What are the 2 different methods of titration to test Sulphur Dioxide in Wine?
The most common methods are probably the Ripper method (uses iodine)[Ripper, 1892] and the aeration oxidation (AO) method. The AO method, also called the Rankine method after Rankine [1962] or the Tanner method after Tanner [1963], is a modification of the Monier-Williams method. It involves the acidification of a sample, followed by the distillation of SO2 (with nitrogen sweeping gas or air aspiration) out of the sample into a peroxide solution. The SO2 and peroxide react to form H2SO4 according to the following equation: H2O2 + SO2 –> SO3 + H2O –> H2SO4 The acid formed is then titrated with NaOH to an end point, and the volume of NaOH required used to calculate the SO2 level. This method avoids the iodine-phenol binding which occurs in the Ripper method. However, it is not without its problems. The acidification of the solution causes a shift in the equilibrium between bisulphite and anthocyanins, and the SO2 bound anthocyanins (red wine pigments). This causes a freeing of some ant
