Patent Application
20150111304
This application relates generally to carbon analysis in an aqueous sample and, more particularly, to the measurement of carbon in an aqueous sample using a ferrate as an oxidizer for the organic components in the sample and measurement of generated carbon dioxide. Embodiments of a method disclosed herein are directed to the measurement of Total Inorganic Carbon (TIC), Total Organic Carbon (TOC) and Total Carbon (TC).
Commercial Total Organic Carbon (TOC) analyzers are used to measure the quantity of organic carbon present in a water sample, which is an indicator of water purity. Applications for TOC measurements include ultrapure water for pharmaceutical and electronics manufacturing, as well as municipal drinking water and wastewater and industrial wastewater from chemical and petrochemical plants, as examples.
Measurement of TOC relies on the conversion or oxidation of organic material in a water sample to CO2, which can then be measured by conductivity or Nondispersive Infrared (NDIR) detection. Two common methods of oxidation include UV/Persulfate and high-temperature combustion. The UV/Persulfate method uses the combination of ultraviolet light and strong chemical oxidants, for example, sodium persulfate, to convert organic material to CO2. High-temperature combustion uses thermal oxidation processes, often in the presence of catalysts, to convert the organic materials to CO2. Both methods use an acid, for example, phosphoric acid, to initially remove “Total Inorganic Carbon” or TIC present in the water sample, as CO2, prior to oxidation. Examples of commercially available TOC Analyzers include a UV/Persulfate TOC analyzer (GE/Sievers 900 Laboratory Analyzer) and a high-temperature combustion TOC analyzer (Shimadzu TOC-L). Another example is a combined catalytic ozone/base oxidizer (Hach Company Biotector B7000).
In TOC oxidative methods, an acid reagent is first added to convert the inorganic carbon in the sample (in the form of bicarbonate and carbonate anions) to gaseous CO2. The CO2 is removed by sparging the solution with a CO2-free carrier gas, for example, purified nitrogen, to remove the liberated CO2 which may then be measured as inorganic carbon (TIC). A chemical oxidant is then added to the solution to oxidize the organic carbon present in the sample to a carbonate species and, in the case of UV/persulfate oxidation, generally with the aid of ultraviolet radiation. The CO2 is again sparged from the solution using a CO2-free gas, which may then be measured as organic carbon (TOC). The sum of the TIC and TOC yields the Total Carbon (TC) in the sample.
An embodiment of a method for measuring total organic carbon in a water sample, comprises the steps of: (a) adding an inorganic acid to the sample to lower the pH of said sample to a pH less than about 4; (b) removing carbon dioxide generated from inorganic carbon present in the sample; (c) providing sufficient ferrate to the sample adjusted to a chosen pH for a sufficient period of time to oxidize the organic carbon therein; (d) acidifying the sample with an inorganic acid to a pH of less than about 4; (e) removing carbon dioxide generated from organic carbon present in the sample; and (f) measuring the carbon dioxide generated from organic carbon present in the sample, whereby the measurement of the total organic carbon present in the sample is obtained.
The method of paragraph [0006], wherein the inorganic acid is chosen from phosphoric acid, sulfuric acid, nitric acid, and hydrochloric acid.
The method of paragraph [0006], wherein the steps of removing the carbon dioxide comprise sparging the sample with a carrier gas.
The method of paragraph [0006], wherein the steps of removing the carbon dioxide comprise agitating the sample.
The method of paragraph [0006], wherein the steps of removing the carbon dioxide comprise applying ultrasonic energy to the sample.
The method of paragraph [0006], wherein the chosen pH value is between about 6 and about 12.
The method paragraph [0006], wherein the step of measuring the carbon dioxide comprises infrared absorption.
The method of paragraph [0006], wherein the step of providing sufficient ferrate to said sample for a sufficient period of time to oxidize the organic carbon therein comprises adding FeO42− to the sample.
The method of paragraph [0006], wherein the step of providing sufficient ferrate to the sample for a sufficient period of time to oxidize the organic carbon therein comprises generating Fe(VI) and other high valence states of iron in solution.
The method of paragraph [0006], further comprising measuring total inorganic carbon after the step of removing carbon dioxide generated from inorganic carbon present in said sample.
The method of paragraph [0006], further comprising the step of adding ozone to the sample.
The method of paragraph [0016], wherein the ozone is added in the presence of ferrate.
The method of paragraph [0006], further comprising the step of irradiating said sample with UV light.
Another embodiment of a method for measuring total organic carbon in a water sample, comprises: dividing the sample into a first aliquot and a second aliquot; adding an inorganic base to the first aliquot to adjust the pH of the first aliquot to a chosen value; providing ferrate to the first aliquot in a sufficient amount for a sufficient time to oxidize the organic carbon therein; acidifying the first aliquot with an inorganic acid to a pH of less than about 4; measuring the carbon dioxide generated from total carbon present in the first aliquot; adding an inorganic acid to the second aliquot to lower the pH of the second aliquot to a value less than about 4; measuring the carbon dioxide generated from total inorganic carbon present in the second aliquot; and determining total organic carbon of the sample by subtracting the amount of measured carbon dioxide from the total inorganic carbon present in the second aliquot from the measured carbon dioxide generated from the total carbon present in the first aliquot.
The method of paragraph [0019], wherein the inorganic acid is chosen from phosphoric acid, sulfuric acid, nitric acid, and hydrochloric acid.
The method of paragraph [0019], further comprising the steps of removing the carbon dioxide from the second aliquot before said step of measuring carbon dioxide generated from total inorganic carbon present in the sample, and removing the carbon dioxide from the first aliquot before the step of measuring the carbon dioxide generated from total carbon present in the sample.
The method of paragraph [0021], wherein the steps of removing the carbon dioxide from the aliquots comprise sparging the aliquots with a CO2-free carrier gas.
The method of paragraph [0021], wherein the steps of removing the carbon dioxide from said aliquots comprise agitating the aliquots.
The method of paragraph [0021], wherein the steps of removing the carbon dioxide from said aliquots comprise applying ultrasonic energy to the aliquots.
The method of paragraph [0019], wherein the chosen pH value is between about 6 and about 12.
The method of paragraph [0019], wherein the inorganic base is chosen from bases comprising hydroxide ions.
The method of paragraph [0026], wherein the inorganic base is chosen from sodium hydroxide, potassium hydroxide, and combinations thereof.
The method of paragraph [0019], wherein the step of measuring carbon dioxide generated from total inorganic carbon present in the second aliquot, and the step of measuring the carbon dioxide generated from total carbon present in the first aliquot comprise measuring infrared absorption.
The method of paragraph [0019], wherein the step of providing ferrate to the first aliquot in a sufficient amount for a sufficient time to oxidize the organic carbon therein comprises adding FeO42− to the first aliquot.
The method of paragraph [0019], wherein the step of providing ferrate to the first aliquot in a sufficient amount for a sufficient time to oxidize the organic carbon therein comprises generating Fe(VI) and other high valence states of iron in solution.
The method of paragraph [0030], wherein the step of generating Fe(VI) and other high valence states of iron in solution comprises electrochemically generating Fe(VI) from lower valences of iron in solution.
The method of paragraph [0019], further comprising the step of adding ozone to said sample.
The method of paragraph [0032], wherein the ozone is added in the presence of ferrate.
The method of paragraph [0019], further comprising the step of irradiating said sample with UV light.
The method of paragraph [0019], wherein the first aliquot and said second aliquot are treated at the same time.
An embodiment of a method for measuring total carbon in a water sample, comprises the steps of: (a) providing sufficient ferrate to the sample adjusted to a chosen pH for a sufficient period of time to oxidize the total carbon therein; (b) acidifying the sample with an inorganic acid to a pH of less than about 4; (c) removing carbon dioxide generated from total carbon present in the sample; and (d) measuring the carbon dioxide generated from total carbon present in the sample, whereby the measurement of the total carbon present in the sample is obtained.
The method of paragraph [0036], further comprising the steps of adding an inorganic acid to the sample to lower the pH of said sample to a pH less than about 4; and removing carbon dioxide generated from inorganic carbon present in the sample, before the step of providing sufficient ferrate to the sample.
The method of paragraph [0036], wherein the inorganic acid is chosen from phosphoric acid, sulfuric acid, nitric acid, and hydrochloric acid.
The method of paragraph [0036], wherein the step of removing the carbon dioxide comprises sparging the sample with a CO2-free carrier gas.
The method of paragraph [0036], wherein the step of removing the carbon dioxide comprises agitating the sample.
The method of paragraph [0036], wherein the step of removing the carbon dioxide comprises applying ultrasonic energy to the sample.
The method of paragraph [0036], wherein the chosen pH is between about 6 and about 12.
The method of paragraph [0036], wherein the step of measuring the carbon dioxide comprises infrared absorption.
The method of paragraph [0036], wherein the step of providing sufficient ferrate to the sample for a sufficient period of time to oxidize the organic carbon therein, comprises adding FeO42− to the sample.
The method of paragraph [0036], wherein the step of providing sufficient ferrate to the sample for a sufficient period of time to oxidize the organic carbon therein comprises generating Fe(VI) and other high valence states of iron in solution.
The method of paragraph [0036], further comprising measuring total inorganic carbon after the step of removing carbon dioxide generated from total carbon present in the sample.
The method of paragraph [0036], further comprising the step of adding ozone to the sample.
The method of paragraph [0047], wherein said ozone is added in the presence of ferrate.
The method of paragraph [0036], further comprising the step of irradiating the sample with UV light.
In the drawings:
Briefly, embodiments disclosed herein include methods for measurement of Total Organic Carbon (TOC), Total Inorganic Carbon (TIC) and Total Carbon (TC) in aqueous samples using higher valence iron compositions as oxidants. For example, the organic material in the sample is oxidized using ferrate either generated in situ or as the salt of an alkali metal, as examples, in a basic solution or in an appropriate pH buffer solution to optimize the oxidation process. Carbon dioxide generated during the oxidation process is measured using standard procedures and related to the carbon present in the sample. During the oxidation, the pH can be gradually lowered by adding a mineral acid such that optimum oxidation conditions may be achieved for different organic species. Oxidation using ferrate does not oxidize chloride ions and hence is not affected by the presence of chloride during organic compound oxidation process.
As used herein, the term “ferrate” means iron in a valence state greater than zero, including +1, +2, +3, +4, +5, and +6, unless the context clearly dictates otherwise.
The term “other high valence states of iron” means Fe(IV) and Fe(V).
The term “lower valences of iron” includes iron with a valence of 0-3, in other words, Fe, Fe+(Fe(I)), Fe2+(Fe(II)), and Fe3+(Fe(III)).
Monitoring of the ferrate depletion caused by oxidation of the organics may be used to determine when the carbon oxidation is complete. When the level of ferrate reaches steady state, further mineral acid is added to the sample to lower the pH of the oxidized sample to a pH of approximately 3, as an example, such that CO2 may be liberated and subsequently sparged from the sample. Carbon dioxide may also be liberated from the sample by agitating the sample, and/or applying ultrasonic energy thereto, lowering the headspace pressure, or heating the sample, as examples. The released, gas-phase carbon dioxide is entrained in a carrier gas and directed to a CO2 measurement device. The quantity of CO2 produced is proportional to the oxidized carbon in the sample. Prior to the oxidation step, inorganic carbon may be removed as TIC, and the direct, indirect or electrochemical measurement of CO2 following oxidation then becomes a measure of the total organic carbon in the sample.
Embodiments disclosed herein provide methods for carbon analysis in samples without the use of toxic reagents, and with high immunity to chloride ion interference. Additionally detection of ferrate depletion permits determination of completion of oxidation of the organic species in the sample.
The oxidation of the organic species by ferrate may be assisted by introducing ozone into the sample along with the ferrate, and/or applying ultraviolet radiation to the sample during the oxidation process. The production of hydroxyl radicals using ozone is described in U.S. Pat. No. 6,623,974 B1 for “Method And Apparatus For The Analysis Of A Liquid Carrying A Suspension Of Organic Matter,” the contents of which are hereby incorporated by reference herein for all that it discloses and teaches.
Sources of ferrate ion include alkali metal salts such as Na2FeO4 (sodium ferrate) and K2FeO4 (potassium ferrate). Iron in the lower valences 0-3 can be oxidized to the higher valences that have sufficient oxidation potential to oxidize organic compounds found in the environment. For example, oxidants such as ozone, hypochlorous acid and hydrogen peroxide, among others, may oxidize the lower valence forms of iron to the higher valences. Ferrate(VI) salts may be generated by oxidizing iron in an aqueous medium with strong oxidizing agents under alkaline conditions, or in the solid state by heating a mixture of iron filings and powdered potassium nitrate (R. K. Sharma (2007), Text Book Of Coordination Chemistry, Discovery Publishing House, pp. 124-125). For example, ferrates are produced by heating iron(III) hydroxide with sodium hypochlorite in alkaline solution:
2Fe(OH)3+3OCI−+4OH−→2[FeO4]2−+5H2O+3CI−
(See, e.g., Gary Wulfsberg (1991), Principles of descriptive inorganic chemistry, University Science Books, pp. 142-143). The anion is typically precipitated as the barium(II) salt, forming barium ferrate. Id.
Ferrate may also be prepared in situ by electrolysis, using an iron anode and a cathode, between which a suitable electrical current is applied, and a light-transparent sample cell for measuring the generated ferrate by colorimetric detection (aqueous ferrate has its maximum absorption at approximately 504 nm). The [FeO4]2− ions are generated at the anode. An amount of alkali metal hydroxide (potassium hydroxide and/or sodium hydroxide, as examples) may be added to the sample cell to bring the cell contents to an alkaline condition. A U.S. application and a PCT application, both entitled “Apparatus, Composition and Method for Determination of Chemical Oxidation Demand” and filed concurrently herewith, describe with more particularity a system and method for generating ferrate and are incorporated by reference in their entirety herein. See also, U.S. Pat. No. 8,449,756 B2 “Method for Producing Ferrate (V) and/or (VI)”, which describes the generation of ferrate in an electrochemical cell, which is hereby incorporated by reference herein for all that it discloses and teaches.
The ferrate anion is unstable at neutral or acidic pH values, decomposing to iron(III):
[FeO4]2−+3e−+8H+Fe3++4H2O.
The reduction goes through intermediate species in which iron has oxidation states +5 and +4 (See. e.g., Egon Wiberg; Nils Wiberg; Arnold Frederick Holleman (2001), Inorganic chemistry, Academic Press, pp. 1457-1458). These anions are more reactive than Fe(VI) (See, e.g., Gary M. Brittenham (1994), Raymond J. Bergeron, ed., The Development of Iron Chelators for Clinical Use, CRC Press, pp. 37-38). In alkaline conditions, ferrates are more stable, lasting for about 5 h to about 50 h at pH ≧9. Id.
Aqueous solutions of ferrates are pink when dilute, and deep red or purple at higher concentrations. The ferrate ion is a stronger oxidizing agent than permanganate (See, e.g., Kenneth Malcolm Mackay; Rosemary Ann Mackay; W. Henderson (2002), Introduction to modern inorganic chemistry (6th ed.), CRC Press, pp. 334-335), and will oxidize chromium(III) to dichromate, (See, e.g., Amit Arora (2005), Text Book Of Inorganic Chemistry, Discovery Publishing House, pp. 691-692) and ammonia to molecular nitrogen (See, e.g., Karlis Svanks (June 1976), “Oxidation of Ammonia in Water by Ferrates (VI) and (IV)” (PDF), Water Resources Center, Ohio State University, p. 3, retrieved 2013-09-30).
It is known that for acidic pH values (below about 6) ferrate oxidization of water predominates. As the pH is increased, a transition occurs where ferrate oxidation of organics begins (generally between about pH 6 to about pH 9). At above about pH 9, ferrate preferentially oxidizes organics as opposed to water.
Carbon analysis in liquid samples using ferrate oxidation may be performed under both flowing and static sample conditions.
Reference will now be made in detail to exemplary embodiments illustrated in the accompanying drawings. In the FIGURES, similar structure will be identified using identical reference characters. It will be understood that the FIGURES are for the purpose of describing particular embodiments and are not intended as limiting. Turning now to
As mentioned hereinabove, ozone and/or ultraviolet radiation may be used to augment the ferrate oxidation by introducing these oxidants into cell 14, by well-known methods (not shown in
Detection of CO2 may be accomplished using an IR detector. Flow-through IR absorption cell 30 in
TOC=S*(C−Cb)/(CS−Cb).
The foregoing description has been presented for purposes of illustration and description and is not intended to be exhaustive or limiting. Many modifications and variations are possible in light of the above teaching.
This application claims priority to U.S. provisional application No. 61/894,906 filed Oct. 23, 2013 and U.S. provisional application No. 61/981,671 filed Apr. 18, 2014.
| Number | Date | Country | |
|---|---|---|---|
| 61981671 | Apr 2014 | US | |
| 61894906 | Oct 2013 | US |
