Direct determination of sodium in soybean oil by flame photometry

The correlation of sodium content of alkalirefined soybean oil with the soap content of the oil has been widely accepted by oil processors. We have found that this sodium content can be determined by aspiration of an oil solvent solution directly into a flame emission spectrophotometer. The intensity of the sodium flame emission produced from the oil solution was compared with that from oil standards containing known amounts of sodium soaps. To prepare standards, sodium oleate was dissolved in ethylene glycol followed by the addition of a solvent and soybean oil containing low sodium of known amount; this solution aspirated at a rapid, constant rate. The method is capable of determining sodium at a lower limit of 0.1 ppm with accuracy comparable to that of neutron activation analysis.