A solid phase extraction method for determination of trace gallium in aluminum–iron samples by atomic spectrometry

Abstract

A solid phase extraction method based on strong acid cation exchange fiber (SACEF) as the sorbent and DTPA as the eluent has been established for atomic spectrometry determination of trace gallium in samples containing iron and aluminum. In pH = 2.5 hydrochloric acid medium, the equilibrium adsorption capacity of SACEF for Ga(III), Al(III), Fe(III) and Fe(II) is 119.3 mg g⁻¹, 23.22 mg g⁻¹, 63.34 mg g⁻¹ and 55.97 mg g⁻¹ respectively. Their equilibrium adsorption time is 25 min, 8 min, 5 min and 5 min respectively. Optimum adsorption conditions for separation of 0.500 μg Ga(III) from the solution containing 3.00 mg aluminum and 1.00 mg iron are as follows: pH of sample solution is 2.5, mass of SACEF is 0.100 g, the molar ratio of ascorbic acid to Fe(III) in the sample solution is 30 and adsorption time is 25 min at room temperature. The Ga(III) loaded on the fiber is eluted at 30 °C for 10 min by 0.004 mol L⁻¹ DTPA with pH 1.5. The method detection limit of gallium measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) is 3.9 × 10⁻³ mg L⁻¹ and is 1.9 × 10⁻³ mg L⁻¹ by graphite furnace atomic absorption spectrometry (GFAAS). The gallium in synthetic samples, metallic-aluminum, alumina and bauxite have been analyzed respectively by the method. For samples without or with less iron, both measured results of Ga by GFAAS and by ICP-AES are basically consistent. For samples containing high content iron such as bauxite, the measured values of Ga by GFAAS is lower than by ICP-AES. Recoveries of ICP-AES are 90.0% to 106%, RSDs (n = 6) are 1.0% to 5.5%. Recoveries of GFAAS are 88.2% to 105%, RSDs (n = 6) are 1.4% to 4.4%. The procedure has been validated by the analysis of three bauxite certified reference materials.