Patent ID: 7026165

Claim:
A method of operating absorbance-based chemical sensors to achieve calibration-free measurements, the method comprising the steps of: a) establishing wavelength accuracy to within about 2-3 nanometers; b) eliminating stray light at all wavelengths to about less than 0.1% incident light; c) preparing an analyte-selectlve reagent at a concentration; d) equilibrating the analyte-selective reagent to an analyte; e) taking an intensity reading of the equilibrated analyte-selective reagent and analyte at a first wavelength (I λ1 ) with a reagent-based optical chemical sensor, wherein the sensor has been modified to allow the renewal of an analyte-selective reagent, wherein the first wavelength corresponds to an un-reacted form of the analyte-selective reagent, and taking an intensity reading of the equilibrated analyte-selective reagent and analyte at a second wavelength (I λ2 ), wherein the second wavelength corresponds to a reacted form of the analyte-selective reagent; f) replacing the equilibrated analyte-selective reagent and analyte with a spectrophotometric blank solution; g) taking an intensity reading of the blank solution at the first wavelength (I λ10 ) and taking an intensity reading of the blank solution at the second wavelength (I λ20 ); h) calculating an absorbance ratio using the equation A R =A λ1 /A λ2 , where A R is the absorbance ratio, A λ1 is absorbence at the first wavelength and A λ2 is absorbance at the second wavelength and, wherein A λ1 and A λ2 are determined by A λ = - log ⁢ ( ⁢ I λ ⁢ / ⁢ I λ ⁢ ⁢ 0 ⁢ ) ; ⁢ and i) calculating the sensor response with the molar absorptivities (ε) of the reacted (a) form of the analyto-selective reagent and the un-reacted form (b) of the analyte-selective reagent using the equation R = - log ⁡ ( A R - ε λ ⁢ ⁢ 1 ⁢ a / ε λ ⁢ ⁢ 2 ⁢ a ε λ ⁢ ⁢ 1 ⁢ b / ɛ λ ⁢ ⁢ 2 ⁢ a - A R ⁢ ε λ ⁢ ⁢ 2 ⁢ β / ε 2 ⁢ a ) = + ⁢ pK a - pH , wherein when the analyte-selective reagent is prepared accurately and reproducibly at the concentration sensor readings between sensors are calibration-free.