Portable Spatially Offset Raman Spectroscopy for Rapid Detection of Methanol and Ethanol in Pisco Through Sealed Containers.

In this study, we introduced a portable spatially offset Raman spectroscopy (SORS) system that permits rapid, non-destructive acquisition of Raman spectra from bottled Pisco spirits, providing a practical and non-invasive solution for in situ quality control. Pisco, a Peruvian distilled spirit, was selected as a case study because methanol occurs naturally during fermentation and distillation, and the product is susceptible to adulteration. Methanol and ethanol levels in Pisco were determined using gas chromatography (GC-FID). Methanol levels in 94 authentic Pisco samples ranged from 7.4 to 67 mg/100 mL, remaining below the regulatory limits established for fruit brandies. For pure Pisco samples, the handheld SORS device demonstrated strong predictive performance for determining methanol (SEP = 0.003%, Rpre = 0.92) and ethanol (SEP = 1.25%, Rpre = 0.98) content. To further assess model applicability across a broader methanol concentration range, randomly selected Pisco samples were fortified with methanol (0.11-9.85%), resulting in a prediction model with excellent performance for methanol quantification (SEP = 0.17%; Rpre = 0.995). Overall, the SORS-based approach showed robust analytical capability, underscoring its potential as a non-contact, non-destructive technique for rapid quantification of methanol and ethanol in sealed glass containers.