Abstract
A green analytical procedure exploiting cloud point extraction for determination of copper and iron in plant materials is presented. After sample digestion with a diluted oxidant mixture (HNO3 + H2O2) in a closed vessel microwave oven, metal ions were simultaneously extracted as hydrophobic complexes formed with 1,2-tiazolylazo-2-naphthol (TAN) using Triton X-114 as extracting agent. Copper and iron were determined by flame atomic absorption spectrometry (FAAS) and iron also by UV-Vis spectrophotometry. For FAAS, the detection limits (99.7% confidence level) were estimated as 1 and 10 μg L-1 for copper and iron, respectively. Linear responses for both analytes were observed in the 25-200 μg L-1 range. The enrichment factors were estimated as 30 for both analytes and the extraction was quantitative, as evaluated by measurements in the supernatant solution remaining after extraction. For iron determination by UV-Vis spectrophotometry, the detection limit was estimated as 1 μg L-1, with linear response within 6 and 60 μg L-1. The accuracy of the procedure was evaluated by determination of the metals in certified reference materials and the results agreed with the certified values at the 95% confidence level. In the whole procedure, the reagent consumption was 1 mL HNO3, 1.1 mL H2O2, 50 mg Triton X-114 and 150 μg TAN per determination.
Highlights
Copper and iron are important for plant nutrition, being classified as essential micronutrients and usually found in very low concentrations (2-50 and g-1, respectively).Iron and copper are essential for chlorophyll synthesis and copper is present in diverse enzymes, acting in the metabolism of carbohydrates.On the other hand, high concentrations of these species may be toxic to plants.[1]
The process results in a two-phase system: a surfactant-rich phase, which contains most of the surfactant and the extracted hydrophobic species and a phase containing a small amount of the surfactant, close to the critical micelle concentration.[9]
In view of its hydrophobic characteristics and reactivity with Cu(II) and Fe(II) ions, this reagent was selected for the cloud point extraction procedure.[22,23,24]
Summary
Copper and iron are important for plant nutrition, being classified as essential micronutrients and usually found in very low concentrations (2-50 and g-1 , respectively).Iron and copper are essential for chlorophyll synthesis and copper is present in diverse enzymes, acting in the metabolism of carbohydrates.On the other hand, high concentrations of these species may be toxic to plants.[1]. Vol 21, No 2, 2010 out from sample solutions obtained by time-consuming digestion procedures which consume large amounts of concentrated inorganic acids.[2] Depending on the analytical technique employed for analysis, extraction and preconcentration can be required in view of the low analyte concentrations and the need for elimination of matrix effects and interfering species. Alternative strategies, based on cloud point extraction, have been applied for separation and preconcentration of trace metals aiming determination in different sample matrices.[4,5,6] The analytes are extracted into micelles after reaction with a hydrophobic complexing agent in the presence of a surfactant above the critical micelle concentration (CMC).[7,8] In the process, aqueous solutions of non-ionic surfactants become turbid upon appropriate alteration of the physical-chemical conditions, usually by heating or introduction of suitable additives. Cloud point extraction shows environmentally friendly characteristics by the substitution of toxic solvents[6,10] by reduced amounts of low toxicity surfactants, in agreement with the green chemistry principles.[11,12]
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