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Determination of Micro Amounts of Fe (II) and Fe (III) in Tea and Rice Samples by Cloud Point Extraction-Spectrophotometry using a New Chelating Agent

Zianab T. Ibrahim, Zuhair A-A Khammas and Khalid J. Khadhim

A new chelating agent namely, 2-[2-(5-nitro thiazolyl) azo]-8 hydroxyquinoline (5-NTA8HQ), was synthesized, characterized and used for the determ ination of iron species in rice and black tea samples by combination of cloud point extraction method and spectrophotmetric techniques. The method involved a selective hydrophobic complex formation between iron (II) and 5-NTA8HQ at pH 5, which can efficiently be extracted in surfactan t-rich phase of Triton X-114 and determined sepectrophotometrically at λ max 650 nm. Also, Iron (III) can selectively form a chelate with 5-NTA8HQ at pH 6 and extracted with Triton X-114 but with less sensitivity than with Fe(II) counterpart. Thus, this limitation is treated via the reduction of Fe(III) to Fe(II) with ascorbic acid and the amount of Fe(III) in samples is found by subtraction. All significant factors for both Fe(II) and Fe(III) species that influence the separation and determination steps were investigated in detail by one factor-at-a-time (OFAT) optimization. At optimum conditions, the enrichment factors of 126 and 52 fold were obtained for Fe(II) and Fe(III) ions respectively, leading to detection limits of 0.35 ng Fe(II) mL -1 and 3.96 ng Fe(III) mL -1 in aqueous solution. The linear dynamic range, relative standard deviation (n = 7 at 10 ng Fe(II) mL -1 and 30 ng Fe(III) mL -1 ), and the recoveries by the standard addi tions method were of 0.5-50 ng mL -1 and 10-150 ng mL -1 , 0.54% and 1.58%, 98.3 ± 2.9 and 98.5 ± 1.26 for Fe(II) and Fe(III) ions, respectiv ely. The described method is sensitive, easy to apply and has a slight interference; thereby, th e determination of iron speci es in rice and black tea samples were performed.