Fibre-optic pH probe based on the use of an immobilised colorimetric indicator

Kirkbright, G. F.; Narayanaswamy, Ramaier; Welti, Neal A.

doi:10.1039/an9840901025

Cited by 129 publications

(35 citation statements)

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“…The decreased quantum yield has a minor effect on the pH sensitive fluorophore due to the short decay time but due to the longer lifetime of the pH insensitive dye, a larger effect is seen when integrating the t ex time window. The observed temperature dependence of the pH spot is similar to that reported for an immobilised sensor spot by Schroeder et al [53], but smaller than reported by Kirkbright et al [77]. The temperature dependence requires the accurate recording of temperature and a correction of the final pH readings.…”

Section: Temperature Dependencesupporting

confidence: 59%

Characterisation and deployment of an immobilised pH sensor spot towards surface ocean pH measurements

Clarke

Achterberg

Rérolle

et al. 2015

Analytica Chimica Acta

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The oceans are a major sink for anthropogenic atmospheric carbon dioxide, and the uptake causes changes to the marine carbonate system and has wide ranging effects on flora and fauna. It is crucial to develop analytical systems that allow us to follow the increase in oceanic pCO2 and corresponding reduction in pH. Miniaturised sensor systems using immobilised fluorescence indicator spots are attractive for this purpose because of their simple design and low power requirements. The technology is increasingly used for oceanic dissolved oxygen measurements. We present a detailed method on the use of immobilised fluorescence indicator spots to determine pH in ocean waters across the pH range 7.6-8.2. We characterised temperature (-0.046 pH/°C from 5 to 25 °C) and salinity dependences (-0.01 pH/psu over 5-35), and performed a preliminary investigation into the influence of chlorophyll on the pH measurement. The apparent pKa of the sensor spots was 6.93 at 20 °C. A drift of 0.00014 R (ca. 0.0004 pH, at 25 °C, salinity 35) was observed over a 3 day period in a laboratory based drift experiment. We achieved a precision of 0.0074 pH units, and observed a drift of 0.06 pH units during a test deployment of 5 week duration in the Southern Ocean as an underway surface ocean sensor, which was corrected for using certified reference materials. The temperature and salinity dependences were accounted for with the algorithm, R=0.00034-0.17·pH+0.15·S(2)+0.0067·T-0.0084·S·1.075. This study provides a first step towards a pH optode system suitable for autonomous deployment. The use of a short duration low power illumination (LED current 0.2 mA, 5 μs illumination time) improved the lifetime and precision of the spot. Further improvements to the pH indicator spot operations include regular application of certified reference materials for drift correction and cross-calibration against a spectrophotometric pH system. Desirable future developments should involve novel fluorescence spots with improved response time and apparent pKa values closer to the pH of surface ocean waters.

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Section: Temperature Dependencesupporting

confidence: 59%

Characterisation and deployment of an immobilised pH sensor spot towards surface ocean pH measurements

Clarke

Achterberg

Rérolle

et al. 2015

Analytica Chimica Acta

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“…Glass pH electrodes are unsuitable for certain applications like determination of intracellular pH, microscopy studies as well as measurement of extreme pH values (<1 or >9) [5]. New kinds of optical sensors have attracted great attention of researchers due to their possible applications in industrial, environmental, and medicinal areas [6,7]. Several kinds of optical pH and ion sensors have been published so far [8][9][10][11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Syntheses and pH Sensing Applications of Imine-Coupled Phenol and Polyphenol Species Derived from 2-Amino-4-Nitrophenol

2012

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Developing of new generation optical polymeric pH sensors has increasing importance due to their stable structures. Available polymeric sensors for different pH ranges are already needed. In the present study new kinds of monomeric and polymeric absorption pH sensors (HBANP and PHBANP) derived from 2-amino-4-nitrophenol were prepared. The novel sensors were investigated in various pH values using spectrophotometric, spectrofluorometric, and electrochemical techniques. The sensors showed sigmoidal correlations vs. pH range in optical measurements. These correlations were improved as mathematical formula to obtain the solution pH. HBANP and PHBANP differed from each other by response fields. HBANP had a sharp absorption increase between the pH of 6.5→7.5 while PHBANP spectrophotometrically responded at lower pHs. HBANP was colorless in acidic pHs, yellow-colored in neutral media and red-colored in alkaline pHs. With its colorimetric responses in various pHs HBANP can be used to develop color-tunable pH sensors. Electrochemical oxidation peak potentials and currents also particularly changed in various pHs.

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“…Different types of immobilization techniques for pH indicating dyes have been used [9], including (a) dye entrapment in different materials such as cellulose acetate [10,11], sol-gel [12], PVC [7], methacrylic-acrylic copolymers [13] and different composites like SiO 2 /ZrO 2 -organic polymer (styrene/methyl methacrylate copolymer or Nafion) [14], (b) retention of dye by ion-exchange materials such as Amberlite XAD-2 resin [15] or Dowex l-X10 resin [16], in some instances including the ionexchanger containing dyes in polymeric encapsulated membranes using PVC [17], (c) adsorption of the dye on materials such as non-ionic styrene/divinylbenzene copolymer [18], polyester/lycra blends textile [19], cellulose [20], cellulose acetate [21], or polymer track membranes combining retention in surface and bulk [22], (d) covalent binding of dye by different synthetic strategies to form microparticles or membranes, in some cases formed on glass fibre, using different polymers such as polyacrylamide [8,23], triacetylcellulose [24], cellulose acetate [25,26], agarose [27] or polyamide [28], among others, (e) polymerization of monomers to prepare both membrane and dye, as with aniline [29] or pyrrole [30].…”

Section: Introductionmentioning

confidence: 99%