By a collaborative study, a standard method was established for determining copper, iron, and nickel in vegetable oils by graphite furnace atomic absorption spectrophotometry.
One gram of sample was dissolved in 10 mL of isobutyl methyl ketone containing a small amount of nitric acid followed by injecting a 10 or 20, μL aliquot of the solution directly into a graphite furnace for atomization according to a heating program. Atomic absorption signals were measured by a peak height or absorbance mode. Metal content was determined from a calibration curve.
This study was conducted at seven laboratories, using various types of equipment and analytical conditions.
The data obtained using soybean oil and hydrogenated soybean oil, added with metals at 0.6 ppm, were statistically analyzed. The coefficients of variation were approximately 5% for copper, 18% for iron, and 10% for nickel, respectively.
This method is simple and rapid. It will prove useful for the analysis of metals in vegetable oils.