Preservatives and antioxidants

Sulfur dioxide: free and total

Both free and total sulfur dioxide can be measured using the Rankine and Pocock aspiration method or by the Lachat Flow Injection Analysis (FIA).

In the aspiration method, sulfur dioxide is sparged from the acidified wine sample in an air stream and trapped in a solution of hydrogen peroxide. The aspiration procedure oxidises the sulfur dioxide to sulfuric acid which is then titrated with standardised sodium hydroxide. The amount of sodium hydroxide required is proportional to the amount of sulfur dioxide.

The determination of free and total sulfur dioxide by flow injection analysis involves the sulfite in the sample being acidified with a dilute hydrochloric acid solution and the acidified sample passing through two channels where it is subsequently heated on one channel but not the other. The heat and acid hydrolyse the acetaldehyde-alpha-hydroxysulfonate bond and other bisulfite complexes to release SO2(g). The resulting sulfur dioxide gas passes through a Teflon membrane and reacts with formaldehyde and pararosaniline dye in an acid solution to form a red-violet coloured complex. The absorbance of the coloured complex measured at 560 nm is directly proportional to the SO32- in the sample.

Ascorbic and erythorbic acids

Ascorbic acid and erythorbic acid function as reducing agents and are used as anti-oxidants in wine production. Commercial Services performs this analysis using High Performance Liquid Chromatography (HPLC). Dehydro ascorbic acid, which results from the oxidation of ascorbic acid, can also be measured.

Sorbic acid

This method involves a colorimetric procedure measuring absorbance after a single extraction with iso-octane. The analysis of this compound is mandatory for all wines that are exported to Japan.

Prices per analysis
Analysis Per Sample (excluding GST) Volume required Total response time
Free sulfur dioxide by FIA $14 10 mL 24 hrs
Total sulfur dioxide by FIA $14
Sulfur dioxide free and total (FIA) $24
Free sulfur dioxide by aspiration $20 50 mL 24 hrs
Total sulfur dioxide by aspiration $20
Sulfur dioxide free and total by aspiration $30
Ascorbic and erythorbic acids $40 10 mL 72 hrs
Sorbic acid $26 10 mL 24 hrs

For more information, please contact AWRI Commercial Services on (08) 8313 6600 or e-mail commercialservices@awri.com.au