Measurement of Calcium and Potassium in Cereals

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.

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.