Raman Analyser

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Raman Analyser

• Dr. Shreeram Oak

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Basic Principles of Vibrational Spectroscopy
Inelastic scattering of light at a molecule
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Raman Principle
When a sample is irradiated with monochromatic
light (e. g. with laser light using discrete
lines between 300 and 1064 nm) Different
physical phenomena happen 1. The main part of
the incident light is transmitted without
interaction 2. Roughly 10-4 part of the light is
elastically scattered with no energy
absorption ---gtRayleigh line 3. A part of the
incident light may be absorbed by electronic
transitions and is emitted as ---gt
Flourescence 4. Only 10-8 of the incident light
is inelastically scattered and interacts
with the sample . The energy is partly
absorbed ---gt Raman spectrum
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Advantages of FT-Raman compared to FT-IR

• Little or no sample preparation
• High sensitivity for symmetric molecules, non
  polar bondings and homonuclear chains
• Only low interferences of water and glass
• (measurement of aqueous solutions in
• glass vials)
• Raman lines are usually narrower
• Low frequency information to 50 cm-1

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Simple measurement
FT-Raman spectrum of caffeine
Blue measurement of powder in sample cup Green
measurement in standard laboratory vial Red
measurement in brown laboratory vial
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FT-Raman Spectroscopy

• Introduced by Hirshfeld and Chase in 1986
• Avoid fluorescence by using near-infrared
• excitation
• Use interferometry instead of dispersive
• methods

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Why FT-Raman Spectroscopy?
FT-Raman versus dispersive Raman

• Near-infrared excitation instead of UV/VIS

• Interferometry
• instead of dispersive
• methods

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Why Near-Infrared Excited Raman Spectroscopy?
Fluorescence - a problem of visible excitation
VIS-Raman
Fluorescence
NIR-Raman
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Fluorescence the Enemy of Raman Scattering
785 nm
FT- Raman spectra of Chocolate top 785
nm bottom 1064 nm
1064 nm
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No Fluorescence of Real World Raman Samples with
1064 nm
Raman spectra of endolithic green algal layer
from Antarctica collected using different laser
excitations
Courtesy Prof. Edwards, Univ. Bradford, UK
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FT-Raman Spectroscopy Why?

• Fluorescence virtually reduced due to long wave
  length excitation at 1064 nm
• Photochemical degradation is unlikely

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Comparison between FT and dispersive Raman

• FT-Raman
• Fluorescence-free Raman spectra by 1064nm
  excitation
• Simple measurement of bulk samples due to
  advantage of sample compartment
• Quantification

• Dispersive Raman
• Better spatial resolution for microscopy
  applications (down to 1µm)
• Higher sensitivity and shorter measurement times
  for non-fluorescing samples
• Selection of different excitation lines
  (488-785nm)

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100 Rupees banknote
blue
white
red
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100 Rupees Banknote White area (reference) and
Red colour
Additional peak due to red colour
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100 Rupees Banknote white area (reference) and
yellowish colour
Additional peak due to yellowish colour
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Copy 10 Euro Banknote White area in comparison
to White area of true banknote
Differences
Paper materials of true and fake bank note differ
largely!
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Summary

• For the investigated banknotes differences could
  be found between true and simulated fake
  banknotes
• - Spectral differences may be observed due to
  differences in the paper and due to differences
  in the ink used for the original and the false
  banknote
• For the paper different fillers and binders used
  for true and false note can provoke different
  Raman spectra
• Especially fillers are very often of inorganic
  nature (e.g. TiO2) and yield good Raman spectra
• - Limitations green and blue colours often
  show fluorescence even with FT-Raman (long
  wavelength excitation!) further fluorescence may
  be increased for old and often used banknotes
  compared to new ones.

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Analyzing cis/trans Isomers with FT-Raman
C-C double bonds
FT-Raman spectrum of cis (upper) and
trans (lower) stilbene
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TLC FT-Raman Accessory

• enables mapping of TLC plates or other
  flat samples
• sampling area 75 x 50 mm
• horizontal arrangement

R 315 X-Y Stage for TLC-FT-Raman
Spectroscopy

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HPTLC-FT-SERS
HPLC1.HGL
Surface Enhanced Spectra of Hypoxanthine
(Estimated Sample Amounts)
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Special Sampling Accessories
Low temperature accessory
Variable Temperature Cell
Heating Stage
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Phase transitions of active agent with
temperature rise
180C
170C
160C
150C
140C
130C
120C
100C
80C
60C
40C
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.... More Accessories
Goniometer
Bottle holder
Sample rotator
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• Well plate accessory for FT-Raman Spectroscopy
• Advantage
• High sample throughput

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HTS-Raman

• Measurement through bottom of well plate
• ? focus is fixed
• ? best reproducibility

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Forensic
Application Textile tissue contaminated with
explosive material
x
SemtexB
Cotton
Red SemtexB Blue Textle tissue, cotton Laser
1064nm, res 8 cm-1, 200mw, 300 scans,10x obj.
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Forensic
Application Cocaine particle on banknote
x
Cocaine
Banknote paper
Red Cocaine Blue Banknote paper Laser 1064nm,
res 8 cm-1, 200mw, 300 scans,10x obj.
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Forensic
Application Heroine secured on
adhesive tape
x
Heroine
Adhesive tape
Red Heroine Blue Adhesive tape Laser 1064nm,
res 8 cm-1, 200mw, 300 scans,10x obj.
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Depth Profiling of the First Three Layers of
a5-Layer Polymer Laminate
Raman laser
OPP 1. Layer 20µm
PA 2. Layer 2µm
EVOH 3. Layer 20µm
Contour Line Map
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Depth Profiling of the First Three Layers of
a5-Layer Polymer Laminate

• Conclusions
• Layer thickness is pertubed by
• refraction (2µm layer is broadened to
• 5µm)
• Refraction causes deeper penetration
• than nominal focal point
• Recommended Solutions
• Use immersion objectives
• Make a cross section and map laterally

Raman laser
OPP 1. Layer 20µm
PA 2. Layer 2µm
EVOH 3. Layer 20µm
Everall, Neil J. Applied Spectroscopy, Volume
54, Number 6, June 2000, pp. 773-782(10)
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Raman Non Destructive Analysis
Diamond
Moissanite
Zirconia
Gemmologic studies of jewellery Diamond (C),
Moissanite (SiC), Zirconia (ZrO2)
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Distribution of API in tablets
Integration of a band relevant for one excipient
Integration of a peak relevant for API
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FT-Raman microscopy Investigation of an Ancient
Manuscript
Red ink Cinnabar (HgS)
Piece of medieval manuscript
Surface map by FT-Raman spectroscopy
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FT-Raman Microscopy
Mineral with inclusions (bright spot position of
laser focus)
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Analysis of Artwork
Ancient tibetian Mandala
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FT-Raman Microscopy
? (S-S)
RAMANSCOPE TM spectrum of a single human hair