Chemistry Reference
In-Depth Information
are significantly advanced by the combinatorial approach. Combinatorial processes
can also be more effectively automated by computer-controlled processes, since the
operations are repeated on all cells of a material library.
11.1.2 Combinatorial Screening
With the increased productivity in material synthesis and processing facilitated
by combinatorial techniques, it becomes a challenge to efficiently screen all the samples
produced in the material library. The characterization of the large amount of samples
requires high-throughput screening techniques to test and evaluate the variation of
composition, structure, and property of the entire material library. Many proprietary
material libraries have been designed considering not only the material processing, but
also the requirements for fast and unambiguous characterizations. X-ray diffraction is
one of the most suitable rapid screening techniques because of the penetrating power of
the X-ray beam, nondestructive to samples, rapid data collection, and the abundant
information contained in the diffraction pattern about the materials. In the pharma-
ceutical industry, powder X-ray diffraction (PXRD) is one of the primary techniques
used in drug discovery and process analysis [10-18]. X-ray diffraction, especially two-
dimensional X-ray diffraction, can be used to measure the structural information of a
material library with high speed and high accuracy [19-21].
The method of XRD combinatorial screening and the corresponding systems and
devices are introduced in this chapter. The method and system design are based on
two-dimensional XRD
2
theory. Various configurations and components designed to
deal with special needs of the screening are introduced. The combined screening
method with XRD and Raman is also introduced.
11.2 XRD
2
SYSTEMS FOR COMBINATORIAL SCREENING
Two-dimensional X-ray diffraction is one of the preferred methods for high-through-
put combinatorial screening. An XRD
2
system designed for combinatorial chemistry
contains equipment with the latest technological advances needed to perform
high throughput, easy-to-use screening on a wide variety of analytical parameters.
When material libraries are analyzed by the conventional X-ray diffractometer, the
material on each cell has to be measured individually. In most cases, the material
libraries are not suitable for loading on a conventional diffractometer, so the materials
may have to be removed from the libraries after the combinatorial reaction process.
The quantity of the material in each cell is also typically much less than the amount
required to fill a standard sample holder. A material library may have to be kept
horizontal since the products of the reaction are in loose powder form or even in
solution form. An X-ray diffraction system dedicated to high-throughput screening of
a combinatorial material library should be able to handle material library plates of
various sizes and designs. Ideally, the materials are measured in the library without
disturbance and can bemeasured between thematerial processing steps or even during
processing. The X-ray optics, detector, and system configuration should be able to
