660 M. Dubernet
12.3.4.2 Determination of Total Sulphur Dioxide in Wines and Musts
According to Ellman (1959), Dubernet et al. (1995a) and Dubernet et al. (1998).
Principle
Chemical Method
The sample to be analysed is diluted in a solution of phosphate buffer, pH8.
After stabilisation, a buffered solution of DTNB (5,5′-dithio-bis(2-nitrobenzoic
acid) (3,3′-6)) or 3-carboxy-4-nitrophenyl disulphide (otherwise known as Ellman’s
reagent) is added to the reaction mixture. This reagent is used for specific detection
of disulphide bonds and results in a yellow colour which is measured at 405 nm.
Characteristics of the Method
Intra-laboratory reproducibility: 12 mg/L
Inter-laboratory reproducibility: 20 mg/L12.3.4.3 Determination of Free Sulphur Dioxide in Wines and Musts
According to Dubernet et al. (1995b).
Principle
Chemical Method
Free sulphur dioxide is stabilised in acid medium and reacted in the presence of
formaldehyde with Fuschine which is de-coloured by phosphoric acid. The reaction
results in a pink colour which is measured by colorimetry. A blank reaction is carried
out to compensate for parasite reactions with wine phenolic compounds.
Characteristics of the Method
Intra-laboratory reproducibility: 6mg/L
Inter-laboratory reproducibility: 12mg/L12.3.4.4 Determination of Glucose and Fructose in Wines and Musts
Principle
Enzymatic Method
Glucose and fructose are phosphorylated in the presence of adenosine triphos-
phate (ATP) in a reaction is catalysed by hexokinase (HK) producing respectively,
glucose-6-phosphate (G6P) and fructose-6-phosphate (F6P):