The pH dependent Raman spectroscopic study of caffeine

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Physical Chemistry

Background:

• Surface-enhanced Raman spectroscopy (SERS) is a powerful technique for analyzing molecules at low concentrations.
• Understanding the influence of environmental factors like pH is crucial for accurate SERS analysis.
• Caffeine is a widely studied molecule with implications in various fields.

Purpose of the Study:

• To investigate the effect of pH on the SERS and normal Raman spectra of caffeine.
• To determine how pH influences caffeine's interaction with silver (Ag) colloid surfaces.
• To assign vibrational modes of caffeine using density functional theory (DFT) calculations.

Main Methods:

• Acquisition of SERS and normal Raman spectra of caffeine in aqueous solutions across a range of pH values.
• Optimization of caffeine molecule geometry using density functional theory (DFT) calculations for vibrational analysis.
• Comparative analysis of spectral data to elucidate pH-dependent effects.

Main Results:

• pH dramatically affects the SERS spectra of caffeine.
• Normal Raman spectra of caffeine aqueous solutions show minimal changes with varying pH.
• DFT calculations aided in detailed vibrational assignments for caffeine.

Conclusions:

• pH significantly influences the reorientation of caffeine molecules on Ag colloid surfaces.
• The intrinsic vibrational frequencies of caffeine's functional groups and chemical bonds are not impacted by pH.
• SERS is sensitive to the adsorption behavior of caffeine, which is pH-dependent.