TH102738A - Methods and equipment for pH measurement of low alkaline solutions. - Google Patents

Abstract

DC60 (25/07/51) A system and method are described for the measurement of pH of low-alkaline samples. The present invention provides a sensor assembly consisting of multiple pH indicators, each with a different indicator concentration. An adjustment function is constructed by applying the sensor assembly to a sample solution with a known pH, thus the pH response from each indicator is recorded simultaneously with the indicator concentration for each indicator. When adjusted, the sensor assembly is applied to a low-alkaline sample with an unknown pH. The result from each pH indicator is then compared to the adjustment function, and the correction function is extrapolated to obtain the true pH of the low-alkaline sample. The results from each pH indicator are then compared to the adjustment function, and the correction function is extrapolated to obtain the true pH of a low-alkaline sample.

Claims (20)

1. The method for measuring pH consists of the following steps: 1. Providing a set of pH sensors with multiple pH indicators, each with a different concentration; 2. Applying the sensor set to a sample solution with a known pH; 3. Measuring the first pH response from each indicator simultaneously; 4. Constructing a correction function representing that first pH response; 5. Applying the sensor set to a low-alkalinity solution with an unknown pH; 6. Measuring the second pH response from each indicator simultaneously; 7. Comparing the second pH response to the correction function to obtain the previous pH value from each indicator; 8. Constructing a correction function representing that previous pH; and 9. Extending the correction function when the indicator concentration is zero to estimate the true pH of the unknown sample. 2. The method of Claim 1, whereby the extrapolation procedure involves constructing a linear intersection of the correction function to obtain the pH of the unknown sample. 3. Method of Claim 2, where the extrapolate procedure consists of the extrapolate algorithm measured by equation; (chemical formula) i is the index associated with each pH indicator; Ini, is the concentration of the indicator itn; pHi is the second pH measurement of the indicator ith; and N is the number of pH indicators. 4. Method of Claim 3 whereby the indicator is a film composed of a solid polymer pH indicator. 5. Method of Claim 4, whereby the indicator is a colorimetric pH indicator or a fluorescent pH indicator. 6. Method of Claim 5, where colorimetric pH indicators are selected from a group comprising: phenol red, cressol red, m-cressol purple, thymol, bromochlorophenol blue W.S., bromocressol green, chlorophenol red, bromocressol purple, bromithymol blue, neutralate, phenol paraline, 0-cressol paraline, Nile blue A, thymol paraline, bromophenol blue, metacressol purple, malachite green, brilliant green, crystal violet, methyl green, methyl green, methyl violet 2B, picric acid, naphthol yellow S, methanol yellow, basic palocene B, methyl yellow, methyl orange, and alizarin. 7. Method of Claim 1 where the pH response is measured by a colorimeter, spectrometer, or fluorescent spectrophytometer. 8. Method of claim 4 where the said solid film is prepared from a water-soluble polymer. 9. Method of Claim 4 where the said solid film is prepared from poly 2-hydroxymethyl thadilate (pHEMA) or cellulose acetate. 10. Method of Claim 4 where the sensor assembly consists of at least four pH indicator substances with concentrations on the order of approximately 0.01% to 10%. 11. The method of claim 3 subsequently consists of steps for creating a visual representation of the aforementioned adjustment and correction functions. 12. The system for pH measurement consists of: a pH sensor set containing multiple pH indicators, each with a different concentration; a method for applying the sensor set to a sample solution with a known pH; a method for simultaneously measuring the first pH response from each indicator; a method for constructing an adjustment function that represents the first pH response; a method for applying the sensor set to a low-alkalinity sample solution with an unknown pH; a method for simultaneously measuring the second pH response from each indicator; a method for comparing the second pH response with the adjustment function to obtain the previous pH value from each indicator; a method for constructing a correction function that represents the previous pH value; and a method for extrapolating the correction function when the indicator concentration is zero to approximate the true pH of the unknown sample. 13. The system of claim 12, whereby the method for such extrapolation involves constructing a linear intersection of such correction function to obtain the pH of the unknown sample. 14. System of claims No. 13, where the method for such extrapolation consists of the extrapolation algorithm which is measured by the equation; (chemical formula) i is the index associated with each pH indicator; Ini, is the concentration of the indicator itn; pHi is the second pH measurement of the indicator ith; and N is the number of pH indicators. 15. Method of Claim 14, whereby the indicator is a film composed of a solid polymer pH indicator. 16. Method of Claim 15 where such indicator is a colorimetric pH indicator or a fluorescent pH indicator. 17. System of Claim 16 where colorimetric pH indicators are selected from a group comprising: phenol red, cressol red, m-cressol purple, thymol blue, bromochlorophenol blue W.S., bromocressol green, chlorophenol red, bromocressol purple, bromithymol blue, neutralate, phenol paraline, 0-cressol paraline, Nile blue A, thymol paraline, bromophenol blue, metacressol purple, malachite green, brilliant green, crystal violet, methyl green, methyl green, methyl violet 2B, picric acid, naphthol yellow S, methanol yellow, basic palocene B, methyl yellow, methyl orange. Alizarin 18. The method of claim 15, where such solid films are prepared from water-soluble polymers, poly2-hydroxymethyl thadilate (pHEMA) or cellulose acetate. 19. Method of Claim 4 where the sensor assembly consists of at least four pH indicator substances with concentrations on the order of approximately 0.01% to 10%. 20. The method of claim 14 subsequently includes a method for constructing a visual representation of the aforementioned adjustment and correction functions.