mobile water analysis with potentiometric sensorspotentiometry with ion-selective electrodes...
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Mobile water analysis with potentiometric sensors
Johannes Schwarz 1, Kathrin Trommer 1, Frank Gerlach 1, Michael Mertig 1,2
1 Kurt-Schwabe-Institut für Mess- und Sensortechnik e.V. Meinsberg
2 Technische Universität Dresden, Professur für Physikalische Chemie, Mess- und Sensortechnik
Introduction
18th Leibniz Conference of Advanced Science
16. - 17. 10. 2014
Lichtenwalde (Sachsen)
1
Introduction
2
Potentiometry with ion-selective electrodes
Principle
• measurements of potentials at interface:
ion-selective membrane / solution with analyte ion
• ion exchange at interface: membrane (ionophor) / solution (ion)
• membrane composition with ion-complexing compound (ionophor)
determines selectivity towards measuring ion
Aim and motivation
● development of new planar screen-printed All-Solid-State-ion-selective
electrodes and reference electrodes for mobile environmental analysis
application fields:
- heavy metal analysis
- water hardness (Ca2+, Mg2+)
- NH4+, NO3
-
● great need for analyzers/sensors for field detection of pollutants
Introduction
Requirements for sensors in field analysis
● simple and robust electrode construction
● easy to handle (no liquid components)
● reproducible results
3
Electrode configuration
Schematic layer structure of a screen-printed All-Solid-State ion-selective electrode
intermediate layer
(solid contact)
SEM of polypyrrole-modified screen-printed graphite electrode
Polypyrrole
(PPy)
Poly-3,4-ethylendioxythiophene
(PEDOT)
ion-complexing compound
4
J. Schwarz, K. Trommer, D. Appelhans, J. Kluge, B. Voit,
M. Mertig, Proceedings 11. Dresdner Sensorsymposium
342-344, DOI 1051620 (2013)
Electrode configuration
Schematic layer structure of a screen-printed All-Solid-State reference electrode
SEM of screen-printed AgCl-layer
6
Planar screen-printed All-Solid-State potentiometric sensors
Electrode configuration
reference electrode
ion-selective electrode
7
0 20 40 60 80 100 120 140 160 180-200
-150
-100
-50
0
50
100
150
-2
11
-1-1
-3
-4
-2
-5
-4
E /
mV
vs.
scre
en
-pri
nte
d R
E
t / min
-3
Results
8
0 20 40 60 80 100 120 140 160
150
200
250
300
350
400
-3
-2
-1
1
-4
E /
mV
vs
. A
g/A
gC
l
t / min
-5
-4
-3
-2
-1
1
Potentiometric response behavior of PPy-modified screen-printed All-Solid-State
NH4+-selective electrodes
slope: › 56 mV/decade
detection limit: <10-6 mol/L
O
OCH3
O O
O
O
O
OO
O
O
O
CH3
HCH3
H
CH3
H3C
CH3
H H
H3C
CH3
H H
H H
J. Schwarz, H. Kaden, S. Kutschke, F. Glombitza
GIT Fachz. 5, 408 - 409, (2007)
0 50 100 150 200
160
200
240
280
-4
-3
-2
-1-1
-2
1
-4
E /
mV
vs.
Ag
/Ag
Cl
sat.
KC
l
t / min
-3
Mg2+
Potentiometric response behavior of screen-printed All-Solid-State ion-selective electrodes
Results
NN
O
OCH3
CH3
(CH2)6CH3
H3C(H2C)6
t-Bu
O
N
t-Bu O N O t-BuN
O
N
t-Bu
S
S
S
S
0 50 100 150 200260
280
300
320
340
-2
-6
-5
-4
E /
mV
vs
. A
g/A
gC
l s
at.
KC
l
t / min
-3Pb
2+
9
-5 -4 -3 -2 -1 0-100
-50
0
50
100
150
200 sample 1
sample 2
sample 3
E / m
V v
s. m
od
ifie
d-s
cre
en
-pri
nte
d-R
E
lg NO3-
80
100
120
140
160
-2.0-4.5 -3.5 -2.5-3.0-4.0
sample 2
E /
mV
vs.
scre
en
-pri
nte
d-R
E
lg Ca2+
sample 1
-5.0
Ca2+-concentration
sample 1: tap water Freiberg (Sachsen) 28 mg/L
sample 2: tap water Minkwitz (Sachsen) 66 mg/L
Calibration curves of PPy-modified screen-printed graphite-based ion-selective electrodes
Results
Applications in environmental samples
NO3--concentration
sample 1: tap water Freiberg (Sachsen) 11 mg/L
sample 2: tap water Hammer (Bayern) 4 mg/L
sample 3: tap water Chemnitz (Sachsen) 16 mg/L
NO3-
Ca2+
10 J. Schwarz, H. Kaden, GIT Labor-Fachz.
3, 228-331, (2010)
0 2 4 6 8 10 12
50
100
150
E /
mV
vs
. s
cre
en
-pri
nte
d-R
E
Addition ml (Na2-EDTA; 0.01 mol/L)
0 2 4 6 8 10 12100
120
140
160
180
200
E /
mV
vs.
Ag
/Ag
Cl
sat.
KC
l
Addition ml (Na2-EDTA; 0.01 mol/L)
Applications in water analysis - Potentiometric titration
0 2 4 6 8 10 12
-80
-60
-40
-20
0
E
/
V
V / ml
Results
0 2 4 6 8 10 12-80
-60
-40
-20
0
E
/
VV / ml
sample: tap water
Enkenbach (Germany)
Ca2+: 52 mg/L (1.30 mmol/L)
water hardness:
middle
reference methods:
- ion chromatography
- colorimetric titration
first
derivative
first
derivative equivalence
point
equivalence
point
Indicator electrode: new PPy-modified Ca2+-selective All-Solid-State electrode
11 J. Schwarz, K. Trommer, M. Richter, M. Mertig
GIT Labor-Fachz. 57, 29-31 (2013)
0 2 4 6 8 10 12 14 16-20
0
20
40
60
80
100
120
140
E /
mV
vs
. s
cre
en
-pri
nte
d-R
E
Addition ml (Na2-EDTA; 0.01 mol/L)
tap water Strasbourg (France)
Ca2+: 72 mg/L
(1.80 mmol/L)
Results
Indicator electrode: new PPy-modified Ca2+-selective All-Solid-State electrode
Applications in water analysis - Potentiometric titration
water hardness: middle
12
0 5 10 15-150
-100
-50
0
E
/
V
V / ml
0 2 4 6 8-120
-80
-40
0
40
E /
mV
vs
. s
cre
en
-pri
nte
d-R
E
Addition ml (Na2-EDTA; 0.01 mol/L)
Ca2+: 38 mg/L
(0.95 mmol/L)
Results
Indicator electrode: new PPy-modified Ca2+-selective All-Solid-State electrode
Applications in water analysis - Potentiometric titration
water hardness: soft tap water Dresden (Germany)
13
0 2 4 6 8
-150
-100
-50
0
E
/
V
V / ml
J. Schwarz, K. Trommer, M. Mertig, Proceedings
11. Dresdner Sensorsymposium 373-375, DOI 105162 (2013)
0 2 4 6 8 10
-12
-8
-4
0
E
/
V
V / ml
0 2 4 6 8 10270
280
290
300
310
E /
mV
vs.
Ag
/Ag
Cl
sat.
KC
l
Addition ml (Na2-EDTA; 0.001 mol/L)
spiked river sample:
20.72 mg/L Pb2+ (10-4 mol/L)
Applications - Potentiometric titration
Indicator electrode: new PPy-modified screen-printed Pb2+-selective electrode
Results
sample: river water
Striegis (Germany)
equivalence
point
14 J. Schwarz, K. Trommer, M. Mertig,
GIT Labor-Fachz. 3, 53-55, (2014)
No sample preparation
necessary !
New development - Potentiometric multiparameter sensors
New development
Aims
● simultaneous potentiometric detection of different ions
● use of highly ion-selective compounds
● integration of ion-selective electrodes and reference
electrodes on common substrate surfaces
Ion 1 (Mg2+)
Ion 1 (Ca2+)
Ion 1- 8
RE
water hardness sensor
15
Summary
New solid-contacted planar All-Solid-State ion-selective electrodes
based on functional layers for determination of different ions
● suitable for on-line determination and in-situ applications
● low cost production, fast response, simplicity in operation
● reproducible layer conformation
● conducting polymer as internal solid-contact (replacing liquid electrolyte)
● determination of electrode parameter (slope, selectivity coefficents,
detection limit, electrode life time, drift, response behavior)
New planar All-Solid-State screen-printed reference electrodes
● reproducible layer conformation
● no liquid components
● stable potentials
Summary
16
Summary
Summary
Applications in environmental samples
- indicator electrodes in potentiometric titrations (complexometry)
- direct potentiometric ion analysis
- no or few sample preparation steps necessary
17
NO3- Cl- Cu2+ Mg2+ NH4
+ Pb2+ Ca2+ Cd2+
● use of new electrode materials
● use of new ion-complexing compounds with high ion-selectivities
(calixarenes, cyclodextrines)
● development of an electrochemical multiparameter (ion) analyzer
- integration of ion-selective electrodes and reference electrodes
- use of different electrochemical detection methods
Outlook
Future prospects
18
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