ion sensor for hydrogen phosphate ions that can be mass-produced at low cost and at the same time has excellent measurement stability and reproducibility, and a highly sensitive and reproducible quantitative method for total phosphorus and hydrogen phosphate ions using this sensor. It can contribute to the measurement of total phosphorus and hydrogen phosphate ions in a wide range of application fields such as environmental measurement, medical work, and various analytical work, and the efficiency of monitoring work and the improvement of reliability.
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Abstract
Description
一方、生体系において、リンはリン酸イオンやDNAやRNAをはじめとした様々なリン酸エステル体として存在する。リンの化合物は、生体系環境における重要な制御因子であり、生物のエネルギー代謝に不可欠なATPやDNAは、リン酸を分子の一部に含むヌクレオチドからできており、生物の現存量は環境中から得られるリン酸の量から大きく制約を受けている。さらに、血液中のリン濃度も重要であり、成人の血しょう無機PO4濃度の基準範囲は2.5~4.5mg/dLとされ、これよりも低いと低リン酸血症と呼ばれ、筋力低下、呼吸不全、心不全、けいれんや昏睡を生じる場合があり、反対に高い場合には高リン酸血症と呼ばれ、慢性腎不全、副甲状腺機能低下症などによって生じる。
なお、前述のように、環境基準や排水基準で定められているのは「全リン」の濃度であり、オルトリン酸態リンに関する環境基準や排水基準はない。また、これらの方法では、オルトリン酸態リンは、試料水のpHを調整することでPO4 3-として存在しており、有機態リンおよびオルトリン酸態リン(無機態リン)はすべて、PO4 3-の形で測定される。したがって、環境中のオルトリン酸態リンについて、その存在形態ごとに濃度を求めることは行われていない状況であり、またこのように存在形態ごとに濃度を決定できる方法は開発されていない。
上記の全リンの濃度範囲は、リンのモル濃度(mmol/L)で表わすと、10-3mmol/L~10mmol/Lの範囲となる。なお、環境基準は「健康を保護し及び生活環境を保全するうえで維持することが望ましい基準」であることから、排水基準よりも低い値に設定されている。上記のように、現在の全リンやリン酸イオンの定量には、試料水に化学処理を行い、すべてのリンをリン酸イオンの形態に変えたのち、リン酸イオンを着色・分光分析する方法か、リン酸イオンをイオンクロマトグラフィーで分離した後、リン酸イオンを含む溶液の電気伝導度を測定するか、または紫外吸収を測定する方法となっており、作業が煩雑で試料水の処理から最終的に濃度を求めるまで時間がかかっていた。また、これらの方法ではリンはすべてPO4 3-に変わるため、これ以外のオルトリン酸態リンの濃度については、個別に測定する手段がなかった。
(1)例えば、(非特許文献2)乃至(非特許文献4)に記載のような、複合酸化物を触媒として試料水のリン酸水素イオンの酸化電流密度を測定する場合、検出される酸化電流密度が小さく、定量できる濃度範囲が広い触媒については、二酸化イリジウムを触媒として用いた場合の1/1000程度の検出感度しかないという課題があった。
(2)また、濃度と酸化電流密度の間には比例関係がなく、これらの関係において直線で近似できる検量線が得られないという課題があった。
(3)一方、前述のように、二酸化イリジウムは測定できる濃度範囲が狭いという課題があった。
(4)また、これまで述べた従来の電気化学的にリン酸水素イオンを検出するいずれの方法も、検出感度がいまだ小さく、また幅広い範囲において、高い検出感度でかつ濃度と酸化電流密度が比例して、高濃度から低濃度まで精度よく濃度を決定できるような触媒がないという課題があった。
本発明のイオンセンサ用触媒は、水中のリン酸水素イオンを電気化学的に酸化する触媒であって、酸化ルテニウムと酸化タンタルの混合酸化物を含む構成を有している。
この構成により、
(1)酸化ルテニウムと酸化タンタルの混合酸化物は、水中でのリン酸水素イオンの電気化学的酸化に対して、リン酸水素イオンの幅広い濃度範囲において、選択的に高い触媒活性を示し、高い酸化電流密度を生じるという作用を有する。これによって、本発明のイオンセンサ用触媒は、他の触媒に比べてリン酸水素イオンを高い検出感度で検出し、その濃度を決定することができる。
(2)リン酸水素イオンの濃度と酸化電流密度に比例関係が成り立つことで、濃度範囲に関わらず精度よく濃度を決定することが可能で、かつ酸化電流が短時間で定常値に達して電流密度の決定までの時間が短く、したがってリン酸水素イオンを定量する時間が短時間であり、リン酸水素イオンの酸化に対して繰り返し安定して応答することができ、測定の安定性、再現性に優れるという作用を有する。
(3)従来技術における複合酸化物や二酸化イリジウムに比べて、本発明のイオンセンサ用触媒は高い検出感度を有し、定量可能な濃度範囲も二酸化イリジウムに比べて非常に広いことなどから、高精度で信頼性に優れるという作用を有する。
(4)ルテニウムはイリジウムに比べて1/10程度の価格であり、タンタルはルテニウムの1/10程度の価格であることから、従来技術に対して、より安価な材料で、高い触媒活性と検出感度、および幅広い濃度範囲におけるリン酸水素イオンの定量を可能にすることができ、省資源性、実用性、測定の安定性に優れるという作用を有する。
(5)本発明の触媒は、リン酸二水素イオンや塩化物イオンのような他の陰イオンや陽イオンの酸化を生じないことから、リン酸水素イオンのみを選択的に検出して、その濃度を決定することができ、測定の確実性、信頼性に優れるという作用を有する。
導電性基体および導電部には、導電性を持つ種々の材料、例えば、金属、合金、種々の炭素材料(導電性ダイヤモンド、グラフェン、フラーレンなどを含む)、導電性プラスチック、導電性酸化物などの化合物、銀などを含む金属ペーストなどが利用可能であるが、これらに限定されるものではない。絶縁性基体には、アルミナなどの種々の絶縁性の酸化物、炭化物、窒化物や、ダイヤモンド、DLC(ダイヤモンドライクカーボン)、シリコン、プラスチックや樹脂などの有機材料などが利用可能であるが、これらに限定されるものではない。
これらの導電部、導電性基体、絶縁性基体は、板状、網状、棒状、シート状、管状、線状、らせん状、多孔板状、多孔質状、真球状、かご状、粒子を結合させた三次元多孔体等の種々の形状をとることができる。また、カーボンファイバー、カーボンナノチューブ、またはこれらを規則的に配置したカーボンファイバーアレイ、カーボンナノチューブアレイなども導電部、導電性基体として利用可能である。さらに、本発明の触媒または本発明の触媒を表面に担持した触媒担体を、上記のような種々の形状の導電部、または導電性基体上に担持、または混合して、本発明の触媒の単位質量あたりの表面積が増加するように工夫するなどしてもよい。
ここで、例として、熱分解法によって本発明の触媒を、導電性基体の一例であるチタン板上に形成する方法について述べる。例えば、無機化合物、有機化合物、イオン、錯体などの様々な形態でよいが、ルテニウムおよびタンタルを溶解した前駆体溶液をチタン板上に塗布し、これを200~600℃で熱分解すると、チタン板上に酸化ルテニウムと酸化タンタルからなる混合酸化物が形成される。
例えば、三塩化ルテニウム水和物と五塩化タンタルを溶解したブタノール溶液を前駆体溶液として、これをチタン板上に塗布して熱分解する。このとき、ルテニウムとタンタルの好適なモル比の範囲は熱分解温度等によって適宜、選択することができる。ただし、ルテニウムとタンタルの総量に対するルテニウムの割合が1%よりも小さくなるにつれ、本発明の触媒自体の導電性が低下し易くなって、検出される酸化電流が小さくなる傾向があり、ルテニウムとタンタルの総量に対するタンタルの割合が1%よりも小さくなるにつれ、ルテニウム酸化物をタンタル酸化物と混合することにより発揮されるリン酸水素イオンに対する高い触媒活性が失われ易くなる傾向があり、いずれも好ましくない。
上記に述べた熱分解法の例は、ブタノール溶媒の使用、ルテニウムとタンタルのモル比やこれに関連した熱分解温度の範囲に限定されたものではなく、上記の条件はあくまでその一例であり、本発明の触媒を得る方法は、上記に示した以外のあらゆる方法において、酸化ルテニウムと酸化タンタルの混合酸化物が得られるものであればよい。
この構成により、さらに以下の作用が得られる。
(1)混合酸化物におけるルテニウムとタンタルのモル比が30:70~80:20であることにより、リン酸水素イオンに対して、特に高い触媒活性が幅広い濃度範囲で得られるという作用を有する。
ここで、ルテニウムの割合が30%よりも小さくなるにつれ、混合酸化物の導電性が低くなり、リン酸水素イオンに対する酸化電流密度が小さくなる傾向があり、ルテニウムの割合が80%よりも大きくなるにつれ、酸化タンタルとの混合による効果が得られにくくなり、リン酸水素イオンに対する酸化電流密度が小さくなる傾向があり、いずれも好ましくない。
この構成により、さらに以下の作用が得られる。
(1)混合酸化物が非晶質の酸化ルテニウムを含むことにより、酸化ルテニウムが全て結晶質である場合に比べて、触媒の反応表面積が増加し、これによって同じ濃度のリン酸水素イオンに対する酸化電流密度が増加することによって、検出感度が大きくなるとともに、定量できる濃度範囲がより広くなるという作用を有する。
ここで、すでに記したように、このような結晶構造の違いは、X線回折法で得られる酸化ルテニウムの回折線の強度から相対的に判断することが可能で、非晶質の酸化ルテニウムを含む混合酸化物では、酸化ルテニウムに対する回折線の強度は低下する。混合酸化物に含まれる酸化ルテニウムがすべて非晶質または混合酸化物が非晶質の酸化ルテニウムと酸化タンタルからなる場合には、酸化ルテニウムに対する回折線は消失する。
この構成により、
(1)酸化ルテニウムと酸化タンタルの混合酸化物を含むイオンセンサ用触媒を検知極に用いて、リン酸水素イオンを酸化する際に流れる電流からリン酸水素イオンの濃度を決定することによって、高い検出感度で、かつ幅広い濃度範囲に対して、リン酸水素イオンを選択的に、かつ精度よく短時間で定量することが可能になるという作用を有する。
(2)本発明のイオンセンサの作動には大型の装置や大電力は不要であり、イオンセンサを携帯可能な大きさまで小型化することが可能で、省エネルギー性、コンパクト性、実用性に優れるという作用を有する。
(3)本発明のイオンセンサに必要なイオンセンサ用触媒やその他の部品は安価に作製することが可能で省資源性、量産性に優れ、リン酸水素イオン濃度の測定に対して、安定性や再現性に優れた定量が可能となるという作用を有する。
(4)本発明のイオンセンサは、検知極上でリン酸二水素イオンや塩化物イオンのような他の陰イオンや陽イオンの酸化を生じないことから、リン酸水素イオンのみを選択的に検出し、その濃度を決定することができ、測定の確実性、信頼性に優れるという作用を有する。
この構成により、さらに以下の作用が得られる。
(1)リン酸水素イオンだけでなく、リン酸水素イオンを含む試料水のpH及び/または温度を同時に測定することができる。
(2)これによって、pHや温度といった試料水の特性値をリン酸水素イオン濃度とともに同時に得ることができる。
(3)さらに、定量されたリン酸水素イオンの濃度に対して、pHや温度が通常値とは異なることによって生じる可能性がある検出異常などの問題の発生の有無を知ることができる。
この構成により、
(1)酸化ルテニウムと酸化タンタルの混合酸化物を含むイオンセンサ用触媒を用いて、リン酸水素イオンを酸化する際に流れる電流から選択的にリン酸水素イオンの濃度を決定できることで、リン酸水素イオンまたは全リンの濃度を、高い検出感度で、かつ幅広い濃度範囲に対して、かつ精度よく短時間で定量することが可能になるという作用を有する。(2)本発明の定量法に用いるイオンセンサは作動に大型の装置や電力が不要であることから、携帯可能な大きさまで小型化することが可能であり、その場で使用する場合或いは測定時に移動が必要な場合など様々な状況の中で定量することが可能となり、汎用性、取扱い性、機能性、量産性に優れるという作用を有する。
(3)本発明の定量法に用いるイオンセンサに必要なイオンセンサ用触媒やその他の部品は安価であり、従来技術のような特定の溶媒や試薬を用いる必要がなく、低コストで安定性や再現性に優れた定量が可能となり、省資源性、実用性に優れるという作用を有する。
(4)本発明の定量法では、検知極上でリン酸二水素イオンや塩化物イオンのような他の陰イオンや陽イオンの酸化を生じないことから、リン酸水素イオンのみを選択的に検出して、その濃度を決定することができ、測定の確実性、信頼性に優れるという作用を有する。
本発明の定量法によれば、試料水の前処理を行うか、行わないかの違いのみで、リン酸水素イオン又は全リンの濃度を決定することが可能となる。
この構成により、さらに以下の作用が得られる。
(1)リン酸水素イオンを含む溶液を検知極の周辺で流動または検知極へ送液することによって対流および拡散が促進され、同じ濃度のリン酸水素イオンに対して、これらを行わない場合に比べて酸化電流密度が増加し、したがってさらに検出感度が向上するという作用を有する。
(2)また、検知極での酸化反応が促進されることによって、安定した電流が観察されるまでの時間が短縮され、測定に必要な時間がさらに短くなるという作用を有する。
この構成により、さらに以下の作用が得られる。
(1)リン酸水素イオンを含む溶液を検知極周辺で流動させる場合や、検知極に対して水平方向に送液する場合に比べて、対流および拡散がより促進され、同じ濃度のリン酸水素イオンに対して酸化電流密度が増加し、したがってさらに検出感度が向上するという作用を有する。
1)一般に知られた簡単な方法でリン酸水素イオンを検出するための触媒を合成することが可能であり、かつイオンセンサの用途、使用頻度、使用環境などに合わせた形状、寸法を有するイオンセンサ用検知極およびこれを用いたイオンセンサを提供できるという効果を有する。
2)また、携帯または持ち運び可能な程度の大きさのイオンセンサが可能となることから、環境分析などにおいて試料水を実験室に持ち帰る必要がなく、現場での即時測定やモニタリングが可能になるという効果を有する。
3)また、本発明によれば、従来に比べて、低濃度のリン酸水素イオンまたは全リンや、排出基準を上回るような高濃度の全リンを、短時間で正確に決定できるようになるという効果を有する。
4)また、同じイオンセンサによって、リン酸水素イオンと全リンの両方の濃度を簡単に測定できるという効果を有する。
5)また、従来に比べてリン酸水素イオンに対する感度が高く、また幅広い濃度範囲でも定量の精度が高いことから、測定者のイオンセンサの使用に関する熟練度によらず、様々な状況や目的において、リン酸水素イオンまたは全リンの濃度を正確に測定することができるという効果を有する。
6)また、短時間でリン酸水素イオンの濃度を決定することができることから、環境または生体内のリン酸水素イオンおよび全リンの測定にかかる時間が短縮され、種々の分析業務、医療業務などの中で測定者の負担を軽減し、測定の効率化を図ることができるという効果を有する。
7)また、本発明によれば、少量の試料水で定量が可能で、かつリン酸水素イオンを処理するための特別な試薬や溶媒を必要としないことから、リン酸水素イオンの定量において、環境負荷の原因となる廃液や排水を低減できるという効果を有する。
図1は本発明のイオンセンサ用触媒を用いたイオンセンサを示す模式図である。
図1中、1は本発明のイオンセンサ用触媒を用いたイオンセンサ、2はアルミナなどの種々の絶縁性の酸化物、炭化物、窒化物や、ダイヤモンド、DLC(ダイヤモンドライクカーボン)、シリコンなどで形成された絶縁性基体、3は絶縁性基体2上に導電性を持つ金属、合金、種々の炭素材料(導電性ダイヤモンド、グラフェン、フラーレンなどを含む)、導電性プラスチック、導電性酸化物などの化合物、銀などを含む金属ペーストなどで線状に形成された3箇所の導電部、4は中央の導電部3の一端部に酸化ルテニウムと酸化タンタルの混合酸化物を含むイオンセンサ用触媒を形成して作製された検知極、5は他の1つの導電部3の一端部に白金、銀、その他の金属、導電性酸化物をはじめとする導電性化合物、導電性プラスチックなど電気化学センサやその他の電極材料として用いられている様々な材料、さらには本発明の触媒などを用いて形成された対極、6は他のもう1つの導電部3の一端部に銀-塩化銀電極、水銀-酸化水銀電極などを用いて形成された参照極、7は検知極4と対極5と参照極6で構成された検知部である。
イオンセンサ1は参照極6に対して検知極4に所定の電位を印加し、検知極4で生じた酸化電流を測定して、演算処理などを介して、最終的にリン酸水素イオン濃度を算出し、算出の結果を表示する制御部8を備えている。
検知極4は、リン酸水素イオンを酸化し、生じた酸化電流を導電部3を通して制御部8へ流す。
制御部8によって、参照極6に対して検知極4でリン酸水素イオンの酸化反応が生じるのに適した電位が印加される。
検知極4と対極5と参照極6を配置した構成の場合、印加する電位の波形は、一定の電位であっても、経時的に変化する電位波形であってもよい。このような電位波形としては、例えば矩形の電位パルスや、段階的に電位を変化させるような波形でもよい。いずれの場合においても、リン酸水素イオンの酸化電流は、その値が最も高くなるような電位を印加した状態で測定されることが望ましい。
試料水中に存在する共存イオンが、検知極4上でのリン酸水素イオンの継続的な酸化を阻害するような作用を有する場合に、例えば、参照極6に対する検知極4の電位を試料水中での自然電位(浸漬電位とも呼ぶ)よりも低い値とし、一時的に検知極4でリン酸水素イオンの酸化が起こらないようにして、このような阻害作用を防止するような電位波形を印加してもよい。
尚、検知部7は検知極4と対極5からなる構成としてもよい。この場合、制御部8によって、検知極4でリン酸水素イオンの酸化反応が生じるのに適した電圧が、検知極4と対極5の間に印加される。
(1)酸化ルテニウムと酸化タンタルの混合酸化物を含むイオンセンサ用触媒を検知極に用いて、リン酸水素イオンを酸化する際に流れる電流からリン酸水素イオンの濃度を決定することによって、高い検出感度で、かつ幅広い濃度範囲に対して、リン酸水素イオンを選択的に、かつ精度よく短時間で定量することが可能になるという作用を有する。
(2)本発明のイオンセンサの作動には大型の装置や電力は不要であり、イオンセンサを携帯可能な大きさまで小型化することが可能で、省エネルギー性、コンパクト性、実用性に優れるという作用を有する。
(3)本発明のイオンセンサに必要なイオンセンサ用触媒やその他の部品は安価に作製することが可能で省資源性、量産性に優れ、水中でのリン酸水素イオンの電気化学的酸化に対して、リン酸水素イオンの幅広い濃度範囲において、選択的に高い触媒活性を示し、高い酸化電流密度を生じるため、濃度範囲に関わらず精度よく濃度を決定することができ、リン酸水素イオン濃度の測定に対して、安定性や再現性に優れた定量が可能となるという作用を有する。
(4)本発明のイオンセンサは、検知極上でリン酸二水素イオンや塩化物イオンのような他の陰イオンや陽イオンの酸化を生じないことから、リン酸水素イオンのみを選択的に検出し、その濃度を決定することができ、測定の確実性、信頼性に優れるという作用を有する。
(実施例1)
市販のチタン板(長さ5cm、幅1cm、厚さ1mm)を10%のシュウ酸溶液中に90℃で60分間浸漬してエッチング処理を行った後、水洗し、乾燥した。次に、6vol%の濃塩酸を含むブタノール(n-C4H9OH)溶液に、ルテニウムとタンタルのモル比が80:20で、ルテニウムとタンタルの合計が金属換算で70g/Lとなるように三塩化ルテニウム三水和物(RuCl3・3H2O)と五塩化タンタル(TaCl5)を溶解して塗布液を調製した。この塗布液を上記乾燥後のチタン板に塗布し、120℃で10分間乾燥し、次いで500℃に保持した電気炉内で20分間熱分解した。この塗布、乾燥、熱分解を計7回繰り返し行い、導電性基体であるチタン板上に実施例1の触媒を形成して検知極を作製した。
市販の塩化カリウム(KCl)試薬を蒸留水に溶解し、KClの濃度を0.05mmol/Lとした溶液を調製し、これにリン酸水素二ナトリウム(Na2HPO4)試薬を蒸留水に溶解して所定の濃度としたリン酸水素二ナトリウム溶液を所定量添加することによって、種々のリン酸水素イオンの濃度の試料水を調製した。なお、この試料水のpHは上記のリン酸水素イオンの濃度範囲において、pH=8~9であった。前述の検知極をポリテトラフルオロエチレン製ホルダーに埋設し、ビーカーに入れた試料水に接触する電極面積を1cm2に規制した状態で、白金板を対極として、ともに試料水中で所定の距離をおいて配置した。また、試料水とは別の容器に塩化カリウム飽和水溶液を入れ、これに市販の銀-塩化銀電極を参照極として浸漬した。この塩化カリウム飽和水溶液と試料水を塩橋とルギン管を用いて接続し、3電極式の電気化学測定セルを作製した。なお、測定中は試料水をスターラーで撹拌した。
実施例1に記した触媒の形成方法の中で、塗布液中のルテニウムとタンタルのモル比を30:70としたことを除いて、他は実施例1と同じ方法で、実施例2の触媒を形成して検知極を作製した。この触媒を分析した結果、実施例1と同様にRuO2とTa2O5の混合物からなることが判った。すなわち、実施例2では、チタン板上に結晶質の酸化ルテニウムと非晶質の酸化タンタルからなる混合酸化物の触媒が形成されていた。この検知極を用いて実施例1と同様にサイクリックボルタメトリーを行った結果、実施例1とほぼ同じ電位にリン酸水素イオンの酸化電流のピークが見られ、その他には酸素発生電流以外に酸化電流、還元電流いずれも見られなかったことから、実施例2の触媒上でリン酸水素イオンが選択的に酸化されることが判った。また、実施例1と同様に、検知極を一定の電位に保持して、種々の濃度のリン酸水素イオンを溶解した試料水での酸化電流密度を測定した結果、検知極に電位を印加してから10~20秒でほぼ一定の電流密度を示した。このようにして得られた酸化電流密度とリン酸水素イオンの濃度の関係を図4および図5に示した。実施例2の触媒を用いることで、低濃度から高濃度までの幅広い濃度範囲で比例関係が見られた。また、濃度と酸化電流密度の直線の傾きから求めた検出感度は182A・cm/molとなった。
市販のチタン板(長さ5cm、幅1cm、厚さ1mm)を10%のシュウ酸溶液中に90℃で60分間浸漬してエッチング処理を行った後、水洗し、乾燥した。次に、6vol%の濃塩酸を含むブタノール(n-C4H9OH)溶液に、金属換算で70g/Lとなるように塩化イリジウム酸六水和物(H2IrCl6・6H2O)を溶解して塗布液を調製した。この塗布液を上記乾燥後のチタン板に塗布し、120℃で10分間乾燥し、次いで470℃に保持した電気炉内で20分間熱分解した。この塗布、乾燥、熱分解を計7回繰り返し行い、導電性基体であるチタン板上に二酸化イリジウムを形成して検知極を作製した。なお、形成された二酸化イリジウムは、X線回折法により同定した。この検知極を用いて実施例1と同様にサイクリックボルタメトリーを行った結果、実施例1とほぼ同じ電位にリン酸水素イオンの酸化電流のピークが見られ、その他には酸素発生電流以外に酸化電流、還元電流いずれも見られなかったことから、比較例1の二酸化イリジウム触媒上でリン酸水素イオンが選択的に酸化されることが判った。また、実施例1と同様に、検知極を一定の電位に保持して、種々の濃度のリン酸水素イオンを溶解した試料水での酸化電流密度を測定した結果、検知極に電位を印加してから10~20秒でほぼ一定の電流密度を示した。このようにして得られた酸化電流密度とリン酸水素イオンの濃度の関係から検出感度を算出した結果、実施例1の触媒を用いた場合の検出感度の0.30倍、実施例2の触媒を用いた場合の検出感度の0.36倍であった。
そして、上記の結果から、本発明の触媒を用いた場合、従来技術である二酸化イリジウムを用いた場合に比べて、同じ濃度範囲、同じ測定条件において、検出感度が2.8倍~3.3倍に向上することがわかった。また、本発明の触媒で得られた検出感度を、(非特許文献4)に記載の値(2.5A・cm/mol~85A・cm/mol)と比較すると、本発明の触媒を用いたほうが最大で83倍も検出感度が高くなることがわかった。
実施例1に記した触媒の形成方法の中で、チタン板の代わりにチタンディスク(直径4mm,厚み4mm)を用いたことを除いて、他は実施例1と同じ方法で実施例3の触媒を形成して検知極を作製した。この触媒を分析した結果、実施例1と同様に、結晶質のRuO2と非晶質のTa2O5の混合物であることがわかった。すなわち、実施例3では、チタンディスク上に実施例1と同様に結晶質の酸化ルテニウムと非晶質の酸化タンタルからなる混合酸化物の触媒が形成されていた。この検知極を用いて実施例1と同様にサイクリックボルタメトリーを行った結果、実施例1とほぼ同じ電位にリン酸水素イオンの酸化電流のピークが見られ、その他には酸素発生電流以外に酸化電流、還元電流いずれも見られなかったことから、実施例3の触媒上でリン酸水素イオンが選択的に酸化されることが判った。また、実施例1と同様に、検知極を一定の電位に保持して、種々の濃度のリン酸水素イオンを溶解した試料水での酸化電流密度を測定したが、実施例1では測定中はビーカー内の試料水をスターラーで撹拌したのに対して、実施例3では回転円盤電極装置を用いて、検知極を回転させた状態で測定した。回転円盤電極装置を用いて検知極を回転させた以外は、実施例1と同じ電気化学測定セルの構成とした。これによって、実施例1では検知極と平行な方向に試料水が流動していたが、実施例3では検知極の回転によって検知極に垂直な方向から試料水が検知極に向かって送液された。なお、このような送液は検知極を回転させる方法以外にも、フローインジェクション法などで用いられるような装置で、静止した検知極に対して垂直な方向から試料水を検知極に向かって流すことによっても同様に行うことが可能である。このようにして得られた酸化電流密度とリン酸水素イオンの濃度の関係を図6および図7に示した。その結果、低濃度から高濃度までの幅広い濃度範囲で比例関係が見られた。また、濃度と酸化電流密度の直線の傾きから求めた検出感度は471A・cm/molとなった。すなわち、実施例3で試料水の供給方法を変えることによって同じ触媒を用いた場合にも、実施例1に比べて検出感度が2.2倍となった。
実施例1に記した触媒の形成方法の中で、チタン板の代わりにチタンディスク(直径4mm,厚み4mm)を用い、260℃に保持した電気炉内で20分間熱分解したことを除いて、他は実施例1と同じ方法で、実施例4の触媒を形成して検知極を作製した。この触媒を分析した結果、実施例1では結晶質のRuO2と非晶質のTa2O5の混合物であったが、実施例4では非晶質のRuO2と非晶質のTa2O5の混合物からなることが判った。すなわち、実施例4では、チタンディスク上に非晶質の酸化ルテニウムと非晶質の酸化タンタルからなる混合酸化物の触媒が形成されていた。この検知極を用いて実施例1と同様にサイクリックボルタメトリーを行った結果、実施例1とほぼ同じ電位にリン酸水素イオンの酸化電流のピークが見られ、その他には酸素発生電流以外に酸化電流、還元電流いずれも見られなかったことから、実施例4の触媒上でリン酸水素イオンが選択的に酸化されることが判った。また、実施例3と同様に、検知極を一定の電位に保持して、種々の濃度のリン酸水素イオンを溶解した試料水での酸化電流密度を測定した結果、検知極に電位を印加してから10~20秒でほぼ一定の電流密度を示した。このようにして得られた酸化電流密度とリン酸水素イオンの濃度の関係を図8および図9に示した。その結果、低濃度から高濃度までの幅広い濃度範囲で比例関係が見られた。また、濃度と酸化電流密度の直線の傾きから求めた検出感度は624A・cm/molとなった。すなわち、実施例4では触媒の酸化ルテニウムが非晶質であることによって、触媒のルテニウムとタンタルの組成比が同じである実施例3に比べて、検出感度は1.3倍となった。また、実施例1と比較すると、酸化ルテニウムが非晶質となり、かつ送液方向を検知極に垂直とすることによって、検出感度は3倍となった。さらに、実施例4ではリニアスケール(図8)、両対数スケール(図9)のいずれでも直線となり、10-2mmol/Lから10mmol/Lの3桁におよぶ幅広い濃度範囲において、検出感度が変わらないことが判った。すなわち、実施例3と比較すると、触媒の酸化ルテニウムが非晶質となることで、検出感度が増加し、さらに定量できる濃度範囲が拡大して、いずれの濃度域においても高い検出感度でリン酸水素イオンを定量できることが示された。
実施例4に記した触媒の形成方法の中で、塗布液中のルテニウムとタンタルのモル比を50:50としたことを除いて、他は実施例4と同じ方法で、実施例5の触媒を形成して検知極を作製した。この触媒を分析した結果、実施例4と同じように、非晶質のRuO2と非晶質のTa2O5の混合物からなることが判った。すなわち、実施例5においても、チタンディスク上に非晶質の酸化ルテニウムと非晶質の酸化タンタルからなる混合酸化物の触媒が形成されていた。この検知極を用いて実施例1と同様にサイクリックボルタメトリーを行った結果、実施例1とほぼ同じ電位にリン酸水素イオンの酸化電流のピークが見られ、その他には酸素発生電流以外に酸化電流、還元電流いずれも見られなかったことから、実施例5の触媒上でリン酸水素イオンが選択的に酸化されることが判った。また、実施例4と同様に、検知極を一定の電位に保持して、種々の濃度のリン酸水素イオンを溶解した試料水での酸化電流密度を測定した結果、検知極に電位を印加してから10~20秒でほぼ一定の電流密度を示した。このようにして得られた酸化電流密度とリン酸水素イオンの濃度の関係を図10および図11に示した。その結果、低濃度から高濃度までの幅広い濃度範囲で比例関係が見られた。また、濃度と酸化電流密度の直線の傾きから求めた検出感度は685A・cm/molとなり、実施例4の触媒よりもさらに高い感度が得られた。また、実施例1と比較すると、酸化ルテニウムが非晶質となり、かつ送液方向を検知極に垂直とすることによって、検出感度は3.3倍となった。さらに、実施例5ではリニアスケール(図10)、両対数スケール(図11)のいずれでも直線となり、4×10-2mmol/Lから10mmol/Lの3桁におよぶ幅広い濃度範囲において、検出感度が変わらないことが判った。すなわち、いずれの濃度域においても高い検出感度でリン酸水素イオンを定量できることが示された。
実施例4に記した触媒の形成方法と同じ方法で、実施例6の触媒を形成して検知極を作製した。また、実施例4と同様に、検知極を一定の電位に保持して、種々の濃度のリン酸水素イオンを溶解した試料水での酸化電流密度を測定した。ただし、この測定の際には、電位を印加した状態であらかじめ5分間保持し、残余電流が十分に減衰した状態から、リン酸水素二ナトリウムを添加した。リン酸水素二ナトリウムを添加した後、20秒程度で酸化電流密度はほぼ一定の値となった。このようにして得られた酸化電流密度とリン酸水素イオンの濃度の関係を図12および図13に示した。その結果、低濃度から高濃度までの幅広い濃度範囲で比例関係が見られた。また、濃度と酸化電流密度の直線の傾きから求めた検出感度は562A・cm/molとなった。また、実施例6ではリニアスケール(図12)、両対数スケール(図13)のいずれでも直線となり、加えて10-3mmol/Lから10mmol/Lの4桁におよぶ幅広い濃度範囲において、検出感度が変わらないことが判った。すなわち、測定時における残余電流を十分に小さくしたことによって、実施例4に比べてさらに広い濃度範囲での定量が可能となり、同時にいずれの濃度域においても高い検出感度でリン酸水素イオンを定量できることが示された。
2 絶縁性基体
3 導電部
4 検知極
5 対極
6 参照極
7 検知部
8 制御部
Claims (11)
- 水中のリン酸水素イオンを電気化学的に酸化するイオンセンサ用触媒であって、酸化ルテニウムと酸化タンタルの混合酸化物を含むことを特徴とするイオンセンサ用触媒。
- 前記混合酸化物におけるルテニウムとタンタルのモル比が30:70~80:20であることを特徴とする請求項1に記載のイオンセンサ用触媒。
- 前記混合酸化物が非晶質の酸化ルテニウムを含むことを特徴とする請求項1または2に記載のイオンセンサ用触媒。
- 水中のリン酸水素イオンを定量するためのイオンセンサであって、請求項1~3のいずれか1項に記載のイオンセンサ用触媒を用いた検知極を備えたことを特徴とするイオンセンサ。
- 前記検知極によりリン酸水素イオンの酸化電流を検出する検出部と、前記検出部と電気的に接続され、前記検出部で検出した前記酸化電流から前記リン酸水素イオンの濃度を算出し、前記算出の結果を表示する制御部とを備えたことを特徴とする請求項4に記載のイオンセンサ。
- 前記検出部が、前記検知極および対極からなるか、または前記検知極、対極および参照極からなることを特徴とする請求項5に記載のイオンセンサ。
- 1つの絶縁性基体をさらに備え、前記検出部における前記検知極と前記対極、または前記検出部における前記検知極と前記対極と前記参照極とが、前記絶縁性基体上に形成されたことを特徴とする請求項6に記載のイオンセンサ。
- リン酸水素イオンを含む試料水のpH及び/または温度を測定する機能を備えたことを特徴とする請求項4~7のいずれか1項に記載のイオンセンサ。
- 水中のリン酸水素イオン及び/または全リンの濃度を決定するための定量法であって、請求項1~3のいずれか1項に記載のイオンセンサ用触媒を検知極に用いて、前記水中のリン酸水素イオンを酸化してその酸化電流を測定する電流測定工程と、前記電流測定工程で測定した酸化電流からリン酸水素イオンまたは全リンの濃度を決定する濃度決定工程と、を備えたことを特徴とする定量法。
- 前記電流測定工程において、リン酸水素イオンを含む溶液を前記検知極の周辺で流動または前記検知極に送液することを特徴とする請求項9に記載の定量法。
- 前記電流測定工程において、リン酸水素イオンを含む溶液を前記検知極に垂直方向から送液することを特徴とする請求項10に記載の定量法。
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