Char‐ashing of glyceride oils preliminary to the atomic absorption determination of their copper and iron contents

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Abstract
Trace amounts of copper and iron were determined by char‐ashing samples of molecularly distilled glyceride oil, copper hydrogenated edible oils and salad oils with added copper salts and copper‐chromite catalysts. Char‐ashing, coupled with the atomic absorption method of analysis, gave excellent reproducibility in a salad oil for copper at 0.025 ± 0.002 ppm and for iron at 0.082 ± 0.012 ppm. Agreement was excellent between the char‐ashing method and the direct solvent method of analysis when levels of the two trace metals were high enough to be analyzed by direct atomic absorption. Copper in edible oils can be accurately analyzed at levels of less than 10 ppb by the char‐ashing technique.