FAAS food: Flavour enhancement

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  • Published: Sep 15, 2012
  • Author: David Bradley
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Gel for heavy metal

Determination of Cd (II), Cu (II), and Pb (II) in Some Foods by FAAS after Preconcentration on Modified Silica Gels with Thiourea Thiobonded silica Credit: Wiley/Author 

A silica gel substrate modified with thiourea has enabled preconcentration of cadmium, copper and lead in food samples, according to research published in the Journal of Food Science.

Durali Mendil of Gaziosmanpasa University, in Tokat, Turkey, points out how metal pollution is a serious international problem. Contamination of the food supply with toxic heavy metals including cadmium, copper and lead represents an increasingly important part of this and so straightforward analytical techniques for the detection of even trace quantities of metals that can accumulate in our bodies are needed. Of course, several techniques exist for metal determination including inductively coupled plasma atomic emission spectrometry (ICP-AES), ICP mass spectrometry (ICP-MS), electro thermal AAS (ETAAS), and flame AAS (FAAS).

Two of the issues of concern for those hoping to determine metals in samples are commonly the need to preconcentrate very tiny quantities present in small volume samples. "Lower levels of analytes and high levels of matrices are the major problems for the measurement of metal ions," Mendil explains. He adds that solid-state extraction as a preconcentration approach has several advantages for preconcentration including high enrichment, high recovery, rapid separation, low cost, and low consumption of organic solvent. It is also amenable to various online and offline detection methods. Various researchers have experimented with active carbon, porous polymers, chelating resins, cellulose, chitin, as well as silica gel.

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Silica gel has a large specific surface, good porosity range, is tough and resistant to heat and acidic environments. Moreover, it is amenable to chemical functionalization. The modification of silica gel with the sulfur compound thiourea boosts the gel's affinity for heavy metals and make characterisation with infrared spectroscopy and C, H, N, S elemental analysis easier.. The silica gel acts as a solid-phase extractant and tests have demonstrated its utility with various types of food including tuna fish, black tea, rice, cheese, honey, tomato paste, and margarine. Mendil optimised the process for eluent type, sample pH and flow rates and obtained detection limits in the range of 0.81, 0.38 and 0.57 micrograms per litre, for the metals cadmium, copper and lead, respectively. Standard deviations were below 10 percent, he adds, while the approach compared very well with tests on standard reference materials.

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Article by David Bradley

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