| US 7,432,109 B2 | ||
| Spetroscopic pH measurement using optimized mixtures of reagents to extend measurement range | ||
| Bhavani Raghuraman, Wilton, Conn. (US); Gale H. Gustavson, Brookfield, Conn. (US); Emilie Dressaire, Beziers (France); Oleg Zhdaneev, Tomsk (Russian Federation); Ronald Van Hal, Ridgefield, Conn. (US); Oliver Mullins, Ridgefield, Conn. (US); and Philippe Salamitou, Mamaroneck, N.Y. (US) | ||
| Assigned to Schlumberger Technology Corporation, Ridgefield, Conn. (US) | ||
| Filed on Feb. 19, 2004, as Appl. No. 10/782,209. | ||
| Claims priority of application No. 0227267.2 (GB), filed on Nov. 22, 2002. | ||
| Prior Publication US 2004/0219064 A1, Nov. 04, 2004 | ||
| Int. Cl. G01N 31/22 (2006.01); G01N 21/00 (2006.01) | ||
| U.S. Cl. 436—163 [436/164] | 11 Claims |
| 1. A method of identifying one or more sets of reagents wherein the one or more sets of reagents is used for determining the
pH of a sample, the method comprising:
a. identifying a target pH measurement range of the sample and a target pH accuracy;
b. identifying a plurality of reagents based on known reagent thermodynamic acid dissociation constants and spectral characteristics
such that their combination is expected to satisfy the targeted pH range of the sample;
c. identifying one or more spectral channels to make the pH measurement wherein the reagents have elevated optical densities;
d. mixing known relative concentrations of two or more reagents of the plurality of reagents to create one or more sets of
reagents;
e. characterizing at least one reagent set of the one or more sets of reagents wherein characterizing includes developing
a relationship between optical density ratio and pH based on the thermodynamic acid dissociation constants of the reagents,
relative concentrations of the reagents, and one or more spectral channels;
f. identifying the spectroscopic noise of a spectral analyzer to be used for the pH measurement;
g. performing an error analysis for at least one reagent set of the one or more sets of reagents wherein the error analysis
comprises developing a relationship between standard deviation in pH and spectroscopic noise in optical density based on the
relation developed in step (e);
h. optimizing the one or more sets of reagents with an optimization algorithm based on the developed relationship in step
(g) to satisfy the target pH accuracy over the target pH measurement range of the sample and determine one of optimum values
for relative concentrations or spectral channels or both; and
i. characterizing the one or more optimized reagent set.
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