Chen, M-J, et al., Flame photometrica determination of salinity in processed foods’, Food Chemistry, 91 (2005) p. 765-770.
Sodium chloride is an essential ingredient of all processed foods; it is needed to enhance flavour and increase shelf life.
In many processed foods, additional sodium is added as a flavour enhancer; potassium and calcium are also naturally present but not normally used as processing additives.
The optimum linear range for sodium measurement is within the range of 5 to 20ppm.
Dilution of food samples to fall within this concentration range also causes the concentration of normally occurring levels of potassium and calcium to fall below an interfering threshold.
High levels of calcium fortification should not interfere with sodium measurement (equivalent to 10g calcium per 100g of starting material).
However, relatively high levels of potassium could interfere with the measurement of sodium.
Procedure
Samples of both plant and animal origin can be analysed; in cases where packing liquid and solid matter are packed together, the entire contents are homogenised.
A 10g portion of the slurry is sampled and mixed with deionised double distilled water (40ml) and centrifuged (15,000g, 40C, 10 min).
The supernatant was diluted and used for analysis.
The resulting solution should be stored in polyethylene bottles prior to analysis. n.b. The bottles should be washed thoroughly and bathed in 5% HNO3 and rinsed twice with double distilled water prior to use.
Preparation of Standard Graph
Set the flame photometer in accordance to MultiPoint/Single Ion Calibration found on page 24 of the BWB Technologies Installation and Operation Manual, to measure potassium emission. Nebulise the working standard solutions and adjust the controls until steady zero and maximum readings are obtained. Nebulise the intermediate working standard solutions and construct a graph relating raw emission data (known as RAW in BWB the flame photometer) to concentration of all the standard solutions.