Molecular Spectroscopy Theory and Overview

The Electromagnetic Spectrum

x-raysultraviolet

visible

near-IR

mid - IR

far-IR

radioRangeRange

WavenumbersWavenumbers(cm-1) 107 106 105 104 103 102

mid - IR

XRF UV-Vis InfraredTechniqueTechnique

2

WavelengthWavelength (m) 10-3 0.01 0.1 1 10 100

Cl H

IR Absorption Requires a Dipole Change

• When HCl vibrates, the dipole (charge separation) increases

N N • N2 has no dipole and is infrared inactive

3

• The dipole must also align with the electric field; this is important in oriented films, IRRAS

Bending Twisting

+ -

Molecular Vibrations Provide Information

60

70

80

90

100

T

C CC C

Stretching Deformation

C

4

20

30

40

50

60

%T

1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

From Interferometry to a Spectrum…

• Interference• When two waves interact, they can reinforce or cancel one another

• Constructiveinterference

• Destructive i t f

+ =

5

interference

+ =

The Michelson Interferometer: “ZPD”

Fixed mirrorFixed mirror

l 0 -l

IR IR SourceSource

BeamsplitterBeamsplitter

6

DetectorDetector

Moving mirrorMoving mirrorPath difference = 0Constructive

Lengthen One Arm by ⅛ Wavelength

Fixed mirrorFixed mirror

l 0 -l

IR IR SourceSource

BeamsplitterBeamsplitter

7

Detector

Moving mirrorMoving mirror

DetectorDetector

Path difference 2 x ⅛ = ¼ Partially destructive

Now Lengthen by ¼ Wavelength

Fixed mirrorFixed mirror

l 0 -l

IR IR SourceSource

BeamsplitterBeamsplitter

8

DetectorDetector

Moving mirrorMoving mirror

l 0 -lPath difference 2 x ¼ = ½ Fully destructive

Fixed mirrorFixed mirror

This Is What It Looks Like When Running…

Varying path

BeamsplitterBeamsplitterl 0l 0 --ll

IR IR SourceSource

Varying path difference

9

BeamsplitterBeamsplitterl 0 l 0 ll

DetectorDetector

FT-IR Advantages

• Measures all wavelengths simultaneously by interferometry

• Wavelength scale (x-axis) is referenced toWavelength scale (x axis) is referenced to internal laser standard

• Perfect mirror alignment maintained in real-time via proprietary dynamic alignment system

• Modular components allow for expandability and flexible method development

10

The Value of FT-IR Spectroscopy

• First “go to” analytical technique for fast materials screening

• Provides chemical identification of…• Solids, Liquids and Gases

• Widely used in any type of laboratoryWidely used in any type of laboratory• Quality Control laboratories

• Qualify raw materials for compliance

• Quantify chemical species in finished products

• Analytical Services and Forensic laboratories

• Identify unknown substances; pure materials and mixtures

• Deformulation of finished products for customer support (failure analysis), competitive products reverse engineering and counterfeiting

11

competitive products reverse engineering and counterfeiting

• Reaction monitoring and kinetic studies… from minutes to nano seconds

• Basic and applied research laboratories

• Research and development of new materials

What You Can Do…

• Qualitative analysis• Known materials

• Need to verify purity

• Need to verify type

• Unknown materials

• By using…

• Spectral correlation

• Class analysis (PCA)

• Unknown materials

• Need to identify composition • Spectral correlation against multiple libraries also known as “Search” Simple search provides “best similarity”

of the main spectral features

12

• By using…

• Beer Lambert or CLS quant

Ch t i l i (PCR PLS)

What You Can Do…

• Quantitative analysis• Known materials

• Need to monitor main ingredient

• Need to monitor multiple • Chemometric analysis (PCR, PLS)

• Multi component search

• TGA IR deformulation

• Chemical imaging and image analysis (FT-IR microscopy)

• Need to monitor multiple ingredients in complex mixtures

• Characterize unknowns

• Mixtures and contaminants

• Finished products

• Material distribution

13

FT-IR Microscopy

14

• FT-IR microscopy is a combination of light microscopy and FT-IR spectroscopy, which allows the viewing of the sample and its chemical characterization

• Essential technique for…• Analytical Services and Applied Research laboratories across industries

• Root cause analysis of defects, inclusions and other types of failure

• Characterization of multi layer structures and materials distribution

The Value of FT-IR Microscopy

• Patent protection and intellectual property

• Forensic and Government laboratories

• Crime scene trace evidence

• Counterfeiting and customs imported goods inspection

• Identification of trace levels of hazardous material

• Contract laboratories

• Microanalysis analytical services

15

• Academic and Research laboratories

• Structural analysis of minerals, art restoration artifacts, biological samples, natural and synthetic fibers, wood and paper chemistry, and material science

The Value of FT-IR Microscopy

• Point and shoot is for…• Single specimen identification

• Fibers

Red Fiber embedded in money

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Abs

Nylon Library match

0 7

0.8

Red Fiber embedded in money

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

Abs

Nylon Library match

0 7

0.8++

Which FT-IR microscopy technique best fits your needs?

• Particles

• Inclusions

• Observe, get a spectrum, and identify

EVOH

Polyethylene

Polyurethane adhesive

Polyethylene

EVAPolyamide

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Abs

500 1000 1500 2000 2500 3000 3500 4000

Wavenumbers (cm-1)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Abs

500 1000 1500 2000 2500 3000 3500 4000

Wavenumbers (cm-1)

+

• Mapping is for…• Sections and small area characterization

• Laminates

• Paint chips and other cross sections

• Small area materials distribution studies

16

• Imaging is for…• Large area characterization• Observe, set an area, get an array of spectra and

extract chemical information

• Observe, get a series of spectra and identify / measure

Raman is an Essential Tool

• Identification of unknowns and mixtures• Forensic unknowns

• Tablet analysis

• Analysis of submicron layers and particlesAnalysis of submicron layers and particles• Thin film layers

• Defect and contaminant analysis

• Analysis of molecular structure and material crystallinity

• Solar silicon

• Polymorphs

• Minerals

• Gems

17

• Gems

• Characterization of advanced carbon materials

• Nanotubes

• Graphene

Raman Microscopy

• Sample applicability• Solids, liquids, and gases

• Surface characterization with mapping• Areas ranging from microns to as much as millimeters

• Subsurface sampling and depth profiling CH

20 microns

Subsurface sampling and depth profiling• Applies to transparent media only

• Depths of microns to as much as 1 cm depending on optical properties of the material

500 1000 1500 2000 2500 3000 Raman shift cm-1

CH4

CH4 CO2Quartz

Trapped gases

18

Raman Microscopy

• Advantages• Sample through glass

• Samples on glass slides, in glass p g gcapillary tubes, etc.

• Small samples down to ~500 nm

• Aqueous Solutions

• Organic and inorganic materials

• Physical characteristics as well as chemical information

• Remote fiber optic sampling possible

19

Applications of Near-IR Spectroscopy

• Raw Material Identification• Qualify materials at the receiving station, non-

destructively, through packaging material

• Multiple Component Quantitative AnalysisMultiple Component Quantitative Analysis• Replace time-consuming wet chemical methods

• Measure processes on-line or in harsh process environments

• Using fiber optic probes

• Spectrometer can be up to 100 meters away from the process line

20

NIR Permits Analysis of Samples “As-is”

• Can measure all sample types

Solids Softgels Films

Liquids Grains Suspensions

Tablets Pastes Syrups

Powders Pellets Botanicals

21

An Antaris NIR Spectrometer for Every Application

Method Development System Multiplex Process Analyzer

22

Explosive Environments Blend Analyzer

Introduction to UV-Visible Spectroscopy

• UV-Visible spectroscopy measures the absorption or reflection of light in the ultraviolet and/or visible region of the spectrum

23

Introduction to UV-Visible Spectroscopy

• Also called electronic spectroscopy because the transitions measured involve valence electrons in the molecules.

Molecules have electrons in discrete molecular orbitals

• If you hit a molecule with light equal in energy to the gap between a filled highest occupied molecular orbital and an empty lowest unoccupied molecular orbital, the electron can absorb that photon and jump up into the higher

Energy gapbetween filled

•

24

photon and jump up into the higher energy orbital

between filledand emptyorbitals

UV-Vis Peaks are Broad

• At normal temperatures, molecules generally:

• Rotate• Vibrate (expand contract flex etc )• Vibrate (expand, contract, flex, etc.)

• Motion causes different molecules of the same chemical to have slightly different absolute energy levels for the filled and unfilled orbitals

• The range of energy levels means that photons across a range of energy levels are absorbed by a sample of a pure

25

are absorbed by a sample of a pure compound.

Examples of Absorption Spectra

26

UV-Visible Spectroscopy

• UV-Vis Helps you • Quantify and Identify components

• Gain information about molecular structure

• Gain information about molecular environment• Gain information about molecular environment

• UV-Vis is• The most cost effective way to measure concentration

• Non-destructive

• As accurate as instruments costing 50X more

• Frequently called out in SOPs and methods for many regulatory agencies

• USP

27

• USP

• ASTM

• ISO

• Able to measure solid materials by reflection

The Value of UV-Vis Spectroscopy

• Tried and true analytical technique for accurate and rapid quantitation of pure or mixed composition samples

• Provides easy and accurate quantitation of…• Solids, liquids and mixed samples, q p

• Widely used in any type of laboratory• Basic and applied research laboratories

• Especially common in Life Science, QA/QC and Material science laboratories

• Quality Control laboratories

• Quantify known species in finished products

• Quantify species as “check step” in advanced work flows

• Provide high resolution archival spectral information for regulated

28

Provide high resolution archival spectral information for regulated environments

• Analytical Services and contract laboratories

• Identify unknown substances; pure materials and even mixtures

• Reaction monitoring and kinetic studies… from days to milli seconds

• By using…• Beer Lambert

• Multicomponent analysis (MCA)

What You Can Do…

• Quantitative analysis• Known materials

• Need to monitor main ingredient

• Need to quantify multiple

• Spectral analysis or overlay

• Need to quantify multiple species in complex mixtures

• Characterize unknowns• Identify peak shifts or

contaminants

29

Comparison of Spectroscopic Techniques

FTIR/Raman/NIR UV-Vis & Fluorescence

Transition Type Vibrational Electronic

Typical Limit of 1% ppmypDetection (Bulk)

pp(Bulk & Trace)

Primary Analysis Qualitative Quantitative

Sampling Non-destructive Non-destructive

Typical Sample Primarily organic Organic & Inorganic

Measurement time Seconds Seconds

• Vibrational spectroscopy is the foremost tool for the identification of

30

Vibrational spectroscopy is the foremost tool for the identification of organic materials

• UV-Vis spectroscopy is the most ubiquitous technique for quantification