Electrochemical sensors for the determination of hydrogen sulfide production in biological samples - Electrochemical Sensors, Biosensors and Their Biomedical Applications - page 220

TABLE 8.1
Performance characteristics of the miniature PHSS a

Sulfi de species detected Hydrogen sulfi de (H 2 S), dissolved or gaseous

Sensitivity 1 nA/µM H 2 S near neutral pH

Detection limits b 10 nM (0.3 ppb) to 200 µM (6000 ppb) linear

Stability 5 pA/h over 10 hours with continuous fl ow of sulfi de sample

2% of concentration determined by 2-PDS c Accuracy

Precision 2% with repeated 10 µM steps within linear range

Response time to 90% 10 s (stirring speed 500 rpm)

new sulfi de level
Sulfi de consumption 1 pmol s 1 at 10 µM, based on current

Operational pH range d pH 8.5 and below

Interference by other compounds None with: S 2 O 3 , SO 2 , SO 4 , cysteine, glutathione, ascorbate,

O 2 , NO, NO 2 , NO 3 , H 2 O 2 HCN gas will cause minor increase

in signal (pH sensitive)

a PHSS confi gured in respirometer with 2 ml phosphate buffered saline at 37ºC
b samples in pH 7
c standard colorimetric method [43]
d pH-dependent signal results from H 2 S/HS pK of approximately 6.8 under the conditions tested

respirometer chamber containing 3 ml stirred (500 rpm) phosphate buffered saline
(PBS; 10 mM sodium phosphate, 150 mM NaCl) at pH 7.3 and 37ºC, with 50 M

diethylenetriaminepentaacetic acid (DTPA) added to chelate metal contaminants that
could otherwise catalyze H 2 S oxidation [45].
Polarizing voltages for the H 2 S microsensor and macrosensor have been given as

µ

100 to 200 mV [36], respectively. The miniature PHSS was
tested for the signal strength of a 20

85 to 150 mV [41] and

M sulfi de injection in anoxic PBS, pH 7.3 and
37ºC, as a function of polarizing voltage over a range of

µ

30 to 300 mV. The rep-
resentative polarogram shown in Fig. 8.4 exhibited a signal plateau from 100 to

200 mV, within which the PHSS signal current was relatively insensitive to changes in
polarizing voltage as the ferricyanide to ferrocyanide ratio was maintained near unity.
Polarizing potentials below or above this plateau region destabilized this equilibrium
towards ferrocyanide or ferricyanide, respectively, so that even small changes in polar-
izing voltage further shifted the ratio, leading to marked increases in signal fl uctua-
tions. A polarizing voltage of 100 to 200 mV was insuffi cient for O 2 reduction, thus
preventing the PHSS from responding to changes in solution O 2 content.

8.5.1 Selectivity
Calibration of the miniature PHSS performed in the respirometer chamber in com-
bination with a POS and PNOS (model ISO-NOP, WPI, Sarasota, FL) is shown in
Fig. 8.5. The selectivity of these sensors is clearly demonstrated, as the PHSS and