Sulfites detection by surface-enhanced Raman spectroscopy: A feasibility study

The exhaustive control required for the correct wine production needs of many chemical analysis throughout the process. The most extended investigations for wine production control are focused on the quantification of total and free SO₂. Most methods described in the literature have an adequate detection limit, but they usually lack reproducibility and require a previous sample treatment for the extraction of the SO₂ from the wine-matrix. In this context, Surface-Enhanced Raman Spectroscopy (SERS) can be a promising technique for free SO₂ determination without the need for any sample pre-processing. This work describes a proof of concept of a new methodology based on SERS and supported by Density Functional Theory (DFT) calculations to identify the active vibrational modes of the key molecules that contribute to the concentration of free SO₂ in solution. Theoretical predictions and experimental outcomes are brought together to chemometrics to get a simple and real-time free SO₂ monitoring. This general procedure could pave the way towards an implementation of a portable SERS detection module for in-field measurements.