WO2011100789A1 - Reagent for analysis - Google Patents
Reagent for analysis Download PDFInfo
- Publication number
- WO2011100789A1 WO2011100789A1 PCT/AU2011/000160 AU2011000160W WO2011100789A1 WO 2011100789 A1 WO2011100789 A1 WO 2011100789A1 AU 2011000160 W AU2011000160 W AU 2011000160W WO 2011100789 A1 WO2011100789 A1 WO 2011100789A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- reagent
- dpd
- hydrogen phosphate
- phosphate
- phosphate buffer
- Prior art date
Links
- 239000003153 chemical reaction reagent Substances 0.000 title claims abstract description 61
- 238000004458 analytical method Methods 0.000 title description 14
- 239000008363 phosphate buffer Substances 0.000 claims abstract description 20
- NBIIXXVUZAFLBC-UHFFFAOYSA-L Phosphate ion(2-) Chemical compound OP([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-L 0.000 claims abstract description 11
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims abstract description 11
- PMZURENOXWZQFD-UHFFFAOYSA-L Sodium Sulfate Chemical compound [Na+].[Na+].[O-]S([O-])(=O)=O PMZURENOXWZQFD-UHFFFAOYSA-L 0.000 claims abstract description 11
- NLJMYIDDQXHKNR-UHFFFAOYSA-K sodium citrate Chemical compound O.O.[Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O NLJMYIDDQXHKNR-UHFFFAOYSA-K 0.000 claims abstract description 11
- KCXVZYZYPLLWCC-UHFFFAOYSA-N EDTA Chemical compound OC(=O)CN(CC(O)=O)CCN(CC(O)=O)CC(O)=O KCXVZYZYPLLWCC-UHFFFAOYSA-N 0.000 claims abstract description 9
- 239000000203 mixture Substances 0.000 claims abstract description 8
- 239000001509 sodium citrate Substances 0.000 claims abstract description 8
- 239000000126 substance Substances 0.000 claims abstract description 7
- 229910052938 sodium sulfate Inorganic materials 0.000 claims abstract description 6
- 235000011152 sodium sulphate Nutrition 0.000 claims abstract description 6
- FBPFZTCFMRRESA-FSIIMWSLSA-N D-Glucitol Natural products OC[C@H](O)[C@H](O)[C@@H](O)[C@H](O)CO FBPFZTCFMRRESA-FSIIMWSLSA-N 0.000 claims abstract description 3
- 239000000600 sorbitol Substances 0.000 claims abstract description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 22
- PEDCQBHIVMGVHV-UHFFFAOYSA-N glycerol group Chemical group OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 claims description 18
- 239000000243 solution Substances 0.000 claims description 18
- 150000003839 salts Chemical class 0.000 claims description 10
- 229960001484 edetic acid Drugs 0.000 claims description 7
- 150000001875 compounds Chemical class 0.000 claims description 6
- 239000002904 solvent Substances 0.000 claims description 6
- 239000000872 buffer Substances 0.000 claims description 5
- 239000007853 buffer solution Substances 0.000 claims description 5
- 239000008139 complexing agent Substances 0.000 claims description 5
- 235000000346 sugar Nutrition 0.000 claims description 4
- AEQDJSLRWYMAQI-UHFFFAOYSA-N 2,3,9,10-tetramethoxy-6,8,13,13a-tetrahydro-5H-isoquinolino[2,1-b]isoquinoline Chemical compound C1CN2CC(C(=C(OC)C=C3)OC)=C3CC2C2=C1C=C(OC)C(OC)=C2 AEQDJSLRWYMAQI-UHFFFAOYSA-N 0.000 claims description 3
- 229940123973 Oxygen scavenger Drugs 0.000 claims description 3
- 125000002091 cationic group Chemical group 0.000 claims description 3
- 239000000176 sodium gluconate Substances 0.000 claims description 3
- 229940005574 sodium gluconate Drugs 0.000 claims description 3
- 235000012207 sodium gluconate Nutrition 0.000 claims description 3
- 238000009835 boiling Methods 0.000 claims description 2
- 239000003960 organic solvent Substances 0.000 claims 1
- 235000011083 sodium citrates Nutrition 0.000 claims 1
- FBPFZTCFMRRESA-JGWLITMVSA-N D-glucitol Chemical compound OC[C@H](O)[C@@H](O)[C@H](O)[C@H](O)CO FBPFZTCFMRRESA-JGWLITMVSA-N 0.000 abstract description 2
- CMDGQTVYVAKDNA-UHFFFAOYSA-N propane-1,2,3-triol;hydrate Chemical compound O.OCC(O)CO CMDGQTVYVAKDNA-UHFFFAOYSA-N 0.000 abstract description 2
- 239000003795 chemical substances by application Substances 0.000 abstract 1
- QNGVNLMMEQUVQK-UHFFFAOYSA-N 4-n,4-n-diethylbenzene-1,4-diamine Chemical compound CCN(CC)C1=CC=C(N)C=C1 QNGVNLMMEQUVQK-UHFFFAOYSA-N 0.000 description 41
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 16
- 239000000460 chlorine Substances 0.000 description 16
- 229910052801 chlorine Inorganic materials 0.000 description 16
- 238000010561 standard procedure Methods 0.000 description 10
- 238000005259 measurement Methods 0.000 description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 6
- 239000000975 dye Substances 0.000 description 6
- 239000007788 liquid Substances 0.000 description 6
- 239000001301 oxygen Substances 0.000 description 6
- 229910052760 oxygen Inorganic materials 0.000 description 6
- OYPRJOBELJOOCE-UHFFFAOYSA-N Calcium Chemical compound [Ca] OYPRJOBELJOOCE-UHFFFAOYSA-N 0.000 description 5
- BNIILDVGGAEEIG-UHFFFAOYSA-L disodium hydrogen phosphate Chemical compound [Na+].[Na+].OP([O-])([O-])=O BNIILDVGGAEEIG-UHFFFAOYSA-L 0.000 description 5
- 230000000694 effects Effects 0.000 description 5
- 229910000403 monosodium phosphate Inorganic materials 0.000 description 5
- 235000019799 monosodium phosphate Nutrition 0.000 description 5
- AJPJDKMHJJGVTQ-UHFFFAOYSA-M sodium dihydrogen phosphate Chemical compound [Na+].OP(O)([O-])=O AJPJDKMHJJGVTQ-UHFFFAOYSA-M 0.000 description 5
- 239000007787 solid Substances 0.000 description 5
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 4
- 229910052791 calcium Inorganic materials 0.000 description 4
- 239000001506 calcium phosphate Substances 0.000 description 4
- 235000011010 calcium phosphates Nutrition 0.000 description 4
- 239000011777 magnesium Substances 0.000 description 4
- 229910052749 magnesium Inorganic materials 0.000 description 4
- GVALZJMUIHGIMD-UHFFFAOYSA-H magnesium phosphate Chemical class [Mg+2].[Mg+2].[Mg+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O GVALZJMUIHGIMD-UHFFFAOYSA-H 0.000 description 4
- 239000004137 magnesium phosphate Substances 0.000 description 4
- 235000010994 magnesium phosphates Nutrition 0.000 description 4
- 238000000034 method Methods 0.000 description 4
- 238000006087 Brown hydroboration reaction Methods 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- LYCAIKOWRPUZTN-UHFFFAOYSA-N Ethylene glycol Chemical compound OCCO LYCAIKOWRPUZTN-UHFFFAOYSA-N 0.000 description 3
- 239000003139 biocide Substances 0.000 description 3
- 239000007789 gas Substances 0.000 description 3
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 3
- 229910021645 metal ion Inorganic materials 0.000 description 3
- 238000001556 precipitation Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 241001550224 Apha Species 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- QDHHCQZDFGDHMP-UHFFFAOYSA-N Chloramine Chemical compound ClN QDHHCQZDFGDHMP-UHFFFAOYSA-N 0.000 description 2
- JLVVSXFLKOJNIY-UHFFFAOYSA-N Magnesium ion Chemical compound [Mg+2] JLVVSXFLKOJNIY-UHFFFAOYSA-N 0.000 description 2
- IURGIPVDZKDLIX-UHFFFAOYSA-M [7-(diethylamino)phenoxazin-3-ylidene]-diethylazanium;chloride Chemical compound [Cl-].C1=CC(=[N+](CC)CC)C=C2OC3=CC(N(CC)CC)=CC=C3N=C21 IURGIPVDZKDLIX-UHFFFAOYSA-M 0.000 description 2
- 238000002835 absorbance Methods 0.000 description 2
- 150000001298 alcohols Chemical class 0.000 description 2
- 230000003115 biocidal effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 239000011575 calcium Substances 0.000 description 2
- 229910000389 calcium phosphate Inorganic materials 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- -1 chlorine iodide ions Chemical class 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-M dihydrogenphosphate Chemical compound OP(O)([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-M 0.000 description 2
- 239000011888 foil Substances 0.000 description 2
- 238000009472 formulation Methods 0.000 description 2
- 229910001425 magnesium ion Inorganic materials 0.000 description 2
- 229910000157 magnesium phosphate Inorganic materials 0.000 description 2
- 229960002261 magnesium phosphate Drugs 0.000 description 2
- 239000007800 oxidant agent Substances 0.000 description 2
- 239000008055 phosphate buffer solution Substances 0.000 description 2
- 230000002000 scavenging effect Effects 0.000 description 2
- 239000011734 sodium Substances 0.000 description 2
- 150000008163 sugars Chemical class 0.000 description 2
- 238000010301 surface-oxidation reaction Methods 0.000 description 2
- HRXKRNGNAMMEHJ-UHFFFAOYSA-K trisodium citrate Chemical compound [Na+].[Na+].[Na+].[O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O HRXKRNGNAMMEHJ-UHFFFAOYSA-K 0.000 description 2
- 229940038773 trisodium citrate Drugs 0.000 description 2
- 239000002351 wastewater Substances 0.000 description 2
- AMVGQNFLBRUCGF-UHFFFAOYSA-N (7-amino-2-methylphenoxazin-3-ylidene)-dimethylazanium;chloride Chemical compound [Cl-].C1=C(N)C=C2OC3=CC(=[N+](C)C)C(C)=CC3=NC2=C1 AMVGQNFLBRUCGF-UHFFFAOYSA-N 0.000 description 1
- KRKNYBCHXYNGOX-UHFFFAOYSA-K Citrate Chemical compound [O-]C(=O)CC(O)(CC([O-])=O)C([O-])=O KRKNYBCHXYNGOX-UHFFFAOYSA-K 0.000 description 1
- 108700035674 EC 1.16.-.- Proteins 0.000 description 1
- KOLOHTSFJKVHEP-UHFFFAOYSA-L EDTA monomagnesium salt Chemical compound [Mg+2].[O-]C(=O)C[NH+](CC([O-])=O)CC[NH+](CC([O-])=O)CC([O-])=O KOLOHTSFJKVHEP-UHFFFAOYSA-L 0.000 description 1
- VTLYFUHAOXGGBS-UHFFFAOYSA-N Fe3+ Chemical compound [Fe+3] VTLYFUHAOXGGBS-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 239000007836 KH2PO4 Substances 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- 238000004378 air conditioning Methods 0.000 description 1
- 238000003149 assay kit Methods 0.000 description 1
- 230000003139 buffering effect Effects 0.000 description 1
- 239000008364 bulk solution Substances 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 238000010790 dilution Methods 0.000 description 1
- 239000012895 dilution Substances 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 229910001447 ferric ion Inorganic materials 0.000 description 1
- 239000012530 fluid Substances 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 230000000813 microbial effect Effects 0.000 description 1
- 229910000402 monopotassium phosphate Inorganic materials 0.000 description 1
- 235000019796 monopotassium phosphate Nutrition 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000012466 permeate Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 235000021317 phosphate Nutrition 0.000 description 1
- GNSKLFRGEWLPPA-UHFFFAOYSA-M potassium dihydrogen phosphate Chemical compound [K+].OP(O)([O-])=O GNSKLFRGEWLPPA-UHFFFAOYSA-M 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 229910052708 sodium Inorganic materials 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 150000005846 sugar alcohols Polymers 0.000 description 1
- 230000009182 swimming Effects 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 238000004448 titration Methods 0.000 description 1
- QORWJWZARLRLPR-UHFFFAOYSA-H tricalcium bis(phosphate) Chemical compound [Ca+2].[Ca+2].[Ca+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O QORWJWZARLRLPR-UHFFFAOYSA-H 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Classifications
-
- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/251—Colorimeters; Construction thereof
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/29—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using visual detection
- G01N21/293—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands using visual detection with colour charts, graduated scales or turrets
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
Definitions
- This invention relates to a method and composition for chemical analysis, especially analysis entailing the automatic detection of substances in solution, for example by reagent addition and titrimetry.
- the invention is especially suited to on- line analysis and control of chlorine content and the measurement and control of pH in pools and air conditioning towers.
- Oxidising compounds such as free and combined chlorine are commonly used as biocides for water in applications such as swimming pools and cooling towers.
- the most widely used method for analysing the level of biocide in the water is reaction with N,N- Diethyl-p-phenylenediamine (DPD) which upon oxidising forms a pink coloured compound (Wurstar dye).
- DPD N,N- Diethyl-p-phenylenediamine
- Free chlorine (colourless) + DPD (colourless) reaction product (pink)
- the intensity of the pink colour is proportional to the concentration of biocide in the water, and can be measured accurately by measuring the absorbance of the solution at the appropriate wavelengths of light.
- APHA.AWWA.WPFC 1985 involves a stoichiometric excess of DPD in a buffer solution, typically at pH 6.3. This pH is chosen to minimize the reaction of DPD with combined chlorine. Nevertheless, the combined chlorine reaction does proceed slowly at pH 6.3 and necessitates the free chlorine measurement be made quickly.
- the buffer solution used in the standard method is a phosphate buffer. It is known that both solid DPD and DPD in solution at pH 6.3 are oxidised by air.
- the concentration of the coloured reaction product can be measured by the level of absorbance of light in the green to blue range. This directly relates to the concentration of free chlorine.
- the present invention provides a single DPD reagent whereby DPD (and possibly other chemicals) is dissolved in a concentrated buffer solution to reduce the ability of air to oxidise the solution.
- the inventive reagent is intended to provide an advantage over solid DPD reagents because mixing is faster and consequently the magnitude of a chloramine error is reduced.
- a single reagent avoids the need for two reagents and having to deliver two separate reagents into an analysis cell, thus simplifying the analyser and reducing reagent cost.
- the invention relates to a single liquid DPD reagent system for performing analyses of oxidising compounds in fluids such as water.
- concentration of the phosphate buffer solution is increased over that stated in the standard method to increase the viscosity of the solution and reduce the ability of air to permeate into the solution.
- DPD is dissolved in the concentrated buffer solution to form a single reagent in which the DPD remains stable for much longer periods of time.
- the standard method for DPD analyses recommends using a phosphate buffer of concentration resulting from adding 46 grams of anhydrous KH2PO4 and 24 grams of anhydrous Na 2 HP0 to one litre of water (Standard Methods for the Examination of Water and Wastewater - 16 th
- this invention provides a storage means containing single DPD reagent whereby the DPD and optionally other chemicals is dissolved in a concentrated phosphate buffer to produce a desired pH, wherein the phosphate buffer includes mono-hydrogen phosphate and di-hydrogen phosphate wherein the concentration of mono-hydrogen phosphate exceeds 0.34 mole per litre, and the concentration of di-hydrogen phosphate exceeds 0.68 mole per litre, and wherein surface contact of said reagent with air is prevented by said storage means.
- This aspect of the invention is predicated on the observation that a very concentrated phosphate buffer comprising a ratio of mono and di-hydrogen phosphates to produce pH 6.3, prevented the deterioration of DPD when the DPD was dissolved in this solution.
- the whole solution showed negligible sign of deterioration over long periods (so far the solution has been observed to be stable in excess of 2 years).
- the preferred concentrations of phosphate buffer for the inventive reagent was: in excess of 0.34 mole per litre of mono-hydrogen phosphate and in excess of 0.68 moles per litre of di-hydrogen phosphate.
- cationic dyes retard the surface oxidation of DPD in the afore described reagent when it is exposed to air.
- Preferred cationic dyes are Basic Blue 3 and Brilliant Cresyl Purple. Accordingly, one or more of these dyes may be advantageously incorporated in the afore described reagent.
- An additional advantage of adding a dye in the case of manual test kits which employ visual comparison against a graded colour intensity scale, is provision of a more recognisable colour gradation as the intensity of the pink colour changes and therefore a better manual estimation of the chlorine concentration.
- the aforementioned standard method incorporates the metal ion complexing agent EDTA (Ethylene Diamine Tetra-Acetic Acid) to prevent oxidising metal ions such as cupric and ferric ions from reacting with DPD to produce false positive readings.
- EDTA prevents precipitation of calcium and magnesium phosphates in cases of high water hardness. Due to the comparatively high concentration of phosphate buffer in the present inventive reagent, EDTA has insufficient solubility to perform these functions. It has been found in practice that the magnesium complex of EDTA is appreciably soluble in the formulation of the present invention. As cupric and ferric complexes of EDTA have higher stability constants than the magnesium complex, these metal ions displace the magnesium ion.
- magnesium EDTA does not overcome calcium phosphate precipitation because the EDTA complexes of calcium and magnesium have similar stability constants. Investigation of other complexing agents for calcium and magnesium has revealed citrate is effective at preventing the precipitation of calcium and magnesium phosphate.
- Other well known complexing agents capable of solubilising calcium and magnesium phosphates could also be employed, such as sodium gluconate.
- the invention of using concentrated buffers to improve stability will also be applicable at pH values other than 6.3 as specified in the standard method for free chlorine analysis and may be applicable to other types of buffers other than phosphate.
- the invention can also be applied for example to analysis of total chorine, and lower buffer pH (for example 5) can be advantageous in this case.
- lower buffer pH for example 5
- Iodide ions could also be added to the inventive reagent to produce a single reagent for the measurement of total chlorine,
- This can be for example a closed container where any enclosed gas is of a type which does not react with DPD, for example an inert gas or nitrogen. It can also be for example by storing the reagent in an air tight container such as a laminated metal foil bag whereby any gas is largely excluded.
- Addition of salts such as sodium citrate and sodium sulphate also have the effect of increasing the viscosity of the solution, and the viscosity may also be increased by adding other classes of compounds such as sugars It is a further aspect of the invention to increase the viscosity of the reagent by increasing the ionic strength through addition of for example high levels of salts. It will be appreciated that both the abovementioned methods of increasing the viscosity (and increasing the stability to air) will be generally applicable to other reagents other than the DPD reagent for analysis of chlorine. Detailed description of the invention
- the preferred concentration of phosphate buffer should be as high as possible, with due consideration to the solubility so that the reagent does not crystallise at the lowest working temperature.
- Glygerol 5 -50 %weight/weight of water Note that substances such as trisodium citrate have an effect on the buffering of the solution.
- the resulting pH of the solution can be adjusted by changing the ratio of monohydrogen phosphate to dihydrogen phosphate, in the examples given the pH is adjusted to 6.3 to correspond to the pH of the standard method, and as such the ratio of monohydrogen phosphate to dihydrogen phosphate differs from the ratio used in the standard method to account for the effect on the pH of the trisodium citrate.
- the invention provides a stable single DPD reagent for manual or automated measurement of oxidising agents.
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- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Food Science & Technology (AREA)
- Medicinal Chemistry (AREA)
- Physics & Mathematics (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Non-Biological Materials By The Use Of Chemical Means (AREA)
Abstract
A single DPD reagent whereby the DPD and optionally other chemicals is dissolved in a concentrated phosphate buffer to produce a desired pH, wherein the phosphate buffer includes mono-hydrogen phosphate and di-hydrogen phosphate wherein the concentration of mono-hydrogen phosphate exceeds 0.34 mole per litre, and the concentration of di-hydrogen phosphate exceeds 0.68 mole per litre, and wherein surface contact of said reagent with air is prevented by said storage means. The solution may contain a glycerol water mixture and include additional agents such as EDTA, sodium citrate, sodium sulfate and Sorbitol. Optionally the reagent may be stored in a storage container that reduces contact with air.
Description
REAGENT FOR ANALYSIS
This invention relates to a method and composition for chemical analysis, especially analysis entailing the automatic detection of substances in solution, for example by reagent addition and titrimetry. The invention is especially suited to on- line analysis and control of chlorine content and the measurement and control of pH in pools and air conditioning towers.
Background to the invention
Oxidising compounds such as free and combined chlorine are commonly used as biocides for water in applications such as swimming pools and cooling towers. The most widely used method for analysing the level of biocide in the water is reaction with N,N- Diethyl-p-phenylenediamine (DPD) which upon oxidising forms a pink coloured compound (Wurstar dye). Free chlorine (colourless) + DPD (colourless) = reaction product (pink)
The intensity of the pink colour is proportional to the concentration of biocide in the water, and can be measured accurately by measuring the absorbance of the solution at the appropriate wavelengths of light. The method published in Standard Methods for the Examination of Water and Wastewaters - 16th edition
APHA.AWWA.WPFC, 1985 involves a stoichiometric excess of DPD in a buffer solution, typically at pH 6.3. This pH is chosen to minimize the reaction of DPD with combined chlorine. Nevertheless, the combined chlorine reaction does proceed slowly at pH 6.3 and necessitates the free chlorine measurement be made quickly. The buffer solution used in the standard method is a phosphate buffer. It is known that both solid DPD and DPD in solution at pH 6.3 are oxidised by air.
The concentration of the coloured reaction product can be measured by the level of absorbance of light in the green to blue range. This directly relates to the concentration of free chlorine.
Manual measurement of an oxidising agent by DPD in the prior art typically involves a test kit which employs a reagent tablet containing solid DPD and a solid buffer sealed in an air impermeable foil sachet. The intensity of the pink colour is
compared to a graded colour scale, or measured by a colorimeter. However, it is known in practice that the solid phosphate buffer does not dissolve instantly. The time taken to effect complete dissolution can produce a chloramine error in a free chlorine measurement.
Currently the state of the art in on-line analysers for automated measurement of chlorine is to use two liquid reagents, one containing DPD at low pH and the other a phosphate buffer solution. The DPD is stored separately at low pH due to sensitivity to air at the higher pH's required for the DPD reaction. The two reagents are delivered separately and mixed in the analysis cell at the time of analysis. It is an object of the invention to provide a single liquid reagent system which is stable for long periods of time.
Brief description of the invention
To this end the present invention provides a single DPD reagent whereby DPD (and possibly other chemicals) is dissolved in a concentrated buffer solution to reduce the ability of air to oxidise the solution.
The inventive reagent is intended to provide an advantage over solid DPD reagents because mixing is faster and consequently the magnitude of a chloramine error is reduced. In the case of automated analysers, a single reagent avoids the need for two reagents and having to deliver two separate reagents into an analysis cell, thus simplifying the analyser and reducing reagent cost.
The invention relates to a single liquid DPD reagent system for performing analyses of oxidising compounds in fluids such as water. In one aspect of the invention the concentration of the phosphate buffer solution is increased over that stated in the standard method to increase the viscosity of the solution and reduce the ability of air to permeate into the solution. DPD is dissolved in the concentrated buffer solution to form a single reagent in which the DPD remains stable for much longer periods of time. The standard method for DPD analyses recommends using a phosphate buffer of concentration resulting from adding 46 grams of anhydrous KH2PO4 and 24 grams of anhydrous Na2HP0 to one litre of water (Standard Methods for the Examination of Water and Wastewater - 16th
edition.APHA.AWWA.WPCF, 1985).
In another aspect this invention provides a storage means containing single DPD reagent whereby the DPD and optionally other chemicals is dissolved in a concentrated phosphate buffer to produce a desired pH, wherein the phosphate buffer includes mono-hydrogen phosphate and di-hydrogen phosphate wherein the concentration of mono-hydrogen phosphate exceeds 0.34 mole per litre, and the concentration of di-hydrogen phosphate exceeds 0.68 mole per litre, and wherein surface contact of said reagent with air is prevented by said storage means.
This aspect of the invention is predicated on the observation that a very concentrated phosphate buffer comprising a ratio of mono and di-hydrogen phosphates to produce pH 6.3, prevented the deterioration of DPD when the DPD was dissolved in this solution. This applied to the bulk solution, but not where a surface exposed is to air, with the result that the DPD became oxidised. However, by minimising surface contact with air, the whole solution showed negligible sign of deterioration over long periods (so far the solution has been observed to be stable in excess of 2 years). It was found in practice the preferred concentrations of phosphate buffer for the inventive reagent was: in excess of 0.34 mole per litre of mono-hydrogen phosphate and in excess of 0.68 moles per litre of di-hydrogen phosphate.
It has been observed that certain cationic dyes retard the surface oxidation of DPD in the afore described reagent when it is exposed to air. Preferred cationic dyes are Basic Blue 3 and Brilliant Cresyl Purple. Accordingly, one or more of these dyes may be advantageously incorporated in the afore described reagent. An additional advantage of adding a dye in the case of manual test kits which employ visual comparison against a graded colour intensity scale, is provision of a more recognisable colour gradation as the intensity of the pink colour changes and therefore a better manual estimation of the chlorine concentration.
It has also been found in practice that the replacement of some of the water solvent in the inventive reagent with a high boiling point, water miscible solvent preferably glycerol also retarded the aforementioned surface oxidation of the inventive reagent. It was found that the aforementioned concentrations of mono- and di-hydrogen phosphates of the inventive reagent could be dissolved in glycerol
- water mixtures of up to 50% volume to volume glycerol to water. Other alcohols with two or more hydroxyl groups, such as ethylene glycol, may also be employed. It was found the glycerol significantly reduced the formation of the pink Wurstar dye i.e. reduced the oxidation of the DPD. Instead, a minor brown oxidation product may be formed. However, due to the high dilution of the inventive reagent with the sample (typically1:100), the brown discolouration does not cause a significant error for measurements in the range 0.5 to 5ppm free chlorine.
The aforementioned standard method incorporates the metal ion complexing agent EDTA (Ethylene Diamine Tetra-Acetic Acid) to prevent oxidising metal ions such as cupric and ferric ions from reacting with DPD to produce false positive readings. As well, EDTA prevents precipitation of calcium and magnesium phosphates in cases of high water hardness. Due to the comparatively high concentration of phosphate buffer in the present inventive reagent, EDTA has insufficient solubility to perform these functions. It has been found in practice that the magnesium complex of EDTA is appreciably soluble in the formulation of the present invention. As cupric and ferric complexes of EDTA have higher stability constants than the magnesium complex, these metal ions displace the magnesium ion. The concentration of released magnesium ion is insufficient to precipitate a significant amount of magnesium phosphate. However, magnesium EDTA does not overcome calcium phosphate precipitation because the EDTA complexes of calcium and magnesium have similar stability constants. Investigation of other complexing agents for calcium and magnesium has revealed citrate is effective at preventing the precipitation of calcium and magnesium phosphate. Other well known complexing agents capable of solubilising calcium and magnesium phosphates could also be employed, such as sodium gluconate.
It was observed that high levels of sodium citrate in the inventive reagent produced a significant retardation of the aforementioned brown oxidation product resulting from the addition of glycerol. It is known that the solubility of gases such as oxygen in water is reduced with increasing levels of metal ion salts. It has been found in practice that adding an inert salt such as sodium sulphate to the inventive reagent further reduces the formation of the brown oxidation product. Other inert salts or salts which have an oxygen scavenging capability could also be employed. As well, combinations of inert salts could be employed.
It will be appreciated that the invention of using concentrated buffers to improve stability will also be applicable at pH values other than 6.3 as specified in the standard method for free chlorine analysis and may be applicable to other types of buffers other than phosphate. The invention can also be applied for example to analysis of total chorine, and lower buffer pH (for example 5) can be advantageous in this case. In the standard method for total chlorine iodide ions are added. Iodide ions could also be added to the inventive reagent to produce a single reagent for the measurement of total chlorine,
It is a further aspect of the invention to make a single DPD reagent stable by using storage means whereby oxygen and /or light is substantially prevented from making contact with the single reagent solution. This can be for example a closed container where any enclosed gas is of a type which does not react with DPD, for example an inert gas or nitrogen. It can also be for example by storing the reagent in an air tight container such as a laminated metal foil bag whereby any gas is largely excluded.
In another form of the invention, a single liquid DPD reagent using the
abovementioned high concentrations of phosphate buffer at pH 6.3 is made even more stable by employing a solvent composed of an alcohol / water mixture, wherein the alcohol has two or more hydroxyl groups. Other classes of compounds such as sugars which do not interfere with the DPD - free chlorine reaction may also be employed to enhance the stability effect through increasing the viscosity of the solution, ionic strength of the solution or oxygen scavenging or combination thereof.
In another form of the invention, a single liquid DPD reagent using the
abovementioned high concentrations of phosphate buffer at pH 6.3 is made even more stable by increasing still further the ionic concentration of the solution through addition of for example salts such as sodium citrate or sodium sulphate. In another form of the invention, a single liquid DPD reagent using the
abovementioned high concentration of phosphate buffer at pH 6.3 is made even more stable by adding an oxygen scavenger or scavengers which do not interfere with the DPD - free chlorine reaction, such as sodium gluconate. Biological means to further reduce the dissolved oxygen concentration may also be employed. This
may be achieved by microbial action on an inert substrate which involves consumption of oxygen.
It is advantageous to use small amounts of reagent in the analytical tests, which is facilitated by the higher concentrations used in the reagent of the invention. It can also be advantageous in analysers which inject reagent on the basis of flow rate to increase the viscosity of the reagent ,to reduce flow rates, and consequently allow better control of the injected volume. Alcohols such as glycerol also have a high viscosity. It is a further aspect of the invention to increase the viscosity of the reagent by employing a solvent composed of a polyalcohol / water mixture, wherein the alcohol has two or more hydroxyl groups. Addition of salts such as sodium citrate and sodium sulphate also have the effect of increasing the viscosity of the solution, and the viscosity may also be increased by adding other classes of compounds such as sugars It is a further aspect of the invention to increase the viscosity of the reagent by increasing the ionic strength through addition of for example high levels of salts. It will be appreciated that both the abovementioned methods of increasing the viscosity (and increasing the stability to air) will be generally applicable to other reagents other than the DPD reagent for analysis of chlorine. Detailed description of the invention
Preferred embodiments of the invention will now be described.
The preferred concentration of phosphate buffer should be as high as possible, with due consideration to the solubility so that the reagent does not crystallise at the lowest working temperature.
By means of example only, preferred embodiments of the formulation are:
Example 1
Anhydrous Sodium Dihydrogen Phosphate 315 gm/L
Anhydrous Disodium Hydrogen Phosphate 75 gm/L
DPD 6 - 24 gm/L
Trisodium Citrate Dihydrate 200 gm/L
Glygerol 5 -50 %weight/weight of water
Note that substances such as trisodium citrate have an effect on the buffering of the solution. The resulting pH of the solution can be adjusted by changing the ratio of monohydrogen phosphate to dihydrogen phosphate, in the examples given the pH is adjusted to 6.3 to correspond to the pH of the standard method, and as such the ratio of monohydrogen phosphate to dihydrogen phosphate differs from the ratio used in the standard method to account for the effect on the pH of the trisodium citrate.
Example 2
Anhydrous Sodium Dihydrogen Phosphate 315 gm/L
Anhydrous Disodium Hydrogen Phosphate 75 gm/L
DPD 6 - 24 gm/L
Trisodium Citrate Dihydrate 200 gm/L
Glygerol 0 -50 %weight/weight of water
Sodium Sulphate 100 gm/L
Example 3
Anhydrous Sodium Dihydrogen Phosphate 315 gm/L
Anhydrous Disodium Hydrogen Phosphate 75 gm/L
DPD 6 - 24 gm/L
Trisodium Citrate Dihydrate 200 gm/L
Glygerol 0 -50 %weight/weight of water
Sodium Gluonate 10 gm/L Example 4
Anhydrous Sodium Dihydrogen Phosphate 315 gm/L
Anhydrous Disodium Hydrogen Phosphate 75 gm/L
DPD 6 - 24 gm/L
Trisodium Citrate Dihydrate 200 gm/L
Glygerol 5 -50 %weight weight of water
Basic Blue 3 0.1-1 gm/L
Example 5
Anhydrous Sodium Dihydrogen Phosphate 315 gm/L
Anhydrous Disodium Hydrogen Phosphate 75 gm/L
DPD 6 - 24 gm/L
Trisodium Citrate Dihydrate 200 gm/L
Glygerol 0 -50 %weight/weight of water
Sorbitol 100 gm/L
In accordance with the objects of the invention, it can be seen the invention provides a stable single DPD reagent for manual or automated measurement of oxidising agents.
Those skilled in the art will also realize that this invention can be implemented in embodiments other than those described without departing from the core teachings of this invention.
Claims
1. A single DPD reagent whereby DPD is dissolved in a concentrated buffer solution to improve the stability of the solution.
2. A storage means containing single DPD reagent whereby the DPD and optionally other chemicals is dissolved in a concentrated phosphate buffer to produce a desired pH, wherein the phosphate buffer includes mono- hydrogen phosphate and di-hydrogen phosphate wherein the concentration of mono-hydrogen phosphate exceeds 0.34 mole per litre, and the concentration of di-hydrogen phosphate exceeds 0.68 mole per litre, and wherein surface contact of said reagent with air is prevented by said storage means.
3. A single DPD reagent whereby the DPD is dissolved in a phosphate buffer to produce a desired pH, wherein the phosphate buffer includes mono- hydrogen phosphate and di-hydrogen phosphate and the solution also includes a cationic dye.
4. A single DPD reagent whereby the DPD is dissolved in a phosphate buffer to produce a desired pH, wherein the phosphate buffer includes mono- hydrogen phosphate and di-hydrogen phosphate wherein the solvent for the buffer and DPD is a mixture of water and a high boiling water miscible organic solvent.
5. A reagent as claimed in claim 4 in which the water miscible solvent is
glycerol.
6. A reagent as claimed in any preceding claim which also includes high
concentrations of inorganic salts and /or includes other compounds which can function as an oxygen scavenger
7. A reagent as claimed in claim 6 in which the salt is sodium citrate, sodium gluconate or sodium sulphate.
8. A reagent as claimed in any preceding claim which also includes a complexing agent.
9. A reagent as claimed in claim 8 in which the complexing agent is selected from sodium citrate and Ethylene Diamine Tetra-Acetic Acid.
10. A reagent as claimed in any preceding claim which includes an inert sugar.
11. A reagent as claimed in claim 10 in which the sugar is sorbitol.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU2010900654A AU2010900654A0 (en) | 2010-02-18 | Reagent for Analyses using DPD | |
| AU2010900654 | 2010-02-18 |
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| Publication Number | Publication Date |
|---|---|
| WO2011100789A1 true WO2011100789A1 (en) | 2011-08-25 |
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ID=44482395
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| PCT/AU2011/000160 WO2011100789A1 (en) | 2010-02-18 | 2011-02-17 | Reagent for analysis |
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| WO (1) | WO2011100789A1 (en) |
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102937579A (en) * | 2012-10-31 | 2013-02-20 | 广东环凯微生物科技有限公司 | Rapid determination tablet for free chlorine residuals for water quality on the spot and preparation method thereof |
| EP2784503A1 (en) * | 2013-03-29 | 2014-10-01 | LaMotte Chemical Products Company | Reagent for Detection and Assessment of Free Chlorine in Aqueous Solution |
| EP2784502A1 (en) * | 2013-03-29 | 2014-10-01 | LaMotte Chemical Products Company | Reagent for detection and assessment of total chlorine in aqueous solution |
| CN110161026A (en) * | 2019-06-14 | 2019-08-23 | 安徽理工大学 | The centrifugal type microfludic chip of chlorine residue in a kind of DPD spectrophotometry water |
| CN110487783A (en) * | 2019-09-08 | 2019-11-22 | 杭州陆恒生物科技有限公司 | A kind of chlorine residue detection reagent, kit and the application method of high stability |
| US12064758B2 (en) | 2021-08-20 | 2024-08-20 | Watts Regulator Co. | Stabilized reagent compositions, systems and methods using the same |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102937579A (en) * | 2012-10-31 | 2013-02-20 | 广东环凯微生物科技有限公司 | Rapid determination tablet for free chlorine residuals for water quality on the spot and preparation method thereof |
| CN102937579B (en) * | 2012-10-31 | 2014-08-27 | 广东环凯微生物科技有限公司 | Rapid determination tablet for free chlorine residuals for water quality on the spot and preparation method thereof |
| EP2784503A1 (en) * | 2013-03-29 | 2014-10-01 | LaMotte Chemical Products Company | Reagent for Detection and Assessment of Free Chlorine in Aqueous Solution |
| EP2784502A1 (en) * | 2013-03-29 | 2014-10-01 | LaMotte Chemical Products Company | Reagent for detection and assessment of total chlorine in aqueous solution |
| US8987000B2 (en) | 2013-03-29 | 2015-03-24 | LaMotte Chemical Products Company | Reagent for detection and assessment of free chlorine in aqueous solution |
| US8993337B2 (en) | 2013-03-29 | 2015-03-31 | LaMotte Chemical Products Company | Reagent for detection and assessment of total chlorine in aqueous solution |
| CN110161026A (en) * | 2019-06-14 | 2019-08-23 | 安徽理工大学 | The centrifugal type microfludic chip of chlorine residue in a kind of DPD spectrophotometry water |
| CN110487783A (en) * | 2019-09-08 | 2019-11-22 | 杭州陆恒生物科技有限公司 | A kind of chlorine residue detection reagent, kit and the application method of high stability |
| US12064758B2 (en) | 2021-08-20 | 2024-08-20 | Watts Regulator Co. | Stabilized reagent compositions, systems and methods using the same |
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