potentiometric sensing of organics for hplc and ce: ready ... filepotentiometric sensing of organics...
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![Page 1: Potentiometric sensing of organics for HPLC and CE: Ready ... filePotentiometric sensing of organics for HPLC and CE: Ready for takeoff! Luc Nagels Antwerp University Hergé, (Belgium)](https://reader030.vdocuments.us/reader030/viewer/2022041211/5dd0dd60d6be591ccb631300/html5/thumbnails/1.jpg)
Potentiometric sensing of organics for HPLC and CE: Ready for takeoff!
Luc NagelsAntwerp University
Hergé, (Belgium)
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Potentiometric sensors for:HPLC detection, CE detection, dissolution testing
conductive poly- and oligomers, ceramics, liquid membranes
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Potentiometry, the "sleeping lion"
Hunting: metal ions, cationic drugs and amines, halogen ions, S2-, SCN-, NO3
-, NO2- and ClO4
-, organic acids, …
Not hunting: biomolecules, multiply charged biomolecules
Why not? too hydrophilic, too expensive, too complex
Pure and Applied Chemistry, to be published 2004
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Potentiometry/HPLC or CE or microchip hyphenation
Application in HPLC: 50 older references
Application in CE and microchip: 20 recent references
Electroanalysis, 15 (5-6): 533-538, 2003.
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Potentiometric sensors for LC and CE
data station
reference electrode
coating on electronic conductor
LC or CE outlet
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plastic wire
Electronic conductor
Ionically conducting membrane
E
Receptor molecules +
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Electronic conductor substrate electrode (or internal solution).
membrane surfaces!
EAnalyte solution
A potentiometric sensor has one or two important surfaces
E depends on analyte concentration
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+
E
++++
++++
Substrate electrode
Liquid membrane phase (polymer + plasticizer + ionophore)
analyte anion counter cation
is the analyte ion extracted or adsorbed?
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1 Tartaric acid2 Malonic acid3 Malic acid4 Lactic acid5 Citric acid6 Fumaric acid7 Succinic acid
2 mV1
2
3
4
5
67
Column: RPC8, 4.6mm i.d.Eluent: 1 mM H3PO4, 1mL/min
pg detection limits for malonic0 10Time, min
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++++
+
lipophilic tail
polar head
“embedded” charge, MTDDACl (methyltridodecylammoniumchloride)
NH
NH
O
NNH2
C18H37
NH
NHO
N
NH
NHO
C18H37
NH
NHO
C18H37C18H37
NH
NHO
N
NH
NHO
NH
NHO
NH
NH
O
NC18H37 N
HNH
O
C18H37
ligand 1 ligand 2
ligand 3 ligand 4
RRN
NH
N
NH
N
NH
NH
NRR
ligand 6 R = H, R1 = C10H21ligand 8 R = R1 = (CH2)3NHCONHC18H37ligand 9 R = R1 = CH2CONHC2H4N(C2H4NHCONHC18H37)2
R R1
RR1
R
N
N
N
N
N
N
R
ligand 7 R = C10H21
ligand 5 R = C8H17
R
RR
R
NN
N
N
N
N
R
R
ligand 10 R = (CH2)4OCONHC18H37
R N
N
N
N
N
NCH3
CH3
CH3
CH3
CH3
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0.2% MTDDACl (embedded type), and 1% ligand (head/tail type)
Lichrosphere 100-5 RP8 column (Merck), 125x4mm, eluens 1mM H3PO4 at 0.5 mL min-1 flow-rate. 10 µL injection of a mixture of tartaric- (1, 10-5M ),malonic- (2, 2x10-7M), malic- (3, 4x10-6M), lactic- (4, 10-4M), citric-(5, 10-
5M), fumaric- (6, 2x10-5M), succinic acid (7, 2x10-5M).
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5
25 50concentration, Mì
10
peak height,mV
injected micromolar concentration
Calibration curves obtained with the HPLC potentiometric sensor. Upper curve: malonic acid, middle curve: tartaric acid, lower curve: citric acid.
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+
E
Substrate electrode
Liquid membrane phase
Eluent phase
++
+
“Embedded” charge type
versus head/tail type
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malonic acid
docking, molecular modeling, gasphase
modeling interface behavior
+++
- -
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UMP AMP
UDP UTP ADP ATP
X-terra C18 (3x50mm), ion-pair
4x10-5M inj in 10µL
0.71mV
0
nucleotides
UV
potentiometric
0 5 time, min 10
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Oligonucleotides, FIA
25-mer CAGACAATAGTAAATGAGAATCAGG
0 60 time, s
UV Potentiometry
4mV 10-5M in 1mM H3PO4
0.3mL/min, 10 µL injection
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0 9 volume, mL 18
45 6 7 8 9 10 11 12 13 14 15 16 17 18-mer
Oligonucleotides d(T)12-18 5‘OH Na+ salt
X-Terra RP18 3x50mm
10mM TEAE, 0.3mL min-1, 8 to 10% AcN
2mV
Potentiometry
UV
unpublished results
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-
E
Substrate electrode
Liquid membrane phase
Eluent phase
p-chloro tetraphenylborate
+-
++
sensing organic cationic substances
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Potentiometric det. of linear aliphatic amines
6543
2
1 4 mV
123 4
5
6
123
4
5
61 Methylamine
…6 Hexylamine
Alltech universal cation exchange 4.6 mm ID, 5mMHNO3 in 5% acetonitrile, 1mL min-1,
2 12Time, min
5×10-5 M inj., 50µL
Analytica Chimica Acta 440 (2) 89-98, 2001.
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1 clenbuterol 2 practolol 3 oxprenolol 4 alprenolol 5 carazolol 6 bevantolol 7,8 unknowns
potentiometric detection of beta-adrenoceptors in RP
10-6 M injections, 20µL
PVC/DOS/TCPB 32:66:2 wt%
X-Terra RP18, 50mmx3mm,acetonitrile/20mM H3PO4, 25:75
Journal of Chromatography A, 973, 85-96, 2002
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detection limits (molar conc., 20µL injected)analyte UV 230nm Borate OctylCD Calix
mol/L mol/L mol/L
ClenbuterolMabuterolCimaterolCarbuterolBufuralolPractololAlprenololOxprenololp-OxprenololBisoprololCeliprololBevantololTolamololPropranololNadololTertatololCarazolol
2.6 x 10-7
2.9 x 10-6
3.0 x 10-7
1.7 x 10-7
3.5 x 10-7
1.7 x 10-7
2.2 x 10-6
1.0 x 10-6
0.7 x 10-6
3.5 x 10-7
1.6 x 10-7
1.3 x 10-6
1.3 x 10-6
2.7 x 10-8
2.3 x 10-7
1.2 x 10-6
4.4 x 10-7
6.7 x 10-7
2.2 x 10-7
2.5 x 10-5
8.5 x 10-5
2.8 x 10-7
5.4 x 10-5
6.7 x 10-7
1.7 x 10-6
1.6 x 10-6
1.3 x 10-5
1.7 x 10-5
2.2 x 10-6
1.4 x 10-5
2.1 x 10-7
5.9 x 10-5
3.5 x 10-7
6.0 x 10-4
1.1 x 10-7
5.6 x 10-8
4.8 x 10-6
7.7 x 10-5
2.2 x 10-8
6.2 x 10-5
3.6 x 10-7
7.7 x 10-7
7.5 x 10-7
3.7 x 10-6
1.6 x 10-5
1.0 x 10-6
1.3 x 10-6
1.0 x 10-7
2.1 x 10-5
1.2 x 10-7
2.0 x 10-5
1.7 x 10-6
3.4 x 10-5
3.6 x 10-5
2.4 x 10-4
1.5 x 10-6
1.9 x 10-4
3.0 x 10-7
5.8 x 10-7
3.5 x 10-7
2.7 x 10-6
6.8 x 10-5
1.6 x 10-6
2.0 x 10-5
5.3 x 10-7
1.0 x 10-4
1.8 x 10-6
2.1 x 10-4
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35 mV
0 2time, min
lysosomotropic alkanolamines
Alltech universal cation exch.
40 mM H3PO4/acetonitrile 85:15
Inj. conc.: 2x10-4M, 20 microL
654
32
1
1: aminoethanol
2: N-methyl- aminoethanol
3: N-ethyl- aminoethanol
4: N,N-dimethyl- aminoethanol
5: N,N -dimethylaminoisopropanol
6: N,N-diethyl- aminoethanol
Analytica Chimica Acta, 472, 11-26, 2002.
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E
liquid membrane phase
++
+
Eluent phase+
high extraction/adsorption tendency → low DL
∆Gtr = ∆Ghydr - (∆Gsolv + ∆Gion + ∆Gcomplex)
logDL = a - blogP + cPvol
Intermolecular interactions → “non-faradaic” potentiometry
Nagels, L. J.; Bazylak, G.; Zielinska, D. Electroanalysis 2003, 15, 533-38.
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40mV
bromhexin
ambroxol
clenbuterol
0 4 min
bromhexin 10-5M inj.
det. lim: 2x10-10 M, 1pg!
HPLC/Potentiometry of Mucolytic drugsCN normal phase 250x4.6mm, 1mL min-1 ACN/HClO4 1.66mM/ethanol 60:38:4 v/v
40mV
Br
Br
NH2
NH
OH
Br
Br
NH2
N
CH3
Chromatographia 57 (11-12): 757-765, 2003
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0 min 4
10-9M bromhexin injected
1mV
Br
Br
NH2
N
CH3
Normal-phase, CN det. lim.bromhexin: 2x10-10M, 1pg!
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Liquid membrane phase (ionic conductivity)
Substrate electrode(electronic conductivity)
Interface A
V
E
Interface A gives interfacial tensions depending on eluent composition. Little is known on substrate/membrane adhesion chemistry
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CE of linear chain aliphatic amines
Potentiometric detection - polymericelectrode, 0.25mm
75 um, 60cm, 15kV, 50mM NaH2PO4
C6
C5
C4
C3
C110-3 M inj
10-4 M inj
10mV
C2
C2 C3 C4 C5 C6
0 10 time, min 20
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Time [min]17127 22 27 32 37 42
40 mV
Cocaine
HeroinAmine
Electropherogram of aliphatic amines (1-6), heroin (7), and cocaine (8). Concentrations injected: 10-3M (amines), 10-4M (drugs). Cyclodextrin was added to the eluent.
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Quinine
Clozapine
Cocaine
Noscapine
40mV
12 24 time, minSample injection electrokinetically 10s at 12.5kV. Separation voltage 12.5kV. Capillary: 75 µm i.d., 30cm length, fused silica, uncoated. Electrolyte: 50mM NaH2PO4 +10% acetonitrile (pH 3.8).
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Cocainey = 73.29x + 380.8
R2 = 0.9993
20406080
100120140160180
-5.5-5-4.5-4-3.5-3
log [c]
mV
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It did not always go that easy..
Electropherogram
hexanoic- (6), pentanoic- (5), butyric- (4), propionic- (3), acetic-(2) and formic acids
5x10-4M in 5mM HEPES (pH 7.6). Electrokinetic inj. 10s 5kV
75µm i.d., 60 cm, fused silica, uncoated, +20kV
Separation voltage: +20kV Electrolyte: 5mM HEPES pH 7.6
Anal. Chim. Acta 401, 21-27, 1999
CO
PPy electrode
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Also terrible...
Same acids in HEPES containing 0.5mM TTAB (tetradecyltrimethylammoniumbromide)
A: conducting trimer electrode, phenylene vinylene type, plus polycarbonate
B: PPy electrode
-20kV (negative polarity)
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Potentiometric detection for HPLC and CE can be made extremely sensitive for organic ionizable substances.
New classes of compounds can be studied, especially bio-organics.
More understanding of surface chemistry is needed
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Thanks to Grzegorz Bazylak, Danuta Zielinska, Jozef Everaert, Lily van Roy, Ying Bao, Hugo Bohets, Bert Vissers, David Dehous,Tom Wuyts, Justyna Sekula
Thanks to the Belgian-Polish bilateral project