Sensor array-based optical portable instrument for determination of pH

A portable optical instrument is presented that makes it possible to determine pH with a colorimetric sensor array. The use of four membranes containing acid–base indicators makes it possible to cover the full range of pH using the H (hue) coordinate measurements of the HSV colour space. pH sensitiv...

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Bibliographic Details
Published in:Sensors and actuators. B, Chemical Chemical, 2011-08, Vol.156 (2), p.840-848
Main Authors: Martinez-Olmos, A., Capel-Cuevas, S., López-Ruiz, N., Palma, A.J., de Orbe, I., Capitán-Vallvey, L.F.
Format: Article
Language:English
Subjects:
algorithms
Arrays
Color
colorimetry
Colour
detectors
Digital colour detector
Full-range optical pH sensor array
HSV colour space
immune system
Mathematical models
Membranes
OLED display
optical equipment
Portability
Portable instrumentation
Sensors
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Summary:A portable optical instrument is presented that makes it possible to determine pH with a colorimetric sensor array. The use of four membranes containing acid–base indicators makes it possible to cover the full range of pH using the H (hue) coordinate measurements of the HSV colour space. pH sensitive membranes were directly cast onto a plastic support to form a two-dimensional array, located between an OLED display as the programmable light source and a set of digital colour detectors. The resulting microcontroller-based system is immune to optical and electrical interferences. A complete optical and electrical characterization and optimization of the hand-held instrument was carried out. The instrument was used to determine pH using a simple algorithm to select the sensor output that was programmed in the microcontroller. The initial eleven candidate pH membranes were reduced to only four, which permit to obtain reliable pH values. The pH response of the selected four sensing elements was modelled, and calibration curves were applied to a validation set and real samples obtaining positive correlations between the real and predicted data.
ISSN:0925-4005
1873-3077
DOI:10.1016/j.snb.2011.02.052