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This work focused on the stability and performance of magnetite (Fe3O4) as a magnetic solid-phase extraction for trace analysis of phosphate in aqueous sample. Fe3O4 particle was synthesized by the chemical co-precipitation method and confirmed by FT-IR spectroscopy. The FT-IR spectrum of the synthesized Fe3O4 showed the characteristic peak in the region of 570-580 cm-1 corresponding to Fe-O vibration. Size distribution of Fe3O4 was measured by laser scattering technique. The results varied from 30.3±23.3 to 87.4±61.6 µm for 5 representative batches. The synthesized Fe3O4 was then tested its performance with our developed extraction method for phosphate analysis. Standard phosphate content of 1.2 µgP and 2 mg Fe3O4 was used as the test sample. Under acidic condition (pH 3.0), phosphate ion was adsorbed onto the surface of Fe3O4 for 15 min to reach maximum adsorption. Subsequently, desorption process occurs within 1 min only using 1.00 mL of 1.5 mol/L NaOH. The synthesized Fe3O4 performed adsorption capacity about 4.9±0.6 mgP/g. Moreover, the batch-to-batch consistency showed no significant extraction efficiency among them by statistical analysis with ANOVA test at 95 % confident level (Fstat 2.04 < Fcrit 3.48). The reproducible extraction was good with the average RSD of 4.2 % (n = 15) even though particle sizes were varied between batch-to-batch. In addition, the Fe3O4 can be reused at least 100 times by washing with acetate buffer pH 3.0 between samples. Under ambient temperature and dry storage condition, the Fe3O4 was effectively used at least 4 months without diminished extraction efficiency.
Keywords: magnetic particle; magnetite; stability and performance; extraction of phosphate
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