Total Sulfite

Rosanaline Method

This method is used for the determination of free and total sulfite in wines and musts using the Astoria flow system. The range for total sulfite is 5.0 to 200 mg/L. The upper range can be extended by sample dilution. The lower range for free sulfite may be extended to 2.0 mg/L by adding a lower calibrant. This cartridge can be configured to determine free or total SO₂.

Summary

The sample is acidified to liberate SO₂ gas from free sulfite and labile bound sulfite. For total sulfite, it is then heated to 90°C to liberate the SO₂ from the aldehyde bound sulfites. The SO₂ gas diffuses through a Teflon membrane where it is reacted with formaldehyde and p-Rosaniline to form p-Rosaniline methylsulfonic acid. The absorbance of this product is measured at 570 nm.

DTNB Method

This method is available as a kit for determination of total sulfite (sulfur dioxide or SO₂) in wine or juice using the rAPID-T™ analyzer or as a cartridge for the flow system. The applicable range is 5.0 – 200 mg/L. Higher concentrations may be determined following sample dilution.

Summary

Samples are mixed with Tris Buffer at pH 7.8. Addition of 5.5’-dithiobis (2-nitrobenzoic acid) (DTNB) reacts with free and bonded SO₂ to produce a color that can be measured photometrically at the wavelength of 420 nm. The measured absorbance at 420 nm is directly proportional to the total sulfite concentration in the sample. On the flow system a teflon membrane is used to separate the SO₂ from the sample to avoid matrix interference, this cartridge can be configured to determine free or total SO₂.

Availability