Inside the new WineScan SO2

SO2 libre y total
By Richard Mills,
With its revolutionary ability to measure sulphur dioxide in parallel with various other parameters, the new WineScan S02 could be called the new 'killer app' within wine analysis. But how does it work exactly and can winemakers be sure of the technology behind the new solution? In focus takes a closer look under the lid of the instrument with the help of the FOSS research and development experts.

With thanks to Henrik Toft, Chemometrician and Henrik Thomsen, Chemist/Chemometrician.


How can the method measure a number of quality parameters simultaneously with S02?

S02 is present in the sample, either freely as sulfite or chemically bound to various wine constituents. The free S02 can be driven off from the sample by aeration and is therefore easily expelled from the sample. The chemically bound S02 on the other hand must be converted to free S02 by acid hydrolysis before it can be driven off the sample. In essence, this two step method is defined by the International Organisation of Vine and Wine (OIV) as the golden standard for S02 analysis in wine.


By ensuring a closed gas circulation system with sufficiently small total gas volume, the liberated S02 can be accumulated over time and can subsequently be quantified into free and total S02 present in the sample. The traditional WineScan parameters are measured as normal in parallel with the hydrolysis process. 


Are we in fact doing a form of acid hydrolysis with the WineScan method and if so how can we do it in a much shorter time?

As mentioned, an acid hydrolysis is in fact performed. The fact that the analysis can be completed in much shorter time than traditional acid hydrolysis reference methods is due to a continuous measurement of liberated gaseous S02 concentration over time as the hydrolysis progresses. The continuous measurement means that the chemical reaction does not have to run for the full time allowing for complete acid hydrolysis, but rather the acquired data can be converted into a calibration allowing for sufficiently robust extrapolation to the concentration of total 502 present in the sample.


The method diverts some of the infrared light away from the liquid sample to the gas cuvette. Does it therefore affect the accuracy of measurement for other parameters?

The light diverted to the gas measurement is taken as a small part of the fringe of the lnfraRed beam. This does not influence the normal liquid WineScan measurement. One of the primary requirements for the integration of the S02 measurement functionality into the existing WineScan was that the performance of the normal liquid parameters must not be compromised.


A feature of the WineScan is that it is quite robust and at home in the lab or in a control room near production - is the new method more susceptible to vibration, temperature etc than the existing WineScan technology?

The same vibration specifications are met. When it comes to other environmental specifications such as temperature and humidity, the maximum ambient operating temperature is reduced from 40° C to 35° C due to the cooling required.


Rapid analysis of sulphur dioxide 


The new method uses a lot less chemicals than the standard reference method - how is this possible?

The sample volume used and hence the volume of acid required for the reaction and measurement is much smaller than that normally used due to the small reaction chamber of the S02 module. The small volume is made possible by the accuracy of the infrared signal detection which, compared to a titration of 'captured gas' for example, is much more precise.


How long has it been under development and how many people have been involved?

The idea of measuring both free and total S02 from the same reaction was developed about two years ago and during this time more than 12 people in the R&D department have been involved in bringing it from an idea to a final product.


In a nutshell, why can we believe in the new method?

If the general concept of signal detection using infrared and subsequent quantifications based on indirect measurements through calibrations can be accepted for traditional liquid measurements, there is no reason why the S02 measurement should not be equally acceptable.


The method has been thoroughly validated against different reference methods. The ease-of-use of the method (place the sample under the pipette and push start) has now made the measurement of S02 simpler than ever and operator independent. Now everybody is capable of measuring S02 within two minutes.


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