Biomedical Engineering Reference
In-Depth Information
(BCP) in the substitutional cladding using a sol-gel process. They report that their sensor
exhibits good repeatability and reversibility. They used the following gases as carrier gases
for ammonia: air, nitrogen, and argon. Out of these three, air gave the best response time
and sensitivity.
Malins et al. (1999)
point out that ammonia has been widely used for the production of
fertilizers, explosives, and as an industrial coolant. It is of importance to detect NH
3
present
in air quickly as even a small dose of ammonia vapor can cause acute poisioning in humans
on inhalation (
Cao and Duan, 2005
).
Cao and Duan (2005)
point out that traditionally
ammonia has been detected in laboratories using potentiometric electrodes (
Bailescu and
Cosofret, 1978; Meyerhoff, 1980; Fraticelli and Meyerhoff, 1981; Morf et al., 1981; West
et al., 1992; Morales-Bahnik et al., 1994; Buhlman et al., 1998
). Even though these detection
methods are accurate, sensitive, and selective,
Cao and Duan (2005)
explain that these
methods are expensive, consume analyte(s), and require the presence of an experienced oper-
ator. These authors report that optical fiber chemical sensors (OFCSs) exhibit some distinc-
tive properties. Their small size and sensor design flexibility makes them excellent tools for
in situ
and
in vivo
analysis. These authors used a sol-gel film to encode bromocresol purple
on the surface of a bared fiber code. Evanescent absorption was measured through a
spectrometer.
Figure 10.10a-c
shows the reversibility of the ammonia sensor.
Figure 10.10a
shows the
binding of 145 ppm NH
3
with air as a carrier gas to the optical fiber-based evanescent ammo-
nia sensor (
Cao and Duan, 2005
). A single-fractal analysis is adequate to describe the binding
kinetics. The values of the binding rate coefficient,
k
, and the fractal dimension,
D
f
, for a sin-
gle-fractal analysis are given in
Table 10.8
.
Figure 10.10b
shows the binding of 145 ppm NH
3
with air as a carrier gas (consecutive run
#2) to the optical fiber-based evanescent ammonia sensor (
Cao and Duan, 2005
). Once again,
a single-fractal analysis is adequate to describe the binding kinetics. The values of the bind-
ing rate coefficient,
k
, and the fractal dimension,
D
f
, for a single-fractal analysis are given in
Table 10.8
.
Figure 10.10c
shows the binding of 145 ppm NH
3
with air as a carrier gas (consecutive run
#3) to the optical fiber-based evanescent ammonia sensor (
Cao and Duan, 2005
). Once again,
a single-fractal analysis is adequate to describe the binding kinetics. The values of the bind-
ing rate coefficient,
k
and the fractal dimension,
D
f
for a single-fractal analysis are given in
Table 10.8
.
The average value of the binding rate coefficient,
k
, and the fractal dimension,
D
f
, presented
in
Table 10.8
for these reversibility runs are 76.895 and 2.279, respectively. This represents a
deviation of 23.96% for the binding rate coefficient,
k
, and 4.87% for the fractal dimension,
