Vegging out: Metals in oils by FAAS

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  • Published: May 15, 2015
  • Author: David Bradley
  • Channels: Atomic
thumbnail image: Vegging out: Metals in oils by FAAS


Multivariate optimization of ultrasound-assisted extraction for determination of Cu, Fe, Ni and Zn in vegetable oils by high-resolution continuum source atomic absorption spectrometry

Optimised ultrasound-assisted liquid-liquid extraction of copper, iron, nickel and zinc from samples of edible vegetable oils facilitates analysis with high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS) analysis.

Chemists Alex Trindade, Alailson Dantas, Sérgio Ferreira and Leonardo Teixeira of Universidade Federal da Bahia, and Daniel Lima of Universidade Estadual de Santa Cruz, both in Bahia, Brazil, point out that vegetables oils are widely used the world over in domestic cooking and across the food industry. They are also used extensively in the cosmetic, pharmaceutical and chemical industries and in the growing area of biofuels. Commonly, vegetable oils are made from extracts of the seeds of cereals and legumes, including soybean, sunflower, canola, peanut and cotton; they can also be extracted from fruits, such as palm and olive.


In terms of nutrition, vegetable oils are important carriers of lipophilic vitamins, such as A, D, E and K. They are also associated with the satiety response and moderate use in the diet has been linked to reduced risk of cardiovascular disease, brain health and other indications. The presence of metal ions in vegetable oils is also of importance from the nutritional point of view, the team reports. Indeed, it is on this latter aspect that they focus in research published online recently in the journal of Food Chemistry.

Copper, iron, nickel, zinc ions are known to be present at low concentrations in vegetable oils. However, the presence of such elements also leads to a shorter shelf-life for the oil product as the ions can catalyse oxidation and degradation reactions. This can lead to impaired taste and reduce the other health benefits of the oil. There may also be present in vegetable oils, depending on source, specifically toxic metal ions that would not be desirable in a food product, such as cadmium and lead. After, all, the metal ions present are there because they have been absorbed by the crop from the soil in which it grows, fertilizers used to promote growth and the proximity of roads or industrial sites. Contaminants may also be introduced into a vegetable oil product during production, processing, transportation or storage.

"The determination of the metal content is an important criterion for assessing the quality of vegetable oils and constitutes an analytical challenge due to the high complexity of the matrix and the low levels of these analytes," the team asserts.

Not so acidic

The researchers point out that atomic spectrometric techniques have in the past been used to test vegetable oils for the presence of various metal ions. Sample preparation is critical to the accuracy of the results. Pre-treatment procedures might include ashing, complete acid digestion, emulsification, solvent dilution, liquid–liquid extraction and other approaches. Each approach has its pros and cons.

As such, the team has now used chemometric techniques to perform a multivariate optimization of another approach - ultrasound-assisted liquid–liquid extraction. They hoped to find a single condition that would allow them to subsequently determine concentrations of Cu, Fe, Ni and Zn in edible vegetable oil samples using high-resolution continuum source flame atomic absorption spectrometry (HR-CS FAAS).

Indeed, they found that their multivariate optimization allowed them to find the best amplitude, cycle and time of sonication for improving extraction efficiency of metal ion analytes. They point out that ultrasound is "a good alternative for the determination of metals in vegetable oils without the use of a time-consuming sample treatment and without the use of concentrated acids."

Related Links

Food Chem 2015, 185, 145-150: "Multivariate optimization of ultrasound-assisted extraction for determination of Cu, Fe, Ni and Zn in vegetable oils by high-resolution continuum source atomic absorption spectrometry"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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