Method and apparatus for measuring pH of low alkalinity solutions

• US 20080280373A1
• Filed: 05/07/2007
• Published: 11/13/2008
• Est. Priority Date: 05/07/2007
• Status: Active Grant

• Current Assignee: BL Technologies Inc. (Ashland Global Holdings, Inc.)
• Original Assignee: General Electric Company
• Inventors: Zhang, Li, Xiao, Caibin, Cui, Weiyi, Chen, Bingzhi
• Granted Patent: US 7,883,898 B2
• Time in Patent Office: Days
• US Class Current: 436/163
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/80 Indicating pH value
• CPC Class Codes: Y10T 436/10 Composition for standardization, calibration, simulation, stabilization, preparation or preservation; processes of use in preparation for chemical testing

Abstract

Systems and methods are described for measuring pH of low alkalinity samples. The present invention provides a sensor array comprising a plurality of pH indicators, each indicator having a different indicator concentration. A calibration function is generated by applying the sensor array to a sample solution having a known pH such that pH responses from each indicator are simultaneously recorded versus indicator concentration for each indicator. Once calibrated, the sensor array is applied to low alkalinity samples having unknown pH. Results from each pH indicator are then compared to the calibration function, and fitting functions are extrapolated to obtain the actual pH of the low alkalinity sample.

Claims

1. A method for measuring pH, comprising the steps of:

providing a pH sensor array having a plurality of pH indicators, each said indicator having a different indicator concentration;

applying said sensor array to a sample solution having a known pH;

measuring a first pH response from each said indicator simultaneously;

generating a calibration function representing said first pH response;

applying said sensor array to a low alkalinity sample solution having an unknown pH;

measuring a second pH response from each said indicator simultaneously;

comparing said second pH response with said calibration function so as to obtain a preliminary pH value from each said indicator;

generating a fitting function representing said preliminary pH values; and

extrapolating said fitting function when indicator concentration is zero to estimate the actual pH of said unknown sample.

2. The method of claim 1, wherein said extrapolating step comprises generating linear intercept points of said fitting function to obtain pH of said unknown sample.

3. The method of claim 2, wherein said extrapolating step comprises an extrapolation algorithm determined by the equation:

4. The method of claim 3, wherein said indicators are solid polymer-based, pH indicator-containing films.

5. The method of claim 4, wherein said indicators are colorimetric pH indicators or fluorescent pH indicators.

6. The method of claim 5, wherein said colorimetric pH indicators are selected from the group consisting of phenol red, cresol red, m-cresol purple, thymol blue, bromochlorophenol blue W.S., bromocresol green, chlorophenol red, bromocresol purple, bromothymol blue, neutral red, phenolphthalein, o-cresolphthalein, nile blue A, thymolphthalein, bromophenol blue, metacresol purple, malachite green, brilliant green, crystal violet, methyl green, methyl violet 2B, picric acid, naphthol yellow S, metanil yellow, basic fuchsin, phloxine B. methyl yellow, methyl orange, alizarin.

7. The method of claim 1, wherein said pH response is measured by colorimeter, spectrophotometer, or fluorescent spectrometer.

8. The method of claim 4, wherein said solid films are prepared from water-soluble polymers.

9. The method of claim 4, wherein said solid films are prepared from Poly 2-Hydroxyethyl Methacrylate (pHEMA) or cellulose acetate.

10. The method of claim 4, wherein said sensor array comprises at least four pH indicators having concentrations on the order of about 0.01% to 10%.

11. The method of claim 3, further comprising the step of generating graphical representations of said calibration and fitting functions.

12. A system for measuring pH, comprising:

a pH sensor array having a plurality of pH indicators, each said indicator having a different indicator concentration;

means for applying said sensor array to a sample solution having a known pH;

means for measuring a first pH response from each said indicator simultaneously;

means for generating a calibration function representing said first pH response;

means for applying said sensor array to a low alkalinity sample solution having an unknown pH;

means for measuring a second pH response from each said indicator simultaneously;

means for comparing said second pH response with said calibration function so as to obtain a preliminary pH value from each said indicator;

means for generating a fitting function representing said preliminary pH values; and

means for extrapolating said fitting function when indicator concentration is zero to estimate the actual pH of said unknown sample.

13. The system of claim 12, wherein said means for extrapolating comprises means for generating linear intercept points of said fitting function to obtain pH of said unknown sample.

14. The system of claim 13, wherein said means for extrapolating comprises an extrapolation algorithm determined by the equation:

15. The system of claim 14, wherein said indicators are solid polymer-based pH indicator containing films.

16. The system of claim 15, wherein said indicators are colorimetric pH indicators or fluorescent pH indicators.

17. The system of claim 16, wherein said colorimetric pH indicators are selected from the group consisting of phenol red, cresol red, m-cresol purple, thymol blue, bromochlorophenol blue W.S., bromocresol green, chlorophenol red, bromocresol purple, bromothymol blue, neutral red, phenolphthalein, o-cresolphthalein, nile blue A, thymolphthalein, bromophenol blue, metacresol purple, malachite green, brilliant green, crystal violet, methyl green, methyl violet 2B, picric acid, naphthol yellow S, metanil yellow, basic fuchsin, phloxine B. methyl yellow, methyl orange, alizarin.

18. The system of claim 15, wherein said solid films are prepared from water-soluble polymers, Poly 2-Hydroxyethyl Methacrylate (pHEMA) or cellulose acetate.

19. The system of claim 15, wherein said sensor array comprises at least four pH indicators having concentrations on the order of about 0.01% to 10%.

20. The system of claim 14, further comprising means for generating graphical representations of said calibration and fitting functions.