presentación oral en el congreso ESEAC 2010

2. DIFFERENTIAL POTENTIOMETRY AND
DIFFERENTIAL DYNAMIC RESPONSE WITH ION
SELECTIVE ELECTRODES: APPLICATION TO
CYCLODEXTRINE-BASED DRUG SELECTIVE
ELECTRODES
María Cuartero, Joaquín A. Ortuño and MªSoledad García
Cuartero
MÉTODOS AUTOMÁTICOS DE ANÁLISIS. SENSORES QUÍMICOS
“AUTOMATIC METHODS OF ANALYSIS. CHEMICAL SENSORS”
Department of Analytical Chemistry. Faculty of Chemistry
University of Murcia. Murcia. Spain

3. ION-SELECTIVE ELECTRODES
Selectivity ISEs Wide linear range
Sensitivity Applications
Simplicity Rapid response
Longterm Low cost
stability
PLASTICIZED POLYMERIC MEMBRANES
Plasticizer Ionophore
PVC Ionic additive
The appropriate selection of the components enables the selectivity of the ISE to be controlled.

4. Response time of the sensor
important
Practical applications
Dynamic response
studies Working mechanism
particulary relevant
(E vs t)
Interfering ions
Data matrix (E and t)
exploited
Qualitative and quantitative
purposes

5. SOFTWARE
TWO-ELECTRODE POTENTIOMETRY
electrode 1
electrode 2
reference electrode Digital control
High impedance buffers
The potential difference between two ELECTRODE 1 A/D converter
ISEs are alternatively measured by Analog
multiplexer + 16 bits Controller
means of two analog circuits, a fast
multiplexer and an analog-to digital ELECTRODE 2 -
converter. The potential difference
between both ISEs is obtained by REFERENCE
Reference voltage
ELECTRODE USB interface
digital substraction of the previous 2.5 V
recording.
This procedure has the advantage that
not only is the potential difference PC
between two ISEs monitored but also
the potential of each electode.

6. Two-electrode potentiometry

7. Two-electrode potentiometry

8. Two-electrode potentiometry
Electrode 1
Electrode 2

9. Two-electrode potentiometry
Electrode 1
Electrode 2
DIFFE RE NTIA L DYNA MIC RE S PONS E (DDR)

10. Two-electrodes potentiometry
Electrode 1
Electrode 2
DIFFE RE NTIA L
POTE NTIOME TRY (DP)
Th e p ote ntial d iffe re nce b e twe e n b oth
e le ctrod e s once th at th e s te ad y-s tate valu e h as
b e e n attaine d
DIFFE RE NTIA L DYNA MIC RE S PONS E (DDR)

11. alkylated cyclodextrin-based
drug selective electrodes Overall potential response
OR''
E (ΔGo, βCD-drug, …)
O H
R'O
OR
H O
n
n=6  α-CD The direct transfer of the Formation constant of
n=7  β-CD ionic drug from water to the complexes between CD
n=8  γ-CD plasticizer is favourable. and drug are not very
high.

12. Overall potential response
E (ΔGo, βCD-drug, …)
benzoyl beta-cyclodextrin
derivative
The direct transfer of the Formation constant of
ionic drug from water to the complexes between CD
plasticizer is favourable. and drug are not very
high.

13. Overall potential response
E (ΔGo, βCD-drug, …)
benzoyl beta-cyclodextrin
derivative
The direct transfer water- Not very high
plasticizer is very favourable
Antimalarial
Antiarrhytmic
H
HO
O
N
H
N
O
Quinine
H2N Procainamide N
N
H Antidepressant
H
N
HO
O
Clomipramine N
N
Quinidine

14. Overall potential response
E (ΔGo, βCD-drug, …)
benzoyl beta-cyclodextrin
derivative
The direct transfer water- Not very high
plasticizer is very favourable
Anesthesics
H H
Lidocaine
N
N Bupivacaine N N
O O
O
Antispasmodic
N
O O
N
O N
H
O
H2N
Procaine Tetracaine N
O
O
Papaverine O

15. Overall potential response
E (ΔGo, βCD-drug, …)
benzoyl beta-cyclodextrin
derivative
The direct transfer water- Not very high
plasticizer is very favourable
Anesthesics
H H
Lidocaine
N
N Bupivacaine N N
O O
O
Antispasmodic
N
O
O
N
O
O N
H
N
H2N
Procaine Tetracaine O
O
lipophilic aromatic ring system and a Papaverine O
nitrogen that can be protonated to provide
a cationic drug

16. Neutral, lipophilic CDs manifest
Overall potential response
recognition by three types of interactions:
E (ΔGo, βCD-drug, βCD-plasticizer…)
benzoyl beta-cyclodextrin  conventional hydrophobic bonding
derivative  -N-H…O and N-C-H…O hydrogen
bonding
The direct transfer water- Not very high
 van der Waals’ forces.
plasticizer is very favourable
Anesthesics
H H
Lidocaine
N
N Bupivacaine N N
O O
O
Antispasmodic
N
O
O
N
O
O N
H
N
H2N
Procaine Tetracaine O
O
lipophilic aromatic ring system and a Papaverine O
nitrogen that can be protonated to provide
a cationic drug

17. Neutral, lipophilic CDs manifest
Overall potential response
recognition by three types of interactions:
E (ΔGo, βCD-drug, βCD-plasticizer…)
benzoyl beta-cyclodextrin  conventional hydrophobic bonding
derivative  -N-H…O and N-C-H…O hydrogen
bonding
The direct transfer water- Not very high
 van der Waals’ forces.
plasticizer is very favourable
ELECTRODE 1 ELECTRODE 2
Membrane:
Membrane Blank Membrane:
100 mg Polyvinyl chloride (PVC)
PVC 30% 100 mg PVC 33%
200 mg Plasticizer 60% 200 mg Plasticizer 66%
30 mg Heptakis(2,3,5-tri-O-benzoyl)-β-cyclodextrin 3 mg TFMPB 1%
(β-CD)
β-CD 9%
3 mg tetrakis[3,5-bis-(trifluoromethyl)phenyl]borate
(TFMPB)
TFMPB 1%

18. MEMBRANES ASSAYED
Membranes 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)

19. MEMBRANES ASSAYED
Membranes 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 stage The electrodes were
conditioned in deionized
water until they reached a
constant potential
H2O

20. MEMBRANES ASSAYED
Membranes 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
A flux of potassium ions from the inner solution
Reproducible initial stage to the sample solution is established until a
steady-state concentration profile inside the
membrane is reached, which is manifested as a
CONSTANT ELECTRODE POTENTIAL

21. Concentration perturbation (Input)
Standard addition method
Adding consecutive volumes of
concentrated solution of the
different drugs

22. Concentration perturbation (Input)
log C
time

23. Concentration perturbation (Input)
log C
time

24. Concentration perturbation (Input)
log C
The duration of each step
depended on the electrode
response observed and, in
general, decreased as the
concentration was increased.
time

25. CONCENTRATION PROFILES
SAMPLE ION-SELECTIVE MEBRANE INTERNAL
SOLUTION SOLUTION
δaq δm
aJ(bulk)
[CD-K]
aK
[CD-J]
aK(bulk) aD
K= potassium
during exposure to the corresponding ionic drug, a flux
J= ionic drug
towards the filling solution is established, coupled to a
CD= cyclodextrin
flux of potassium in the opposite direction
δ= diffusion layer

26. S A MPLE S OLUTION ME MB RA NE INTE RNA L S OLUTION
CD K+
J+
K+
J+
J+ J+ J+
K+
J+ K+
K+ K+ K+
J+
J+ K+
K+
J+ K+
J+ KCl 10-4 M

27. DDR of lidocaine (different plasticizers)
250 60
DOS 50
TCP
200
3
40 3
150 4
E1-E2 / mV
E1-E2 / mV
30
2
100
4
1 5 6 7 8
20
2
50 5
1 6 10
7 8
0 0
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
250 250
200
4
NPOE 200 4 FNDPE
150
3 150 3
E1-E2 / mV
E1-E2 / mV
5
100 100
50 50
2
1 2
1 6
7 8 0 5
0 6
7 8
-50 -50
0 500 1000 1500 2000 0 200 400 600 800 1000 1200 1400 1600 1800
t/s t/s
(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

28. DDR of lidocaine (different plasticizers)
250 60 The lidocaine
DOS TCP
200
50
concentration at which
this inversion occured
3
40 3
150 4
E1-E2 / mV
E1-E2 / mV
100
30
1
2
4
5 6 7 8
depend on the
plasticizer used. For
20
2
50 5
1 6 10
DOS, NPOE and
7 8
0 0
FNDPE increased with
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
250
250
the dielectric constant
200
4
NPOE 200 4 FNDPE (ε=4, 24 and 50
150
3
E1-E2 / mV
150 3 respectively).
E1-E2 / mV
5
100
The potential
100
50 50
2
corresponding to the
1 2
1 6
7 8 0 5
0 6
7 8
-50
0 500 1000 1500 2000
-50
0 200 400 600 800 1000 1200 1400 1600 1800
inversion was roughly
t/s t/s
the same for these
(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
three plasticizers.

29. DDR of lidocaine (different plasticizers)
250 60 One drawback of the
DOS TCP
200
50
membranes
constructed with DOS,
3
40 3
150 4
E1-E2 / mV
E1-E2 / mV
100
30
1
2
4
5 6 7 8
NPOE and FNDPE, is
that the response is
20
2
50 5
1 6 10
not reproducible
7 8
0 0
because the membrane
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
250
250
can not be regenerated
200
4
NPOE 200 4 FNDPE after a concentration
150
3
E1-E2 / mV
150 3 perturbation.
E1-E2 / mV
5
100 100
50 50
2
1 2
1 6
7 8 0 5
0 6
7 8
-50 -50
0 500 1000 1500 2000 0 200 400 600 800 1000 1200 1400 1600 1800
t/s t/s
(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
DOS, NPOE and FNDPE  none reproducible
TCP  reproducible

30. DDR of lidocaine (different plasticizers)
250 60 In contrast, the
DOS TCP
200
50
membrane constructed
with TCP displayed a
3
40 3
150 4
E1-E2 / mV
E1-E2 / mV
100
30
1
2
4
5 6 7 8
much lower potential
respose but its
20
2
50 5
1 6 10
response was
7 8
0 0
reproducible.
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
250
250
The different behaviour
4
NPOE FNDPE
200 200 4
displayed by TCP can
be explained from
3 150 3
150
E1-E2 / mV
E1-E2 / mV
5
100
some results reported
100
50 50
2
in the literature that
1 2
1 6
7 8 0 5
0 6
7 8
-50
0 500 1000 1500 2000
-50
0 200 400 600 800 1000 1200 1400 1600 1800
point to an interaction
t/s t/s
between TCP and
(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
protonated amines.
DOS, NPOE and FNDPE  none reproducible
TCP  reproducible

31. DP of lidocaine (different plasticizers)
Plots of DP versus logarithmic
concentration of lidocaine
250
200
The response of the
electrode containing CD is
150 higher than the response
DOS
TCP of the electrode without
NPOE
CD at low concentration,
mV
100 FNDPE
while the response is
more similar at higher
50 concentrations.
0
-50
-6 -5 -4 -3
log [L] / M

32. DDR of different ionic drugs (membranes with TCP)
40
60
PROCAINE
30
50 LIDOCAINE
20
40
E1-E2 / mV
E1-E2 / mV
3 3
10 30
2
4 4
0 2 1 5 6 7 8
20
5
1 6 7 8
-10 10
-20 0
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
60 100
50
2 PAPAVERINE 80 CLORMIPRAMINE
40 60
E1-E2 / mV
E1-E2 / mV
2
30 40 3
3 4
4 5 6 7
20 20 8
5 6 7 1
8
1
10 0
0
0 500 1000 1500 2000 2500 3000 0 1000 2000 3000
t/s t/s
(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

33. DDR of different ionic drugs (membranes with TCP)
40
60
PROCAINE
30
50 LIDOCAINE
20
40
E1-E2 / mV
E1-E2 / mV
3 3
10 30
2
4 4
0 2 1 5 6 7 8
20
5
1 6 7 8
-10 10
-20 0
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
60 100
50
2 PAPAVERINE 80 CLORMIPRAMINE
40 60
E1-E2 / mV
E1-E2 / mV
2
30 40 3
3 4
4 5 6 7
20 20 8
5 6 7 1
8
1
10 0
0
0 500 1000 1500 2000 2500 3000 0 1000 2000 3000
t/s t/s
(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
The more lipophilic the ionic drug
(clomipramine>papaverine>lidocaine>procaine), the lower the inversion
concentration and the higher the inversion potential

34. DDR of different ionic drugs (membranes with TCP)
40
60
PROCAINE
30
50 LIDOCAINE
20
40
E1-E2 / mV
E1-E2 / mV
3 3
10 30
2
4 4
0 2 1 5 6 7 8
20
5
1 6 7 8
-10 10
-20 0
0 1000 2000 3000 4000 0 1000 2000 3000
t/s t/s
60 100
50
2 PAPAVERINE 80 CLORMIPRAMINE
40 60
E1-E2 / mV
E1-E2 / mV
2
30 40 3
3 4
4 5 6 7
20 20 8
5 6 7 1
8
1
10 0
0
0 500 1000 1500 2000 2500 3000 0 1000 2000 3000
t/s t/s
(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
The different DDR obtained for all the drugs assayed could well be used for
qualitative purposes

35. DP (membranes with TCP)
Plots of DP versus logarithmic concentration of the
different compounds assayed
80
Na+
K+
Mg2+
Ca2+
60 NH4+
TEA
Procainamide
Procaine
mV
40 Lidocaine
Tetracaine
Bupivacaine
Quinidina
Quinina
20 Papaverine
Clormipramine
0
-10 -8 -6 -4 -2
log [C] / M

36. Concentration concentration
Perturbation ofperturbation (Input) The electrode is re-
conditioned in deionised
water after each
concentration perturbation
log C
time

37. Concentration perturbation (Input) The electrode is re-
conditioned in deionised
water after each
concentration perturbation
log C
time

38. DDR of lidocaine (membranes with TCP)
1x10-6 M 5x10-6 M 1x10-5 M
E1-E2 / mV (1div=5mV)
t / s (1div=50 s)
E1-E2 / mV (1div=20mV)
5x10-5 M 1x10-4 M 5x10-4 M
E1-E2 / mV (1div=20mV)
t / s (1div=20 s)

39. DDR of lidocaine (membranes with TCP)
log C mV
time time
CONCENTRATION PERTURBATION DDR
(INPUT=MONOTONIC)
(OUTPUT=NON-MONOTONIC)
This type of signals has been reported for the dynamic response of several
types of ISEs in the presence of interfiring ions.

40. DDR of lidocaine (membranes with TCP)
electrode 1
electrode 2 (Blank membrane)
300
5x10-4 M
250
1x10-6 M 5x10-6 M 1x10-5 M
1x10-4 M
200
/2 -E (1div=5mV)
mV E
1
5x10-5 M
150
mV
t / s (1div=50 s)
1x10-5 M
100
5x10-6 M
5x10-5 M 1x10-4 M 5x10-4 M
1x10-6 M
50
/2 -E E
mV (1div=20mV)
/ mV E
/2 -E E
mV (1div=20mV)
1
-E (1div=20mV)
1
0
t / s (1div=20 s)
0 200 400 600 800 1000 1200 1400 1600
t/s
DR DDR
(MONOTONIC) (NON-MONOTONIC)

41. Calibration graphs for DP and DDR of lidocaine (membranes
with TCP)
250
B 200
DDR
150
A
mV
100
50
0
CONVENTIONAL
DP
-50
-6 -5 -4 -3
│A│-│B│ log [L] / M
E(mV)=724.84+151.44log[L(M)+1.06x10-5]

42. rather odd signals
two ionic drug trasport inside the membrane
free ionic drug complexed ionic drug
lower concentrations higher concentrations
the difussion of CD to the sample
interface is insufficient to complex
all the ionic drug arising from the
sample solution

43. CONCLUSIONS
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.

44. THANK Y OU F OR Y OUR ATTENTION