Solvent Techniques for the Direct Colorimetric Determination of Copper and Iron in Oils

Abstract

SUMMARY— The standard procedure for determining trace metals in biological materials requires the ashing of the sample to obtain an aqueous solution. Once this sample is prepared, numerous methods may be employed to determine the metal content. With oils the common ashing techniques lead to serious errors because of spattering, foaming, and volatilization of the sample. In the past, several methods have been developed to eliminate the ashing procedure but large samples (20–50 g) or special equipment was necessary. To allow use of very small oil samples (0.5–2 g) for determining iron and copper, solvent procedures which eliminated the ashing step were developed. The iron procedure is based on the standard aqueous 1,10‐o‐phenanthroline method modified to employ an initial solvent extraction procedure. Comparison of this method with the aqueous ash procedure on oils of known iron content showed the methods to be equivalent in precision. The solvent procedure is capable of determining 0.1 ppm of iron in the oil. The direct solvent copper procedure based on the sodium‐diethyldithiocarbamate aqueous method showed similar results. Because of the ease of performance and the small sample size required, these tests would be useful in food and biological research.

Determination of copper in edible soybean oils

“…Assaying for traces of copper in glyceride oils is difficult because this metal occurs m natural oils in extremely small amounts (8), usually at a few hundredth ppm. Direct extraction methods (2,13) have been proposed for copper determinations in petroleum oils, but they lack the sensitivity required for glyceride oils. Also, evidence exists that metals may occur in glyceride oils in a form not available for extraction by acids or chelating agents.…”

Determination of lead in frying oils by direct current plasma atomic emission spectrometry

“…The standard procedure for determining lead in oils requires asking of the sample to obtain an aqueous solution, followed by the analysis of the metal by spectrophotometry, atomic absorption spectrometry or other suitable techniqu~ With vegetable oils, the common asking techniques are time-consuming and may lead to serious errors due to losses from spattering, foaming and volatilization (1). Dry asking technique was used by Ybanez (2) for determination of Pb, Cd, Cu and Zn in animal fats by atomic absorption spectrometry.…”