Measurement of Calcium
and Potassium in Cereals 1

Commercial cereals vary considerably
in composition, both in their formulation and the ingredients added to enrich
these products.  

 

Sodium is the predominant cation in breakfast cereals, at levels reaching 8mg/g. Potassium and calcium also vary, particularly in wheat-based products and those enriched with milk products or calcium salts. 

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Procedure    

A representative sample of the cereal is ground thoroughly to obtain good homogenisation. 

 

The powder is stored in sealed plastic bags, under cool dry conditions. 
A representative sample of approximately 100g is prepared. The prepared samples are analysed in triplicate using a wet ash digestion. Calcium analyses are performed with the addition of 4% 8-hydroxyquinoline to serve as a protecting agent to prevent the formation of refractory species.     

 

Typically 5g samples are added to cleaned test tubes and 1ml of concentrated sub-boiling distilled nitric acid is added. The mixture is heated to 80°C overnight.    

 

The digest is treated with 1ml of 50% hydrogen peroxide, added dropwise and heated at 1000°C for several hours, repeating the process until sample digests are clear.    

 

Digest is heated overnight at 80°C and 1ml HCl is added and the digests are heated for 3-4 hours at 80°C.    

 

The digest is filtered using ashless filter paper (Whatman No.41) and diluted to a final volume of 15ml and stored in polyethylene bottles until analysed.