5.ElectrochemistryIon Selective ElectrodesAnodic Stripping VoltammetrySampleSamplePrepInstrumentInstrument Out putSignal (Data)DependsOn chemistryAbraham Lincoln was born Feb. 12, 1808.

Liquid Junction++--++--++--++--Concentration gradient phase phaseMobility, u, is greater, in this example, for negative than positive species++--++--++--++-- phase phaseNet charge develops due toDifference in mobilitiesNov 18 1863 at Gettysburg: Four score and seven years ago our fathers brought forth

J, Junction potentialZ, charge on ionHenderson Equation for a liquid junction diffusion potentialconcentrationAlso develop potential across a membranePotential is due to both a diffusion gradient and to interfacial equilbrium. mobilityon this continent a new nation, conceived in Liberty, and dedicated to the proposition

Consider a membrane in which only a single ion can move within the membrane ++--Aza+-++-- phase phaseAza+Interfacial regions where work is required to bring ions to The surfaceThat all men are created equal. Now we are engaged in a great civil war, testing whether

Fix this activityThis term represents the work it takes to move an ion of charge a in a potential field at the interfaceThis term representsThe diffusion gradient betweenThe two phasesRepresents the work at the interfaceAnd the composition of the inner compartmentthat nation, or any nation, so conceived and so dedicated, can long endure. We are met.

Often have to worry about the contribution to the potential from competitive ionsMembrane potential equationon a great battle-field of that war. We have come to dedicate a portion of that field, as a

ISE EquationDifference in theInterfacial workrequiredfinal resting place for those who here gave their lives that that nation might live. It is

Difference in work at the interfaceBetween the two competing ionsSelectivity coefficient, converts the impactOf the activity of the competitorto the corresponding activityOf the analytealtogether fitting and proper that we should do this.

Nikolskii- Eisenman EquationIf you have a competing ion, you can convert its activity to that of the analyte byThe selectivity coefficient and sum it upKey PointsActivitiesTemperatureDifference in interfacial work controls the selectivity coefficient4. Also means response is SLOWBut, in a larger sense, we can not dedicatewe can not consecratewe can not

Activity coefficientconcentrationIonic strengthCharge on the ionActivitieshallowthis ground. The brave men, living and dead, who struggled here, have

If there is no ionic strength buffer, increasing the concentration changes the ionicStrength, which changes the activity coefficient, which drives the activity away fromThe concentration, and, therefore, the ISE response is non-linear with concentrationIf activity was directly proportional to conc. the ISE response would be linear withConcentration.consecrated it, far above our poor power to add or detract. The world will little note, nor

Temperature Effects80oF50oFSuppose you calibrate at 50oF but make A measurement of -140mV at 80oFYou would conclude the concentrationIs log(conc.) = -5.2=6.3x10-6The real log conc. From the80oF calibration curve wouldbeLog(conc) = -4.8 = 1.6x10-5That is an errorOf a factor of 2!long remember what we say here, but it can never forget what they did here. It is for us

Selectivity impact is concentration dependentPb2+H+Lets calculate the selectivity coefficient for H+ vs Pb2+ to check the manufacturersdataManufacturers datathe living, rather, to be dedicated here to the unfinished work which they who fought here

Electrode is 1/0.0665 Or 15 more responsiveTo lead than to protonshave thus far so nobly advanced. It is rather for us to be here dedicated to the great task

Equation does not give model lines thatMatch the manufacturers reported dataremaining before usthat from these honored dead we take increased devotion to that

Calculate a value for z from the slopescause for which they gave the last full measure of devotionthat we here highly resolve

Using the manufacturers data and the equationpH 1pH 2pH 3pH 4Looks like a good match!that these dead shall not have died in vainthat this nation, under God, shall have a

2009 experimental Resultsnew birth of freedomand that government of the people, by the people, for the people,

2009 ISE resultsBlank: -235 -218 -216 -223+/-10.44

LODsignal = -223+3(10.44)=-192LODconc=3(10.44)/25=1.25ppm

Total concentration used:1.13 ppm!!

Experimentalconditionsshall not perish from the earth.

Modeled behavior usingPbTotal = 6x10-5ConstantPb = -115KPbH = 3545ZPb = 2ZH=1Allowed Pb2+ to changeWith pHData, 2009 ~0.06~10-6~10-4Both terms contribute! So you have Pb2+ and H+ decreasingWith pH making a complicated plotMar 4, 1865, 2nd Inaugural address, Fellow Countrymen:On the occasion corresponding to this four years ago all thoughts were anxiously directed to an impending civil war. All dreaded it, all sought to avert it. While the

Types of Ion Selective ElectrodesCrystallinePolymeric MembraneGas sensingField Effect transitorsinaugural address was being delivered from this place, devoted altogether to saving the Union without war, insurgent agents were in the city seeking to destroy it without warseeking to dissolve the Union and divide

Pb2+S2-Ag+Pb2+S2-Pb2+Pb2+S2-S2-Ag+S2-S2-S2-Pb2+Ag+S2-H+Cl-SO42-Fixed internal Ag+ activityVSilver moves in membrane down a concentration gradientCharge develops across the membrane leading to a voltage differenceThe interfacial concentration of silver in the bulk solution is controlled by solubilityeffects by negotiation. Both parties deprecated war, but one of them would make war rather than let the nation survive, and the other would accept war rather than let it perish. And the war came.

Similar crystalline commercial electrodes:One-eighth of the whole population were colored slaves, not distributed generally over the Union, but localized in the southern part of it. These slaves constituted a peculiar and powerful interest. All knew that this interest was

Analyte ionConc. Range, pMInterferencesBr-0 to 4.3CN-, I-, S2-Cd2+1 to 7Fe2+, Pb2+, Hg2+, Ag+, Cu2+Cl-0 to 3.3CN-, I-, Br-, S2-, OH-, NH3Cu2+1 to 8Hg2+, Ag+, Cd2+CN-2 to 6S2-, I-F-Satd to 6OH-I-0 to 7.3CN-Pb2+1 to 6Hg2+, Ag+, Cu2+Ag+/S2-0 to 7Hg2+SCN-0 to 5.3I-, Br-,CN-, S2-

http://grandinetti.org/Research/Applications/GlassStudies/assets/GlassStructure.gifExchange reaction at the surface:Other common ion selective electrodes? pH electrodesomehow the cause of the war. To strengthen, perpetuate, and extend this interest was the object for which the insurgents would rend the Union even by war, while the Government claimed no right to do more than to restrict

http://www.rsc.org/ej/CP/2002/b201721k/Image of Na hopping through glassTo different coordinate sites with oxygenA. N. Cormack, J. Du and T. R. Zeitler School of Ceramic Engineering and Materials Science, New York State College of Ceramics, Alfred University, 2 Pine St., Alfred, NY 14802, USA Received 15th February 2002, Accepted 9th May 2002First published on the web 13th June 2002 the territorial enlargement of it. Neither party expected for the war the magnitude or the duration which it has already attained. Neither anticipated that the cause of the conflict might cease with or even before the conflict

Physical Chemistry Chemical Physics DOI: 10.1039/b201721k Alkali ion migration mechanisms in silicate glasses probed by molecular dynamics simulations

Types of Ion Selective ElectrodesCrystallinePolymeric MembraneGas sensingField Effect transitorsMay have greater selectivityMay have faster response (rise) timeCreate a plastic membrane with an ionophoreWhose job is to ferry the ion across the membranePb2+Pb2+Pb2+PVCwww.3dchem.com/molecules.asp?ID=327 Link to PVC structureitself should cease. Each looked for an easier triumph, and a result less fundamental and astounding. Both read the same Bible and pray to the same God, and each invokes His aid against the other. It may seem strange that

From the Critical Reviewsany men should dare to ask a just God's assistance in wringing their bread from the sweat of other men's faces, but let us judge not, that we be not judged. The prayers of both could not be answered. That of neither has been

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Sensitivity (slope)Selectivity (selectivity coefficients)Response TimeLinear Rangeanswered fully. The Almighty has His own purposes. 'Woe unto the world because of offenses; for it must needs be that offenses come, but woe to that man by whom the offense cometh.' If we shall suppose that American

Response to Pb2+Response to Pb2+slavery is one of those offenses which, in the providence of God, must needs come, but which, having continued through His appointed time, He now wills to remove, and that He gives to both North and South this terrible war

Next works on right ionophore to plastic compositionsensitivityLinear RangeSelectivityAs the woe due to those by whom the offense came, shall we discern therein any departure from those divine attributes which the believers in a living God always ascribe to Him? Fondly do we hope, fervently do we pray,

SelectivityResponse Timethat this mighty scourge of war may speedily pass away. Yet, if God wills that it continue until all the wealth piled by the bondsman's two hundred and fifty years of unrequited toil shall be sunk, and until every drop of blood

Response TimeSelectivityLinear RangesensitivityDetection LimitThey havent reported thesblank so we cannotConfirm their LODconc.

Key conceptsSelectivity depends upon mobility and interfacial equilibriatherefore often slow responsemay be complicated by solution chemistryPotential depends upon activity therefore dependent upon ionic strength, IPotential depends temperature!SampleSamplePrepInstrumentInstrument Out putSignal (Data)Signal depends on physics of membrane transportWhich ALSO depends upon chemistry of leaddrawn with the lash shall be paid by another drawn with the sword, as was said three thousand years ago, so still it must be said 'the judgments of the Lord are true and righteous altogether'.

5.ElectrochemistryIon Selective ElectrodesAnodic Stripping VoltammetryWith malice toward none; with charity for all; with firmness in the right, as God gives us to see the right, let us strive on to finish the work we are in; to bind up the nation's wounds; to care for him who shall have borne the battle, and for his widow, and his orphan to do all which may achieve and cherish a just and lasting peace, among ourselves, and with all nations.Abraham Lincoln was born Feb. 12, 1808.

Mercury is stable as a liquid at potentials less than 0.268 V vs NHELead, tin, nickel, cadmium, iron, and zinc metals are soluble in liquid mercuryElectrons roll away from negativeIf the applied potential is more positive than -0.76 then Zn metalWill oxidize (electrons will flow from Zn metal into an acceptor in soln.)If the applied potential is more negative than 0.799 then silver ionWill be reduced (electrons will flow from electrode to aqueous ion)NHE = Normal Hydrogen Electrode

ReactionEo at 25oC, V vs NHESolubility Metal in Hg Wt(%)-0.76265.6-0.444-0.40255-0.2570.0021-0.13751.3-0.12051.200.2680.3400.0080.7991

Reduce Mercury to form a film (small volume container) of thickness,

HgHold voltage negative of0.268 V vs NHEWorking electrode where current is measuredReference electrode (comparison point)eCounter Electrode (sacrificial reactions)eeVHg deposition timeHg+

Remove Hg2Cl2 solution and replace with analyte solution; holding potential such that no current flowsHgHold voltage between negative of0.268 V and positive of -0.1205 V vs NHEWorking electrode where current is measuredReference electrode (comparison point)Counter Electrode (sacrificial reactions)eVPb2+ Sn2+quiet time allows Solution to revert toBulk solution like conditions

Step potential negative to reduce metals into the liquid HgHgHold voltage between negative For example, -0.8 V vs NHEWorking electrode where current is measuredReference electrode (comparison point)Counter Electrode (sacrificial reactions)eVAnalyte deposition time, tdee

Step potential negative to reduce metals into the liquid HgHgHold voltage between negative For example, -0.8 V vs NHEWorking electrode where current is measuredReference electrode (comparison point)Counter Electrode (sacrificial reactions)eVAnalyte deposition time, tdeeDeposition current And time of deposition control theAmount deposited Initially we remove all the Pb2+ and Sn2+ near the Hg film .

If we dont stir then we set up a concentration gradient and deposition will be determined bydiffusion to the surface

Step potential negative to reduce metals into the liquid HgHgHold voltage between negative For example, -0.8 V vs NHEWorking electrode where current is measuredReference electrode (comparison point)Counter Electrode (sacrificial reactions)eVAnalyte deposition time, tdeeHanging mercury drop electrode spherically shaped

Concentration in the drop dependsOn deposition timeNotice that we have transferredMoles from a large volume toA small volume = pre-concentration!

4. Scan potential negative to remove metals from the liquid Hg (oxidize back into aqueous phase)Scan voltage between -0.8 and 0 V vs NHEWorking electrode where current is measuredReference electrode (comparison point)Counter Electrode (sacrificial reactions)eVeeThe rate at which you scan, v, affects the shape and peak current of the oxidationScan rate# e transferredMercury Film ElectrodeArea of electrodeHg film thickness

Starting Potential; soln contains only salts and Hg2Cl2Potential range to deposit Mercury thin liquid filmChange to analyte containing solution;

Set potential to NOT oxidize the deposited Hg AND to NOT reduce the analytesSet potential to reduce the metalsChange potential with time to oxidizeDeposition time, tdScan rate = = dV/dtDo not keepScanning to thesePotentials, why?

2001 Student Data800 microL Pb Std addition120 microL Pb Std. additionRaw DataFFT data

Standard series (FFT filtered)Allows you to get a veryNice calibration curve!2001 Student Data

Pb2+Cd2+Difference in peak potential allowsBoth metals to be measured simultaneously!Good selectivity!2001 Student Data

To make this method more acceptable to commercial testing need toGet rid of the mercury.JChem Ed 2007

8 mmol Cu2+/L8 mmol Cd2+/Lblank8 mmol Pb2+/L8 mmol/L Zn2+

Note the selectivity in potential and the discrimination between variousmetalsAu particle modifiedAu electrodeOrdinary Au electrodeNote scaleChange!!blank8 mmol/L ofPb2+, Cu2+, Cd2+ and Zn2+Measures Pb2+ and Cu2+Selective against Cd2+And Zn2+; Increased sensitivity