Medical brain notes 14

  INTRODUCTION In oxidation-reduction methods bromine is employed as an oxidizing agent in place of iodine, because it is reduced quantitatively be the readily oxidized pharmaceutical organic substances in a reaction which results in either water-insoluble bromine substitution products, for instance : or corresponding water-insoluble bromine-addition products, such as : However, the standard solution used does not have bromine (Br 2 ) as such but it does contain an equivalent amount of potassium bromate and an excess of potassium bromide and the resulting mixture on subsequent acidification liberates bromine. The reaction may be expressed as follows : The liberated bromine helps in oxidizing iodide to an equivalent amount of iodine as shown below : The free iodine thus produced is titrated with previously standardized sodium thiosulphate solution as depicted below :   THEORY In oxidation-reduction assays the use of bromine is judiciously carried out as an oxidizing agent effec...

  ASSAY METHODS Assay methods based on bromine may be classified under the following  three  heads, namely :   ( i ) Titrations with 0.1 N Bromine,   ( ii ) Titrations with Potassium Bromate, and   ( iii ) Titrations with Potassium Iodate.     1. TITRATIONS WITH 0.1 N BROMINE   This involves the preparation of 0.1 N bromine solution and subsequent standardization with 0.1 N sodium thiosulphate solution. Bromine solution is also known as Koppeschaar’s Solution in some literature.   1.1. Preparation of 0.1 N Bromine Solution   Materials Required :  Potassium bromate : 3.0 g ; potassium bromide : 15 g.   Procedure :  Weigh 3 g of potassium bromate and 15 g of potassium bromide in a beaker and dissolve   with water. Transfer it quantitatively into a 1 litre volumetric flask and make up the volume with DW.     1.2. Standardization of 0.1 N Bromine with 0.1 N Sodium Thiosulphate Solution   Materials Requ...