This document discusses modern pharmaceutical analytical techniques, specifically X-ray diffraction and crystallography. It defines X-ray crystallography and X-ray diffraction, explaining how crystal structures cause diffraction patterns. It describes the seven crystal systems and 14 Bravais lattices that define crystal structures. It outlines several applications of X-ray diffraction, including determining unknown crystal structures, analyzing polymers and metals, measuring particle size, and studying complexes.
3. X-ray crystallography
X-ray crystallography (XRC) is the
experimental science determining the atomic
and molecular structure of a crystal, in which
the crystalline structure causes a beam of
incident X-rays to diffract into many specific
directions.
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4. X-ray diffraction
X-ray diffraction, a phenomenon in which the
atoms of a crystal, by virtue of their uniform
spacing, cause an interference pattern of the
waves present in an incident beam of X rays.
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7. Crystal Lattice
• A crystal lattice is a 3-D arrangement of unit
cells.
• Unit cell is the smallest unit of a crystal, by
stacking identical unit cells, the entire lattice
can be constructed.
• A crystal’s unit cell dimensions are defined by
six numbers, the lengths of the 3 axes, a, b,
and c, and the three inter axial angles, α, β
and γ.
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19. 1.Structure of crystals
• X-ray Diffraction Method is non-destructive
and gives information on the molecular
structure of the sample.
• Comparing diffraction patterns from crystal of
unknown composition with patterns from
crystal of known compounds permits the
identification of unknown crystalline
compound.
• This method can also be used to distinguish
between a mixture of crystals.
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20. 2. Polymer characterization
• Determine degree of crystallinity.
• Non-crystalline portion scatters x-ray beam to
give a continuous background(amorphous
materials)
• Crystalline portion causes diffraction lines that
are not continuous(crystalline materials).
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21. 3. State of anneal in metals
• A property of metals than can be determined
by X-ray diffraction is the state of anneal.
• Well-annealed metals are in well-ordered
crystal form and give sharp diffraction lines.
• It is occasionally necessary to check moving
parts for metal fatigue, such as airplane wings.
This check can be done by x-ray diffraction
without removing the part from its position
and without weakening it in the process of
testing
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23. A. Spot counting method
This method is used for determining size of
particles larger than 5 microns.
v=V. δθ. cosθ/2n
Where,
o V=volume of individual crystallite
o V=total volume irradiated
o n=no. of spots in diffraction ring at a Bragg
angle of θ
o δθ =divergence of x-ray beam.
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24. B. Broadening Of Diffraction Lines
• Crystallites smaller than 120nm create
broadening of diffraction peaks. This peak
broadening can be used to quantify the
average crystallite size of nano particles Using
the scherrer’s equation.
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25. C. Low-Angle Scattering
• From the Bragg relation,
nλ=2d sinθ
• it follows that if one desire to have
information about large structural features
(i.e.,large d values),attention should be
focussed on small scattering angles,2θ to get
better resolution.
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26. 5. Diffraction methods to
complexes
A. Determination of Cis-Trans:
Isomerism-X-ray diffraction study has been
used to make the distinction between cis and
trans isomers of a complex.
B. Determination of Linkage Isomerism:
By X- ray studies, it becomes possible to
identify linkage isomers of complexes.
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27. References
Instrumental Analysis by James W Robinson,
Eileen M. Skelly Frame George M. Frame II. 3rd
edition.
Journal - x Ray crystallography by MS Smyth
and JHJ Martin.
Pharmaceutical Analysis – A textbook for
pharmacy students and Pharmaceutical
chemists edited by David G Watson.
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