Voltammetry Chemical Modification of Working Electrodes Voltammetry Working

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Voltammetry Chemical Modification of Working Electrodes

Voltammetry Chemical Modification of Working Electrodes

Voltammetry - Working Electrodes chemical modification of working electrodes modification – inference of chemically

Voltammetry - Working Electrodes chemical modification of working electrodes modification – inference of chemically functional groups to the electrode surface unmodified electrode surface mainly electrochemical reactions only modified electrode surface electrochemical AND chemical reactions possible functional groups

Voltammetry - Working Electrodes conventional surface modification as with homogeneous solid electrodes coating with

Voltammetry - Working Electrodes conventional surface modification as with homogeneous solid electrodes coating with membranes adsorption covalent binding films chemical deposition electrochemical deposition monolayers self-assembled monolayers Langmuir-Blodgett layers bulk modification of heterogeneous electrode material (composite el. ) additionally possible direct mixing (suspensions - particulate matter) dissolution in liquid binder (lipophilic) adsorption/deposition on particles

Voltammetry - Working Electrodes advantages of bulk modification simple preparation mild conditions (no temperature

Voltammetry - Working Electrodes advantages of bulk modification simple preparation mild conditions (no temperature or UV curing) particularly important for biosensors also possible for labile systems simple multiple modification particularly important for biosensors modification with biocomponent plus mediator etc. very widespread method quick testing of complex systems possible electrochemistry of water-insoluble analytes possible in aqueous media „solid state“ electrochemistry of lipophilic compounds

Voltammetry - Working Electrodes electrode surface coating with membranes „inert“ membranes „physical“ function used

Voltammetry - Working Electrodes electrode surface coating with membranes „inert“ membranes „physical“ function used as diffusion barriers e. g. , size exclusion immobilization of enzymes at electrode surface e. g. , by dialysis membrane incorporation of actual modifiers (catalysts, electroactive) e. g. , enzymes PVC, PE, Teflon, dialysis membranes, etc. example: dialysis membrane as protective membrane in a SPE

Voltammetry - Working Electrodes electrode surface coating with membranes redox membranes contain reducible/oxidizable groups

Voltammetry - Working Electrodes electrode surface coating with membranes redox membranes contain reducible/oxidizable groups may act as mediators („electrocatalysts“) can be reduced to –NH 2 some redox polymers good mediators for biosensors

Voltammetry - Working Electrodes electrode surface coating with membranes polymers with functional groups charged

Voltammetry - Working Electrodes electrode surface coating with membranes polymers with functional groups charged groups act as charge barriers repel ions of same charge act as ion exchanger for ions with opposite charge accumulation, immobilization e. g. , Nafion, poly(vinylpyridine)

Voltammetry - Working Electrodes surface modification by adsorption chemisorption yields rather stable modifiactions olefins

Voltammetry - Working Electrodes surface modification by adsorption chemisorption yields rather stable modifiactions olefins on Pt-electrodes p-electron systems on C electrodes S-compounds on gold often basis for self-assembled monolayers surface modification by covalent binding functional groups attached via covalent bonds usually oxides (often reduced to hydroxide) or hydroxides groups attached (via -Si. Cl with metals or other reactions with C) carbon oxidized to =C=O, reduced to –C-OH

Voltammetry - Working Electrodes surface modification by film deposition by chemical deposition e. g.

Voltammetry - Working Electrodes surface modification by film deposition by chemical deposition e. g. , Prussion blue(Fe 4[Fe(CN)6]3 as catalyst for H 2 O 2 from Fe 3+ and [Fe(CN)6]4 - precursors from Fe 2+ and [Fe(CN)6]4 - and electrooxidation by electrochemical deposition monomers are electrochemically oxidized wide conjugated p-systems yield electric conductivity polyaniline different oxidation states polypyrrole polythiophen

Voltammetry - Working Electrodes surface modification by monolayers self assembled monolayers bifunctional molecules attaching

Voltammetry - Working Electrodes surface modification by monolayers self assembled monolayers bifunctional molecules attaching to the surface between attaching group and functional group alkyl chain van der Waals interaction even small molecules cannot enter high degree of order should be dense, but often „pinholes“ examples: thiol compounds on gold surfaces silicates on glass carboxylates on metals

Voltammetry - Working Electrodes surface modification by monolayers self assembled monolayers example: adsorption of

Voltammetry - Working Electrodes surface modification by monolayers self assembled monolayers example: adsorption of dithiobis(N-succinimidylpropionate] at a gold electrode, covalently coupled to HRP forms a SAM with immobilized active enzyme

Voltammetry - Working Electrodes surface modification by monolayers Langmuir-Blodgett layers (LBL) thin molecular layers

Voltammetry - Working Electrodes surface modification by monolayers Langmuir-Blodgett layers (LBL) thin molecular layers of surfactants formed on water surfaces can be transferred to solid surfaces dipping depends on desired orientation of molecules fatty acids usually too soft often contain polymerizable groups for crosslinking hydrophilicity of polar group should be high for stable films not too high to prevent dissolution good model for biological membranes e. g. , hydrophilicity on a C 16 -chain

Voltammetry - Working Electrodes surface modification by monolayers Langmuir-Blodgett layers (LBL) orientation depends on

Voltammetry - Working Electrodes surface modification by monolayers Langmuir-Blodgett layers (LBL) orientation depends on way of submersion/dipping

Voltammetry - Working Electrodes bulk modification of heterogeneous electrodes direct mixing reagents are added

Voltammetry - Working Electrodes bulk modification of heterogeneous electrodes direct mixing reagents are added directly to the electrode material carbon paste carbon ink reagents should be not soluble in solutions in contact or at least stronly adsorbed on the carbon particles otherwise: „bleeding“ of the electrode main reasons for modification accumulation to lower detection limits to separate off interferences electrocatalysis to achieve electroactivity to decrease overpotentials to increase specifity (e. g. , biosensors) to improve the detection limit

Voltammetry - Working Electrodes direct mixing particulate modifier

Voltammetry - Working Electrodes direct mixing particulate modifier

Voltammetry - Working Electrodes accumulation with modified electrodes accumulation reaction salt formation exchange complexation

Voltammetry - Working Electrodes accumulation with modified electrodes accumulation reaction salt formation exchange complexation covalent bond formation

Voltammetry - Working Electrodes electrocatalysis with modified electrodes catalytic oxidation („mediation“) catalytic reduction („mediation)

Voltammetry - Working Electrodes electrocatalysis with modified electrodes catalytic oxidation („mediation“) catalytic reduction („mediation)