Granted Patent B2

US 8,847,163 · App. 12/744,404 · Granted Sep 30, 2014

Abstract

Claims (68)

1. A method of estimating the respective concentrations [X] and [Y] of at least two components, X and Y, in a solution, the method comprising:

acquiring absorption spectra for a plurality of solutions comprising variable concentrations of X and Y and thereby generating a library of reference data;

acquiring an absorption spectrum for the solution;

determining the wavelength, λ max , at which maximum absorbance occurs within a first wavelength range of the absorbance spectrum for the solution; and

comparing λ max with the reference data to derive first estimates of [X] and [Y].

2. The method of claim 1 , further comprising:

defining first ranges of possible values for each of [X] and [Y], the ranges including the first estimates of [X] and [Y], respectively;

selecting a first set of pairs, each pair comprising a value from each of the first ranges;

for each pair, calculating a total theoretical absorbance at a plurality of wavelengths and extrapolating the theoretical absorbances so calculated, to produce a continuous theoretical absorption spectrum over a wavelength range substantially overlapping the range of the acquired spectrum of the solution;

comparing the continuous theoretical absorption spectra so obtained with the absorption spectrum of the solution; and

selecting as second estimates of [X] and [Y], the members of the pair giving rise to the continuous theoretical absorption spectrum which most closely matches the absorption spectrum for the solution.

3. The method of claim 2 , further comprising:

defining second ranges of possible values for each of [X] and [Y], the ranges including the second estimates of [X] and [Y], respectively;

selecting a second set of pairs, each pair comprising a value from each of the second ranges;

for each pair in the second set, calculating a total theoretical absorbance at a plurality of wavelengths and extrapolating the theoretical absorbances so calculated, to produce a continuous theoretical absorption spectrum over the wavelength range substantially overlapping the range of the acquired spectrum of the solution;

comparing the continuous theoretical absorption spectra so obtained with the absorption spectrum of the solution; and

selecting as third estimates of [X] and [Y], the members of the pair giving rise to the continuous theoretical absorption spectrum which most closely matches the absorption spectrum for the solution.

4. The method of claim 2 , further comprising:

calculating from the second estimate of [X], a theoretical absorbance due to X at a wavelength, λ 2 , outside of the first wavelength range;

subtracting the theoretical absorbance so calculated from the absorbance at λ 2 indicated by the absorption spectrum for the solution, to yield an estimated absorption A Z at λ 2 , attributable to a third component, Z, of the solution; and

calculating from A Z , a first estimate of [Z], the concentration of component Z in the solution.

5. The method of claim 4 , further comprising:

defining a second range of possible values of [X], the second range including the second estimate of [X], and a first range of possible values of [Z], the first range including the first estimate of [Z];

selecting a second set of pairs, each pair comprising a value from the second range of possible values of [X] and a value from the first range of possible values of [Z];

for each pair in the second set, calculating a total theoretical absorbance at a plurality of wavelengths and extrapolating the theoretical absorbances so calculated, to produce a continuous theoretical absorption spectrum over the wavelength range substantially overlapping the range of the acquired spectrum of the solution;

comparing the continuous theoretical absorption spectra so obtained with the absorption spectrum of the solution and;

selecting as a third estimate of [X] and a second estimate of [Z], the members of the pair giving rise to the continuous theoretical absorption spectrum which most closely matches the absorption spectrum for the solution.

6. The method of claim 4 , wherein the acquired absorption spectra are ultraviolet spectra.

7. The method of claim 6 , where X═NO 3 − .

8. The method of claim 7 , where Y═OCl − .

9. The method of claim 8 , where Z═HOCl.

10. The method of claim 4 , wherein at least one of X, Y and Z is selected from:

ozone, monochloramine, chlorine dioxide, potassium permanganate and iodine.

11. An apparatus for estimating the respective concentrations [X] and [Y] of at least two components, X and Y, in a solution, the apparatus comprising:

a source of electromagnetic radiation of variable wavelength;

a cell suitable for retaining a sample of the solution and substantially transparent to the electromagnetic radiation;

a detector arranged to detect electromagnetic radiation radiated from the source and passing through the cell and sample;

a processor operable to vary the wavelength produced by the source of radiation and to store, in a computer readable data storage medium, data produced by the detector as the wavelength is varied, thereby generating an absorption spectrum for the solution;

wherein the computer readable data storage medium contains a library of reference data representing absorption spectra for a plurality of solutions comprising variable concentrations of X and Y; and

wherein the processor is configured to determine the wavelength, λ max , at which maximum absorbance occurs within a first wavelength range of the absorption spectrum for the solution and compare λ max with the library of reference data to derive first estimates of [X] and [Y].

12. The apparatus of claim 11 , wherein the processor is further configured to:

define first ranges of possible values for each of [X] and [Y], the ranges including the first estimates of [X] and [Y], respectively;

select a first set of pairs, each pair comprising a value from each of the first ranges;

for each pair in the first set, calculate a total theoretical absorbance at a plurality of wavelengths and extrapolate the theoretical absorbances so calculated, to produce a continuous theoretical absorption spectrum over a wavelength range substantially overlapping the range of the acquired spectrum of the solution;

compare the continuous theoretical absorption spectra so obtained with the absorption spectrum of the solution; and

select as second estimates of [X] and [Y], the members of the pair giving rise to the continuous theoretical absorption spectrum which most closely matches the absorption spectrum for the solution.

13. The apparatus of claim 12 , wherein the processor is further configured to:

define second ranges of possible values for each of [X] and [Y], the ranges including the second estimates of [X] and [Y] respectively;

select a second set of pairs, each pair comprising a value from each of the second ranges;

for each pair in the second set, calculate a total theoretical absorbance at a plurality of wavelengths and extrapolate the theoretical absorbances so calculated, to produce a continuous theoretical absorption spectrum over the wavelength range substantially overlapping the range of the acquired spectrum of the solution;

compare the continuous theoretical absorption spectra so obtained with the absorption spectrum of the solution; and

select as third estimates of [X] and [Y], the members of the pair giving rise to the continuous theoretical absorption spectrum which most closely matches the absorption spectrum for the solution.

14. The apparatus of claim 10 , wherein the processor is further configured to:

calculate from the second estimate of [X] a theoretical absorbance due to X at a wavelength, λ 2 , outside of the first wavelength range;

subtract the theoretical absorbance so calculated from the absorbance at λ 2 indicated by the absorption spectrum for the solution, to yield an estimated absorbance A Z at λ 2 , attributable to a third component, Z, of the solution; and

calculate from A z , a first estimate of [Z], the concentration of component Z in the solution.

15. The apparatus of claim 14 , further wherein the processor is further configured to:

define a second range of possible values of [X], the second range including the second estimate of [X], and a first range of possible values of [Z], the first range including the first estimate of [Z];

select a second set of pairs, each pair comprising a value from the second range of possible values of [X] and a value from the first range of possible values of [Z];

for each pair in the second set, calculate a total theoretical absorbance at a plurality of wavelengths and extrapolate the theoretical absorbances so calculated, to produce a continuous theoretical absorption spectrum over the wavelength range substantially overlapping the range of the acquired spectrum of the solution;

compare the continuous theoretical absorption spectra so obtained with the absorption spectrum of the solution; and

select as a third estimate of [X] and a second estimate of [Z], the members of the pair giving rise to the continuous theoretical absorption spectrum which most closely matches the absorption spectrum for the solution.

16. The apparatus of claim 15 , wherein the absorption spectra are ultraviolet.

17. The apparatus of claim 16 , wherein the first range includes values between 250 nm and 330 nm.

18. The apparatus of claim 17 , wherein the first range includes values between 290 nm and 320 nm.

19. The apparatus of claim 18 , wherein λ 2 is between 235 nm and 245 nm.

20. The apparatus of claim 19 , wherein the cell provides a path length for ultraviolet radiation of greater than 50 cm.

21. The apparatus of claim 19 , wherein the cell provides a path length for ultraviolet radiation of greater than 100 cm.

Assignments (6)