Title: Calibration-free optical chemical sensors

Abstract

An apparatus and method for taking absorbance-based chemical measurements are described. In a specific embodiment, an indicator-based pCO₂ (partial pressure of CO₂) sensor displays sensor-to-sensor reproducibility and measurement stability. These qualities are achieved by: 1) renewing the sensing solution, 2) allowing the sensing solution to reach equilibrium with the analyte, and 3) calculating the response from a ratio of the indicator solution absorbances which are determined relative to a blank solution. Careful solution preparation, wavelength calibration, and stray light rejection also contribute to this calibration-free system. Three pCO₂ sensors were calibrated and each had response curves which were essentially identical within the uncertainty of the calibration. Long-term laboratory and field studies showed the response had no drift over extended periods (months). The theoretical response, determined from thermodynamic characterization of the indicator solution, also predicted the observed calibration-free performance.

Inventors:

DeGrandpre, Michael D.

Issue Date:

Tue Apr 11 00:00:00 EDT 2006

Research Org.:

Univ. of Montana, Missoula, MT (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1175700

Patent Number(s):

7026165

Application Number:

09/775,386

Assignee:

University Of Montana

Patent Classifications (CPCs):

G - PHYSICS G01 - MEASURING G01N - INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES

Y - NEW / CROSS SECTIONAL TECHNOLOGIES Y02 - TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE Y02A - TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE

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G - PHYSICS G01 - MEASURING G01N - INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES

G01N21/274 - {Calibration, base line adjustment, drift correction}
G01N33/0039 - {for O3}

Y - NEW / CROSS SECTIONAL TECHNOLOGIES Y02 - TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE Y02A - TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE

Y02A50/20 - Air quality improvement or preservation

Y - NEW / CROSS SECTIONAL TECHNOLOGIES Y10 - TECHNICAL SUBJECTS COVERED BY FORMER USPC Y10T - TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION

Y10T436/20 - Oxygen containing
Y10T436/204998 - Inorganic carbon compounds

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DOE Contract Number:  

FG03-94ER6224

Resource Type:

Patent

Country of Publication:

United States

Language:

English

Subject:

47 OTHER INSTRUMENTATION