Analysis & Structure of Molecules

문 명 희화학과 분석화학전공

CHEMISTRY

물질의 특성 및 변화

물질의 합성

유기화학무기화학

에너지변화

물리화학

분석분석법개발

분석화학

Analytical Chemistry & Life

Drunken driverAthletesRiver contaminationExplosives by terroristsFoodEnvironmentsQC in ManufacturingClinical ExaminationsEtc.

Detection of Chemicals

Accuracy Precision

Development of Analytical Technologies

ClassicalTechnologies

InstrumentalAnalysisComputer

Robotics

•Titration acid-base, redox, complex•Precipitation-Weighing Group Analysis•Colorimetry litmus paper,

•Spectrophotometric methods X-ray, Atomic Spectroscopy UV-VIS, IR, microwave•Separation (chromatography) GC, HPLC, SFC•Electrochemical

instrumentalreproducibleUltra low detection(10 억분의 1 영역 )

manualTime takingLabor orientedpoor detection limit

Classical Analytical Chemistry

• Quantitative Analysis– gravimetric analysis ( 중량분석 )

Ni Ni-dimethylglyoxime salt ( 침전 )

– Volumetric analysis ( 부피분석 )

titration ( 적정 )

무게측정

지시약첨가 색변화관찰

What is Titration ?

농도를 아는 용액( 산 , 또는 염기 )

분석대상용액( 염기 또는 산 )

H-Acid + M-Base BH + MA

Final Goal : Amount ?

types

Acid-Base titrationRedox titrationPrecipitation

Spectrophotometric

Physical Methods in AC

• A Great Advance

19th century - Atomic Spectroscopy

Chemicalcompound Light Colored

light

Ex) Na ---- 589.0 nm (bright yellow)

ICP (Inductively Coupled Plasma)

What if light source is plasma ?

Arsample solution

load coil(~27MHz, 2kW)

plasma

atomic emission

Inductively Coupled Plasma “torch”

(11~17L/min)

Ar 의 이온화 – coil 의 spark

4000 ~8000 K

ICP/ optical emissionspectrum of 100 ppm Cerium solution

ICPMS spectrumof 10 ppm Cerium

Ce emission

140Ce+

plasma continuum

Analysis of Complicated Mixtures ?

Needs Simplification of Matrix Separation (or isolation)

Emergence of Chromatography

ChromatographyIn Greek Word, Color + To Write

1903 Tswett (Russian Botanist)

First Observed Separation of Plant Pigments as bands on chalk column (CaCO3) with ether

Chromatographic Separation

SampleA

SampleB

Glass wools

SamplesA & B

Solid materials

M.P

Modern Instruments of Chromatography

injector

detector

PC

pump column

Data record

InjectorSample loop

column

Separation Process in Chromatography

Sample Components are carried by a mobile phase through a bed of stationary phase

Mobile Phase : Gas

LiquidStationary Phase : Solid (silica, alumina, etc.)

Liquid

Classifications by Phase Type

Mobile Stationary

Liquid Solid LSCLiquid LLC

Gas Solid GSCLiquid GLC

Supercritical Fluid SFC

Retention of sample molecules !

Where ? -- Stationary Phase (S.P.) By how ? -- Various Mechansims

1. Adsorption2. Partition3. Ion-Exchange4. Size Exclusion5. Affinity

1. Adsorption

Stationary Phase - Solid : silica, alumina LSC, GSC

Separation is due to a series of Adsorption/Desorption Steps

Solid(particle)

M.P.

Adsorption

Common S.P. : Silica & alumina

Both Solutes and Solvent are attracted to the Polar Sites on the S.P.

For Separation, Solutes need to have different degrees of ATTRACTION to the phase

2. Partition (distribution)

Solute Partitioning between TWO PHASESS.P.: Lig. M.P.: Gas --- GLCS.P.: Lig. M.P.: Liq --- LLC

Separation is Based on RELATIVE SOLUBILITY

Phase A Phase B

How does liq. S.P. exist ?Liq. Immobilized to solid (C18-silica)

Partition

Basic Principle - similar to EXTRACTION

High Affinity (Solubility) for S.P. Retain Longer

Separation of Solutes is based on differences in this relative solubility

One phase - polarThe other phase - nonpolar

i.e. S.P. : Nonpolar (C18) M.P.: Water or Methanol * separation order- order of interaction

between C18-sample

Example

3. Ion Exchange

Stationary Phase has ionically charged surfaceinteraction between

Surface-ions: counterionsS.P. : Exchange Resins (Cation, Anion Types)

-Solid(particle)

M.P.

+

+

+

sample

Ion Chromatography (IC)

Chromatographic Process to separateIons and some polar molecules

Stationary Phase attract ionic species by the following principles.

Typical Mechansims 1. Ion Exchange - IEC 2. Ion Exclusion 3. Complexation Effect

Ion Exchange Chromatography

Stationary PhasesAnion Exchange Resins Cation Exchange Resin

resin+

resin+

+

(analyte) ++

Ion exchange

resin NH+ Cl-

R

R

resin NH+ Cl-

H

H

strong

weak

resin SO3-H+

resin COO-H+

resin SO3-H

Ion Exchange

What Affects the Separation Order ?

Ionic Charge : Larger the stronger attraction

Li+, Na+, K+ < Ca+2, Mg+2

F-, Cl-, Br-, H2PO4-, < SO4

2-

Atomic Number : Higher the larger Electron Cloud -- stronger van der Waals Force

Li+ < Na+ < K+ , Ca+2 < Mg+2

F- < Cl- < Br- < H2PO4-

Ion ExchangeExample

Separation of Common AnionsEluent: 1.8mM Na2CO3, 1.7mM NaHCO3

Ion ExchangeExample

Separation of Common CationsEluent: 20mM HCl or Methansulfonic acid

Ion ExchangeExample

Separation of Organic AcidsEluent: 1.6mM Heptafluorobutyric acid

4. Size Exclusion

Stationary Phase : Porous GelSolute passes pores or is excluded Gel Permeation Chromatography

or Gel Filtration Chromatography

M.P.

polymer Porousparticle

Schematics of Porous Particlesbeing used in SEC

Size Exclusion

Various Columns needed to separate SAMPLES of SPECIFIC SIZE RANGES

Large Species Elute Firstsince they can pass through as many poresso they spend little time in S.P.

Useful for Determining Size & Size Distribution for

Polymers, Proteins, ...

Example Application by SEC

Gas Chromatography (GC)

First Commercial Instrumental Chromatographic System

Separation in GC

Sample should be converted to Vapor StateMobile Phase : Inert Gas (H2, He, N2, Ar)

GCTypes of Stationary Phases

Solid (GSC) : silica gel, alumina, charcoal, etcLiquid(GLC): nonvolatile liq. Coated on

firebrick (Chromosorb..), diatomaceous earththickness : ~ 0.25 m

i.e.: Poly(dimethyl siloxane)(Dipheny)0.05(dimethyl)0.95polysiloxane

Separation is achieved by order of Sample’s Polarity.Nonpolar Solute - attracted to Nonpolar S.P.

GCTypes of Columns

GCTypes of Columns

Conventional1/8-1/4 inch OD, SS or glass tube6-20 feet in length

Capillary0.1 - 0.5 mm ID10-100 meters in length

WCOTOTC

GC Operation

Isothermal : Constant TemperatureTemperature Programming :

Temp. varies during the analysis

By Increasing T,Increase the activity(diffusion, ad/desorption,etc.)

Increase speed recovery

For Temperature Programming, Solubility Variations, Volatility of Solutes should be considered

Example Applications

Example Applications

Example Applications

Chemical Structure ? By How

Molecule• Electromagnetic

- Radiation

• Electron Beam

• Neutron

MeasurePhysical & Chemical

changes

Most Typical Probe !

Electromagnetic Radiation

What is electromagnetic Radiation ?

 

Light, microwaves, x-rays, and TV and radio transmissions are all kinds of electromagnetic radiation.

They are all the same kind of wavy disturbance that repeats itself over a distance called the wavelength.

The different names refer to different wavelengths.

   

      

chhE

Planck const.

frequency Light speed

wavelength

What can happen when light shines on a material ?

heat

Visible light

Inner shellElectron transitionX-ray Diffraction

Outer shellElectron transition

UV-VIS SpectroscopyAtomic AbsorptionAtomic Emission Molecular vibration

IR SpectroscopyRaman Spectroscopy

Rotational MotionNMR, MRI, ESR

Atomiclevel

Molecularlevel

X-ray Diffraction or

X-ray Crystallography X-rays are diffracted by crystals scattered by the electron cloud of an atom of comparable size.

Diffraction Pattern Molecular structure

Crystallattice

X-Ray Diffraction (X-Ray Crystallography)

• The most straightforward way of examining the structure of a compound

Bragg’s Law

Conditions for constructive interference of the beam at angle θ

AP + PC = n

AP = PC = d sin θ

n = 2d sin θ

sin θ = d

n

2

1. Crystals are rotated through all angles to obtain diffraction pattern 2. The conversion of diffraction pattern to structure

If we know, and θ,We can get d (inter-atomic distance)

Bright X-ray:Synchrotron radiation

High-resolution X-ray crystallography

X-ray Diffraction or X-ray Crystallography

Light Spectroscopy II

UV-VIS Absorption Spectroscopy

• Interaction of UV-VIS light with electronic energy levels in molecules

• Good means of identification for transition metal coordination compound or some organic compounds (double bond 포함 시료의 경우 )

• Good for quantitation ( 정량분석 , HPLC 의 검출기 )

• Spectral band: provides a great deal of information about the electronic structures of molecules

v=1

v=2

v=3

h1

ho

ho-

h 1

RamanScattering

Fluorescence IRAbsorption

NIRAbsorption

virtual

state

excitedelectronic

state

Groundstate

Energy

rotational levels

UV-Visabsorption

S2

S1

overtones

Light Spectroscopy III

IR Spectroscopy

• Information on chemical groups in molecules

• Stretching and shaking of molecules: IR region (4000 cm-1 – 200 cm-1)

• Provides ‘fingerprint’ of the various chemical groups in the molecule ( 예 : carbonyl group: 1700 – 1800 cm-1)

• FT-IR (fast, better resolution and S/N) see box 2

CO stretching band

Vibrational Modes of Molecules

chhE

Light speed

wavelength

Vibrations in polyatomic molecules:

linear molecule: 3N-5 (N = number of atoms)

nonlinear molecule: 3N-6

for water: 3N-6 = 3

symmetric stretch 3652 cm-1

asymmetric stretch 3756 cm-1

bend1595 cm-1

30

22 12

16

67

1

3000 2500 2000 1500 1000

OSU FTIR(between NaCl plates)

Galactic Library1994 [Chloroform w/ 0.75% Ethanol; liquid]

3021

2401

1522

1425

1216

1045 92

9

772

3000 2500 2000 1500 1000

CHCl3

cm-1

abso

rban

ce

H

Cl

CCl

Cl

CHCl3 normal modes

3019 cm-1

(C-H stretch)364 cm-1

667 cm-1

(sym. stretch)

760 cm-1 260 cm-1

1215 cm-1

(C-H bend)

mode labels are from Hyperchem, e vibrations are doubly degenerate

4 3 9

7,8 1,2 5,6

Mirror travel

Frequency, (cm-1)

x = 0

x = 0

4004000

Interferogram:

Single beam spectrum of air:

FT

100%

H2O H2OCO2

Fourier Transform IR (FT-IR)

He-Ne lasertop of

beamsplitter

Perkin Elmer Galaxy 2000 FTIR

Nuclear Magnetic Resonance (NMR)

magnet

시료주입

Nuclear Magnetic Resonance • Depends on magnetic properties of certain nuclei (H, C, F, ..)• Certain nuclei rotates about an axis and thus have a property of spin• A spinning charged nucleus creates a magnetic field, thus magnetic moment.

Energy ~ radio wave 영역

Spin - spin coupling

Nuclear Magnetic Resonance I

Radio frequency 영역의 빛 흡수 (megahertz): depends on magnetic field and nucleus being studied

(chemical structure 에 의존 )

초기 NMR: radiowave 파 : 고정된 frequency 사용- magnetic field: 시간에 따라 변화시킴 Signal vs magnetic field

최근 NMR (Pulse FT NMR)- 강한 radiofrequency ( 다양한 frequency 함유 ) 의 pulse 를 가함- Free induction decay(FID) decayed- Time domain 의 신호를 Fourier Transformation 으로 frequency 의 영역으로 변화시킴

Magnetic Resonance Imaging (MRI)

Imaging tool for clear and detailed pictures of internal organs and tissuesusing magnet and radio frequency

MRI is particularly good for some types of brain tumour, for primary bone tumours and soft tissue sarcomas and f

or tumours affecting the spinal cord.