Pressure-and temperature-dependent thermal decomposition rates for the primary alkoxy radicals derived from OH-initiated oxidation of isoprene have been calculated. The master-equation calculations are based on ab initio energetics and structures previously reported. We also provide analytical descriptions of the theoretical falloff curves using the semiempirical Troe formalism. Additional calculations are also provided for two isomers not previously reported and to further characterize basis set effects on the energetics. The results indicate that the decomposition rates for these radicals should not be considered to be in the high-pressure limit at 760 Torr. Under atmospheric conditions the alkoxy radicals will be activated, and we find that prompt reaction for several isomers may be significant. The results are compared to recent estimates of overall alkoxy radical decomposition rates derived from OH cycling studies.

A novel approach for the analysis of inkjet inks is being reported. A time-of-flight mass spectrometer, coupled with a Direct Analysis in Real Time (DART™) ion source (AccuTOF™ DART™), was used to determine if inkjet inks from various manufacturers and models of printers could be reliably differentiated, characterized, and identified. A total of 217 ink standards were analyzed. As inkjet printing often involves the use of multiple colors (e.g., cyan, magenta, yellow, and black) to form an image or text, two different approaches to creating a library of standards and sampling methods were evaluated for implementation in a standard operating procedure. This research will show that a microscopic examination of the region of interest is requisite to identify what colors were utilized during the printing process, prior to comparing with known standards. Finally, blind testing was administered with 10 unknown samples to assess the validity and accuracy of the methodology.

Utilizing a database of standards for forensic casework is a valuable resource. Undoubtedly, as more standards (and corresponding information about the specimens) are collected, there is a greater certainty of identification when a questioned and a known item cannot be distinguished after a series of analyses. The United States Secret Service and the Internal Revenue Service National Forensic Laboratory jointly maintain the largest known forensic collection of writing inks in the world, which is comprised of over 8500 ink standards collected worldwide, dating back to the 1920s. This study was conducted to evaluate the reliability of matching arbitrarily purchased pens with known inks from a database. One hundred pens were randomly obtained from a variety of sources and their respective ink compositions were compared with standards. Eighty-five of the inks were determined to be suitable for comparison utilizing optical examinations and thin-layer chromatography. Three of the inks did not match any of the specimens on record; one of these inks was similar to an ink from an identical brand of pen that was in the database, but had a modified formulation.

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