Schwingungsspektroskopie

Theoretische Grundlagen, Instrumentierung, Anwendungen derMittel-Infrarot, Nah-Infrarot und Raman Spektroskopie

C.W. HuckInstitut für Analytische Chemie und RadiochemieLeopold-Franzens UniversitätInnrain 52a6020 Innsbruck, Österreich

Christian.W.Huck@uibk.ac.at

1

Why Analytical Innovations?

High sample throughput

Improved detection limit

Needle in haystack

Speed

Sensitivity

Selectivity

„To see what one could not see before“

Christian Huck

http://www.uibk.ac.at/acrc/mitarbeiter/huck/

Christian Huck

Christian Huck

Kwansei-Gakuin UniversitySanda, Hyogo, Japan

Christian Huck

Kwansei-Gakuin University

Christian Huck

Kwansei-Gakuin University

Christian Huck

8

What is Spectroscopy? What is Light?

• Spectroscopy is the interaction of light with matter

• Light is electromagnetic radiation

• Isaac Newton showed that light consists of different visible components

• Frederic William Herschel detected also components beyond the visible region ⇒infrared region

Christian Huck

W. Herschel, "Investigation of the powers of the prismatic colours to heat and illuminate objects", Phil. Trans. (1800) 255.Herschel, W., "Experiments on the refrangibility of the invisible rays of the sun.", Phil Trans. (1800) 284.

Frederick William Herschel (1738 - 1822)

Herschel's Experiment zur Messung der Temperatur jeder Farbe im Spektrum

Geschichte der Infrarotspektroskopie

9Christian Huck

Newton/Herschel

sun lightvisible spectrum

Actually, the infrared consists of three regions: near-infrared mid-infraredfar-infrared

∆ T

infrared spectrum

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Wellendarstellung des Lichtes. Das elektrische Feld Esteht normal auf das magnetische Feld M und beidewiederum normal auf die Ausbreitungsrichtung

Die elektromagnetische Welle ist eine Kopplung aus elektrischen und magnetischen Feldern. Die beiden Felder stehen normal aufeinander und beide stehen normal zur Ausbreitungsrichtung z

Die elektromagnetische Welle

Christian Huck

Wechselwirkung von Licht mit Materie

12

Jedes Elektronenniveau entspricht einem definierten Energielevel das nur durch Zuführen einer definierten Menge an Energie in das nächst höhere angehoben werden kann. Die Energie der Elektronen ist also gequantelt.

▭(ΔE=E1-E2 ) Glg. 1

E1 und E2 bezeichnen die Energien des Elektrons in Orbit 1 bzw. 2. Die Energie für den Übergang von Niveau 1 auf 2 kann zum Beispiel durch die Wechselwirkung mit Licht stattfinden. Für einen erfolgreichen Übergang muss die Bedingung in Glg. 2 erfüllt sein. Man spricht von der Frequenzbedingung.

▭(E1-E2=h*ν) Glg. 2

h … Planck’sches Wirkungsquantumν … Frequenz

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13

The Electromagnetic Spectrum

X - Rays

Far Ultraviolet

Ultraviolet

Near Infrared

Mid Infrared

Far Infrared

Microwave

Visible

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Spectral Ranges of Electromagnetic Radiation and the TypicalExcitations

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The Origin of Mid- and Near-Infrared Spectroscopy

15

m M

m Mk

µπν k

osc 21

=

MmmM+

=µ reduced mass

k = force constant

+=

21υν oscosc hE

2

21

21

+−

+= υνχυν oscoscosc hhE

χ = anharmonicity constant

Mid-Infrared Near-Infrared

Christian Huck

Vibrational Spectroscopy

16

SCATTERING TECHNIQUE ABSORPTION TECHNIQUES

SOURCEMONOCHROMATIC RADIATION

(LASER VIS-NIR)

INFORMATION CONTAINEDIN SCATTERED RADIATION

IRaman ≈ 10-8 ISource

SOURCES(DISPERSED) POLYCHROMATIC RADIATION

(GLOBAR TUNGSTEN)

INFORMATION CONTAINEDIN ABSORBED RADIATION

RAMAN MID-INFRARED NEAR-INFRARED

M m

q

V V

qq

VV

Anti-StokesStokes

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Vibrational Spectroscopy ⇔ Excitation Conditions or

Why do we see a Signal in the Spectrum ?

17

RAMAN MID-INFRARED NEAR-INFRARED

M m

HOMONUCLEAR POLARe.g. C=C FUNCTIONALITIES e.g. C=O FUNCTIONALITIES

HIGH STRUCTURAL SELECTIVITYLOW STRUCTURAL

SELECTIVITY

0≠∂∂

qα 0≠

∂∂

qµ 0≠

∂∂

qµ ANHARMONICITY

m<<M

CH / OH / NH

/

OFTEN CHEMOMETRICSNECESSARY

polarizability dipole moment mechanical anharmonicity

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Comparison MIR versus NIR

ABSORPTION INTENSITY

MIR: dominated by the dipole moment

NIR: dominated by the anharmonicity

SOME FUNCTIONAL GROUPS WITH LARGE ABSORPTION INTENSITIES OF FUNDAMENTAL VIBRATIONS:

-C-F, C=O, -C-O-C- , -Si-O-Si- 18Christian Huck

19

Fundamental Vibrations → Overtones

11 λ

ν c=

fundamental vibration mid-infrared (MIR) spectroscopy

ν = frequency c = velocity of light λ = wavelength

λ1

12

2 2 νλ

ν ⋅==c

1st overtone vibration near-infrared (NIR) spectroscopy

λ 2

Christian Huck

Wavenumber-Wavelength Conversion

20

Because IR spectra are almost exclusively represented with the wavenumber scale it is highly recommended to represent the NIR spectra also in wavenumbers.

[ ] [ ]71 101~ ⋅=−

nmcm

λν

[ ] [ ]41 101~ ⋅=−

mcm

µλν

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Band Position as a Function of Bonding Strength andAtomic Mass

FUNCTIONALITY BAND POSITION FUNCTIONALITY BAND POSITION

[cm-1] [cm-1]

C – C 800 – 1400 C – Cl 400 - 700

C = C 1500 – 1800 C – C 800 - 1400

C C 2000 – 2300 C – H 2800 - 3200

21

BON

DIN

G ST

REN

GTH

ATO

MIC

MAS

S

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Some Characteristic Vibrations

22

Geometry Vibration Nomenclature

symmetric CH2-stretching

antisymmetric CH2-stretching

CH2-bending

CH2-twisting

CH2-wagging

CH2-rocking

OH in-plane bending

OH out-of-plane bending

CCC-bending

νs (CH2)

νas (CH2)

δ(CH2)

γt (CH2)

γw (CH2)

γr (CH2)

δ(OH)

γw (OH)

∆(CCC)

CHH

CHH

CHH

CHH

CHH

CHH

C OH

C OH

CC

C

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NIR-Spectrum of Water

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45005000550060006500700075008000

Wavenumber [cm-1]

0.0

0.5

1.0

1.5

2.0Ab

sorb

ance

ν1(OH) + ν3(OH)

ν(OH) + δ(OH)

Water is one of the best NIR absorbers.

However, this has consequences for the FT-Raman spectrum ……

Christian Huck

24

Building Principle of an IR/NIR-Spectrometer

Source Monochromator Detector

Globar Tungsten-Halogen Lamp

GratingInterferometerAOTF

MCT InGaAs, InSb PbS, Si, Ge Diode-Array

Today IR-spectroscopy is almost exclusively operated with interferometers in the Fourier-Transform mode.

Sample Sample

or

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INTERACTANCEFibre optic probe

T R I

I0 ItI0

TRANSMISSION REFLECTANCEor transflectance0-45°optics or integrating sphere

Ir+

-

I0

∞

It=0

SAMPLE PRESENTATION MODE

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NEAR-INFRARED

(BEER´S LAW)

MID-INFRARED

cbaA ⋅⋅==IIlog 0

A = absorbancea = absorptivity (cm2 mol-1)b = sample thickness (cm)c = sample concentration (mol cm-3)

Quantitative Vibrational Spectroscopy

The intensity I can be evaluated by the peak height or by the peak area of a substance specific signal (univariate evaluation). Alternatively, thewhole spectrum can be used and evaluated by so-called multivariate, chemometric techniques.

Christian Huck

Diffuse Reflection

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Sample Preparation

NO SAMPLE PREPARATIONONLY VIA ATR

RAMAN MID-INFRARED NEAR-INFRARED

NO SAMPLEPREPARATION

NO SAMPLEPREPARATION

For the detection of polymorphism, for example, destruction-free sample handling is the prerequisite.

Therefore, these techniques offer high-throughput analysis.

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2929

NIR isn´t always as bad as it is generally thought to be!!MIR- and NIR-spectra of Poly(dimethylsiloxane)

2AB

SORB

ANCE

4000 3000 2000 1500 1000 5000

1

WAVENUMBERS

MIR30 µm

6500 6000 5500 5000 4500 40000.0

0.2

WAVENUMBERS

NIR200 µm

ABSO

RBAN

CE 0.4

O SiCH3

CH3n

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3030 30

What Information is Available fromNear-Infrared Spectra of Materials ?

The NIR spectrum is a fingerprint of the investigated material. It is characteristic of its chemical and physical properties.

4000500060007000800090000.

51.

01.

52.

0Ab

sorb

ance

Aspirin

Cellulose

400050006000700080009000Wavenumber [cm-1]

0.2

0.6

1.0

1.4

Abso

rban

ce

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3131 3131

Grating Spectrometer

Sample

Lenses

Detector

Entrance Slit

Source

Grating

Exit Slit

The different wavelengths/wavenumbers

are recorded successively in time. Christian Huck

3232 323232

FT-IR/FT-NIR ⇔ Michelson Interferometer

Sample

Mirror 1Source

Detector

∆X

Lenses

Beam Splitter

Mirror 2

Mirror Retardation ∆X

Inte

nsity

Wavenumber (cm-1)

Abso

rban

ce

Interferogram Spectrum

Fourier-Transformation

The different wavelengths/wavenumbers

are recorded simultaneouslyChristian Huck

Sample Presentation for Non-DestructiveDiffuse Reflection NIR Spectroscopy

Source

Mirrors

Detector

Sample

Beam Splitter

Lightfiber-Bundle

Probe Head with Sapphire Window

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34

Application of Diffuse-Reflection FT-IR Spectroscopy

Structure of a Glass/Polymer Composite

Christian Huck

MIR/NIR chemicalimaging

NIR spectroscopy

FTIR-ATR spectroscopy

Instrumentation

Christian Huck

Miniaturisierung

20152008

2005

1972

1940

?

Christian Huck

Factor plot of 141 spectra of different wines (Lagrein, Chianti, Cabernet Sauvignon). Conditions: Normalisiation, 1st derivative; wavenumer range, 4500 - 10000 cm-1; thickness, 3 mm; scans, 10; temperature, 23°C.

Wein-Analytik

12.5 15.0 17.5 20.0

12.5

15.0

17.5

20.0Validation spectra f(x)=0.9692x+0.4539 r=0.994863Calibration spectra f(x)=0.9839x+0.2672 r=0.991921

a

Validation spectra f(x)=0.6104x+3.0884 r=0.852905Calibration spectra f(x)=0.8616x+1.0340 r=0.928229

4 6 8 10 12tr

ue v

alu

e[K

MW

]

predicted value [KMW]

carbohydrate content

b6

8

10

tru

e va

lue

[g/l]

predicted value [g/l]

total acid content

2 3 4 5 6 7 5

predicted value [g/l]ctr

ue

valu

e [g

/l]

tartaric acid content

3

6

4

5

7 Validation spectra f(x)=0.6941x+1.6032 r=0.845581Calibration spectra f(x)=0.8219x+0.9089 r=0.906583

3 4 5 6 7 8

predicted value [g/l]

true

val

ue

[g/l]

34567

8

d

Validation spectra f(x)=0.4460x+2.7197 r=0.711211Calibration spectra f(x)=0.7274x+1.2762 r=0.852891

malic acid content

3.0 3.2 3.4 3.6 3.8

e

pH

3.13.23.33.43.53.6 Validation spectra f(x)=0.4802x+1.7244 r=0.732065

Calibration spectra f(x)=0.5398x+1.5406 r=0.852891

predicted value

true

val

ue

SEE /SEP

f7654321

factorSE

E /S

EP

[%

]

0255075

100125150

pH

carbohydrates

total acid [g/l]

tartaric acid [g/l]

malic acid [g/l]

Lagrein

Chianti

Cabernet

Christian Huck

Verbena officinalis

Cornelia Pezzei

seeding in March 2013

from July till September (blooming time) NIR measurements of the leaves using a Büchi NIRFlex N-500 FT-NIR spectrometer and a handheld NIR material analyzer (Phazir)

Christian Huck

Prostatakrebs - Gewebeanalytik

Christian Huck

Installation of a Bypass System

quick and reliable filling/purging procedure probe tip cleaning mechanism

reproducible sample density optical and easy mechanical access

Christian Huck