Thomasin C. Miller

Micro X-ray fluorescence in materials characterization

Micro X-ray fluorescence (MXRF) offers the analyst a new approach to materials characterization. The range of applications is expanding rapidly. Single point analysis has been demonstrated for nanoliter volumes with detection limits at the 0.5 ng level. MXRF can be used as an element specific detector for capillary electrophoresis. Elemental imaging applications include analysis of sample corrosion and polymers, use as a combinatorial chemistry screening tool, and integration with molecular spectroscopic imaging methods to provide a more comprehensive characterization. Three-dimensional elemental imaging is a reality with the development of a confocal X-ray fluorescence microscope. Stereoview elemental X-ray imaging can provide unique views of materials that flat two-dimensional images cannot achieve. Spectral imaging offers chemical imaging capability, moving MXRF into a higher level of information content. The future is bright for MXRF as a materials characterization tool.

Elemental imaging for pharmaceutical tablet formulation analysis by micro X-ray fluorescence

The analysis of the distribution of pharmaceutical materials in tablet formulations, such as drugs and matrix elements, is critical to product performance and is used in such areas as quality control, impurity testing, and process monitoring. Recently imaging techniques, such as Raman, near-IR, and fluorescence imaging, have become popular for “visualization” of pharmaceutical formulations, allowing for spatial and chemical composition information to be obtained simultaneously. These methods have been primarily focused on molecular imaging, or spatial analysis of the molecular characteristics of the tablet formulation. However, elemental species are also an important part of pharmaceuticals. Micro X-ray fluorescence (MXRF) elemental imaging offers complementary information to molecular imaging techniques. In this study, MXRF was used for the elemental imaging of various commercial pharmaceutical drug and vitamin supplements. Specifically, elemental composition and heterogeneity were monitored for each different tablet.

High-throughput screening with micro-x-ray fluorescence

Micro-x-ray fluorescence (MXRF) is a useful characterization tool for high-throughput screening of combinatorial libraries. Due to the increasing threat of use of chemical warfare (CW) agents both in military actions and against civilians by terrorist extremists, there is a strong push to improve existing methods and develop means for the detection of a broad spectrum of CW agents in a minimal amount of time to increase national security. This paper describes a combinatorial high-throughput screening technique for CW receptor discovery to aid in sensor development. MXRF can screen materials for elemental composition at the mesoscale level (tens to hundreds of micrometers). The key aspect of this work is the use of commercial MXRF instrumentation coupled with the inherent heteroatom elements within the target molecules of the combinatorial reaction to provide rapid and specific identification of lead species. The method is demonstrated by screening an 11-mer oligopeptide library for selective binding of the degradation products of the nerve agent VX. The identified oligopeptides can be used as selective molecular receptors for sensor development. The MXRF screening method is nondestructive, requires minimal sample preparation or special tags for analysis, and the screening time depends on the desired sensitivity.

DETECTION OF VISIBLE AND LATENT FINGERPRINTS BY MICRO-X-RAY FLUORESCENCE

Numerous methods are available to forensic scientists for detecting fingerprints in which the prints are treated with various agents to enhance the visual contrast between the print and the surface. In the present work, the spatial elemental imaging capabilities of micro-X-ray fluorescence (MXRF) were used to visualize fingerprint patterns based on inorganic elements present in the prints. A major advantage of using MXRF is that the prints are left unaltered for other analyses such as DNA extraction or for archiving. Most of the fingerprints which were examined were imaged from the potassium and chlorine present in the print residue. Among the various prints studied, lower count rates were also observed in the elemental maps of Ca, Al, Na, Mg, Si, P, S, and the X-ray source scatter. A sebaceous oily fingerprint left by one subject was successfully imaged by MXRF, but sebaceous prints left by a different person were undetectable, indicating print elemental composition may be person and/or diet dependent. Prints containing substances that might be found in real world cases were also visualized including sweat, lotion, saliva, and sunscreen.

F16 Nanoliter Dried Spot Deposition Using an Automated Dispenser for MXRF Quantitative Analyses

An alternative method to manual nanoliter deposition is an automated, non-contact dispensing apparatus (BioDot, AD3050). Since this automated dispensing apparatus offers high throughput and precision in addition to a wide dynamic range, it has been used in the development of biosensors, Lab-on-a-Chip, and BioChips. Additionally, automated deposition is an ideal technique for rapid and reproducible micro x-ray fluorescence (MXRF) sample preparation. Droplets of the same or varying concentrations can be deposited in an array at predetermined locations and in precise volumes. The BioDot instrument increases sample throughput significantly compared to manual nanoliter deposition. For example, a 10 x 10 array of droplets can be deposited in one minute.

Micro X-Ray Fluorescence Imaging for Silicide Diffusion Coating Inspection

Micro Xray fluorescence (MXRF) imaging is a relatively new method to map the constituent elements of a surface to a depth of tens to hundreds of microns, and at high spatial resolution, i.e., 40 to 50 microns. The feasibility of MXRF imaging is investigated as a potential NDE method to detect and characterize spalling failure of chromium disilicide diffusion coatings on Space Shuttle Reaction Control System (RCS) thruster chambers.

F-32 Micro X-ray Fluorescence as an Analytical Tool in Cashmere Hair Characterization

Hair and fiber analysis plays a key role in the realm of forensic science. A single hair or fragment of clothing could be the key to placing a suspect at the scene of a crime. Most current analyses involve animal hair classification based upon the appearance and physical characteristics of these hairs. However, in the event that two different types of animal hairs are nearly identical in all of their physical characteristics, other analytical methods must be employed. On the physical level, fine cashmere wool hairs are difficult to distinguish based on microscopic techniques from their twins, the lesser-valued yak wool fibers. Studies exploring such qualities as cashmere hair curvature and length, mean fiber diameter and resistance to compression have not been able to conclusively discriminate between the two samples. Another analytical method is needed in order to explore deeper into the molecular and elemental makeup of these fibers to determine if compositional differences may exist, thus aiding in the identification process.