Ultramicroelectrodes Electroanalytical Chemistr Lecture #7 22-Feb-211
22-Feb-21 1 Ultramicroelectrodes Electroanalytical Chemistry Lecture #7
UMES Geometries ◆Disk ◆ Recessed disk C.S. Henry: I Fritsch Anal. Chem 199971.550-6. ◆Band Cylinder ◆ Materials Carbon fiber
UME’s Geometries Disk Recessed disk C.S. Henry; I. Fritsch Anal. Chem. 1999, 71, 550-6. Band Cylinder Materials Carbon fiber
UME's- Advantages ◆ Reduced capacitance ◆ Low iR drop
UME’s - Advantages Reduced capacitance Low iR drop
UMES- Disadvantages ◆ Noise Electrochemical Fouling ◆ Analyte Method of electrode prep'n(epoxy) Stray capacitance ◆ Impurities ◆ Maintenance ◆Cost ◆ fragile construction
UME’s - Disadvantages Noise Electrochemical Fouling Analyte Method of electrode prep’n (epoxy) Stray capacitance Impurities Maintenance Cost Fragile construction
UME's- Applications ◆ Determine[ analyte ◆ Study reactions at low temperatures frozen glasses o in solvents of moderate to high permittivity W/o electrolyte in solvents of high resistance ◆ in solid state ◆ in gas phase
UME’s - Applications Determine [analyte] Study reactions at low temperatures = frozen glasses in solvents of moderate to high permittivity w/o electrolyte in solvents of high resistance in solid state in gas phase
UMES-Applications (contd) ◆ Biological systems ◆ Single cells ◆ organelles ◆ Fast kinetics 4 development of analytical tools for electrode/solution interface ◆SECM(Bard) ◆EQCM ◆SERS( Van Duyne)
UME’s - Applications (cont’d) Biological systems Single cells organelles Fast kinetics Development of analytical tools for electrode/solution interface SECM (Bard) EQCM SERS (Van Duyne)
Scanning electrochemical Microscopy(seCM) R Diffusion is hemispherical =nfC D where a= diam of UME Acquire I vs tip position (x, y) Plot of d vs tip position piezoelectric positioning d ◆ Bipotentiostat Sample Ref Bard et al. Science 1991.254.68-74
Scanning Electrochemical Microscopy (SECM) Diffusion is hemispherical i ss = 4 n F Co * Do a where a = diam. of UME Acquire I vs. tip position (x,y) Plot of d vs. tip position piezoelectric positioning Bipotentiostat Sample C W R Ref.: Bard et al. Science 1991, 254, 68-74. d
SECM(cont'd CwR◆W-100n( diam) Determines resolution ◆2 nm best at present Sample ◆ Conducting ◆ Insulator Mineral ◆ Biological Sample ◆ Semiconductor
SECM (cont’d) W - 100 nm (diam.) Determines resolution 2 nm best at present Sample Conducting Insulator Mineral Biological Semiconductor Sample C W R
Common modes of Operation Feedback ◆ Positive or negative ◆ Collection flux of species generated/consumed probed
Common Modes of Operation Feedback Positive or negative Collection flux of species generated/consumed probed
SECM- Positive W F eeabac k R t If sample conductive we get positive feedback 1>1 SS R O Conductive Samp
SECM- Positive Feedback If sample conductive, we get positive feedback i > iss Conductive Sample C W R R O
