A combination of X-ray diffraction and computational techniques can determine unknown crystal structures in powder mixtures
The characterization of individual components in an unknown crystalline powder mixture is a challenge that has eluded scientists for many years. Now, A*STAR researchers have for the first time invented a methodology to accurately determine the crystal structures present in such mixtures1.
A new method that combines X-ray diffraction with computational analysis can be used to measure mixtures of unknown solids and identify their individual components.
© 2014 A*STAR Institute of Chemical and Engineering Sciences
Powder X-ray diffraction (PXRD) is a powerful tool used to determine the structure of crystalline solids. Every solid has its own unique crystal structure which, when hit by X-rays, produces a unique diffraction pattern — a ‘fingerprint’ from which the solid can then be identified and characterized through computational analysis.
However, traditional PXRD works best with pure single-component powders; mixed powders of unknown solids are far more difficult to analyze because the diffraction patterns overlap and are difficult to separate. Another complication is that individual solids can produce slightly different diffraction patterns depending on how the crystals are shaped and orientated in the powder samples.
Marc Garland and co-workers at the A*STAR Institute of Chemical and Engineering Sciences in Singapore have developed a new methodology, the PXRD-BTEM-Rietveld method, which combines two existing techniques to determine the individual crystal structures in a powder mixture.
“Many analytical problems in the chemical sciences involve mixtures of unknown solids,” explains Garland. “The extension of PXRD analysis to these mixtures opens up a myriad of new possibilities for the experimentalist because a purified single-component sample is no longer needed.”
First, Garland and his team used PXRD to obtain diffraction datasets from pre-prepared mixtures of several different powders. They then used their own algorithm, called band-target entropy minimization (BTEM), to sift through the entire dataset, looking for the simplest underlying patterns and to untangle overlapping diffraction patterns.
“BTEM is a blind separation technique,” explains Garland. “By searching for the simplest patterns — those with the smoothest profiles and the least signal disorder — we obtain accurate estimates of each pure component’s diffraction pattern.”
Garland and his team then used computational structure determination, including so-called Rietveld refinement, to obtain the crystal structures for each solid. This allowed the researchers to characterize the unknown components in the mixtures.
“One example of an application for our new technique could be investigating polymorphism in pharmaceuticals,” says Garland. “Each polymorphic pharmaceutical solid has a unique diffraction pattern resulting from its crystal structure, and it is incredibly important to the pharmaceutical industry to identify these from mixtures.”
The researchers plan to further refine their methodology, and hope to eliminate the problem of measuring irregularities due to crystal orientation.
Schreyer, M., Guo, L., Thirunahari, S., Gao, F. & Garland, M. Simultaneous determination of several crystal structures from powder mixtures: The combination of powder X-ray diffraction, band-target entropy minimization and Rietveld methods. Journal of Applied Crystallography 47, 659–667 (2014).
A*STAR Research | ResearchSEA
When AI and optoelectronics meet: Researchers take control of light properties
20.11.2018 | Institut national de la recherche scientifique - INRS
How to melt gold at room temperature
20.11.2018 | Chalmers University of Technology
Max Planck researchers revel the nano-structure of molecular trains and the reason for smooth transport in cellular antennas.
Moving around, sensing the extracellular environment, and signaling to other cells are important for a cell to function properly. Responsible for those tasks...
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
19.11.2018 | Event News
09.11.2018 | Event News
06.11.2018 | Event News
20.11.2018 | Life Sciences
20.11.2018 | Life Sciences
20.11.2018 | Physics and Astronomy