An Interference-Free Voltammetric Method for the Detection of Sulfur Dioxide in Wine Based on a Boron-Doped Diamond Electrode and Reaction Electrochemistry

At a Glance

Metadata	Details
Publication Date	2023-08-17
Journal	International Journal of Molecular Sciences
Authors	Eva Culková, Zuzana Lukáčová-Chomisteková, Renata Bellová, Miroslav Rievaj, Jarmila Švancarová-Laštincová
Institutions	Catholic University in Ruzomberok
Citations	3
Analysis	Full AI Review Included

Executive Summary

This research introduces a novel, highly selective voltammetric method for detecting free and total sulfur dioxide (SO₂) in complex wine matrices, utilizing an unmodified Boron-Doped Diamond (BDD) electrode.

Core Value Proposition: The method achieves interference-free detection of SO₂ by leveraging a chemical redox cycling mechanism, significantly enhancing the sensor’s voltammetric response.
Mechanism: Detection is based on the electrogeneration of iodine (I₂) from iodide (I^-) at the BDD surface. I₂ reacts with SO₂ (Bunsen reaction), regenerating I^-, which then diffuses back and is re-oxidized, creating a catalytic current loop.
Material Advantage: The unmodified BDD electrode provides an extremely low background current and a wide working potential range, crucial for reliable electrogeneration in complex media like wine.
Selectivity Strategy: Selectivity is ensured through chemical pre-treatment steps: NaOH releases bonded SO₂ (for total SO₂ measurement), while formaldehyde is used to bond free SO₂ for accurate blank/interference subtraction.
Performance: The estimated detection limit (LOD) is exceptionally low (10^-6 to 10^-7 mol dm^-3), allowing for high sample dilution and low chemical consumption.
Validation: Results for free and total SO₂ content in commercial white wines showed statistical agreement with classic titrimetric methods, confirming the platform’s accuracy and reliability.

Technical Specifications

Parameter	Value	Unit	Context
Working Electrode Material	Boron-Doped Diamond (BDD)	N/A	Unmodified, 1.5 mm radius.
Reference Electrode	Ag/AgCl (3 mol dm^-3 KCl)	N/A	Standard reference.
Counter Electrode	Platinum Macroelectrode	cm²	Area of 1 cm².
Optimal Supporting Electrolyte	0.1 mol dm^-3 HClO₄	Concentration	Provides optimal acidic environment (pH ≈ 1).
Optimal Iodide Concentration	2 x 10^-5 mol dm^-3	Concentration	Initial KI concentration for redox cycling.
Scan Rate	50 mV s^-1	N/A	Used for Linear Sweep Voltammetry (LSV).
Operating Temperature	25.0 ± 0.5	°C	Controlled cell temperature.
Estimated Detection Limit (LOD)	9 x 10^-6 (initial)	mol dm^-3	Calculated via 3S_A/B criterion.
Optimized LOD Range	10^-6 to 10^-7	mol dm^-3	Achievable with further optimization.
Calibration Linearity (R²)	0.999	N/A	Standard addition plot for real wine samples.
Sample Volume Used	1	mL	Diluted into 25 mL cell volume.

Key Methodologies

The analytical methodology relies on precise chemical pre-treatment and optimized electrochemistry on the BDD surface:

BDD Electrode Cleaning: The working electrode surface is cleaned chronoamperometrically in 0.6 mol dm^-3 H₂SO₄ at a constant potential of -3 V vs. Ag/AgCl for 300 s prior to each measurement sequence.
Electrolyte Selection: 0.1 mol dm^-3 HClO₄ was selected as the optimal supporting electrolyte due to its high acidity (pH 1), which maximizes the rate of the Bunsen reaction (SO₂ + I₂ + 2H₂O → H₂SO₄ + 2I^- + 2H⁺) and ensures the stability of reactants.
Free SO₂ Determination (Direct Analysis): A 1 mL wine sample is added directly to the optimized KI/HClO₄ solution. The voltammetric signal is measured, representing the free SO₂ content plus any interfering species that react with I₂.
Total SO₂ Determination (Bonded SO₂ Release): The wine sample is pre-treated with 4 mol dm^-3 NaOH for 5 minutes. This strongly alkaline environment releases SO₂ that is chemically bonded to aldehydes (e.g., HCHOSO₂), allowing the measurement of total SO₂ content.
Interference Subtraction (Blank Measurement): To isolate the signal contribution of SO₂, a blank measurement is performed. The free SO₂ in the sample is intentionally bonded using formaldehyde (HCHO) and Chelaton III (EDTA) is added to complex metal ions. The resulting signal, representing only non-SO₂ interfering species, is subtracted from the direct and total SO₂ measurements.
Quantification: SO₂ concentration is determined using a multiple standard addition calibration plot, where known amounts of Na₂SO₃ are sequentially added to the sample solution.

Commercial Applications

The robust, fast, and low-cost nature of this BDD-based voltammetric platform makes it highly suitable for integration into various analytical and industrial control systems:

Food and Beverage Quality Control: High-throughput, routine analysis of preservatives (sulfites) in wine, fruit juices, and other processed foods, ensuring compliance with regulatory limits (e.g., EU 200 mg/L total SO₂ limit).
Analytical Instrumentation: Development of compact, field-portable electrochemical sensors for rapid on-site testing, replacing slower, reagent-intensive titrimetric methods.
Chemical Process Monitoring: Real-time monitoring of sulfur compound concentrations in industrial streams, leveraging the BDD electrode’s chemical inertness and stability in aggressive media.
Electrochemical Sensor Manufacturing: The methodology validates the use of unmodified BDD electrodes for complex matrix analysis, supporting the demand for high-performance BDD materials (relevant to BDD suppliers).
Environmental Analysis: Detection of trace levels of sulfite or other redox-active pollutants in water sources, utilizing the high sensitivity achieved through catalytic redox cycling.

View Original Abstract

This paper describes a new, simple, and highly selective analytical technique for the detection of sulfur dioxide in wine, as a real sample with a relatively complicated matrix. The detection of the above analyte was based on the electrogeneration of iodine from iodide on a boron-doped diamond electrode, without modifications, in the presence of 0.1 mol dm−3 HClO4 as a supporting electrolyte. The electrogenerated iodine reacted with sulfur dioxide, forming iodide ions and sulfuric acid (i.e., a Bunsen reaction). The product of this reaction, the iodide ion, diffused back to the surface of the boron-doped diamond electrode and oxidized itself again. This chemical redox cycling enhanced the voltammetric response of the boron-doped diamond electrode. The selectivity of the determination was assured using NaOH and formaldehyde during sample preparation, and a blank was also measured and taken into account. The detection limit was estimated to be 10−6-10−7 mol dm−3. However, the content of sulfur dioxide in wine is significantly higher, which can lead to more accurate and reliable results.

Tech Support

Original Source

DOI: https://doi.org/10.3390/ijms241612875

References

2016 - Food Safety Risk Assessment for Estimating Dietary Intake of Sulfites in the Taiwanese Population [Crossref]
2013 - Determination of Sulfites in Wine
2015 - A Headspace Gas Detection Tube Method to Measure SO2 in Wine without Disruption SO2 Equilibria [Crossref]
2013 - Determination of Sulfur Dioxide in Wine Using Headspace Gas Chromatography and Electron Capture Detection [Crossref]
2015 - Headspace Thin-Film Microextraction Coupled with Surface-Enhanced Raman Scattering as a Facile Method for Reproducible and Specific Detection of Sulfur Dioxide in Wine [Crossref]
2020 - Direct Quantification of Sulfur Dioxide in Wine by Surface Enhanced Raman Spectroscopy [Crossref]
2021 - The Effects of Sulphur Dioxide on Wine Metabolites: New Insights from H-1 NMR Spectroscopy Based In-Situ Screening, Detection, Identification and Quantification [Crossref]
2021 - Microanalytical Flow System for the Simultaneous Determination of Acetic Acid and Free Sulfur Dioxide in Wines [Crossref]