Flashcards in Test 3 Deck (88):
produces electrical energy
consumes electrical energy
when positive solution is applied to electode, layers of solution adjacent to electrode acquire ? charge
In cell notation, the anode is on the ? side
nonlinear data in plot of potential versus current is indicative of ?
ideal polarized electrode
current remains constant and independent of potential over wide range
ideal nonpolarized electrode
potential remains constant and independent of current over wide range
measuring potential of cell without drawing appreciable current
typical potentiometer cell in cell notation
ref !! analyte soln ! indicator electrode
reference electrode in potentiometry
half cell of accurately known potential that is independent of concentration of analyte or other ions in solution
indicator electrode in potentiometry
immersed in solution and develops a potential based on activity of the analyte
Potential measure of cell
difference between reference and indicator, add junction potential
Two common reference electrodes
Calomel and silver-silver chloride
Hg in contact with solution saturated with mercury chloride and known concentration of KCl
potential of calomel
advantage of calomel electrode
disadvantage of calomel
large temperature coefficient, slow to reach equilibrium when temperature is changed. can only be used at low temperature.
when potential of electrode is lowered
reduction of analyte occurs. electron adds to LUMO
when potential of electrode is increased
oxidation of analyte occurs. electron leaves HOMO
no current passes through ? electrode
advantage of Ag-AgCl electrode
can be used at temps above 60C
disadvantage of Ag-Ag-Cl electrode
silver ions react with more sample components than Hg
at low pH, potential Eb is positive/negative. external barrier poternatial is higher /lower
as pH increases, error increases. lower reading than actual
asymmetric error fixed using?
glass membrane composition
SiO2 > Na2O > CaO. Each Si bound to four O. Singly charged cations are mobile in lattice and are responsible for conduction and balancing negatively charged SiO4-.
mechanism of CO2 snsing by gas probe
CO2 effues through gas permeable membrane and glass membrane. Combines with water to change pH. measured by internal glass calomel electrode.
L for metallic electrodes
standard electrode potential
L for membrane electrodes
sum of many constants
measure current in EChem cell w/ polarization conditions
reference electrode in voltammetry
used in maintaining potential at WE
movement of electrons across electrode due to redox species in solution
movement of charged species due to charge buildup on electrode surface
movement of species due to chemical or electrical gradient
influencing movement due to charge
influencing movement due to chemical gradient
influencing movement due to agitation
sum of migration, diffusion and convection
migration eliminated by ?
diluting with inert supporting electrolytes. inert electrolyte does the migrating instead of analyte
convection resolved with ?>
rotating disk or motionless electrode
fick's first law
chemical species diffuses down concentration gradient
peak current increases/decreases with scan rate. Why?
increases. stronger concentration gradient, more rapid diffusion
? bind to Au
1st gen glucose biosensor
glucose diffuses through outer membrane into immobilized glucose oxidase that catalyzes formation of H2O2 from oxygen. H2O2 diffuses through inner membrane and dissociates releasing two electrons. electrons current genrated is proportional to glucose concentration.
2nd gen glucose biosensor
glucose oxidase transfers electrons to a mediator instead of O2.
benefit of 2nd gen glucose biosensor
can oxidize mediator at low potential, lowering interference
ferrocene derivatives, organic conducting salts
Cell response to glucose meter implantation in subcutaneous tissue
leukocytes generate fibrous capsule around meter. causes inflammation
electrochemical DNA hybridization detection method
modify Au electrode with thiolated ssDNA. expose to complement. Expose viologen probe that binds to DNA and produces EC signal.
multiply cationic dimer. forms radical when reduced. overlap of singly occupied pi* orbitals
xenobiotic induced carcinogens
metabolism process tries to eliminate using cyt p450. generates reactive metabolites what can damage dna
looks for straight dna damage
use bacteria to see whether a chemical reaction can cause cancer. gives yes/no answer
problems with detection of dna damaging chemicals
interspecies metabolism differences. fixed by using human enzymes
site specific dna damage
carcinogens adduct at specific locations
dna damage studies
electrode modified with dna oligomer containing known hotspot sequence. expose carcinogen for timed period. monitor voltammetry as function of BPDE exposure.
CV fit and isotherm. frumpkin curve fit.
integrate waves in plot of potential vs current. find how much dna on electrode.
voltammetry pulse method plot
staircase in plot of time vs potential
benefits of pulse methods
better signal to noise ratio
when is current measured in pulse methods
when difference between the desired faradaic curve and the interfering charge is large
as pXc increases, Ecell ?
pulse voltammetry curve decays with
negative square root of time
more sensitive pulse method
? determines speed of scan in square wave
? determines potential step in square wave
how is square wave plotted
plot difference of forward and reverse curent
chomatography equilibrium constant
retention factor doesn't depend on ?
geometry or flow rate
retention factor formula
? retention factors go through column quickly
ratio of elution rate between two species
Want high/low plate number
want high/low plate height
relationship between plate number and height
L=N*H where L is column length
van deemter plots
flow rate vs plate height
LC vs GC. lower flow rates
LC vs GC. lower heights
LC vs GC. lower plate number
LC vs GC. superior in terms of separation efficiency.
van deemter eqn
H=A + B/U +CsU + CmU
enhanced with higher flow rates, increases plate height
linear diffusion decreased by ?
higher flow rate, lowers plate height
parameters of packed columns
parameters of open column
diameter of tube
good resolution value