Jul 13, 2015
DIFFERENTIAL POTENTIOMETRY AND DIFFERENTIAL POTENTIOMETRY AND DIFFERENTIAL DYNAMIC RESPONSE WITH IONDIFFERENTIAL DYNAMIC RESPONSE WITH ION
SELECTIVE ELECTRODES: APPLICATION TO SELECTIVE ELECTRODES: APPLICATION TO CYCLODEXTRINE-BASED DRUG SELECTIVECYCLODEXTRINE-BASED DRUG SELECTIVE
ELECTRODESELECTRODES
María CuarteroMaría Cuartero, Joaquín A. Ortuño and MªSoledad García
MÉTODOS AUTOMÁTICOS DE ANÁLISIS. SENSORES QUÍMICOS
“AUTOMATIC METHODS OF ANALYSIS. CHEMICAL SENSORS”
Department of Analytical Chemistry. Faculty of Chemistry
University of Murcia. Murcia. Spain
PLASTICIZED POLYMERIC MEMBRANES
ION-SELECTIVE ELECTRODESION-SELECTIVE ELECTRODES
ISEsISEsSelectivity
Sensitivity
Simplicity Rapid response
Longterm stability
Wide linear range
Low cost
Applications
PVCPlasticizer
Ionic additiveIonophore
The appropriate selection of the components enables the selectivity of the ISE to be controlled.
Dynamic response Dynamic response studiesstudies
(E vs t)
Response time of the sensor
Working mechanism
Practical applications
Interfering ions
Data matrix (E and t)
Qualitative and quantitative purposes
important
particulary relevant
exploited
electrode 1
reference electrode
electrode 2
SOFTWARETWO-ELECTRODE POTENTIOMETRY
ELECTRODE 1
ELECTRODE 2
REFERENCE ELECTRODE
High impedance buffers
Analogmultiplexer
A/D converter16 bits+
-
Reference voltage2.5 V
Digital control
Controller
USB interface
PC
ELECTRODE 1
ELECTRODE 2
REFERENCE ELECTRODE
High impedance buffers
Analogmultiplexer
A/D converter16 bits+
-
Reference voltage2.5 V
Digital control
Controller
USB interface
PC
The potential difference between two ISEs are alternatively measured by means of two analog circuits, a fast multiplexer and an analog-to digital converter. The potential difference between both ISEs is obtained by digital substraction of the previous recording.
This procedure has the advantage that not only is the potential difference between two ISEs monitored but also the potential of each electode.
Two-electrode potentiometryTwo-electrode potentiometry
Electrode 1
Electrode 2
DIFFERENTIAL DYNAMIC RES PONS E (DDR)DIFFERENTIAL DYNAMIC RES PONS E (DDR)
Two-electrodes potentiometryTwo-electrodes potentiometry
Electrode 1
Electrode 2
DIFFERENTIAL DYNAMIC RES PONS E (DDR)DIFFERENTIAL DYNAMIC RES PONS E (DDR)
DIFFERENTIAL DIFFERENTIAL POTENTIOMETRY (DP)POTENTIOMETRY (DP)
The potential d iffe re nce be twe e n both
e le ctrod e s once that the s te ad y-state value has
be e n attaine d
Overall potential response
E (ΔGo, βCD-drug, …)
The direct transfer of the ionic drug from water to the
plasticizer is favourable.
Formation constant of complexes between CD and drug are not very
high.
OR''
O
H
ORH
O
n
R'O
n=6 α-CD
n=7 β-CD
n=8 γ-CD
alkylated cyclodextrin-based drug selective electrodes
Overall potential response
E (ΔGo, βCD-drug, …)
The direct transfer of the ionic drug from water to the
plasticizer is favourable.
Formation constant of complexes between CD and drug are not very
high.
benzoyl beta-cyclodextrin derivative
AntiarrhytmicAntiarrhytmic
N
N
O
HO
H
H
H2N
O
N
Procainamide
Quinidine
AntimalarialAntimalarial
N
N
HO
O
H
H
Quinine
AntidepressantAntidepressant
N
N
Clomipramine
Overall potential response
E (ΔGo, βCD-drug, …)
The direct transfer water-plasticizer is very favourable
Not very high
benzoyl beta-cyclodextrin derivative
AnesthesicsAnesthesics
HN
N
O
BupivacaineHN N
O
Lidocaine
H2N
O
N
O
Procaine
NH
O
N
O
TetracaineN
O
O
O
O
Papaverine
Overall potential response
E (ΔGo, βCD-drug, …)
The direct transfer water-plasticizer is very favourable
Not very high
AntispasmodicAntispasmodic
benzoyl beta-cyclodextrin derivative
AnesthesicsAnesthesics
HN
N
O
BupivacaineHN N
O
Lidocaine
H2N
O
N
O
Procaine
NH
O
N
O
TetracaineN
O
O
O
O
Papaverine
AntispasmodicAntispasmodic
benzoyl beta-cyclodextrin derivative
lipophilic aromatic ring system and a nitrogen that can be protonated to provide
a cationic drug
Overall potential response
E (ΔGo, βCD-drug, …)
The direct transfer water-plasticizer is very favourable
Not very high
Overall potential response
E (ΔGo, βCD-drug, βCD-plasticizer…)
The direct transfer water-plasticizer is very favourable
Not very high
Neutral, lipophilic CDs manifest recognition by three types of interactions:
conventional hydrophobic bonding
-N-H…O and N-C-H…O hydrogen bonding
van der Waals’ forces.
AnesthesicsAnesthesics
HN
N
O
BupivacaineHN N
O
Lidocaine
H2N
O
N
O
Procaine
NH
O
N
O
TetracaineN
O
O
O
O
Papaverine
AntispasmodicAntispasmodic
benzoyl beta-cyclodextrin derivative
lipophilic aromatic ring system and a nitrogen that can be protonated to provide
a cationic drug
ELECTRODE 1ELECTRODE 1
MembraneMembrane:
100 mg Polyvinyl chloride (PVCPVC) 30%30%
200 mg PlasticizerPlasticizer 60%60%
30 mg Heptakis(2,3,5-tri-O-benzoyl)-β-cyclodextrin (β-CDβ-CD) 9%9%
3 mg tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate (TFMPBTFMPB) 1%1%
ELECTRODE 2ELECTRODE 2
Blank Membrane:Blank Membrane:
100 mg PVCPVC 33%33%
200 mg PlasticizerPlasticizer 66%66%
3 mg TFMPBTFMPB 1%1%
Overall potential response
E (ΔGo, βCD-drug, βCD-plasticizer…)
The direct transfer water-plasticizer is very favourable
Not very high
Neutral, lipophilic CDs manifest recognition by three types of interactions:
conventional hydrophobic bonding
-N-H…O and N-C-H…O hydrogen bonding
van der Waals’ forces.
benzoyl beta-cyclodextrin derivative
MEMBRANES ASSAYEDMembranes DOS NPOE TCP FNDPE PVC TFMB Β-CD
A - - - 66 33 1 -
B - - - 60 30 1 9
C - - 66 - 33 1 -
D - - 60 - 30 1 9
E - 66 - - 33 1 -
F - 60 - - 30 1 9
G 66 - - - 33 1 -
H 60 - - - 30 1 9
dioctyl sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), tricresyl phosphate (TCP), 2-fluoro-2’-nitrodiphenyl ether (FNDPE), polyvinyl chloride (PVC) , potassium tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate (TFMB) and
Heptakis(2,3,5-tri-O-benzoyl)-β-cyclodextrin (β-CD)
MEMBRANES ASSAYEDMembranes DOS NPOE TCP FNDPE PVC TFMB Β-CD
A - - - 66 33 1 -
B - - - 60 30 1 9
C - - 66 - 33 1 -
D - - 60 - 30 1 9
E - 66 - - 33 1 -
F - 60 - - 30 1 9
G 66 - - - 33 1 -
H 60 - - - 30 1 9
dioctyl sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), tricresyl phosphate (TCP), 2-fluoro-2’-nitrodiphenyl ether (FNDPE), polyvinyl chloride (PVC) , potassium tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate (TFMB) and
Heptakis(2,3,5-tri-O-benzoyl)-β-cyclodextrin (β-CD)
H2O
Ag-AgCl│KCl (1x10-4 M)│internal solution, 1x10-4 M KCl│PVC membrane│sample solution
Reproducible initial stage The electrodes were conditioned in deionized
water until they reached a constant potential
MEMBRANES ASSAYEDMembranes DOS NPOE TCP FNDPE PVC TFMB Β-CD
A - - - 66 33 1 -
B - - - 60 30 1 9
C - - 66 - 33 1 -
D - - 60 - 30 1 9
E - 66 - - 33 1 -
F - 60 - - 30 1 9
G 66 - - - 33 1 -
H 60 - - - 30 1 9
dioctyl sebacate (DOS), 2-nitrophenyl octyl ether (NPOE), tricresyl phosphate (TCP), 2-fluoro-2’-nitrodiphenyl ether (FNDPE), polyvinyl chloride (PVC) , potassium tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate (TFMB) and
Heptakis(2,3,5-tri-O-benzoyl)-β-cyclodextrin (β-CD)
Ag-AgCl│KCl (1x10-4 M)│internal solution, 1x10-4 M KCl│PVC membrane│sample solution
Reproducible initial stageA flux of potassium ions from the inner solution
to the sample solution is established until a steady-state concentration profile inside the
membrane is reached, which is manifested as a CONSTANT ELECTRODE POTENTIALCONSTANT ELECTRODE POTENTIAL
Concentration perturbation (Input)Concentration perturbation (Input)
Standard addition methodStandard addition method
Adding consecutive volumes of concentrated solution of the
different drugs
Concentration perturbation (Input)Concentration perturbation (Input)
time
log C
The duration of each step depended on the electrode response observed and, in general, decreased as the
concentration was increased.
SAMPLE SOLUTION
ION-SELECTIVE MEBRANE INTERNAL SOLUTION
δaq δm
aK
[CD-K]
[CD-J]
aDaK(bulk)
aJ(bulk)
CONCENTRATION PROFILESCONCENTRATION PROFILES
K= potassium
J= ionic drug
CD= cyclodextrin
δ= diffusion layer
during exposure to the corresponding ionic drug, a flux towards the filling solution is established, coupled to a
flux of potassium in the opposite direction
MEMBRANEMEMBRANE INTERNAL S OLUTION INTERNAL S OLUTION S AMPLE S OLUTIONS AMPLE S OLUTION
K+
K+
K+
K+
K+
KCl 10KCl 10-4-4 M M
K+
K+
K+
J+
J+
J+
J+
J+
J+
J+
J+ J+
K+K+
J+
CD
t / s
0 1000 2000 3000 4000
E1-
E2 /
mV
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-E
2 /
mV
-50
0
50
100
150
200
250
t / s0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 /
mV
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
DDR of lidocaine (different plasticizers)DDR of lidocaine (different plasticizers)
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
t / s
0 1000 2000 3000 4000
E1-
E2
/ m
V
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-
E2
/ m
V
-50
0
50
100
150
200
250
t / s
0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 / m
V
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
t / s
0 1000 2000 3000 4000
E1-
E2
/ m
V
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-
E2
/ m
V
-50
0
50
100
150
200
250
t / s
0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 / m
V
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
DDR of lidocaine (different plasticizers)DDR of lidocaine (different plasticizers)
The lidocaine concentration at which this inversion occured
depend on the plasticizer used. For
DOS, NPOE and FNDPE increased with the dielectric constant
(ε=4, 24 and 50 respectively).
The potential corresponding to the
inversion was roughly the same for these three plasticizers.
t / s
0 1000 2000 3000 4000
E1-
E2
/ m
V
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-
E2
/ m
V
-50
0
50
100
150
200
250
t / s
0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 / m
V
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
t / s
0 1000 2000 3000 4000
E1-
E2
/ m
V
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-
E2
/ m
V
-50
0
50
100
150
200
250
t / s
0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 / m
V
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
DDR of lidocaine (different plasticizers)DDR of lidocaine (different plasticizers)
One drawback of the membranes
constructed with DOS, NPOE and FNDPE, is that the response is
not reproducible because the membrane can not be regenerated
after a concentration perturbation.
DOS, NPOE and FNDPE none reproducible
TCP reproducible
t / s
0 1000 2000 3000 4000
E1-
E2
/ m
V
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-
E2
/ m
V
-50
0
50
100
150
200
250
t / s
0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 / m
V
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
t / s
0 1000 2000 3000 4000
E1-
E2
/ m
V
0
50
100
150
200
250
t / s0 1000 2000 3000
E1-E
2 / m
V
0
10
20
30
40
50
60
t / s0 500 1000 1500 2000
E1-
E2
/ m
V
-50
0
50
100
150
200
250
t / s
0 200 400 600 800 1000 1200 1400 1600 1800
E1-E
2 / m
V
-50
0
50
100
150
200
250
DOS TCP
NPOE FNDPE
1
2
3
4
56
7 8
1
2
3
4
5
6
8
1
2
3
4
5 6 8
1 2
3
4
56
8
7
7
7
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
DDR of lidocaine (different plasticizers)DDR of lidocaine (different plasticizers)
In contrast, the membrane constructed with TCP displayed a much lower potential
respose but its response was reproducible.
The different behaviour displayed by TCP can
be explained from some results reported
in the literature that point to an interaction
between TCP and protonated amines.
DOS, NPOE and FNDPE none reproducible
TCP reproducible
DP of lidocaine (different plasticizers)DP of lidocaine (different plasticizers)
log [L] / M
-6 -5 -4 -3
mV
-50
0
50
100
150
200
250
DOS TCP NPOE
FNDPE
Plots of DP versus logarithmic concentration of lidocaine
The response of the electrode containing CD is higher than the response of the electrode without CD at low concentration,
while the response is more similar at higher
concentrations.
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000
E1-
E2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
DDR of different ionic drugs (membranes with TCP)DDR of different ionic drugs (membranes with TCP)
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
LIDOCAINE
CLORMIPRAMINEPAPAVERINE
PROCAINE
81
2
3
4
5 6 7
81
2
3
4
576
81
2
3
4
657
1
2
3
4
6 85 7
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000E
1-E
2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-
E2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
LIDOCAINE
CLORMIPRAMINEPAPAVERINE
PROCAINE
81
2
3
4
5 6 7
81
2
3
4
576
81
2
3
4
657
1
2
3
4
6 85 7
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000E
1-E
2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-
E2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000E
1-E
2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-
E2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
LIDOCAINE
CLORMIPRAMINEPAPAVERINE
PROCAINE
81
2
3
4
5 6 7
81
2
3
4
576
81
2
3
4
657
1
2
3
4
6 85 7
DDR of different ionic drugs (membranes with TCP)DDR of different ionic drugs (membranes with TCP)
The more lipophilic the ionic drug (clomipramine>papaverine>lidocaine>procaine), the lower the inversion
concentration and the higher the inversion potential
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000E
1-E
2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-
E2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
LIDOCAINE
CLORMIPRAMINEPAPAVERINE
PROCAINE
81
2
3
4
5 6 7
81
2
3
4
576
81
2
3
4
657
1
2
3
4
6 85 7
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000E
1-E
2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-
E2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
t / s0 1000 2000 3000
E1-E
2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000E
1-E
2 /
mV
0
20
40
60
80
100
t / s
0 500 1000 1500 2000 2500 3000
E1-
E2 /
mV
0
10
20
30
40
50
60
t / s
0 1000 2000 3000 4000
E1-E
2 /
mV
-20
-10
0
10
20
30
40
(1) 0 M, (2) 1x10-6 M, (3) 5x10-6 M, (4) 1x10-5 M, (5) 5x10-5 M, (6) 1x10-4 M, (7) 5x10-4 M, (8) 1x10-3 M
LIDOCAINE
CLORMIPRAMINEPAPAVERINE
PROCAINE
81
2
3
4
5 6 7
81
2
3
4
576
81
2
3
4
657
1
2
3
4
6 85 7
DDR of different ionic drugs (membranes with TCP)DDR of different ionic drugs (membranes with TCP)
The different DDR obtained for all the drugs assayed could well be used for qualitative purposes
DP (membranes with TCP)DP (membranes with TCP)
log [C] / M
-10 -8 -6 -4 -2
mV
0
20
40
60
80Na+
K+
Mg2+
Ca2+
NH4
+
TEA ProcainamideProcaineLidocaineTetracaineBupivacaineQuinidina
QuininaPapaverineClormipramine
Plots of DP versus logarithmic concentration of the different compounds assayed
Perturbation of concentrationPerturbation of concentrationConcentration perturbation (Input)Concentration perturbation (Input)
time
log C
The electrode is re-conditioned in deionised
water after each concentration perturbation
Concentration perturbation (Input)Concentration perturbation (Input)
time
log C
The electrode is re-conditioned in deionised
water after each concentration perturbation
t / s (1div=50 s)
E1-
E2
/ mV
(1d
iv=
20m
V)
E1-
E2
/ mV
(1
div
=5
mV
)
t / s (1div=20 s)
E1-
E2
/ m
V (
1d
iv=
20m
V)
DDR of lidocaine (membranes with TCP)DDR of lidocaine (membranes with TCP)
1x10-6 M 5x10-6 M 1x10-5 M
5x10-5 M 1x10-4 M 5x10-4 M
log C
time
mV
time
CONCENTRATION PERTURBATION
(INPUT=MONOTONIC)DDR
(OUTPUT=NON-MONOTONIC)
DDR of lidocaine (membranes with TCP)DDR of lidocaine (membranes with TCP)
This type of signals has been reported for the dynamic response of several types of ISEs in the presence of interfiring ions.
t / s
0 200 400 600 800 1000 1200 1400 1600
mV
0
50
100
150
200
250
300
5x10-4 M
1x10-4 M
5x10-5 M
1x10-5 M
5x10-6 M
1x10-6 M
electrode 1
electrode 2 (Blank membrane)
t / s
0 200 400 600 800 1000 1200 1400 1600
mV
0
50
100
150
200
250
300
5x10-4 M
1x10-4 M
5x10-5 M
1x10-5 M
5x10-6 M
1x10-6 M
electrode 1
electrode 2 (Blank membrane)
electrode 1
electrode 2 (Blank membrane)
DDR of lidocaine (membranes with TCP)DDR of lidocaine (membranes with TCP)
t / s (1div=50 s)
E1-E
2 / mV
(1d
iv=20
mV
)
E1-E
2 / mV
(1d
iv=5
mV
)
t / s (1div=20 s)
E1-E
2 / mV
(1d
iv=20
mV
)
1x10-6 M 5x10-6 M 1x10-5 M
5x10-5 M 1x10-4 M 5x10-4 M
t / s (1div=50 s)
E1-E
2 / mV
(1d
iv=20
mV
)
E1-E
2 / mV
(1d
iv=5
mV
)
t / s (1div=20 s)
E1-E
2 / mV
(1d
iv=20
mV
)
1x10-6 M 5x10-6 M 1x10-5 M
5x10-5 M 1x10-4 M 5x10-4 M
DDR(NON-MONOTONIC)
DR(MONOTONIC)
log [L] / M
-6 -5 -4 -3
mV
-50
0
50
100
150
200
250
E(mV)=724.84+151.44log[L(M)+1.06x10-5]
Calibration graphs for DP and DDR of lidocaine (membranes Calibration graphs for DP and DDR of lidocaine (membranes with TCP)with TCP)
A
B
│A│-│B│
CONVENTIONAL DP
DDR
rather odd signals
two ionic drug trasport inside the membrane
free ionic drug complexed ionic drug
the difussion of CD to the sample interface is insufficient to complex all the ionic drug arising from the
sample solution
lower concentrations higher concentrations
CONCLUSIONSCONCLUSIONS
I. The new differential dynamic response technique, applied to ion-selective electrodes, and exploited here for the first time, is a source of signals not usually seen that can be useful for quantitative an qualitative analysis.
IV.When the DDR is applied to ISEs based on a β-cyclodextrin, the ionic drugs assayed seem to be transported across the membrane following two different processes.