K. Toda et al., MINIATURIZED DETECTOR OF SULFUR-DIOXIDE BASED ON THE FLOW CONDUCTOMETRY OF AN ABSORBING SOLUTION, Bunseki Kagaku, 47(10), 1998, pp. 727-734
A miniaturized detector based on absorbing conductometry was construct
ed in order to measure the SO2 concentration in air. This detector is
not only small, but is also capable of continuous measurement of SO2,
unlike the conventional detectors for intermittent SO2 measurements. T
wo bilateral pairs of Pt electrodes were fabricated on a glass-epoxy s
ubstrate through conventional photolithography and sputtering. On this
substrate, a cavity for the flow of an absorbing solution was formed
with a Teflon sheet and a gas-permeable membrane. The absorbing soluti
on, H2SO4-H2O2, was made to flow through this cavity of 2 mm in width
and 0.5 mm in thickness by applying pressure to a reservoir of the sol
ution. The sample gas was introduced into the other side of the membra
ne. Gaseous SO2 permeated through the membrane and dissolved into the
absorbing solution, resulting in an increase in the electrical conduct
ivity of the solution. Any change in the conductivity was monitored us
ing Pt electrodes located both up- and downstream of the absorbing zon
e, and thus the SO2 concentrations were determined. The sensitivity an
d response time largely depended on the flow rate of the absorbing sol
ution. Since the standard flow rate employed was 20 mu l min(-1), the
volume of the waste solution, even over long-time operation, was suffi
ciently small to be carried. When the absorbing solution was flowed at
this rate, from 10 ppb to 1 ppm of SO2 could be measured and the chan
ge ratio in the conductivity was 0.971 ppm(-1). The response time (T-9
0%) was 82 sec under the same conditions. Other gases interfered sligh
tly; e.g. the sensitivity to CO2 was about 1/30000 of that of SO2, so
the selectivity; of this method was sufficiently good for facile use.
This study furnished a step for constructing a miniaturized total chem
ical analysis system (mu TAS) for SO2 measurements.