NIR Fundamentals and

1
NIR Fundamentals and a little more

• Graduate Students
• Yleana M. Colón
• Andres Román
• Daniel Mateo

2
Electromagnetic Spectrum
12,800 cm-1 (780 nm)
4,000 cm -1 (2500 nm)
Frequency (cm-1)
108 107 106 105 104 103 102 101 1 10-1 10-2 10-3

?-Ray
NMR
ESR
FIR
MIR
X Ray
visible
NIR
Ultraviolet
Radio, TV Waves
Microwave
Infrared
Region
NuclearTransitions
SpinOrientation in MagneticField
MolecularRotations
MolecularVibrations
ValanceElectron Transitions
InnerShell Electronic Transitions
Interaction

10-10 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 1 11
Wavelength (nm)
Courtesy of Bruker Optics
3
Spectroscopy

• is based on the interaction of electromagnetic
  waves and matter.
• Spectral Absorptions
• Microwave Rotation of molecules
• IR Fundamental molecular vibrations
• NIR Overtones and combinations of IR
• UV / Visible Electronic transitions
• X-Ray Core electronic transitions in the atom

4
Units of spectra- nm, ?m, cm-1

• 1cm 1 x 107 nm 1 nm 1 x 10-3 µm

Where cm-1 1 x 107 nm

• Sometimes see cm-1
• 10,000 cm-1 (1/10,000) cm or 0.0001 cm 1 ?m
  1000 nm
• 6,000 cm-1 (1/6000) cm or 0.000167cm 1.67 ?m
  1670 nm
• 5,000 cm-1 (1/5000) cm or 0.0002 cm 2 ?m
  2000 nm
• 4000 cm-1 (1/4000) cm or 0.00025 cm 2.5 ?m
  2500 nm.

5
What is Infrared Spectroscopy?

• Sir Isaac Newton set up an experiment in which a
  beam of sunlight passed through window shutters
  into a dark room.

(Algodoo v1.8.5)
6
What is Infrared Spectroscopy? (cont)

• Much later, Frederic William Herschel, the
  discoverer of planets and many other celestial
  objects, imagined the existence of other
  components of white light, outside the visible
  region.
• The region after the red part is called Infrared
  Region.
• Herschel set up an experiment to measure this
  radiation under the red which is not visible to
  human eye, thus he used a thermometer.

7
What is Infrared Spectroscopy? (cont)

• In March of 1800 Herschel placed a sample of
  water in the path of the beam, and the difference
  of temperature was then associated with
  absorption.

8
Mid-IR

• Today, the mid-infrared region is normally
  defined as the frequency range of 4000 cm-l to
  400 cm-1.
• The upper limit is more or less arbitrary, and
  was originally chosen as a practical limit based
  on the performance characteristics of early
  instruments.
• The lower limit, in many cases, is defined by a
  specific optical component, such as, a
  beamsplitter with a potassium bromide (KBr)
  substrate, which has a natural transmission
  cut-off just below 400 cm-1.

104 103 102 101
Frequency (cm-1)
FIR
MIR
NIR
Infrared
J. Coates, Vibrational Spectroscopy
Instrumentation for Infrared and Raman
Spectroscopy, Applied Spectroscopy Reviews,
1998, 33(4), 267 425.
9
Far IR

• The region below 400 cm-1, is now generally
  classified as the far infrared, characterized by
  low frequency vibrations typically assigned to
  low energy deformation vibrations and the
  fundamental stretching modes of heavy atoms.
• There is only one IR-active fundamental vibration
  that extends beyond 4000 cm-1, and that is the
  H-F stretching mode of hydrogen fluoride.
• The original NIR work was with extended UV-Vis
  spectrometers. Indicates that mid and NIR should
  be considered the same field.

NIR
104 103 102 101
Frequency (cm-1)
FIR
MIR
NIR
Infrared
J. Coates, Vibrational Spectroscopy
Instrumentation for Infrared and Raman
Spectroscopy, Applied Spectroscopy Reviews,
1998, 33(4), 267 425.
10
Spectroscopy Provides Information

• Presence of functional groups
• Variation of functional groups, or elements
  throughout a surface (chemical information)
• Differences in the crystal structure of compounds
• Qualitative and quantitative analysis

11
Mid-IR Spectroscopy widely used in

• Identification of pharmaceutical raw materials
  and finished products.
• Combination with MS and NMR to determine
  structure of process impurities and degradation
  products.
• Characterization of natural products, use of
  GC/FT-IR.
• Forensic analysis, IR-Microscopy.
• Environmental analysis GC/FT-IR.
• Surface analysis, diffuse reflectance, attenuated
  total reflectance, grazing angle.
• Studies of protein structure and dynamics.

12
NIR Spectroscopy used in

• Identification of solid sample forms
• Physical characteristic analysis of solid samples
  such as particle size and packing density of a
  material.
• Provide information on moisture content
• Monitor process parameters such as flow rates,
  blending process end time and even by-products.
• Non-invasive remote monitoring of different
  processes.
• Medical uses such as measurement of the amount of
  oxygen content of hemoglobin.

13
Molecular Vibrational Spectroscopy

• The physical origin of molecular vibrations are
  due to
• - absorption of radiation by a material (MIR and
  NIR techniques)
• - scattering of radiation by a material (Raman
  technique)

• Vibrational frequencies are very sensitive to
  the structure of the investigated compound
• - structure elucidation, finger print spectra

14
Hookes Law
In order to understand the absorption phenomenon,
lets compare a molecule to the vibration of a
spring,
m2
m1
15
Simple Harmonic Oscillator
Energy curve for vibrating spring
where, V potential energy E total energy K
kinetic energy as a function of position
16
Quantized Vibration Theory
In the harmonic oscillator model, the potential
energy well is symmetric.

• Molecular vibrations have
• Discrete energy values,
• Energy levels are equally spaced,
• Each energy level is defined by n quantum number
  whose integers values are 0, 1, 2,
• Only effective for relatively small deformations
  in the spring.

17
Vibration Theory
On the basis of the equation above it is possible
to state the following 1) The higher the force
constant k, i.e., the bond strength, the higher
the vibrational frequency (in wavenumbers).
Courtesy of Bruker Optics
18
Vibration Theory
2) The larger the vibrating atomic mass, the
lower the vibrational frequency in wavenumbers.
Courtesy of Bruker Optics
19
A Molecule Absorbs Infrared Energy when

• Change in dipole moment must occur.
• The dipole moment is a measure of the degree of
  polarity of molecule (magnitude of the separated
  charges times the distance between them).
• A measurement of degree of unequal distribution
  of charges in molecule.

20
Molecular Dipole

• HBr does have a dipole change as it stretches,
  the intensity of the absorption is related to the
  magnitude of the dipole change. This dipole
  aligns with the electric field of the beam of
  light, then the light is absorbed.

21
Band Intensity in IR and Spectrum

• Band intensity depends on the rate of change of
  dipole moment during absorption of IR light.
• Stronger bands occur when the change in dipole
  moment is greatest.
• A spectrum is a plot that shows the absorption or
  reflection of radiation as wavelength or
  frequency of the radiation is varied.

A.S. Bonanno, J. M. Olinger, and P.R. Griffiths,
in Near Infra-Red Spectroscopy, Bridging the Gap
Between Data Analysis and NIR Applications, Ellis
Horwood, 1992.
22
Molecules that absorb Infrared energy vibrate in
two modes
Stretching is defined as a continuous change in
the inter-atomic distance along the axis of the
bond between two atoms.
Bending is defined as a change in bond angle
23
Molecular Spectroscopy

• This situation is simplified considering every
  functional group in the molecule independently.
• Each functional group has a set of group
  frequencies which correspond to the normal modes
  for the group.

24
Degrees of Freedom
Molecule Degrees of freedom
Non linear Linear 3N -6 3N- 5
Example The fundamental vibrations for water,
H2O are given in below. Water which is nonlinear,
has three fundamental vibrations.
25
Molecular Vibration

• Hexane C6H14 has 20 atoms (3(20)-6 54) normal
  modes, it is very difficult to analyze each mode.

26
NIR bands

• O-H, N-H, C-H, S-H bonds etc., are NIR strong
  absorbers since they have the strongest overtones
  as the dipole moment is high
• R-H stretch or R-H stretch / bend form most NIR
  bands
• The overtone and combination bands are 10 100 X
  less intense than the fundamental bands in
  mid-IR.
• Differences in spectra are usually very subtle.
  Instruments have a high signal to noise ratio.

27
Combination Bands

• The frequency of a combination is approx. the sum
  of the frequencies of the individual bands.
• Combinations of fundamentals with overtones are
  possible as well as well as fundamentals
  involving two or more vibrations.
• The vibrations must involve the same functional
  group and have the same symmetry.

C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer. Assn. of Cereal Chemists 2nd Ed. (November
15, 2001) .
28
NIR Anharmonicity

• A number of bands are observed that cannot be
  explained on the basis of the harmonic
  oscillator.
• A more accurate model of a molecule is given by
  the anharmonic oscillator.
• The allowed energy levels for an anharmonic
  oscillator have to be
• modified
• Where ? is the anharmonicity constant.
• The potential energy curve is represented by an
  asymmetric Morse function.

29
Morse Potential Simple Anharmonic Oscillator
Transition Name Range n0 n1 Fundamental mid-
IR n0 n2 1st Overtone mid-NIR n0 n3 2nd
Overtone NIR Interaction of two Combination NIR o
r more different vibrations
30
Example
1st Overtone
Fundamental Vibration
2nd Overtone
31
Calculations of overtones and anharmonicities
The wave number position of the fundamental
position v1 or an overtone vn of the anharmonic
oscillator can be given by
v0 is not directly accessible from the absorption
spectra only the wave number v1, v2 . may be
obtained.
H.W. Siesler, Basic Principles of Near Infrared
Spectroscopy, In Handbook of Near Infrared
Analysis Ed. D.A. Burns and E.W. Ciurczak, 3rd
ed., CRC Press, Boca Raton, FLA.
32
NIR gets complicated
Fermi Resonance
Is an interaction between transitions of the same
symmetry that occur at approximately the same
wavenumber as that of a fundamental vibration.
Mid IR spectrum magnesium stearate solid sample
C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer. Assn. of Cereal Chemists 2nd Ed. (November
15, 2001) .
33
NIR continues to complicate
Local Mode

• Treats a molecule as if it was made up of a set
  of equivalent diatomic oscillators
• As the stretching vibrations are excited to high
  energy levels, the anharmonicity term ??0 tends
  to overrule the effect of interbond coupling and
  the vibrations become uncoupled vibrations and
  occur as local modes.

C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer. Assn. of Cereal Chemists 2nd Ed. (November
15, 2001) .
34
NIR complicates even more
Darling-Dennison Resonance

• May lead to the presence of two bands where only
  one would be expected.
• Resonance between higher order overtone modes
  and the more intense combination bands.
• Particularly evident for X-H vibrations since
  interacting energy levels are close together and
  vibrational anharmonicity is high.
• Provides a complicating effect in NIR spectra,
  different from the simplifying effect that would
  be expected from local modes.

C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer. Assn. of Cereal Chemists 2nd Ed. (November
15, 2001) . And L. Bokovza in Chapter 2 of Near
Infrared Spectroscopy, H. W. Siesler, Y. Ozaki,
S. Kawata, H.M. Heise, Wiley, VCH.
35
Electronic NIR Spectroscopy

• Electronic NIR bands
• Involves the change in the electronic state of a
  molecule (movement of an electron between
  different energy levels)
• Electronic transitions are generally of higher
  energy than vibrational transitions
• higher-energy visible and ultraviolet regions of
  the spectrum
• Electronic NIR bands are affected by
  intermolecular interactions and sample state.

C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer Assn of Cereal Chemists 2nd Ed. (November
15, 2001) .
36
Electronic NIR Spectroscopy
C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer Assn of Cereal Chemists 2nd Ed. (November
15, 2001) .
37
The NIR Complicating Factor

• Multitude of overtone and combination bands
  produced from only a few vibrations
• Large number of NIR-active groups (e.g CH, NH,
  OH, and CO), each of which contributes its own
  set of overtone and combination bands
• Possibility of resonances between vibrational
  modes. which results in bands that cannot be
  assigned to "pure vibrations in the molecule
• Possibility of several molecular configurations,
  each of which could produce a slightly different
  spectrum.
• This complications are also an advantage
• The complexity of NIR spectra help to identify
  every single difference (Chemical and Physical).

C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer Assn of Cereal Chemists 2nd Ed. (November
15, 2001) .
38
The NIR Complicating Factor (CHCl3)
C.E. Miller, Chemical Principles of Near
Infrared Technology, Chapter 2 in Near Infrared
Technology In the Agricultural and Food
Industry, P. Williams and K. Norris (Editors),
Amer Assn of Cereal Chemists 2nd Ed. (November
15, 2001) .
39
Understanding Hydrogen Bonding on vibrational
spectra
Free surface O-H
Hydrogen bonded surface O-H
1st overtone region for O-H bond stretching and
free surface water
Miller, C.E. (2001). Chemical Principles of
Near-Infrared Technology. In Williams, P. and
Norris, K. Near-Infrared Technology in the
Agricultural and Food Industries. 2nd ed.
Minnesota, USA American Association of Cereal
Chemists, Inc. St. Paul, p19-36.
40
MIR and NIR Absorption Bands
Typical NIR Spectra
Typical MID IR Spectra
41
MIR and NIR Absorption Bands
Courtesy of Bruker Optics
42
IR Instrumentation
Near IR
Mid IR
43
Advantages of Near Infrared Spectroscopy over
Mid-IR

• No sample preparation required leading to
  significant reductions in analysis time and waste
  and reagents.(non-destructive testing).
• Possibility of using it in a wide range of
  applications (physical and chemical), and viewing
  relationships difficult to observe by other
  means.
• In-line monitoring of process.
• Spectrum may be used to identify the formulation
  and to quantify drug in the formulation.

M. Blanco, J. Coello, A. Eustaquio, H Iturriaga,
and S. Maspoch, Development and Validation of a
Method for the Analysis of a Pharmaceutical
Preparation by Near-Infrared Diffuse Reflectance
Spectroscopy, Journal of Pharmaceutical Sciences,
1999, 88(5), 551 556.
44
Infrared Equipment

• Classical (Dispersive)

Thermocouple (Detector)
Sample
Diffraction Grating
Reference
Spectrum
45
Infrared Equipment

• Modern (Fourier Transform)

46
Visualizing the Interaction of Light Particles

• No sample preparation in NIR spectroscopy.
• Light interactions with particles.
• Need to learn to visualize the particles and
  their interaction with light.

J.L. Ramirez, M. Bellamy, R.J. Romañach, AAPS
Pharmscitech, 2001, 2(3), article 11.
47
Diffuse Reflectance
Common NIR Techniques
Tramittance
Light may be remitted, transmitted absorbed
Detector for transmission
48
Isc Iin (?, ?, d, n) The intensity of
scattered light is a function of the scattering
angle, the wavelength ?, particle size d, and the
refractive index n.
Scattering reflection refraction
diffraction.
Dahm DJ, Dahm KD. 2001. The Physics of
Near-Infrared Scattering. In Williams P, Norris
K, editors. Near Infrared Technology in the
Agricultural and Food Industries, 2nd ed., Saint
Paul American Association of Cereal Chemists, p
19-37.
49
Scattering and Diffuse Reflectance

• Light propagates by scattering.
• As light propagates, both scattering and
  absorption occur, and the intensity of the
  radiation is reduced.

• The radiation that comes back to the entry
  surface is called diffuse reflectance.

50
Visualizing light interaction
Smaller particle sizes More remission, less
transmission
Larger particle sizes Less remission, more
transmission
Multiple path lengths are possible
Prepared by Martha Barajas Meneses, MS 2006.
51
Subtle Differences,Valuable Info.

• Cristallinity high degree of molecular order
  (narrower bands)
• Amorphous no molecular order (broader bands)

Crystalline sugar
Amorphous sugar
52
Particle size effect
Changes in spectra due to physical properties of
a material
Jackeline I. Jerez, Sept. 2009
53
Changes in spectra due to physical properties of
a material
Tablet Packing density
NIR spectra of pure lactose tablet at different
packing density
Ropero, J. et al. 2011. Near-Infrared Chemical
Imaging Slope as a New Method to Study Tablet
Compaction and Tablet Relaxatio. Appl. Spect. 65,
4.
54
Changes in spectra due to variation in analysis
Probe-sample distance
NIR spectra of pure lactose analyzed at different
distances
55
Changes in sugar spectra due variation in
temperature
56
NIR aspects as functions of wavelength
57
NIR Applications
CDI Lab Scale NIRS system, www.controldevelopment.
com
58
Powder and Solids Probe Courtesy Bruker Optics
Diffuse Reflection Probe Schematic
Powder Solids Probe with liquid attachment
Extra-long immersion depth 12
59
Diffuse Reflectance Examples
60
Diffuse Reflectance for Flowing Powder
I detected 1/c x Ireflected Adetected -
log (Rdetected) - log (Idetected/I0)
log c log (I0/Ireflected) c A
J. Ropero, L. Beach, M. Alcalà, R. Rentas, R.N.
Davé, R.J. Romañach, Journal of Pharmaceutical
Innovation, J. Pharm. Innov. 2009, 4(4), 187-197.
61
Transflection
Analyte
Mirror or Reflector
mirror
Fiber probe for solids
Courtesy Bruker Optics
62
Transflectance using gold plate reflector.
M. Blanco, M.A. Romero, Near infrared
transflectance spectroscopy Determination of
dexketoprofen in a hydrogel, Journal of
Pharmaceutical and Biomedical Analysis, 30 (2002)
467472.
63
Transmittance
Tablet Sample
Prepared by María A. Santos
R.J. Romañach and M.A. Santos, Content
Uniformity Testing with Near Infrared
Spectroscopy, American Pharmaceutical Review,
2003, 6(2), 62 67.
64
Transmittance

• Transmittance mode preferred since radiation
  interacts with a greater sample volume.
• Very interesting and often complex interaction
  between radiation and particles.
• Depth penetration depends on particle size
  (scattering properties) of particles within the
  tablet (Iyer, Morris, Drennen, J. Near Infrared
  Spectrosc., 2002, 10, 233 245.).

65
Recommended reading

• J. Coates, Vibrational Spectroscopy
  Instrumentation for Infrared and Raman
  Spectroscopy, Applied Spectroscopy Reviews,
  1998, 33(4), 267 425.
• A.S. Bonanno, J. M. Olinger, and P.R. Griffiths,
  in Near Infra-Red Spectroscopy, Bridging the Gap
  Between Data Analysis and NIR Applications, Ellis
  Horwood, 1992.
• C.E. Miller, Chemical Principles of Near
  Infrared Technology, Chapter 2 in Near Infrared
  Technology In the Agricultural and Food
  Industry, P. Williams and K. Norris (Editors),
  Amer. Assn. of Cereal Chemists 2nd Ed. (November
  15, 2001) .
• H.W. Siesler, Basic Principles of Near Infrared
  Spectroscopy, In Handbook of Near Infrared
  Analysis Ed. D.A. Burns and E.W. Ciurczak, 3rd
  ed., CRC Press, Boca Raton, FLA.
• M. Blanco, J. Coello, A. Eustaquio, H Iturriaga,
  and S. Maspoch, Development and Validation of a
  Method for the Analysis of a Pharmaceutical
  Preparation by Near-Infrared Diffuse Reflectance
  Spectroscopy, Journal of Pharmaceutical Sciences,
  1999, 88(5), 551 556.
• Dahm DJ, Dahm KD. 2001. The Physics of
  Near-Infrared Scattering. In Williams P, Norris
  K, editors. Near Infrared Technology in the
  Agricultural and Food Industries, 2nd ed., Saint
  Paul American Association of Cereal Chemists, p
  19-37.