19
i
nterference
Chemical interferences are give in the table below for both types
of hydrogen sulfide sensors .
In addition, Type II sensors are sensitive to light because ferro
cyanide reacts in light, especially blue (short-wave) light, which
gives a false H
2
S signal . This reaction causes the zero current to
increase leading to an overestimation of the H
2
S concentration in
light . Thus, when measuring through a light gradient (e .g . when
measuring into an illuminated biofilm) the signal will decrease
slightly, when entering the biofilm . In many systems the light will
be almost completely attenuated within the first few hundred
microns .
The sensor has been painted black to reduce this phenomenon,
however light may still enter the sensor through the tip, which is
not possible to paint .
Micromanipulator
i
nterferences
for
gases
in
gas
Phase
(%)
1
i
nterferences
for
gases
dissolved
in
water
(%)
2
n
ame
Formula
SULF
H
2
S
SULF
H
2
S
m
ethane
CH
4
0
0
0
0
c
arbon
dioxide
CO
2
0
0
0
0
n
itrogen
N
2
0
0
0
0
o
xygen
O
2
0
0
0
0
a
ir
O
2
, N
2
, Ar
0
0
0
0
n
itrous
oxide
N
2
O
0
0
0
0
a
mmonia
NH
3
0
0
0
0
h
ydrogen
H
2
0 .8
0 .03
96
4
c
arbon
monoxide
CO
0 .6
4
77
487
d
imethyl
sulfide
(CH
3
)
2
S
18
3
18
3
m
ethyl
mercaPtan
CH
3
SH
174
117
44
30
e
thyl
mercaPtan
C
2
H
6
S
13
8
14
9
s
ulfur
dioxide
SO
2
40
34
1
1
1
Given as signal for the interfering species in % of H
2
S signal at equal partial pressures
2
Given as signal for the interfering species in % of H
2
S signal at equal molar concentrations
