Biomedical Engineering Reference
In-Depth Information
H
2
S
PEEK
Membranes are
cemented together
H
2
S permeable
MEM - 213
S
2H
H
HS
H
2
S impermeable
FEP, Mylar, Saran
2[Fe(CN)
6
]
3
2[Fe(CN)
6
]
4
overlap serves
as virutal
guard ring
2e
electrolyte
buffered to
pH 8-10
Pt
cathode
Pt
cathode
Pt anode polarized 0.1 to 0.2 V
FIGURE 8.2
Diagram of the macro polarographic H
2
S sensor (PHSS). A side view and expanded tip view
of the macro PHSS, 25 mm long and 12 mm diameter, illustrates the component parts. The platinum anode
and cathode are cemented into the polyether-ether ketone (PEEK) housing with epoxy. The membranes are
cemented together with a silicone cement. The 0.5 mm hole in the H
2
S-impermeable membrane is concentric
with the anode and provides a small reservoir of electrolyte between the anode and the H
2
S-permeable mem-
brane. Lateral H
2
S diffusion from this region at the tip into the bulk electrolyte is limited and greatly shortens
response time as the impermeable membrane serves as a virtual guard ring. Electrochemical reactions within
the electrolyte are described in the text (after [36]; reproduced with permission of the Company of Biologists).
8.2.2 Multi-sensor respirometry
The PHSS operates over a concentration range and with a response time ideal for
kinetic studies of H
2
S metabolism in broken cell systems, cell suspensions, intact
tissues, and whole organisms. The PHSS selectivity enables it to be combined with
other real-time polarographic sensors for O
2
(POS) and NO (PNOS) to determine the
interaction of these factors with H
2
S in biological systems. Because the existence of
free H
2
S may be in rapid equilibrium with thiol and sulfane sources and sinks through
enzymatic and spontaneous reactions, only the PHSS can follow concentration changes
in a physiological time frame and under physiological conditions. As a result, complex
kinetic responses of tissues, cells, and mitochondria are observed as O
2
and NO levels
are adjusted within physiological limits. Using the PHSS in combination with POS
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