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
X – Ray
Ultraviolet
v i s i b l e
NIR
MIR
FIR
ESR
NMR
Region
Infrared
Microwave
Radio, TV Waves
Nuclear Transitions
Inner Shell Electronic
Transitions
Valance Electron
Transitions
Molecular Vibrations
Molecular Rotations
Spin Orientation in Magnetic Field
Interaction
Wavelength
(nm)
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1 1 11
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 nm = 1 x µm
Where cm-1 = x 107 # nm
Sometimes see cm-1 :
10,000 cm-1 = (1/10,000) cm or cm = 1 m = 1000 nm
6,000 cm-1 = (1/6000) cm or cm = 1.67 m = 1670 nm
5,000 cm-1 = (1/5000) cm or cm = 2 m = 2000 nm
4000 cm-1 = (1/4000) cm or 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.
Reference software
(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.
References!

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.
Introducion de “sissler”. Modificar y add algo mas visual. Comparacion de los rangos en el mismo slide.
Comparaciones
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.
104
103
102
101
Frequency
(cm-1)
NIR
MIR
FIR
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)
NIR
MIR
FIR
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. Hooke’s Law
In order to understand the absorption phenomenon, let’s compare a
molecule to the vibration of a spring,
Vibrating bond
Vibrating
spring
F = -k x
F – restoring force exerted by the spring
k – rate of spring constant
x – displacement of the spring from equilibrium m2 m1

15. Simple Harmonic Oscillator
For diatomic molecules it is possible to calculate:
Potential energy
k – force constant of the bond, r – inter nuclear distance during vibration,
re – equilibrium inter nuclear distance, q – displacement coordinate
Vibrational frequency
-or-
Wavenumber
m – reduced mass
c – speed of light
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.
where,
h – Plank’s constant
0 - vibrational frequency
n – quantum number
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).
3 absorption peaks for different force constants. Note that by convention, in infrared spectroscopy wavenumbers are plotted right-to-left; i.e., highest wavenumber to the left.
Courtesy of Bruker Optics

18. Vibration Theory
2) The larger the vibrating atomic mass, the lower the vibrational frequency in wavenumbers.
3 absorption peaks for different atomic masses. Note that by convention, in infrared spectroscopy wavenumbers are plotted right-to-left; i.e., highest wavenumber to the left.
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. + - H Cl

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.
3rd overtone CH3-Sym
3rd overtone CH2- Sym
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
MOLECULAR VIBRATION
There are three motions involved in vibration molecular, called normal modes.
Bend
Symetric stretch
Antisymetric stretch
All non linear molecule has 3N-6 normal modes (N is the number of atoms in the molecule)

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
Example: The fundamental vibrations for water, H2O are given in below. Water which is nonlinear, has three fundamental vibrations.
Symmetric
stretching
Anti-symmetric stretching
Symmetric Bending

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 χ is the anharmonicity constant.
The potential energy curve is represented by an asymmetric Morse function.
Ref siesler

29. Morse Potential – Simple Anharmonic Oscillator
Transition Name Range
n=0 n=1 Fundamental mid-IR
n=0 n=2 1st Overtone mid-NIR
n=0 n=3 2nd Overtone NIR
Interaction of two Combination NIR
or more different
vibrations

30. Example 1st Overtone Fundamental Vibration 2nd Overtone
2876cm-1
-C-H2 sym
2930cm-1
-C-H2 asym
2962cm-1
-C-H3 asym
2885cm-1
-C-H3 sym
2nd Overtone
Analytical lab examples

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.
Reference book
Thus, if the wave number position £˛ν1 of the fundamental vibration and the anharmonicity constant
χ are known, the wave number positions of the overtones can be calculated by Equation (2.13).
Alternatively, χ can be calculated if, for example, £˛ν1 and £˛ν2 are known.
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.
Firstly, if the transitions do not absorb at exactly the same wavenumber, the wavenumber of the lower frequency band is decreased while that of the higher frequency band is increased by about the same amount.
In addition, the intensity of the weaker band is increased while that of the stronger band is decreased ("intensity borrowing”).
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 χν0 tends to overrule the effect of interbond coupling and the vibrations become uncoupled vibrations and occur as “local modes”.
NR spectrum n-pentane liquid 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) .

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.
Add example
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.
Although most practical NIR applications exploit vibrational absorption bands, the presence of electronic NIR bands cannot be overlooked.
When atoms are combined to make molecules, the electrons of the atoms are distributed between newly defined molecular orbitals, each of which corresponds to a different electronic energy level.
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
Add reference
Verify if some minerals may contain electronic aspects
highly conjugated organic molecules such as hemoglobin
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 C=O), 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).
Referencia a Miller (estara presente)
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
Solid minerals
Wavenumber (cm-1)
Response
donor H
: acceptor
H : acceptor
Lone pair of e-
Hydrogen bond
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 MID IR Spectra
Typical NIR Spectra
Characterized by Wide Bands

41. MIR and NIR Absorption Bands
Absorbance
Wavenumber cm-1
Oleic Acid
NIR
MIR
Courtesy of Bruker Optics 41

42. IR Instrumentation
Mid IR
Near 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.*
Pharmaceutical samples have both chemical and physical properties. The physical properties are usually of significant interest to industrial pharmacists and process engineers. However, as the majority of analytical samples require sample preparation and dissolving this information is lost or thrown away. NIRS offers an opportunity to use this information.
*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) Spectrum Sample Reference
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. Common NIR Techniques Tramittance
Light may be remitted, transmitted & absorbed
Diffuse Reflectance
Detector for transmission

48. Scattering = reflection + refraction + diffraction.
No interaction undeviated ray
Diffracted ray
Reflected ray
Transmitted after internal reflection
Transmitted ray
Refracted ray
Contributes to remission
Contributes to transmission
Isc = Iin (θ, λ, d, n) The intensity of scattered light is a function of the scattering angle, the wavelength λ, particle size d, and the refractive index n.
Scattering = reflection + refraction + diffraction.
Dahm DJ, Dahm KD 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

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
Low Scattering
High scattering
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. Changes in spectra due to physical properties of a material
Particle size effect
Jackeline I. Jerez, Sept. 2009

53. Tablet Packing density
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 Near-Infrared Chemical Imaging Slope as a New Method to Study Tablet Compaction and Tablet Relaxatio. Appl. Spect. 65, 4.

54. Probe-sample distance
Changes in spectra due to variation in analysis
Probe-sample distance
Response
Wavelength (nm)
1.3 cm
0.3 cm
0.6 cm
0.8 cm
1.0 cm
NIR spectra of pure lactose analyzed at different distances

55. Changes in sugar spectra due variation in temperature
Wavenumber (cm-1)

56. NIR aspects as functions of wavelength

57. CDI Lab Scale NIRS system, www.controldevelopment.com
NIR Applications
CDI Lab Scale NIRS system,

58. Powder and Solids Probe – Courtesy Bruker Optics
Diffuse Reflection Probe Schematic
IR Source
IR Energy
Sample
Delivery Fiber Bundle
Collection Fiber Bundle
Reflected IR Energy
Detector
Powder & Solids Probe with liquid attachment
references
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),

61. Transflection I0 Itrans Analyte Mirror or Reflector mirror
Source I0
Detector
Itrans
Analyte
Mirror
or Reflector
mirror
Fiber probe for solids
Courtesy Bruker Optics
Pathlength is twice the distance from probe to mirror.

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) 467–472.

63. Transmittance Tablet Sample Prepared by: María A. Santos
Detector Position
IR Beam
Johansson and co-workers used time resolved spectroscopy to estimate that the optical path through a 3.5 mm thick tablet is 20 – 25 mm, because of the numerous reflections of the radiation with the particles within the tablet.
J. Johansson, S. Folestad, M. Josefson, a. Sparen, C. Abrahamsson, S. Andersson-Engels, and S. Svanberg, Time-Resolved NIR/Vis Spectroscopy for Analysis of Solids: Pharmaceutical Tablets, Applied Spectroscopy, 2002, 58(6), 725 – 731.
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.).
It is very important to visualize particle and radiation interactions.

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 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