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.

Nobel Prize in Physics, 1915, for Diffraction of X-rays by Crystals.

(1862-1942) (1890-1971)

W.L. Bragg, “X-ray Crystallography,” Scientific American (1968)

X-ray

d

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

Q or 2

Inte

nsity

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.

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.

Incident beamx-rays or neutrons

Sample(111)

(200)

(220)

Real Space - Debye-Scherrer cones

Typically 1010 grains of 1 m (109 molecules) each, packed to 50% density

R anitid ine Hydrochloride, raw data = 0.7 Å

26.80 27.00 27.20 27.40 27.60 27.80

Two Theta (degrees)

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Part of a “typical” powder diffraction pattern.

Where does a powder diffraction pattern come from?

Instrument – Strong pitch for use of synchrotron radiationNot giving an unbiased comparison of available

instruments

Properties of sample – emphasize todayCollection of peaks (fingerprint)

Collection of data so that intensities are meaningfulFind 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.

Powder diffraction station at X3B1 beamline, National Synchrotron Light Source,

Brookhaven National Laboratory, U. S. A.(available for general users, rent, or

collaboration)

Ion chamber sample

GE (111) analyzer crystal

Scintillation detector

Parallel,MonochromaticX-ray beam

Si(111) double monochromator

From storagering

5 7 9 11 13 15 17 19 21 232 the ta (degrees)

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"unknow n" sam ple,0.6997 Å , cap illa ry

lact_raw .grf

What’s in your pill? (fake)

Data taken with very good (~0.007º FWHM) resolution at NSLS – available for scientific collaboration or proprietary access

Example 1

A little work turns up this entry in the Powder Diffraction File

5 7 9 11 13 15 17 19 21 232 the ta (degrees)

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c)Lactose M onohydrate0.6997 Å , cap illa ry

lact_pdf.grf

Pow der D iffraction F Ile #27-1947Lactose H ydrate (1975)

What are these weak peaks? The active ingredient?

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.

4 6 8 10 12 14 16 18 20 22 242 the ta (degrees)

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Lactose M onohydrate0.6997 Å , cap illaryR ietve ld re finem ent

lac tgsas.grf

Pow der D iffraction F ile

Not the best fit in the world, but clear enough

“Missing” peaks are actually from lactose monohydrate, not in PDF!

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.

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.

Example 2

Indeed, the two patterns agree within 20%, except for four of the strongest peaks!

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In tensity from PD F# 33-1529

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F#

33-1

530

Am picillin

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.)

Bragg-Brentano

Broad beam

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?

Example 3

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2theta (deg)

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Data on client’s raw material, collected with very good angular resolution using synchrotron radiation

Patent claims

Real problem. Somebody is interested in knowing if their material would infringe that patent

21

What can we learn about this material?

Any crystalline material is characterized by its lattice.

a

b

c

The lattice dimensions (lattice parameters) govern the position of all possible diffraction peaks.

FklEhlDklClBkAhd 22222

2/1

sin4

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.

Indexing: First step is to get accurate peak positions.(locally developed software, model lineshapes, we’re not GUI programmers)

xmxmxxmx

0 5 10 15 20 252 (degrees)

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Raw Data

zoom

Lineshapefit

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, CHOICE=3, IDIV=0,D1=.0001,D2=.0001,VOL=8000, CEM=40,MONO=140, MERIT=20,END

Data for computer

search

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

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

Armed with a probable lattice, we can check how it fits the data.

Use a profile fit (Pawley or Le Bail).Peak positions are controlled by the latticeAdjust parameters which control the diffraction peak widths, etc.

Indexed

Form 2Form 1

D ata, m odel

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1 0 1 1 1 22 t h e t a ( d e g r e e s )

E x c i p i e n t s

Active P harm aceutica l Ingred ient

Tablet

cla im s: form 2 form 1

2 4 6 8 10 12 14 16 18 20 22 242the ta (degrees)

Excip ients

Active Pharm aceutica l Ingred ient

Table t

cla im s: form 2 form 1

x20

x32

API is only a few percent of the tablet weight. Shows up very clearly in the intact tablet. No sample grinding, etc.

Indexing the pattern allows us to account for EVERY observed diffraction peak.

Strong statement about sample purity (of crystalline phases).

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.

Example 4

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IU C r Q uant R ound R obinP harm Sam ple 1

The IUCr furnished lab data for people who wanted to analyze it.

4 6 8 10 12 14 16 18 20 22 24 26 28 30 322 the ta (degrees)

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IU C r Q uant R ound R obinP harm . Sam ple 11.15 Å , cap illa ry

pharm 1gsas.grf

ValineN izatid ine

1 5 1 6 1 7 1 8 1 9 2 02 t h e t a ( d e g r e e s )

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IU C r Q uant R ound R obinP harm . Sam ple 11.15 Å , cap illary

pharm 1gsasm .grf

ValineN izatid ine

Blow up part of the pattern

Results of IUCr Quantitative Phase Analysis Round RobinPharmaceutical sample #1

0% 20% 40% 60% 80% 100%

Patricipant from CPDdata

Participant 2

Participant 1

Synch

Prepared Mannitol SucroseValine

Nizatidine

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IU C r Q uant R ound R obinP harm Sam ple 2

pharm 2_ lab_synch.grf

4 6 8 10 12 14 16 18 20 22 24 26 28 30 322 the ta (degrees)

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IU C r Q uant R ound R obinP harm . Sam ple 21.15 Å , cap illa ry

pharm 2gsas.grf

ValineN izatid ine

0% 20% 40% 60% 80% 100%

Patricipant from CPDdata

Participant 2

Participant 1

Synch

Prepared Mannitol Sucrose Valine Nizatidine

Pharm sample 2 – only show crystalline components – there was also 30 wt% amorphous starch

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.