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Halide (Cl-) Quenching of Quinine Sulfate Fluorescence: A Time-Resolved Fluorescence Experiment for Physical Chemistry

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Jonathan H. Gutow

Department of Chemistry, University of Wisconsin–Oshkosh, Oshkosh, WI 54901

J. Chem. Educ., 2005, 82 (2), p 302

DOI: 10.1021/ed082p302

Publication Date (Web): February 1, 2005

Section:

History, Education, and Documentation

Abstract

A time-resolved fluorescence experiment for use in physical chemistry is described. Students investigate the halide quenching of the fluorescence from quinine sulfate in water (similar to tonic water). The students are able to determine that the fluorescence is quenched dynamically by collision with the halide, not by forming an equilibrated complex. Students reproduce the literature unquenched lifetime of about 19 ns and observe a nearly diffusion-limited collisional quenching rate of 5.2 × 109 M^–1 in 0.5 M H₂SO₄. The experiment is popular with the students. The samples are easy to handle. It provides the students experience with modern equipment (lasers, fast data collection, and computer data analysis), while also requiring the students to review and use knowledge of the kinetics of competing processes and electronic spectroscopy. Samples of different concentration are divided among the students for analysis; in this manner nine students can complete the data collection for the experiment in one three-hour laboratory using a single fluorescence apparatus. If time resolution is not available this experiment can still be performed using intensity measurements. The quenching yields linear Stern–Volmer plots with a K_sv ≈107 M^–1.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Physical Chemistry

Keywords (Pedagogy):

Hands-On Learning / Manipulatives

Keywords (Subject):

Kinetics

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