The Determination of Sulphur in Foodstuffs Using the Oxygen Flask Technique

The need to estimate the sulphur content of protein containing food directly (i.e. not by applying a factor to the nitrogen content) has recently been realised. The oxygen flask technique, slightly modified, has proved to be a quick and reliable method for the combustion procedure. A literature survey of the methods available for the determination of sulphur has shown that interference often occurs, especially from the phosphate naturally present in many foods.
Four promising methods were selected for further study, i.e.,
1. Colorimetric method using barium chloranilate,
2. Titrimetric method using barium perchlorate and Thorin as indicator,
3. Turbidimetric method using Tween-80 to stabilize the barium sulphate precipitate.
4. Titration of hydrogen sulphide with mercuric acetate using dithizone: Sulphate is reduced and the hydrogen sulphide is swept into the titration vessel with nitrogen.
The difficulties encountered with each method, including interferences, have been investigated and the results are presented and discussed. The turbidimetric and ‘reduction’ methods are shown to be suitable for routine and precise determinations respectively, a number of foodstuffs have been analysed and the results obtained are discussed.