Tianyi Guan

About

This project investigated the fluorescence behaviour of quinine under controlled concentration, ionic, and pH conditions. Quantitative spectrofluorimetric calibration was combined with chloride-induced fluorescence quenching and Stern-Volmer analysis to characterize the response of quinine emission to changes in its chemical environment. A complementary qualitative pH experiment examined changes in fluorescence intensity and colour across acidic to mildly basic conditions, while diluted tonic water provided a practical quinine-containing sample.

Research Focus

To characterize the quantitative fluorescence response of quinine and determine how chloride concentration and solution pH modify its emission behaviour.

Study Design

Quinine calibration standards covering approximately 0.25–2.0 ppm were analyzed by fluorimetry using excitation and emission wavelengths near 350 and 450 nm, respectively. A second series maintained quinine concentration while increasing NaCl from approximately 100 to 2000 ppm to evaluate fluorescence quenching. The resulting F₀/F ratios were analyzed using a Stern-Volmer relationship. Quinine fluorescence was also examined qualitatively in buffers spanning pH 2–8 under UV illumination, allowing changes in intensity and emission colour to be compared across chemical environments. A diluted tonic-water sample was included as an applied analytical matrix.

Key Findings

Quinine fluorescence showed a highly linear concentration response across the calibration range (R² = 0.9995). Increasing chloride concentration produced strong concentration-dependent quenching, with the Stern-Volmer relationship remaining approximately linear across the tested range (R² = 0.9917). Qualitative pH analysis showed pronounced environmental sensitivity, with particularly strong blue fluorescence near pH 4 and changes in both intensity and colour as the solution approached neutral and mildly basic conditions. F₀/F = 0.002611[NaCl] + 1.000

Key Methods

Spectrofluorimetry; fluorescence calibration; fluorescence quenching; Stern-Volmer analysis; solution preparation; quantitative dilution; pH-dependent fluorescence analysis; UV fluorescence observation;

Keywords

Fluorescence spectroscopy; quinine; spectrofluorimetry; fluorescence quenching; Stern-Volmer analysis; chloride quenching; pH dependence; molecular fluorescence; tonic water; quantitative spectroscopy;

Project Status

Completed (2026)