Fluorescence quenching study of humic-fraction-modified silica gel in a solid state after association with a variety of pesticidal analytes in hexane and acetonitrile

In this paper, we investigate the fluorescence quenching of acidic humic-fraction-modified silica gel in the solid state after association with a variety of pesticidal analytes in hexane and acetonitrile. The percentage of fluorescence quenching is found to be dependent on the contact time and linearly on the number of moles of analyte involved in the association process. However, any - complexation interaction arising from the acidic aromatic ring on the analyte due to the derivatization of a bulky electron-withdrawing group is not observed. Also, any mechanism leading to adsorption or any quenching process occurring as a result of the steric hindrance obtained by a theoretical interaction simulation is not observed. The Fourier transform infrared (FTIR) data and simulation results, instead, suggest that electron-rich atoms on the analyte, such as oxygen, sulfur, nitrogen, and phosphorus, are responsible for fluorescence quenching, following dipole-dipole interaction with the humic-fraction-modified adsorbent.