Course on spectroscopic Methods Why this course? Why at this time the course? What is the expected coverage of this course?

Course on spectroscopic Methods

Why this course?

Why at this time the course?

What is the expected coverage of this course?

What is the expected coverage of this course?

As usual nothing much is expected from this course and hence please do not have great expectations from this course. It can be one of the umpteen courses one would have taken or undergone during his career and this is one more to the list.

However it will be our effort that we will try to satisfy the possible immediate needs of students in this domain.

PROPOSED BRIEF COVERAGE1. OPTICAL SPECTROSCOPY – ESSENTIALLY UV-VIS AND IR

SPECTROSCOPY ( UNLESS INFORMATION ON OTHER SPECTROSCOPIES ARE REQUIRED)

2. ELECTRON SPECTROSCOPIES – XPS, UPS AND AES ( DEMAND FOR MORE)

3. ELECTRON MICROSCOPY ALONE – TEM AND SEM NOT CONTACT MICROSCOPIES UNLESS DEMANDED

4. THERMAL METHODS ( IF TIME AVAILABLE)

Technique Acronym Type of information

Low energy electron diffraction LEED Two dimensional structure

Auger electron spectroscopy AES Elemental analysis

X-ray Photoelectron spectroscopy XPS Elemental analysis

Ion Scattering spectroscopy ISS Elemental analysis

UV photoelectron spectroscopy UPS Electronic structure

X ray diffraction XRD Crystal structure

Extended x ray absorption fine structure EXAFS Molecular structure

Infra red spectroscopy IRS Molecular structure

Electron energy loss spectroscopy EELS Molecular structure

Transmission electron microscopy TEM Crystal shape, size, morphology

Scanning tunnelling microscopy SEM Microstructure

Most often used methods

XRDAdsorption / BET

InfaredXPS / UPS

TP TechniquesTEM / SEM

NMRUV-visEXAFS

ESREDX

XANESAES

LEEDRaman

MossbauerSTM

ISS / LEISCalorimetry

Neutron scatteringSIMS

4946463836252316141210

8755443211

0 10 20 30 40 50

Number of times characterization techniques were used at the 11th ICCBaltimore 1996

total number of paperspresented orally: 143

THE ANSWER

Why this course?

The need to employ these analytical techniques in day to day learning efforts has increased considerably and hence this knowledge domain has become important for every student.

Acronym Technique

AEAPS Auger Electron Appearance Potential Spectroscopy

AES Auger Electron Spectroscopy

AFM Atomic Force Microscopy

APECS Auger Photoelectron Coincidence Spectroscopy

APFIM Atom Probe Field Ion Microscopy

APS Appearance Potential Spectroscopy

ARPES Angle Resolved Photoelectron Spectroscopy

ARUPS Angle Resolved Ultraviolet Photoelectron Spectroscopy

ATR Attenuated Total Reflection

BEEM Ballistic Electron Emission Microscopy

BIS Bremsstrahlung Isochromat Spectroscopy

CFM Chemical Force Microscopy

CHA Concentric Hemispherical Analyser

CMA Cylindrical Mirror Analyser

CPD Contact Potential Difference

CVD Chemical Vapour Deposition

DAFS Diffraction Anomalous Fine Structure

DAPS Disappearance Potential Spectroscopy

DRIFT Diffuse Reflectance Infra-Red Fourier Transform

EAPFS Extended Appearance Potential Fine Structure

EDX Energy Dispersive X-ray Analysis

EELS Electron Energy Loss Spectroscopy

  Ellipsometry, see RDS

EMS Electron Momentum Spectroscopy

EPMA Electron Probe Micro-Analysis

ESCA Electron Spectroscopy for Chemical Analysis

ESD Electron Stimulated Desorption

ESDIAD Electron Stimulated Desorption Ion Angle Distributions

EXAFS Extended X-ray Absorption Fine Structure

FEM Field Emission Microscopy

FIM Field Ion Microscopy

FTIR Fourier Transform Infra Red

FT RA-IR Fourier Transform Reflectance-Absorbtion Infra Red

HAS Helium Atom Scattering

HDA Hemispherical Deflection Analyser

HEIS High Energy Ion Scattering

HREELS High Resolution Electron Energy Loss Spectroscopy

IETS Inelastic electron tunneling spectroscopy

KRIPES k-Resolved Inverse Photoemission Spectroscopy

ILS Ionisation Loss Spectroscopy

INS Ion Neutralisation Spectroscopy

IPES Inverse Photoemission Spectroscopy

IRAS Infra-Red Absorbtion Spectroscopy

ISS Ion Scattering Spectroscopy

LEED Low Energy Electron Diffraction

LEEM Low Energy Electron Microscopy

LEIS Low Energy Ion Scattering

LFM Lateral Force Microscopy

MBE Molecular Beam Epitaxy

MBS Molecular Beam Scattering

MCXD Magnetic Circular X-ray Dichroism

MEIS Medium Energy Ion Scattering

MFM Magnetic Force Microscopy

MIES Metastable Impact Electron Spectroscopy

MIR Multiple Internal Reflection

MOCVD Metal Organic Chemical Vapour Deposition

MOKE Magneto-Optic Kerr Effect

NIXSW Normal Incidence X-ray Standing Wave

NEXAFS Near-Edge X-ray Absorption Fine Structure

NSOM Near Field Scanning Optical Microscopy

PAES Positron annihilation Auger Electron Spectroscopy

PECVD Plasma Enhanced Chemical Vapour Deposition

PEEM Photo Emission Electron Microscopy

Ph.D. Photoelectron Diffraction

PIXE Proton Induced X-ray Emission

PSD Photon Stimulated Desorption

RAIRS Reflection Absorbtion Infra-Red Spectroscopy

RAS Reflectance Anisotropy Spectroscopy

RBS Rutherford Back Scattering

RDS Reflectance Difference Spectroscopy

REFLEXAFS Reflection Extended X-ray Absorption Fine Structure

RFA Retarding Field Analyser

RHEED Reflection High Energy Electron Diffraction

RIfS Reflectometric Interference Spectroscopy

SAM Scanning Auger Microscopy

SEM Scanning Electron Microscopy

SEMPA Scanning Electron Microscopy with Polarisation Analysis

SERS Surface Enhanced Raman Scattering

SEXAFS Surface Extended X-ray Absorption Spectroscopy

SHG Second Harmonic Generation

SH-MOKE Second Harmonic Magneto-Optic Kerr Effect

SIMS Secondary Ion Mass Spectrometry

SKS Scanning Kinetic Spectroscopy

SMOKE Surface Magneto-Optic Kerr Effect

SNMS Sputtered Neutral Mass Spectrometry

SNOM Scanning Near Field Optical Microscopy

SPIPES Spin Polarised Inverse Photoemission Spectroscopy

SPEELS Spin Polarised Electron Energy Loss Spectroscopy

SPLEED Spin Polarised Low Energy Electron Diffraction

SPM Scanning Probe Microscopy

SPR Surface Plasmon Resonance

SPUPS Spin Polarised Ultraviolet Photoelectron Spectroscopy

SPXPS Spin Polarised X-ray Photoelectron Spectroscopy

STM Scanning Tunnelling Microscopy

SXAPS Soft X-ray Appearance Potential Spectroscopy

SXRD Surface X-ray Diffraction

TDS Thermal Desorption Spectroscopy

TEAS Thermal Energy Atom Scattering

TIRF Total Internal Reflectance Fluorescence

TPD Temperature Programmed Desorption

TPRS Temperature Programmed Reaction Spectroscopy

TXRF Total Reflection X-ray Fluorescence

UHV Ultra High Vacuum

UPS Ultraviolet Photoemission Spectroscopy

XANES X-ray Absorption Near-Edge Structure

XPD X-ray Photoelectron Diffraction

XPS X-ray Photoemission Spectroscopy

XRR X-ray Reflectometry

XSW X-ray Standing Wave

Fig. 2.2. Representation of the techniques based on Electrons in – electron, ion, neutral and photon out LEED: Low Energy Electron Diffraction; HEED: High Energy Electron diffraction; RHHED: Reflected High Energy Electron Diffraction; ILEED: Ineleastic Low Energy Electron Diffraction; AES: Auger Electron Spectroscopy; EELS: Electron Energy Loss Spectroscopy; EIID: Electron Induced Ion Desorption; SEPSMS: Electron Probe Surface Mass Spectrometry; EID: Electron Induced Desorption; SDMM: Surface Desorption Molecular Microscope; CIS: Characteristic Isochromat Spectroscopy; APS: Appearance Potential Spectroscopy

Fig. 2.3. Schematic representation of the techniques that can be generated from Photon- in photon, neutral, electron or ion-out methodology. XPS: X ray Photoelectron Spectrroscopy; ESCA: Electrons Spectroscopy for Chemical Analysis

Fig. 2.4. Schematic representation of the techniques that can be generated from Ions-in ion-, neutral-, electron- or photon-out methodology. ISS: Ion Scattering Spectroscopy, SIMS: Secondary Ion Mass Spectrometry, INS: Ion Neutralization Spectroscopy, PIX: Proton Induced X ray emission

Table 2.1 Typical information that can be obtained employing surface analytical techniques and the possible limitations of these techniquesSurface Analytical technique

Typical applications

Signaldetected

Elementsdetected

Detection limits

Depthresolution

Imaging/Mapping possibility

Lateral resolution(Probe size)

Auger spectroscopy

Elemental analysis, depth profiling

Atomic scale roughness Li-U - 206nm yes 100 nm

Rutherford Back scattering (RBS)

Quantitative think film composition

Backscattered He atoms Li-U 1-10 at%(for Z<20)0.01-1 at % for X 20-70

2-20 nm yes 2 mm

Secondary Ion Mass Spectrometry

Dopant and impurity depth profiling, microanalysis

Secondary ions H-U ppb/ppm <5 nm yes <5 micron imaging<30 micron depth profiling

X-ray Photoelectron Spectroscopy

Surface analysis both inorganic and organic

Photoelectrons Li-U 0.01-1 at% 1-10 nm yes 10μm -2μ

X ray Fluorescence

Thin film thickness composition

X-rays Na-U 10 ppm - no 100μm

Low Energy Electron Diffraction

Surface structure adsorbate structure

Elastic back scattering of low energy electrons

Only geometry

submonolayer - yes Atomic dimensions

High Resolution Electron Energy Loss Spectroscopy

Structure and bonding of surface atoms and adsorbates

Vibrational excitation of surface atoms adsorbates by inelastic low energy electrons

All adsorbate molecuels

Sub monolayer - - Observation of direct adsorbate-adsorbent bond

Infra red absorption spectroscopy

Structure and bonding of adsorbates

Vibrational excitation of surface bonds

Adsorbates internal bonds

Sub monolayer - - -

Ion Scattering Spectroscopy

Atomic structure composition

Elastic reflection of inert gas ions

Any element mass dependent

- possible possible Atomic dimensions

Extended X ray Absorption Fine structure

Atomic structure of surface atoms and adsorbates

Interference effects in photo-emitted electron wave function in x-ray absorption.

Mostly all species

Intermediate- coordination

- possible Atomic dimensions

Thermal Desorption Spectroscopy

Adsorption energy

Thermally induced desorption or decomposition of adsorbates

All species Sub monolayer Not normally done

- No

What responses are available?

1. Counting the number

2. Identifying the species

3. Energy analysis

4. Angular analysis

THERMAL ANALYSIS

MASSTEMPERATURE

HEAT FLOW

THERMAL ANALYSIS (DTA)

OTHER PARAMETERSe.g. LENGTH

THERMODILATOMETRY (TD)

DIFFERENTIAL THERMAL

ANALYSIS(DTA)

THERMODILATOMETRY (TD)

Thermo-mechanical analysis (TMA)

DIFFERENTIAL SCANNING

CALORIMETRY(DSC)

Thermo-optical analysis(TOA)

Thermo-sonimetry

THERMO-GRAVIMETRY(TG)

Simple diagram for Thermal Analysis

Thermal Analysis refers to a number of methods that measure change in any property of a system with respect to temperature, when it is subjected to a controlled temperature variation.

What is Thermal Analysis?

Thermo gravimetric analysis (TGA)- Monitoring the change of weight as a function of temperature.

Differential Thermal analysis (DTA)-Change in thermal energy as a function of temperature. (exo- or endothermic).

Differential scanning calorimetry (DSC)- Change in heat as a function of temperature.

4. Thermomechanical analysis (TMA)- Change of dimensions. There are other techniques such as Electrothermal analysis,

Thermoacoustimetry and so on

THERMAL ANALYSIS TECHENIQUES

TGA-DTGThe first derivative of TG (rate of weight change) as a function of temperature is called DTG, i.e., the rate of weight change (dW/dt) as a function of temperature. This facilitates clear pinpointing of maximum weight change. DTA: In this technique the difference in temp. (T) between the sample and an inert reference material is measured as a function of temperature.

Exotherm T > 0 Endotherm T < 0 

DSC: In DSC instead of allowing a temperature difference to be developed, heat/energy is supplied to maintain same temperature of the sample and reference.  EGA : It is nothing but the analysis of volatile products released on heating, analyzed generally through a QMS or IR. (called as hyphenated techniques, TG-MS etc).

Exo

Endo

Principle behind various TA methods

It is useful to examine the behaviour of a sample by more than one thermal method while heating the sample in a programmed way.TG and DTA- SimultaneousTG and EGA-Coupled technique (TG-MS, TG-IR).TG-DTG (no extra cost involved)

Cost effectiveness is also one consideration to use simultaneous thermal measurement.

Fig1.3a

Multiple thermal techniques

1. Determination of thermal constants,Heat of fusion, specific heat , freezing point and melting point.The MP of pure metals (Au, Pb, Sn etc) is often used for calibration of DTA/DSC. The area under a melting endotherm is proportional to the latent heat of fusion of the sample.

2. Phase changes and phase equilibriaSolid to liquid phase change or liquid to gaseous state.

3. Structural changesSolid-solid transitions where a change in crystal structure occurs, it could be exo-or endothermic.

4. Thermal stabilityOne can monitor the thermal stability of an oxide, particularly stability of a porous material.

Applications of thermal methods

1. Determination of thermal constants,Heat of fusion, specific heat , freezing point and melting point.The MP of pure metals (Au, Pb, Sn etc) is often used for calibration of DTA/DSC. The area under a melting endotherm is proportional to the latent heat of fusion of the sample.

2. Phase changes and phase equilibriaSolid to liquid phase change or liquid to gaseous state.

3. Structural changesSolid-solid transitions where a change in crystal structure occurs, it could be exo-or endothermic.

4. Thermal stabilityOne can monitor the thermal stability of an oxide, particularly stability of a porous material.

Applications of thermal methods

Quantitative analysis (TGA)Plaster contains gypsum (CaSO42H2O), lime Ca(OH)2 and chalk

CaCO3.

Fig 1.4m

Applications of thermal methods contd

It is is a thermo balance consisting of

(a) High precision balance,(b) A furnace for achieving high

temperatures, e.g.., 1500 oC(c) A temperature programmer,(d) Data acquisition system.(e) Auxiliary equipment to

provide inert atmosphere

A – beamB – Sample cupC –Counter weightD – Lamp and photodiodeE – Coil

F – MagnetG – control amplifierH – Tare calculatorI – AmplifierJ – Data station

Thermo gravimetric analysis-Instrumentation

Gas outlet stopcoc

k

Cooling

Vacuum and purge gas tubing

Reactive and protective gas inlets

Vacuum connection and purge gas inlet

Balance : 1g,5g;1µ,0.1µgBalance : 1g,5g;1µ,0.1µg

GAS FLOW

Cross Section of TGA (Horizontal)

Gas outlet stopcoc

k

Cooling

Vacuum and purge gas tubing

Reactive and protective gas inlets

Vacuum connection and purge gas inlet

Balance : 1g,5g;1µ,0.1µgBalance : 1g,5g;1µ,0.1µg

GAS FLOW

Cross Section of TGA (Horizontal)

1. A thermo balance should provide accurate weight of the sample as a function of temperature. (capacity upto 1g,

typical sample in mg). Its reproducibility should be very high and also highly sensitive.

2. It should operate over a wide temperature range, say from RT to 1000/1500 oC.

3. The design of thermo balance should be such that sample container is always located within a uniform hot zone inside the furnace.

4. The sample container should be such that it does not react with the sample at any given temperature.

5. The balance should not be subject to radiation or convection effects arising from the proximity of the furnace.

6. It will be advantageous if thermo balance can be coupled to a GC or IR or to QMS.

Requirements of a TG balance:

Null point balance: As weight change occurs, the balance beam starts to deviate from its normal position, a sensor detects the deviation and triggers the restoring force to bring the balance beam back to the null position. The restoring force is directly proportional to the weight change.

Deflection balance: When balance arm is deflected by a change in weight, the relative illumination of photocells from light source changes due to the movement of shutter attached to the balance beam, resulting in flow of compensating current through one of the pair of photocells.

The current produced is proportional to the change in sample weight and after amplification is passed to the coil thus restoring it to its original position. There are two types of deflection balances, (i) Beam type and (ii) Cantilever type.

Types of Balances

Null point balance: As weight change occurs, the balance beam starts to deviate from its normal position, a sensor detects the deviation and triggers the restoring force to bring the balance beam back to the null position. The restoring force is directly proportional to the weight change.

Deflection balance: When balance arm is deflected by a change in weight, the relative illumination of photocells from light source changes due to the movement of shutter attached to the balance beam, resulting in flow of compensating current through one of the pair of photocells.

The current produced is proportional to the change in sample weight and after amplification is passed to the coil thus restoring it to its original position. There are two types of deflection balances, (i) Beam type and (ii) Cantilever type.

Types of Balances

1. Buoyancy effect of sample container

It is nothing but apparent gain in weight when an empty, thermally inert crucible is heated. It has three components;

(i) decreased buoyancy of atmosphere around the sample at higher temperatures;

(ii) the increased convection effect; and (iii) the possible effect of heat from the furnace on the balance itself.

Modern instruments take care of these factors. A blank run with an empty crucible is always preferable.

 Archimedes principle : any object, when wholly or partially immersed in a fluid, is buoyed up by a force equal to the weight of the fluid displaced by the object

The density of gases decreases with increasing temperature :e.g. Air : 25°C 1.29 mg/ml

225°C 0.62 mg/ml425°C 0.41 mg/ml

Sources of error in Thermogravimetry

2. Furnace and temperature effectsHeat from the furnace may cause convection. Magnetic and inductive interaction between certain samples and winding of the furnace. Thermocouple calibration

3. Other effectsTurbulence in the gas flow. Temperature measurement effects. Placement of the thermocouple. Quantity of sample used for analysis.Packing of the sample Container materials. Mostly Pt, Alumina crucibles are used.Gas flow to evacuate the decomposition products.

Sources of Error in Thermogravimetry

Decomposition of calcium oxalateStep-I CaC2O4.H2O CaC2O4 + H2OMW 146 128 18

Step-II CaC2O4 CaCo3 + COMW 128 100 28 Step-III CaCo3 CaO + CO2

MW 100 56 44

Applications of TGA

Ca, Sr and Ba are precipitated as monohydrated oxalates.In the first step, H2O is removed from all the three oxalates, while in the second carbonates are formed by losing CO. The third step, stable oxides are formed by losing CO2.

Applications of TGA in Quantitative analysis

Experimental conditions can alter the onset as well as the end of decomposition.

Shape/sharpness of curves change with heating rate.

Experimental conditions should be known for comparison of curves from different sources. Change of atmosphere influences the decomposition. Oxidation takes place in air, while decomposition takes place in its absence.

Factors affecting TGA curves

• High flow purge rates ? Not recommended, specially for vertical TGA balances due to more turbulence) :

• Better controlled atmosphere (inert) specially at higher temperatures

• Typical purge gas flow rate for small furnace : 60 ml/min for a vertical TGA , but can be increased up to 500 ml/min ( even 1000 ml/min ) in case of horizontal models, to rapidly purge the furnace without the use of vacuum.

GAS FLOW RATES

DTA: Gives information on heat change by measuring difference in temp. between sample and reference.DSC: Temperature of sample as well as reference is maintained same by supply of required heat to the sample/reference depending on exo- or endothermic change.

Peak areas: DTA: peak area (A) = K. H.m m- mass of sample, H- heat of reaction and K –constant

which depends upon sample geometry as well as thermal conductivity. K varies with the temperature, hence instrument has to be calibrated at each temperature.

DSC: Peak area can be calculated similar way as in DTA, however K is electrical conversion factor which does not change with temp for well designed equipment.

DTA and DSC

Ultraviolet/Visible (UV-Vis) Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium Spectroscopy of Potassium

PermanganatePermanganate

Thiagarajar college, MaduraiThiagarajar college, Madurai

Importance to industryImportance to industry

• Potassium Permanganate is used to kill bacteria in reclaimed water

• Use UV-Vis to ensure that the concentration of Potassium Permanganate is at acceptable limit

OverviewOverview

• Theory

• Light Absorption Spectrum

• Experimental Procedure

• Results

• Conclusion

• Q & A

THEORYTHEORY

Properties of LightProperties of Light11

• c = λν c = speed of light in vacuum (2.998 x 108 m/s)

λ = wavelength (m)

v = frequency (Hz) • E = hc/ λ = hcv`

h = Planck’s constant (6.626 x 10-34 J•s)

v` = wavenumber (m-1)

Understanding Beer’s LawUnderstanding Beer’s Law22

• Transmittance T = P/P0

Schematic of Single-Beam Spectrophotometer, P0 is the irradiance entering sample, P is the irradiance leaving sample, and b is pathlength2

P = irradiance (energy per unit area of light beam)

Understanding Beer’s LawUnderstanding Beer’s Law33

• Absorbance A = log (P/P0) = -log (T)

• Beer’s Law A = εbc

ε = molar absorptivity (M-1 cm-1)

b = pathlength (cm)

c = concentration (M)

LIGHT ABSORPTION LIGHT ABSORPTION SPECTRUMSPECTRUM

Absorption Spectrum of LightAbsorption Spectrum of Light44

Wavelength of maximum absorption (nm)

Color Absorbed Color Observed

380 – 420 Violet Green-Yellow

420 - 440 Violet-Blue Yellow

440 – 470 Blue Orange

470 – 500 Blue-Green Red

500 – 520 Green Purple

520 – 550 Yellow-Green Violet

550 – 580 Yellow Violet-Blue

580 – 620 Orange Blue

620 – 680 Red Blue-Green

680 - 780 Purple Green

EXPERIMENTAL EXPERIMENTAL PROCEDUREPROCEDURE

Detecting Potassium Detecting Potassium PermanganatePermanganate

• Potassium permanganate (KMn04) in solution is purple / violet color meaning maximum absorption should be at 500 – 550 nm

• Prepared 5 known concentrations of KMnO4: 1ppm, 20ppm, 40ppm, 60ppm, 80ppm

Detecting Potassium Detecting Potassium PermanganatePermanganate

• Calibration Standards measured first on a Perkins-Elmer Lambda 35 over entire UV-Vis region to determine max absorption

• KMnO4 absorbed best at ≈ 520 nm

• A Bausch & Lomb Spectronic 21 was used to make all measurements

RESULTSRESULTS

UV-Vis Absorbance Readings for UV-Vis Absorbance Readings for Potassium Permanganate at 520 nmPotassium Permanganate at 520 nm

Average %A (after 3 runs)

Standard Deviation (%A)

1 ppm 0.015 0.004

20 ppm 0.256 0.001

40 ppm 0.520 0.004

60 ppm 0.753 0.002

80 ppm 1.046 0.001

Unknown #4 0.462 0.001

Calibration Curve for KMnOCalibration Curve for KMnO44 using UV-Vis using UV-Vis

Spectroscopy, Absorption vs. ConcentrationSpectroscopy, Absorption vs. Concentration

y = 0.0129x

R2 = 0.9990

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100

Concentration (ppm)

%A

bso

rban

ce

Determination of Unknown Determination of Unknown Concentration of KMnOConcentration of KMnO44

• Used cuvette of 1cm length

• ε = slope of line = 0.029 ppm-1 cm-1

• Unknown #4 concentration found using

c = A/0.029

• 36 ppm = 0.462 %A / 0.029 ppm-1

Error AnalysisError Analysis

• Used 10.00 ± 0.05mL volumetric pipette to make all solutions

• Measured density of water with:

= (999.8392 + 16.945176t – 7.9870401*10-3t2 – 46.170461*10-6t3 + 105.56302*10-9t4 – 280.54253*10-12t5)/(1 + 16.879850*10-3t)5

H2O = 0.997883 g/mL at 21.5°C

• Measured accuracy of scale to be 0.0005g

Error in UnknownError in Unknown

• Errors determined graphically from calibration curve

• A = ± 0.01%

• Concentration = ± 1.00 ppm

• Final concentration of Unknown #4 was

36 ± 1.00 ppm

CONCLUSIONCONCLUSION

ConclusionConclusion

• How accurate are results?

Can be determined by R2 value for slope of calibration curve.

For this example R2 = 0.999

ConclusionConclusion

• Use Beer’s law to determine concentration of unknown concentration

• Find the molar absorptivity through the slope of calibration curve

• Determined ε = 0.029 ppm-1 cm-1

• Determined Unknown #4 concentration to be 36 ± 1.00 ppm

Q & AQ & A

ThanksThanks

ReferencesReferences

1. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 408-409. New York: W.H. Freeman and Company, 2003.

2. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 410. New York: W.H. Freeman and Company, 2003.

3. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 411-412. New York: W.H. Freeman and Company, 2003.

4. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 413. New York: W.H. Freeman and Company, 2003.

5. CRC Handbook of Chemistry and Physics. Pg. F-6. Cleveland, Ohio: The Chemical Rubber Co., 1968.

Ultraviolet/Visible (UV-Vis) Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium Spectroscopy of Potassium

PermanganatePermanganate

Thiagarajar college, MaduraiThiagarajar college, Madurai

Importance to industryImportance to industry

• Potassium Permanganate is used to kill bacteria in reclaimed water

• Use UV-Vis to ensure that the concentration of Potassium Permanganate is at acceptable limit

OverviewOverview

• Theory

• Light Absorption Spectrum

• Experimental Procedure

• Results

• Conclusion

• Q & A

THEORYTHEORY

Properties of LightProperties of Light11

• c = λν c = speed of light in vacuum (2.998 x 108 m/s)

λ = wavelength (m)

v = frequency (Hz) • E = hc/ λ = hcv`

h = Planck’s constant (6.626 x 10-34 J•s)

v` = wavenumber (m-1)

Understanding Beer’s LawUnderstanding Beer’s Law22

• Transmittance T = P/P0

Schematic of Single-Beam Spectrophotometer, P0 is the irradiance entering sample, P is the irradiance leaving sample, and b is pathlength2

P = irradiance (energy per unit area of light beam)

Understanding Beer’s LawUnderstanding Beer’s Law33

• Absorbance A = log (P/P0) = -log (T)

• Beer’s Law A = εbc

ε = molar absorptivity (M-1 cm-1)

b = pathlength (cm)

c = concentration (M)

LIGHT ABSORPTION LIGHT ABSORPTION SPECTRUMSPECTRUM

Absorption Spectrum of LightAbsorption Spectrum of Light44

Wavelength of maximum absorption (nm)

Color Absorbed Color Observed

380 – 420 Violet Green-Yellow

420 - 440 Violet-Blue Yellow

440 – 470 Blue Orange

470 – 500 Blue-Green Red

500 – 520 Green Purple

520 – 550 Yellow-Green Violet

550 – 580 Yellow Violet-Blue

580 – 620 Orange Blue

620 – 680 Red Blue-Green

680 - 780 Purple Green

EXPERIMENTAL EXPERIMENTAL PROCEDUREPROCEDURE

Detecting Potassium Detecting Potassium PermanganatePermanganate

• Potassium permanganate (KMn04) in solution is purple / violet color meaning maximum absorption should be at 500 – 550 nm

• Prepared 5 known concentrations of KMnO4: 1ppm, 20ppm, 40ppm, 60ppm, 80ppm

Detecting Potassium Detecting Potassium PermanganatePermanganate

• Calibration Standards measured first on a Perkins-Elmer Lambda 35 over entire UV-Vis region to determine max absorption

• KMnO4 absorbed best at ≈ 520 nm

• A Bausch & Lomb Spectronic 21 was used to make all measurements

RESULTSRESULTS

UV-Vis Absorbance Readings for UV-Vis Absorbance Readings for Potassium Permanganate at 520 nmPotassium Permanganate at 520 nm

Average %A (after 3 runs)

Standard Deviation (%A)

1 ppm 0.015 0.004

20 ppm 0.256 0.001

40 ppm 0.520 0.004

60 ppm 0.753 0.002

80 ppm 1.046 0.001

Unknown #4 0.462 0.001

Calibration Curve for KMnOCalibration Curve for KMnO44 using UV-Vis using UV-Vis

Spectroscopy, Absorption vs. ConcentrationSpectroscopy, Absorption vs. Concentration

y = 0.0129x

R2 = 0.9990

0.2

0.4

0.6

0.8

1

1.2

0 20 40 60 80 100

Concentration (ppm)

%A

bso

rban

ce

Determination of Unknown Determination of Unknown Concentration of KMnOConcentration of KMnO44

• Used cuvette of 1cm length

• ε = slope of line = 0.029 ppm-1 cm-1

• Unknown #4 concentration found using

c = A/0.029

• 36 ppm = 0.462 %A / 0.029 ppm-1

Error AnalysisError Analysis

• Used 10.00 ± 0.05mL volumetric pipette to make all solutions

• Measured density of water with:

= (999.8392 + 16.945176t – 7.9870401*10-3t2 – 46.170461*10-6t3 + 105.56302*10-9t4 – 280.54253*10-12t5)/(1 + 16.879850*10-3t)5

H2O = 0.997883 g/mL at 21.5°C

• Measured accuracy of scale to be 0.0005g

Error in UnknownError in Unknown

• Errors determined graphically from calibration curve

• A = ± 0.01%

• Concentration = ± 1.00 ppm

• Final concentration of Unknown #4 was

36 ± 1.00 ppm

CONCLUSIONCONCLUSION

ConclusionConclusion

• How accurate are results?

Can be determined by R2 value for slope of calibration curve.

For this example R2 = 0.999

ConclusionConclusion

• Use Beer’s law to determine concentration of unknown concentration

• Find the molar absorptivity through the slope of calibration curve

• Determined ε = 0.029 ppm-1 cm-1

• Determined Unknown #4 concentration to be 36 ± 1.00 ppm

Q & AQ & A

ThanksThanks

ReferencesReferences

1. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 408-409. New York: W.H. Freeman and Company, 2003.

2. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 410. New York: W.H. Freeman and Company, 2003.

3. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 411-412. New York: W.H. Freeman and Company, 2003.

4. Harris, Daniel C. Sixth Edition Quantitative Chemical Analysis. Pg. 413. New York: W.H. Freeman and Company, 2003.

5. CRC Handbook of Chemistry and Physics. Pg. F-6. Cleveland, Ohio: The Chemical Rubber Co., 1968.

UV / visible Spectroscopy

• Introduction

• Identification of organic species

• Quantitation of inorganic species

Colorimetric analysis

UV / visible Spectroscopy

• The origin of the analytical signal

• Excitation of an atom or molecule by ultraviolet or visible radiation.

• 190 - 900nm

UV / visible Spectroscopy

• The radiation which is absorbed has an energy which exactly matches the energy difference between the ground state and the excited state.

• These absorptions correspond to electronic transitions.

UV / visible Spectroscopy

/ nm

Abs

/ nm

Abs

UV / visible Spectroscopy

UV / visible Spectroscopy

• Electronic transitions involve the promotion of electrons from an occupied

orbital to an unoccupied orbital.

• Energy differences of 125 - 650 kJ/mole.

UV / visible Spectroscopy

• Beer-Lambert Law

A = log(IO/I) = cl

UV / visible Spectroscopy

A = log(IO/I) = cl

– A = Absorbance (optical density)

– IO = Intensity of light on the sample cell

– I = Intensity of light leaving the sample cell– c = molar concentration of solute– l = length of sample cell (cm) = molar absorptivity (molar extinction

coefficient)

UV / visible Spectroscopy

• The Beer-Lambert Law is rigorously obeyed when a single species is present

at relatively low concentrations.

UV / visible Spectroscopy

• The Beer-Lambert Law is not obeyed:

– High concentrations

– Solute and solvent form complexes

– Thermal equilibria exist between the ground state and the excited state

– Fluorescent compounds are present in solution

UV / visible Spectroscopy

• The size of the absorbing system and the probability that the transition will take place

control the absorptivity ().

• Values above 104 are termed high intensity absorptions.

• Values below 1000 indicate low intensity absorptions which are forbidden transitions.

UV / visible Spectroscopy

• Organic Spectroscopy

• Transitions between

MOLECULAR ORBITALS

UV / visible Spectroscopy

• Highest occupied molecular orbital

HOMO

• Lowest unoccupied molecular orbital

LUMO

UV / visible Spectroscopy

UV / visible Spectroscopy

• Not all transitions are observed

• There are restrictions called

Selection Rules

• This results in

Forbidden Transitions

UV / visible Spectroscopy

• The characteristic energy of a transition and the wavelength of radiation absorbed are properties of a group of atoms rather

than of electrons themselves.

• The group of atoms producing such an absorption is called a

CHROMOPHORE

UV / visible Spectroscopy

UV / visible Spectroscopy

UV / visible Spectroscopy

• It is often difficult to extract a great deal of information from a UV spectrum by

itself.

• Generally you can only pick out conjugated systems.

UV / visible Spectroscopy

UV / visible Spectroscopy

ALWAYSuse in conjunction with

nmr and infrared spectra.

UV / visible Spectroscopy

• As structural changes occur in a chromophore it is difficult to predict exact energy and intensity changes.

• Use empirical rules.

Woodward-Fieser Rules for dienes

Woodward’s Rules for enones

UV / visible Spectroscopy

1. Bathochromic shift (red shift)– lower energy, longer wavelength

– CONJUGATION.

2. Hypsochromic shift (blue shift)– higher energy, shorter wavelength.

3. Hyperchromic effect– increase in intensity

4. Hypochromic effect– decrease in intensity

Organic Compound Identification Using Infrared

Spectroscopy

This exercise is intended to familiarize you with the identification of functional groups in organic compounds using infrared spectra. Before you can use this technique, you need to have an introduction to infrared spectroscopy and to what an IR spectrum is.

Infrared spectroscopy deals with the interaction of infrared light with matter. The energy of an infrared photon can be calculated using the Planck energy relation.The frequency, and speed of light, c, are related through the relation

E = h ν

Where h = 6.6 X 10-34 joules second and nu is the frequency of the photon

where c = 3.0 x 108 meter/second and l = wavelength for the light

These two equations can be used to identify a common spectroscopic unit called wavenumber, , which is the reciprocal of the wavelength.

E = h = h c ; E = h = hcν = wavenumber = has units of (cm-1)

You can see that both frequency and wavenumber are directly proportional to energy.Molecules are flexible, moving collections of atoms. The atoms in a molecule are constantly oscillating around average positions. Bond lengths and bond angles are continuously changing due to this vibration. A molecule absorbs infrared radiation when the vibration of the atoms in the molecule produces an oscillating electric field with the same frequency as the frequency of incident IR "light".

All of the motions can be described in terms of two types of molecular vibrations. One type of vibration, a stretch, produces a change of bond length. A stretch is a rhythmic movement along the line between the atoms so that the interatomic distance is either increasing or decreasing

The second type of vibration, a bend, results in a change in bond angle. These are also sometimes called scissoring, rocking, or "wig wag" motions

Note the high wavenumber (high energy) required to produce these motions. The bending motions are sometimes described as wagging or scissoring motions

Each of these two main types of vibration can have variations. A stretch can be symmetric or asymmetric. Bending can occur in the plane of the molecule or out of plane; it can be scissoring, like blades of a pair of scissors, or rocking, where two atoms move in the same direction.

Different stretching and bending vibrations can be visualized by considering the CH2 group in hydrocarbons. The arrows indicate the direction of motion. The stretching motions require more energy than the bending ones.

You can see that the lower wavenumber values are consistent with lower energy to cause these vibrations.A molecule absorbs a unique set of IR light frequencies. Its IR spectrum is often likened to a person's fingerprints. These frequencies match the natural vibrational modes of the molecule. A molecule absorbs only those frequencies of IR light that match vibrations that cause a change in the dipole moment of the molecule. Bonds in symmetric N2 and H2 molecules do not absorb IR because stretching does not change the dipole moment, and bending cannot occur with only 2 atoms in the molecule. Any individual bond in an organic molecule with symmetric structures and identical groups at each end of the bond will not absorb in the IR range. For example, in ethane, the bond between the carbon atoms does not absorb IR because there is a methyl group at each end of the bond. The C-H bonds within the methyl groups do absorb.

In a complicated molecule many fundamental vibrations are possible, but not all are observed. Some motions do not change the dipole moment for the molecule; some are so much alike that they coalesce into one band.Even though an IR spectrum is characteristic for an entire molecule, there are certain groups of atoms in a molecule that give rise to absorption bands at or near the same wavenumber, ,(frequency) regardless of the rest of the structure of the molecule. These persistent characteristic bands enable you to identify major structural features of the molecule after a quick inspection of the spectrum and the use of a correlation table. The correlation table is a listing of functional groups and their characteristic absorption frequencies.The infrared spectrum for a molecule is a graphical display. It shows the frequencies of IR radiation absorbed and the % of the incident light that passes through the molecule without being absorbed. The spectrum has two regions. The fingerprint region is unique for a molecule and the functional group region is similar for molecules with the same functional groups.

The nonlinear horizontal axis has units of wavenumbers. Each wavenumber value matches a particular frequency of infrared light. The vertical axis shows % transmitted light. At each frequency the % transmitted light is 100% for light that passes through the molecule with no interactions; it has a low value when the IR radiation interacts and excites the vibrations in the molecule.A portion of the spectrum where % transmittance drops to a low value then rises back to near 100% is called a "band". A band is associated with a particular vibration within the molecule. The width of a band is described as broad or narrow based on how large a range of frequencies it covers. The efficiencies for the different vibrations determine how "intense" or strong the absorption bands are. A band is described as strong, medium, or weak depending on its depth.In the hexane spectrum below the band for the CH stretch is strong and that for the CH bend is medium. The alkane, hexane (C6H14) gives an IR spectrum that has relatively few bands because there are only CH bonds that can stretch or bend. There are bands for CH stretches at about 3000 cm-1. The CH2 bend band appears at approximately 1450 cm-1 and the CH3 bend at about 1400 cm-1.

The spectrum also shows that shapes of bands can differ.

ProcedureEvery molecule will have its own characteristic spectrum. The bands that appear depend on the types of bonds and the structure of the molecule. Study the sample spectra below, noting similarities and differences, and relate these to structure and bonding within the molecules.The spectrum for the alkene, 1-hexene, C6H12, has few strong absorption

bands. The spectrum has the various CH stretch bands that all hydrocarbons show near 3000 cm-1. There is a weak alkene CH stretch above 3000 cm-1. This comes from the C&emdash;H bonds on carbons 1 and 2, the two carbons that are held together by the double bond. The strong CH stretch bands below 3000 cm-1 come from carbon-hydrogen bonds in the CH2 and CH3 groups. There is an out-of-plane CH bend for

the alkene in the range 1000-650 cm-1. There is also an alkene CC double bond stretch at about 1650 cm-1 .

The spectrum for cyclohexene, (C6H10) also has few strong bands. The main band is a strong CH stretch from the CH2 groups at about 3000 cm-1. The CH stretch for the alkene CH is, as always, to the left of 3000 cm-1. The CH2 bend appears at about 1450 cm-1. The other weaker bands in the range 1000-650 cm-1 are for the out of plane CH bending . There is a very weak alkene CC double bond stretch at about 1650 cm-1.

The IR spectrum for benzene, C6H6, has only four prominent bands because it is a very symmetric molecule. Every carbon has a single bond to a hydrogen. Each carbon is bonded to two other carbons and the carbon-carbon bonds are alike for all six carbons. The molecule is planar. The aromatic CH stretch appears at 3100-3000 cm-1 There are aromatic CC stretch bands (for the carbon-carbon bonds in the aromatic ring) at about 1500 cm-1. Two bands are caused by bending motions involving carbon-hydrogen bonds. The bands for CH bends appear at approximately 1000 cm-1 for the in-plane bends and at about 675 cm-1 for the out-of-plane bend.

The IR spectrum for the alcohol, ethanol (CH3CH2OH), is more complicated. It has a CH stretch, an OH stretch, a CO stretch and various bending vibrations. The important point to learn here is that no matter what alcohol molecule you deal with, the OH stretch will appear as a broad band at approximately 3300-3500 cm-1. Likewise the CH stretch still appears at about 3000 cm-1.

The spectrum for the aldehyde, octanal (CH3(CH2)6CHO), is shown here. The most

important features of the spectrum are carbonyl CO stretch near 1700 cm-1 and the CH stretch at about 3000 cm-1. If you see an IR spectrum with an intense strong band near 1700 cm-1 and the compound contains oxygen, the molecule most likely contains a carbonyl group,

The spectrum for the ketone, 2-pentanone, appears below. It also has a characteristic carbonyl band at 1700 cm-1. The CH stretch still appears at about 3000 cm-1, and the CH2 bend shows up at approximately 1400 cm-1. You can see the strong carbonyl CO stretch at approximately 1700 cm-1. You can also see that this spectrum is different from the spectrum for octanal. At this point in your study of IR spectroscopy, you can't tell which compound is an aldehyde and which is a ketone. You can tell that both octanal and a 2-pentanone contain C-H bonds and a carbonyl group.

Carboxylic acids have spectra that are even more involved. They typically have three bands caused by bonds in the COOH functional group. The band near 1700 cm-1 is due to the CO double bond. The broad band centered in the range 2700-3300 cm-1 is caused by the presence of the OH and a band near 1400 cm-1 comes from the CO single bond . The spectrum for the carboxylic acid, diphenylacetic acid, appears below. Although the aromatic CH bands complicate the spectrum, you can still see the broad OH stretch between 2700-3300 cm-1. It overlaps the CH stretch which appears near 3000 cm-1. A strong carbonyl CO stretch band exists near 1700 cm-1. The CO single bond stretch shows up near 1200 cm-1.

The spectrum for 1-bromobutane, C4H9Br, is shown here. This is

relatively simple because there are only CH single bonds and the CBr bond. The CH stretch still appears at about 3000 cm-1. The CH2 bend

shows up near 1400 cm-1, and you can see the CBr stretch band at approximately 700 cm-1.

IR spectra can be used to identify molecules by recording the spectrum for an unknown and comparing this to a library or data base of spectra of known compounds. Computerized spectra data bases and digitized spectra are used routinely in this way in research, medicine, criminology, and a number of other fields.In this exercise you will try to identify the outstanding bands characteristic of certain bonds and functional groups in the spectra you examine. You are certainly not expected to identify all the absorption bands in each IR spectrum at this point in your work. When you analyze the spectra, it is easier if you follow a series of steps in examining each spectrum. 1. Look first for the carbonyl C::O band. Look for a strong band at 1820-1660 cm-1. This band is usually the most intense absorption band in a spectrum. It will have a medium width. If you see the carbonyl band, look for other bands associated with functional groups that contain the carbonyl by going to step 2. If no C::O band is present, check for alcohols and go to step 3.

ACID Look for indications that an O-H is also present. It has a broad absorption near 3300-2500 cm-1. This actually will overlap the C-H stretch. There will also be a C-O single bond band near 1100-1300 cm-1. Look for the carbonyl band near 1725-1700 cm-1.

ESTER Look for C-O absorption of medium intensity near 1300-1000 cm-1. There will be no O-H band.

ALDEHYDE Look for aldehyde type C-H absorption bands. These are two weak absorptions to the right of the C-H stretch near 2850 cm-1 and 2750 cm-1 and are caused by the C-H bond that is part of the CHO aldehyde functional group. Look for the carbonyl band around 1740-1720 cm-1.

KETONE The weak aldehyde CH absorption bands will be absent. Look for the carbonyl CO band around 1725-1705 cm-1.

2. If a C::O is present you want to determine if it is part of an acid, an ester, or an aldehyde or ketone. At this time you may not be able to distinguish aldehyde from ketone and you will not be asked to do so.

ALCOHOL Look for the broad OH band near 3600-3300 cm-1 and a C-O absorption band near 1300-1000 cm-1.

 ALKENE Look for weak absorption near 1650 cm-1 for a double bond. There will be a CH stretch band near 3000 cm-1.

 AROMATIC Look for the benzene, C::C, double bonds which appear as medium to strong absorptions in the region 1650-1450 cm-1. The CH stretch band is much weaker than in alkenes.

3. If no carbonyl band appears in the spectrum, look for an alcohol O-H band.

ALCOHOLLook for the broad OH band near 3600-3300 cm-1 and a C-O absorption band near 1300-1000 cm-1.

4.. If no carbonyl bands and no O-H bands are in the spectrum, check for double bonds, C::C, from an aromatic or an alkene.

5. If none of the previous groups can be identified, you may have an alkane.

ALKANEThe main absorption will be the C-H stretch near 3000 cm-1. The spectrum will be simple with another band near 1450 cm-1.

6. If the spectrum still cannot be assigned you may have an alkyl bromide.

ALKYL BROMIDE

Look for the C-H stretch and a relatively simple spectrum with an absorption to the right of 667 cm-1.

Each of these two main types of vibration can have variations. A stretch can be symmetric or asymmetric. Bending can occur in the plane of the molecule or out of plane; it can be scissoring, like blades of a pair of scissors, or rocking, where two atoms move in the same direction.

Different stretching and bending vibrations can be visualized by considering the CH2 group in hydrocarbons. The arrows indicate the direction of motion. The stretching motions require more energy than the bending ones.

This exercise is intended to familiarize you with the identification of functional groups in organic compounds using infrared spectra. Before you can use this technique, you need to have an introduction to infrared spectroscopy and to what an IR spectrum is.