Quantitative Analysis of Solutions Using a High Resolution Portable Raman Spectrometer

Importance of the topic

A portable, high-resolution Raman spectrometer enables rapid, non-destructive quantification of molecular species in aqueous solutions, a capability essential for quality control, food analysis and pharmaceutical monitoring directly at the point of use. By combining fiber-optic sampling and multivariate chemometric modeling, this approach overcomes challenges of water interference and provides precise concentration measurements of key solutes such as sugars.

Objectives and study overview

This study aimed to develop and validate a quantitative calibration model for determining glucose, fructose and sucrose concentrations in a tertiary aqueous mixture. Using the i-Raman Plus portable spectrometer and BWIQ chemometric software, the work focused on constructing robust Partial Least Squares (PLS) regression models and assessing their predictive performance on independent test samples.

Methodology and instrumentation

The experimental design included 31 standard solutions of glucose, fructose and sucrose in distilled water, each at a total sugar concentration of 0.4 M. Spectrum acquisition was performed using:

• i-Raman Plus portable Raman spectrometer (785 nm excitation, ~300 mW laser power)
• Fiber-optic probe sampling through glass scintillation vials
• Integration time of 50 s per scan over the 176–3200 cm⁻¹ Raman shift range

The complete dataset comprised 62 spectra (each sample measured in duplicate). Data for 25 standards (50 spectra) formed the calibration set, while 6 standards (12 spectra) constituted an independent prediction set. Spectral analysis was carried out directly without baseline or smoothing preprocessing, focusing on the 250–1500 cm⁻¹ region. Multivariate modeling employed PLS1 regression for each sugar component.

Key results and discussion

Three-factor PLS models were developed for glucose, fructose and sucrose. For glucose, the calibration and validation plots yielded an R² exceeding 0.999, with both calibration and prediction root mean square errors (RMSEC and RMSEP) below 0.008 M. Similar high accuracy and precision were observed for fructose and sucrose models. Prediction on the independent test set confirmed the robustness of the models, demonstrating minimal deviation between measured and predicted concentrations.

Benefits and practical applications

This approach offers several advantages:

• Rapid, reagent-free quantification of sugars in aqueous media
• High accuracy and sensitivity enabled by high spectral resolution
• Portability for in-field or at-line deployment
• Minimal sample preparation and no extensive spectral preprocessing required

Potential applications span food and beverage quality control, fermentation monitoring and pharmaceutical excipient analysis.

Future trends and potential applications

Advancements may include:

• Extension to more complex matrices and multi-component formulations
• Integration of advanced chemometric algorithms (e.g., support vector machines, adaptive weighting methods)
• Miniaturization of probe and spectrometer designs for handheld use
• Real-time monitoring in continuous processes or industrial lines

Conclusion

The study validates the use of a portable i-Raman Plus spectrometer combined with BWIQ software for accurate, non-destructive quantification of glucose, fructose and sucrose in aqueous mixtures. The high correlation, low prediction error and ease of deployment underscore the method’s value for rapid on-site analysis.