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)

Screen-printed All-Solid-State ion-selective electrode

Electrode configuration

5

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

Thank you !

19