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Sensing free sulfur dioxide in wine.

Monro TM, Moore RL, Nguyen MC, Ebendorff-Heidepriem H, Skouroumounis GK, Elsey GM, Taylor DK - Sensors (Basel) (2012)

Bottom Line: These processes and others consume the SO(2) over time, resulting in wines with little SO(2) protection.This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte.We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

View Article: PubMed Central - PubMed

Affiliation: Institute for Photonics & Advanced Sensing and School of Chemistry & Physics, The University of Adelaide, Adelaide, SA 5005, Australia. tanya.monro@adelaide.edu.au

ABSTRACT
Sulfur dioxide (SO(2)) is important in the winemaking process as it aids in preventing microbial growth and the oxidation of wine. These processes and others consume the SO(2) over time, resulting in wines with little SO(2) protection. Furthermore, SO(2) and sulfiting agents are known to be allergens to many individuals and for that reason their levels need to be monitored and regulated in final wine products. Many of the current techniques for monitoring SO(2) in wine require the SO(2) to be separated from the wine prior to analysis. This investigation demonstrates a technique capable of measuring free sulfite concentrations in low volume liquid samples in white wine. This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte. We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

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Maximum absorbance reading for three concentrations of working solution as a function of model wine sulfite concentration.
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f5-sensors-12-10759: Maximum absorbance reading for three concentrations of working solution as a function of model wine sulfite concentration.

Mentions: In order to investigate the level of substitution and its impact on the maximum absorbance obtained, three PRA working solutions were produced with PRA concentrations of 1.56 × 10−4, 3.12 × 10−4 and 4.68 × 10−4 mol/L. These concentrations are equivalent to sulfite concentration of 10, 20 and 30 ppm (1:1 ratio). The latter sulfite concentration is typical of a finished white wine whilst the former would be considered to be a level where the wine is highly susceptible to oxidation or spoilage. Each of the PRA solutions (300 μL) was mixed with model wine solutions (300 μL) containing 0–60 ppm of sulfites and diluted with water. Absorbance was measured over a 400 nm wavelength range to identify the position of the maximum absorbance obtained and also to investigate peak shape. Figure 5 illustrates the highest absorbance value obtained for each resultant colored solution plotted against sulfite concentration. This clearly illustrates the importance of the stoichiometry for this reaction. The graph illustrates the point where there are insufficient PRA molecules available to react with all of the sulfites in solution and hence the development of color, and therefore absorbance, begins to plateau. It is interesting to note that until this point, the absorbance values of the three PRA colored solutions were similar, suggesting that the maximum absorbance values obtained are independent of the PRA concentration provided that enough PRA exists to react with the sulfites. Figure 5 shows that the absorbance values of the lowest concentration of PRA (1.56 × 10−4 mol/L) begins to deviate from the trend between 10 and 15 ppm of sulfites, and by 20 ppm the plateau effect is more evident, a similar observation can be made for the mid-strength PRA solution at a concentration between 30–40 ppm sulfite concentration. The most concentrated PRA working solution was able to maintain linearity in absorbance until 60 ppm, suggesting that the di-substituted alkyl amino sulfonic acid predominates. From this point forward, a 1:2 molar ratio of PRA:sulfite was used to find the appropriate concentration in the working solution for the detection of sulfites in wine.


Sensing free sulfur dioxide in wine.

Monro TM, Moore RL, Nguyen MC, Ebendorff-Heidepriem H, Skouroumounis GK, Elsey GM, Taylor DK - Sensors (Basel) (2012)

Maximum absorbance reading for three concentrations of working solution as a function of model wine sulfite concentration.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472855&req=5

f5-sensors-12-10759: Maximum absorbance reading for three concentrations of working solution as a function of model wine sulfite concentration.
Mentions: In order to investigate the level of substitution and its impact on the maximum absorbance obtained, three PRA working solutions were produced with PRA concentrations of 1.56 × 10−4, 3.12 × 10−4 and 4.68 × 10−4 mol/L. These concentrations are equivalent to sulfite concentration of 10, 20 and 30 ppm (1:1 ratio). The latter sulfite concentration is typical of a finished white wine whilst the former would be considered to be a level where the wine is highly susceptible to oxidation or spoilage. Each of the PRA solutions (300 μL) was mixed with model wine solutions (300 μL) containing 0–60 ppm of sulfites and diluted with water. Absorbance was measured over a 400 nm wavelength range to identify the position of the maximum absorbance obtained and also to investigate peak shape. Figure 5 illustrates the highest absorbance value obtained for each resultant colored solution plotted against sulfite concentration. This clearly illustrates the importance of the stoichiometry for this reaction. The graph illustrates the point where there are insufficient PRA molecules available to react with all of the sulfites in solution and hence the development of color, and therefore absorbance, begins to plateau. It is interesting to note that until this point, the absorbance values of the three PRA colored solutions were similar, suggesting that the maximum absorbance values obtained are independent of the PRA concentration provided that enough PRA exists to react with the sulfites. Figure 5 shows that the absorbance values of the lowest concentration of PRA (1.56 × 10−4 mol/L) begins to deviate from the trend between 10 and 15 ppm of sulfites, and by 20 ppm the plateau effect is more evident, a similar observation can be made for the mid-strength PRA solution at a concentration between 30–40 ppm sulfite concentration. The most concentrated PRA working solution was able to maintain linearity in absorbance until 60 ppm, suggesting that the di-substituted alkyl amino sulfonic acid predominates. From this point forward, a 1:2 molar ratio of PRA:sulfite was used to find the appropriate concentration in the working solution for the detection of sulfites in wine.

Bottom Line: These processes and others consume the SO(2) over time, resulting in wines with little SO(2) protection.This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte.We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

View Article: PubMed Central - PubMed

Affiliation: Institute for Photonics & Advanced Sensing and School of Chemistry & Physics, The University of Adelaide, Adelaide, SA 5005, Australia. tanya.monro@adelaide.edu.au

ABSTRACT
Sulfur dioxide (SO(2)) is important in the winemaking process as it aids in preventing microbial growth and the oxidation of wine. These processes and others consume the SO(2) over time, resulting in wines with little SO(2) protection. Furthermore, SO(2) and sulfiting agents are known to be allergens to many individuals and for that reason their levels need to be monitored and regulated in final wine products. Many of the current techniques for monitoring SO(2) in wine require the SO(2) to be separated from the wine prior to analysis. This investigation demonstrates a technique capable of measuring free sulfite concentrations in low volume liquid samples in white wine. This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte. We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

Show MeSH