Effective and inexpensive HPLC analogue for first-year students: buret chromatography of food dyes in drinks

Chromatography is a ubiquitous technique in analytical chemistry, and high-performance liquid chromatography (HPLC) is the industry standard for quantitation of components in solution mixtures. However, demonstrating the principles of liquid chromatography to undergraduates via HPLC-based experiments often proves ineffective because of the fully automated nature of modern HPLC units. This paper details a novel laboratory exercise that is accessible to students in first-year chemistry and high school and helps to demonstrate and demystify the principles involved in HPLC. Using only common and inexpensive laboratory equipment found in most general-chemistry laboratories (burets and benchtop spectrophotometers), students are able to replicate results that are equivalent to those obtained on research-grade HPLC instruments, while gaining valuable insight into chromatography principles.Accepted manuscrip

Femtosecond photodissociation dynamics of 1,4-diiodobenzene by gas-phase X-ray scattering and photoelectron spectroscopy

We present a multifaceted investigation into the initial photodissociation dynamics of 1,4-diiodobenzene (DIB) following absorption of 267 nm radiation. We combine ultrafast time-resolved photoelectron spectroscopy and X-ray scattering experiments performed at the Linac Coherent Light Source (LCLS) to study the initial electronic excitation and subsequent rotational alignment, and interpret the experiments in light of Complete Active Space Self-Consistent Field (CASSCF) calculations of the excited electronic landscape. The initially excited state is found to be a bound 1B1 surface, which undergoes ultrafast population transfer to a nearby state in 35 ± 10 fs. The internal conversion most likely leads to one or more singlet repulsive surfaces that initiate the dissociation. This initial study is an essential and prerequisite component of a comprehensive study of the complete photodissociation pathway(s) of DIB at 267 nm. Assignment of the initially excited electronic state as a bound state identifies the mechanism as predissociative, and measurement of its lifetime establishes the time between excitation and initiation of dissociation, which is crucial for direct comparison of photoelectron and scattering experiments.</p