Mercury(II) sulphate solution 80 g/l, 1 l

Determination of chemical oxygen demand (COD)

COD (chemical oxygen demand) is a measure of all the oxidisable components in water under specific conditions. The water sample is mixed with sulphuric acid and heated together with a defined quantity of potassium dichromate, with silver sulphate added as the catalyst. Chloride must be removed beforehand or masked with mercury sulphate. The remaining potassium dichromate is measured by means of titration, using an ammonium iron(II) sulphate solution and ferroin as the indicator. The equivalent amount of oxygen can then be calculated from the amount of potassium dichromate that is used up.

A volumetric standard solution is a solution containing a precisely known concentration of a substance. The concentration of a volumetric standard solution is determined using a primary standard, which is accurately weighed and dissolved to make a specific volume. Volumetric standard solutions are made using reagent-grade (p.a.) substances as source materials.

The advantages of this over making them yourself are:

• Manufactured and tested using modern manufacturing and analytical methods
• Ready-to-use solutions
• High accuracy for precise analyses
• Application of NIST-certified reference substances for checking
• Connection to standard titrators is possible