Transcript What’s in your pill? What about theirs? Answers from powder x-ray diffraction Lots of help from Ashfia Huq, Silvina Pagola, Cristian Botez, many other.

What’s in your pill?
What about theirs?
Answers from powder x-ray diffraction
Lots of help from Ashfia Huq, Silvina Pagola,
Cristian Botez, many other people who don’t care
to be mentioned.
Some illustrations here are proxies for real
problems.

d
(1862-1942)
(1890-1971)
Nobel Prize in Physics, 1915,
for Diffraction of X-rays by Crystals.
W.L. Bragg, “X-ray Crystallography,” Scientific American (1968)
If the sample is a powder, there will
probably be many grains aligned to
diffract the incident beam of x-rays.
X-ray beam
2
Diffraction peak positions depend on
geometry of the packing of unit cells.
Diffraction peak intensities are related to the
positions of the atoms within the unit cell.
Intensity
One only measures 2 for a given peak, not
its orientation with respect to the lattice.
This makes the experiment simpler to
perform, but the interpretation harder.
Peaks may overlap, and it may not be
possible to guess the 3d geometry from
only the peak positions.
Q or 2
Real Space - Debye-Scherrer cones
(220)
Incident beam
x-rays or neutrons
(200)
Sample
Typically 1010 grains of 1 m
(109 molecules) each, packed
to 50% density
(111)
Part of a “typical” powder diffraction pattern.
Normalized X-ray counts
40000
Ranitidine Hydrochloride, raw data
 = 0.7 Å
30000
20000
10000
0
26.80
27.00
27.20
27.40
Two Theta (degrees)
27.60
27.80
Where does a powder diffraction pattern come from?
Instrument –
Strong pitch for use of synchrotron radiation
Not giving an unbiased comparison of available instruments
Properties of sample – emphasize today
Collection of peaks (fingerprint)
Collection of data so that intensities are meaningful
Find a specific lattice, measure one component in tablet
Quantitative analysis of mixtures from structures
Given two patterns, do they come from the same stuff?
Given an x-ray diffraction pattern, can you figure out what it comes
from? (If you’ve seen it before? If you haven’t?)
How well can one quantify composition of mixtures?
National Synchrotron Light
Source ground broken in 1978,
started operating (sort of) in
1982.
Currently has the most users,
and publishes the most papers
(and most papers / $) of any
dedicated SR facility.
From
storage
ring
GE (111)
analyzer crystal
Parallel,
Monochromatic
X-ray beam
Scintillation
detector
Ion chamber
sample
Si(111) double
monochromator
Powder diffraction station at X3B1 beamline,
National Synchrotron Light Source,
Brookhaven National Laboratory, U. S. A.
(available for general users, rent, or collaboration)
What’s in your pill? (fake)
Example 1
Normalzed X-ray Intensity (counts / sec)
50000
"unknown" sample,
0.6997 Å, capillary
40000
30000
Data taken with very good (~0.007º
FWHM) resolution at NSLS –
available for scientific collaboration
or proprietary access
20000
10000
0
5
7
9
11
13
15
2 theta (degrees)
17
19
21
lact_raw.grf
23
A little work turns up this entry in the Powder Diffraction File
Normalzed X-ray Intensity (counts / sec)
50000
Lactose Monohydrate
0.6997 Å, capillary
40000
Powder Diffraction FIle #27-1947
Lactose Hydrate (1975)
30000
20000
10000
0
5
7
9
11
13
15
2 theta (degrees)
17
19
What are these weak peaks?
The active ingredient?
21
lact_pdf.grf
23
Lattice parameters -> possible peak positions
Space group -> some of those peak positions are not seen
Positions of atoms within the unit cell -> relative intensities
of peaks within each phase
X-ray diffractometer optics -> lineshape parameters
(fundamental parameters on well-characterized instrument)
Crystallite size, internal strain, lattice defects -> lineshape
parameters (not usually very interesting; adjust parameters
to give a good fit to lineshape data)
Rietveld method: look at all of your data. Compare the
profile with a model, not just the intensities of the
diffraction peaks.
Normalzed X-ray Intensity (counts / sec)
50000
Lactose Monohydrate
0.6997 Å, capillary
Rietveld refinement
40000
“Missing” peaks are actually
from lactose monohydrate, not
in PDF!
30000
20000
10000
Difference
0
Powder Diffraction File
Rietveld
Not the best fit in the world, but clear enough
5000
0
-5000
lactgsas.grf
4
6
8
10
12
14
16
2 theta (degrees)
18
20
22
24
We should have read the fine print, and been suspicious.
The only systematic absences in P21 are (0 odd 0).
Lesson learned:
Don’t depend on a measurement of a few peaks,
when you can utilize all of the structural
information that may be available.
Known structures are better than poorly
controlled data.
Example 2
Can we use intensities from somebody else’s measurement
(e.g., in data base) to characterize materials?
Patents are frequently written with claims of powder
diffraction data – d spacings and maybe intensities.
U.S. Pharmacopea says that intensities should agree ±20%.
(U.S. Pharmacopea also says that peak positions should be
within ±0.1º to ±0.2º of the claimed position. Are you
sure your data are that accurate?)
Example, two patterns of Ampicillin (C16H19N3O4S), taken
(evidently) on the same sample, by the same (well known)
operator. Good data: indexed, collected with internal
standard.
Ampicillin

100
Intensity from PDF# 33-1530
80
Indeed, the two
patterns agree
within 20%, except
for four of the
strongest peaks!
60
40
20
0
0
20
40
60
Intensity from PDF# 33-1529
80
100
Lesson learned:
The sample geometry can have a profound influence on
the measured intensity.
Preferred orientation.
There are various means to minimize issues of
preferred orientation. It is usually best to load
samples in a thin glass tube.
(Not a perfect guarantee.)
Broad beam
Bragg-Brentano
Example 3
Patent no. 0,000,000, “ process.”
“Disclosed is a new method of producing  which involves
reacting the magnesium halide salt of … Also disclosed are two
polymorphic crystalline Forms I and II of , and methods
of their production.
“The x-ray powder diffraction pattern [of Form I] is characterized
by d-spacings of 6.44, 5.69, 5.36, 4.89, 4.55, 4.31, 3.85, 3.59, and
3.14.
“The x-ray powder diffraction pattern [of Form II] is
characterized by d-spacings of 14.09, 10.36, 7.92, 7.18, 6.40, 5.93,
5.66, 5.31, 4.68, 3.90, 3.60, and 3.25.”
The x-ray data gives almost no information.
“If you make  with those diffraction peaks,
we’ll sue.”
How accurately do peaks have to match? All of them?
Real problem. Somebody is interested in knowing
if their material would infringe that patent
Data on client’s raw material, collected with very good
angular resolution using synchrotron radiation
120000
80000
40000
0
Patent claims
2
2
4
1
6
8
10
12
14
2theta (deg)
16
18
20
22
24
What can we learn about this material?
Any crystalline material is characterized by its lattice.
c
a
 

b
The lattice dimensions
(lattice parameters) govern
the position of all possible
diffraction peaks.
The math is a bit tedious, but the problem is to find A,B,…,F
such that every peak can be assigned (h,k,l) so that its position
is given by this equation.
4 sin2 
2
 1 / d 2  Ah2  Bk 2  Cl 2  Dkl  Ehl  Fkl
Indexing: First step is to get accurate peak positions.
(locally developed software, model lineshapes, we’re not GUI programmers)
X-ray intensity
120000
Raw Data
80000
zoom
40000
0
0
5
10
15
2 (degrees)
xmxmxxmx
20
25
Lineshape
fit
Data for
computer
search
5.0767,
10.6731,
12.5566,
14.4478,
15.2812,
5.7644, 10.3653, 10.5453,
11.4275, 11.5492, 11.7545,
12.8797, 13.7433, 13.7912,
14.5417, 14.5872, 14.8089,
15.3578, 15.4558, 15.7842,
CHOICE=3, IDIV=0,
D1=.0001,D2=.0001,
VOL=8000, CEM=40,
MONO=140, MERIT=20,
END
Output from
TREOR
5.0767
5.7644
10.3653
10.5453
10.6731
11.4275
11.5492
11.7545
12.5566
12.8797
13.7433
13.7912
14.4478
14.5417
14.5872
14.8089
15.2812
15.3578
15.4558
15.7842
A = xxxxxxxxx .000847 A ALFA = 90.000000 .000000 DEG
B = xxxxxxxxx .000375 A BETA = 90.000000 .000000 DEG
C = xxxxxxxxx .000244 A GAMMA = 90.000000 .000000 DEG
UNIT CELL VOLUME = xxxxxxx A**3
H K L SST-OBS SST-CALC DELTA 2TH-OBS 2TH-CALC D-OBS FREE PARAM.
2 0 0 .001961 .001964 -.000003 5.077 5.080 12.9782
0 1 0
.002040
5.178
1 1 0 .002528 .002531 -.000003 5.764 5.768 11.4310
0 2 0 .008160 .008161 -.000001 10.365 10.366 6.3630
1 0 1 .008445 .008447 -.000002 10.545 10.546 6.2547
1 2 0 .008650 .008652 -.000002 10.673 10.674 6.1800
4 1 0
.009897
11.419
2 0 1 .009912 .009920 -.000008 11.427 11.432 5.7733
0 1 1
.009996
11.476
2 2 0 .010123 .010125 -.000001 11.549 11.550 5.7127
1 1 1 .010485 .010487 -.000001 11.755 11.755 5.6132
2 1 1 .011959 .011960 -.000001 12.557 12.557 5.2560
3 2 0 .012580 .012580 .000000 12.880 12.880 5.1246
5 1 0 .014315 .014316 -.000001 13.743 13.744 4.8040
3 1 1 .014415 .014415 -.000001 13.791 13.791 4.7874
4 0 1 .015812 .015812 .000000 14.448 14.448 4.5709
4 2 0 .016017 .016017 .000000 14.542 14.542 4.5416
0 2 1 .016117 .016116 .000001 14.587 14.587 4.5275
1 2 1 .016608 .016607 .000001 14.809 14.808 4.4601
6 0 0 .017678 .017678 .000000 15.281 15.281 4.3230
4 1 1 .017855 .017852 .000002 15.358 15.357 4.3016
2 2 1 .018082 .018080 .000002 15.456 15.455 4.2745
1 3 0 .018853 .018852 .000001 15.784 15.784 4.1861
NUMBER OF OBS. LINES = 20
NUMBER OF CALC. LINES = 23
M( 20)= 192 AV.EPS.= .0000015
F 20 = 620.( .001009, 32)
M( 20)= 192 AV.EPS.= .0000015
F 20 = 620.( .001009, 32)
M CF. J.APPL.CRYST. 1(1968)108
F CF. J.APPL.CRYST. 12(1979)60
0 LINES ARE UNINDEXED
M-TEST= 192 UNINDEXED IN THE TEST= 0
Armed with a probable lattice, we can check how it fits the data.
Normalized x-ray counts
Use a profile fit (Pawley or Le Bail).
Peak positions are controlled by the lattice
Adjust parameters which control the diffraction peak widths, etc.
120000
100000
80000
X 50
60000
40000
Data, model
20000
0
Indexed
Form 2
Form 1
1
3
5
7
9
11
13
deg
15
17
19
21
23
25
API is only a few percent of the tablet weight. Shows up very
clearly in the intact tablet. No sample grinding, etc.
Excipients
x32
Tablet
x20
Active Pharmaceutical
Ingredient
claims: form 2
form 1
2
Excipients
Tablet
Active Pharmaceutical Ingredient
claims: form 2
form 1
4
6
8
10 12 14 16
2theta (degrees)
18
20
22
24
10
11
2theta (degrees)
12
Indexing the pattern allows us to account for EVERY
observed diffraction peak.
Strong statement about sample purity (of crystalline
phases).
Example 4
Quantitative Analysis of Mixtures
The International Union of Crystallography sponsored a
Round-Robin to assess accuracy of methods in use by
participants.
Pharmaceutical mixtures of crystalline Mannitol, Sucrose,
Valine, Nizatidine, starch (amorphous).
From the IUCr’s standpoint, this was a disappointment. Only
two participants submitted solutions from their own data, and
one from IUCr’s data. (I wasn’t any of these. Cast no stones.)
Why? I can only guess:
• IUCr’s data on one component was a little bit wrong
(P21/n vs. P21/c), coordinates on another were wrong(?), etc.
• The patterns are complicated – call for good resolution.
The IUCr furnished lab data for people who wanted to analyze it.
160000
40000
120000
30000
80000
20000
40000
10000
0
0
4
8
12
16
20
24
28
32
36
40
44
Synchrotron data, capillary,
Converted from 1.15A
IUCr - furnished lab data
IUCr Quant Round Robin
Pharm Sample 1
IUCr Quant Round Robin
Pharm. Sample 1
1.15 Å, capillary
Normalzed X-ray Intensity (counts / sec)
40000
30000
20000
10000
Difference
0
Nizatidine
Valine
Sucrose
Mannitol
5000
0
pharm1gsas.grf
-5000
4
6
8
10
12
14
16
18
20
2 theta (degrees)
22
24
26
28
30
32
IUCr Quant Round Robin
Pharm. Sample 1
1.15 Å, capillary
Normalzed X-ray Intensity (counts / sec)
40000
Blow up part
of the pattern
30000
20000
10000
Difference
0
Nizatidine
Valine
Sucrose
Mannitol
5000
0
pharm1gsasm.grf
-5000
15
16
17
18
2 theta (degrees)
19
20
Results of IUCr Quantitative Phase Analysis Round Robin
Pharmaceutical sample #1
Prepared
Sucrose
Mannitol
Valine
Nizatidine
Synch
Participant 1
Participant 2
Patricipant from CPD
data
0%
20%
40%
60%
80%
100%
100000
30000
IUCr Quant Round Robin
Pharm Sample 2
20000
60000
40000
10000
Synchrotron data, capillary,
Converted from 1.15A
IUCr - furnished lab data
80000
20000
0
0
4
8
12
16
20
24
28
32
36
40
44
pharm2_lab_synch.grf
IUCr Quant Round Robin
Pharm. Sample 2
1.15 Å, capillary
Normalzed X-ray Intensity (counts / sec)
30000
20000
10000
Difference
Nizatidine
Valine
Sucrose
Mannitol
0
0
pharm2gsas.grf
4
6
8
10
12
14
16
18
20
2 theta (degrees)
22
24
26
28
30
32
Pharm sample 2 – only show crystalline components
– there was also 30 wt% amorphous starch
Prepared
Mannitol
Sucrose
Valine
Nizatidine
Synch
Participant 1
Participant 2
Patricipant from CPD
data
0%
20%
40%
60%
80%
100%
Lesson learned, QPA round robin:
Maybe quantitative analysis from x-ray diffraction is
not as mature a technique as everybody imagines.
All of our performance in this task is below what we
could be proud of.
The example given was a hard problem! Really
demanded high resolution, and had serious problems
with preferred orientation.
Conclusions:
High quality data is very important. Resolution and
sample preparation.
Think about x-ray diffraction as giving information about
the fundamental structure of your material, not just a
list of peaks.
I have not discussed structure solutions from
powder data. Covered in talk by A. Huq, and
posters by C. Botez and S. Cuffini.
I do not want to leave the impression that
synchrotron radiation is prerequisite to good data.
It certainly helps.