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Abstract
A reservoir type of capillary microsensor for pCO(2) measurements is presented. The
sensor is based on the measurement of the fluorescence intensity of the anionic form
of the pH indicator 1-hydroxy-3,6,8-pyrenetrisulfonate in the form of its ion pair
with a quaternary ammonium base in an ethyl cellulose matrix. The glass capillary
containing the reservoir sensor was prepared by immersing the tip of the optical fiber
into the sensing agent very close to the sensor tip thus providing a very small volume
for the sensing reaction. The purpose of the sensing approach is to regenerate the
dye/buffer system by diffusion, which may be poisoned by interfering acids, or bleach
by photolysis. The fresh cocktail from the reservoir takes the place of protonated
form of the dye. The internal buffer system also makes the protonation-deprotonation
equilibria reversible. The distal tip of the internal buffer containing reservoir
is coated with a gas-permeable but ion-impermeable teflon membrane. The dynamic range
for the detection of pCO(2) is between 1 and 20 hPa, which corresponds to the range
of dissolved CO(2) in water. The response time is 15 s and the detection limit is
1 hPa of pCO(2.) The recovery performance of this sensor can be improved by means
of mechanical adjustment of the sensor tip in a micrometric scale.