Vibrational Spectroscopy for
Pharmaceutical Analysis
VIII. Applications of Raman Spectroscopy
Rodolfo J. Romañach, Ph.D.
ENGINEERING RESEARCH CENTER FOR
STRUCTURED ORGANIC PARTICULATE SYSTEMS
RUTGERS UNIVERSITY
PURDUE UNIVERSITY
NEW JERSEY INSTITUTE OF TECHNOLOGY
UNIVERSITY OF PUERTO RICO AT MAYAGÜEZ
10/11/2005
1
An Investigation of Solvent-Mediated Polymorphic
Transformation of Progesterone Using in Situ Raman
Spectroscopy
Progesterone has five known
polymorphs
Form I – melting point of 129.1oC
From II – melting point of 121.2oC
Immersible fiber optic probe
and Raman spectroscopy used
to monitor the transformation
from form II to form I.
F. Wang, J.A. Wachter, F.J. Antosz, K.A. Berglund, Organic Process
Research and Development, 2000, 4, 391-395.
2
Raman Spectra of Form I and II
3
Crystallization Progesterone
• 2 grams in 25 mL of an organic solvent were
added to 500 mL of distilled water, kept at
constant temperature.
• Following completion of addition the solution was
stirred at isothermal conditions for several hours.
• During this period the transition from Form II to
Form I was monitored with Raman spectroscopy.
• Takes advantage of water being a poor Raman
scatterer.
F. Wang, J.A. Wachter, F.J. Antosz, K.A. Berglund, Organic Process
Research and Development, 2000, 4, 391-395.
4
Change in Spectra During
Phase Transformation
Bold spectra obtained at the beginning
and end of crystallization.
5
Determination of Drug Content in Tablets Using Raman
Spectroscopy
• The progress of this application has been slowed by the
very small size of the sampling area interrogated by Raman
beam (making representative measurements difficult).
• Sample may be rotated to increase area in contact with
beam (J. Johansson, S. Pettersson, S. Folestad, J. Pharm. Biomed.
Anal. 39 (2005) 510.
6
Research Efforts
•
•
M. Kim, H. Chung, Y. Woo, M. Kemper “New reliable Raman
collection system using the wide area illumination (WAI)
scheme combined with the synchronous intensity correction
standard for the analysis of pharmaceutical tablets”, Analytica
Chimica Acta, 2006, 579, 209–216.
H. Wikström, S. Romero-Torres, S. Wongweragiat, J. A. Stuart
Williams, E.R. Grant, and L.S. Taylor, “On-Line Content
Uniformity Determination of Tablets Using Low-Resolution
Raman Spectroscopy”, Appl. Spectrosc., 2006, 60(6), 672 –
681.
7
Representative Measurement -
Area
PhAT System
6 mm Diameter
Traditional Dispersive
and FT-Raman 2-80500 microns
PhAT
System
3 mm Diameter
10 mm
Slide – Courtesy Kaiser Optics.
8
Monitoring of Lyophilization with Non-Invasive
Raman Spectroscopy
• Lyophilization enhances product stability by
removing water without submitting formulation to
high temperatures that can cause drug
degradation.
• Removal of water is important since water may
serve as solvent for drug degradation reactions,
or re-crystallization, and also participate in
hydrolysis reactions.
S. Romero-Torres, H. Wikström, E.R. Grant, L.S. Taylor, “Monitoring of Mannitol Phase Behavior during
Freeze-Drying Using Non-Invasive Raman Spectroscopy, PDA Journal of Pharmaceutical Science &
Technology, 2007, 61(2), 131 – 145.
9
Experimental
• Replaced door of lyophilizer with an in-house built
door that included a circular quartz window with a
diameter of 4.5 cm to allow monitoring of a vial in
the top sample shelf
• Raman spectra collected every five minutes, with
total exposure time of 2 minutes.
• Used a small spot Raman instrument with beam
diameter of 150 μm and a second with 6 mm
beam diameter.
• All sample vials contained 2 mL of 10% (w/v)
mannitol solution.
• Paper describes manner in which three different
mannitol polymorphs and its hemihydrate were
obtained.
10
Freeze Drying Monitoring Set-Up
Quartz Window
PhAT System
Freeze-Drier Shelf
Timely measurements
Raman Probe
Intensity Units
150
767
350
550
750
950
1150 1350
BELL
787
807
827
847
867
887
907
Raman Shift [cm-1]
11
Why Mannitol?
 Mannitol is a common excipient
 Has three reported anhydrate polymorphs (beta, alpha and delta)
Outcome will depend on the freeze drying history and concentration
Delta
Alpha
Beta
Intensity
Beta
850
Alpha
Delta
900
950
1000
Raman Shift [cm-1]
1050
9
11
13 15
17 19
21 23
25 27
29
Two Theta [˚]
High resolution Raman spectroscopy has proven to discriminate
between mannitol polymorphs
12
Results
• Before freezing the mannitol solution provided a spectrum
similar to that of amorphous mannitol.
• As freezing started and progressed the intensity of the
mannitol peaks decreased until a minimum was reached.
• Minimum in mannitol peaks corresponded to ice
crystallization (confirmed by monitoring product
temperature).
• Mannitol peaks corresponding to crystalline mannitol were
then observed, and their intensity increase.
• Comparison of spectra obtained during freeze drying to
reference spectra of the polymorphs, showed that the β
form crystallizes during lyophilization, and the hemihydrate
in some instances.
13
On-Line Slow Freezing
Before Freezing
After Freezing
1044 cm-1
873 cm-1
1054 cm-1
1024 cm-1
937 cm-1
967 cm-1
894 cm-1
1019 cm-1
Raman Shift [cm-1]
Bands associated to mannitol solution disappear (black arrows)
Hemihydrate mannitol Raman features emerge (red arrows)
14
Reaction Monitoring
• Raman Spectroscopy May
be Used to Monitor the
Progress of a Reaction in the
Synthesis of an Active
Pharmaceutical Ingredient.
Immersible Fiber Optic probe used to
monitor progress of reaction.
R. Wethman, C. Ray, J. Wasylyk, “Development and Implementation of an In-Line
Quantitative Raman Method for In-Process Pharmaceutical Monitoring”, American
Pharmaceutical Review, 2005, 5(6), 57 – 63.
15
Reasons for Choosing Raman Spectroscopy for In-Line
Reaction Monitoring
Wethman and collaborators provide the following
reasons:
1.
2.
3.
Relative insensitivity of Raman spectroscopy to
the water used in reactions.
The use of a fiber optic line between the probe
and the spectrometer allowed the spectrometer
to be located outside of the processing center
and eliminated the need for it to be explosion
proof.
The ability to insert the probe directly into the
reaction chamber, avoided the need for
developing a sampling system.
16
Raman Imaging & Mapping
ENGINEERING RESEARCH CENTER FOR
STRUCTURED ORGANIC PARTICULATE SYSTEMS
RUTGERS UNIVERSITY
PURDUE UNIVERSITY
NEW JERSEY INSTITUTE OF TECHNOLOGY
UNIVERSITY OF PUERTO RICO AT MAYAGÜEZ
10/11/2005
17
Imaging and Mapping
• Arise from the use of microscopy with Raman
spectrometers.
E. Smith and G. Dent, “Modern Raman Spectroscopy A Practical
Approach”, John Wiley & Sons Ltd; (Chichester, United Kingdom),
2005, pages 47 – 50.
18
Imaging
• A set of filters may be used, so that only radiation
of the frequency range of interest passes through
to the detector.
19
Mapping
• Motorized samples stages (XYZ device) are used to move
the sample. A spectrum is obtained from a small area, then
the sample is moved to place a new area under microscope
objective and a second spectrum is obtained. This is done
repeatedly until spectra from a selected area are obtained.
• After collecting the samples, a spectral band is selected
and a map of the intensity variation for that vibration is
plotted.
E. Smith and G. Dent, “Modern Raman Spectroscopy A Practical Approach”, John Wiley & Sons
Ltd; (Chichester, United Kingdom), 2005, pages 47 – 50.
20
The AAPS Journal, 2004, 6(4), article 32
Raman intensity ratio map of deposits from stages 3 (left) and 5 (right) of Andersen Cascade
Impactor. Ratio of intensity of 1610 cm-1 (salbutamol) and 1662 cm-1 to BDP
(beclometasone dipropionate). Orange light components relate to salbutamol and and
black components to BDP. Scale bars represent 10 μm.
21
D. Fraser Steele, P.M. Young, R. Price, T. Smith, S. Edge, and D. Lewis, “The Potential Use of
Raman Mapping to Investigate In Vitro Deposition of Combination Pressurized MeteredDose Inhalers, The AAPS Journal, 2004, 6(4), article 32
22
Advantages & Disadvantages Imaging
vs. Mapping
• Imaging is rapid but only a particular region of
the spectra is examined at one time and the
resolution is limited.
• Mapping stores the entire spectrum, but is slow
(time consuming).
23
Acquisition Time & Area Sampled
• Images of approximately 2 x 2 mm2 were
acquired with a spatial resolution of 25 μm, with a
typical acquisition time of 21 hours for Raman
mapping and 3 hours in a similar NIR system.
S. Ŝaŝiĉ, Appl. Spectrosc., 2007, 61(3), 239 -250.
24
Further Reading Imaging & Mapping
S. Ŝaŝiĉ, “An In-Depth Analysis of Raman and NearInfrared Chemical Images of Common
Pharmaceutical Tablets”, Appl. Spectrosc., 2007,
61(3), 239 -250.
25
Confocal Raman Spectroscopy
•
The microscope allows a change in the beam focus in the Z
direction. The confocal arrangement consists of a pin hole in the
focal plane. The pinhole avoids the collection of the majority of the
other radiation that is not focused sharply in the plane of the
pinhole.
E. Smith and G. Dent, “Modern Raman Spectroscopy A Practical Approach”,
John Wiley & Sons Ltd; (Chichester, United Kingdom), 2005, pages 45 - 47.
26
Solid Dispersions of Drugs
• There is significant interest in formulations that increase the
bioavailability of insoluble drugs.
• Some studies have indicated that solid dispersions of drugs
increase the bioavailability of these compounds.
• Researchers have applied both NIR and Raman spectroscopy
to these systems, since both allow their study without
sample preparation.
• Interested in learning about drug distribution within the
suspension, and the crystalline form of the drug.
27
J. Breitenbach, W. Schrof, and J. Neumann, “Confocal Raman Spectroscopy:
Analytical Approach to Solid Dispersions and Mapping of Drugs.
Pharmaceutical Research”, 1999, 16(7), 1109- 1113.
28
Authors found that ibuprofen band shifts to 1613 cm-1 in the PVP
extrudates This band is observed a lower Raman shift in crystalline
(lower energy) state. This spectral band was also observed at
1613 cm-1 when ibuprofen was dissolved. Band at 1613 cm-1
indicates that ibuprofen in the amorphous state, as confirmed by
other analytical methods.
J. Breitenbach, W. Schrof, and J. Neumann, Pharmaceutical Research,
1999, 16(7), 1109- 1113.
29
Additional Information
•
A He:Ne laser at 633 nm, was used without any fluorescence
problems.
•
Recorded ratio of 1613 cm-1 band from ibuprofen and 1673 cm-1
band from PVP in area of 45 x 25 micrometers (200
measurements) to evaluate homogeneity. Each measurement was
performed with a resolution of 2 μm3.
•
The method did not show reveal ibuprofen crystalline aggregates
in the extruded material.
J. Breitenbach, W. Schrof, and J. Neumann, “Confocal Raman Spectroscopy: Analytical Approach to
Solid Dispersions and Mapping of Drugs. Pharmaceutical Research”, 1999, 16(7), 1109- 1113.
30