Determination of the silicon content of food

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Abstract
The determination of silicon in biological material was investigated using solution absorption spectrometry (SAS) and atomic absorption spectrometry (AAS). Most analytical reagents and ion‐free waters contain enough silicon to cause high blanks, and require purification. Glassware and silica ware should not be used. Standard silica solutions do not polymerise in a week if the silicon concentration is below 100mg litre−1. Biological materials were dry‐ashed and then fused with pure sodium tetraborate before dissolution in dilute nitric acid. Phosphates interfere with SAS if the P:Si ratio exceeds 5:1 but can be removed by precipitation. They interfere somewhat less with AAS if the P:Si ratio exceeds 20:1. Borates, calcium, potassium and sodium do not interfere with AAS at ratios B:Si = 500:1, Ca:Si = 200:1, K:Si = 100:1, Na:Si = 1000:1. Determinations of silicon in foods by both methods agreed, and barley and oats were found to have a high silicon content. The average British diet is estimated to contain 31 mg silicon day−1.