Magnetic solid phase extraction of cadmium and lead from water prior to FAAS determination: Which is better? Sorbent modification with organic acids or adding organic acids to the extraction medium

Abstract

The purpose of the present work was to compare two protocols for magnetic solid phase extraction (MSPE) of cadmium (Cd(II)) and lead (Pb(II)) from aqueous medium prior to their determination by flame atomic absorption spectroscopy (FAAS). The first protocol (organic acid modification protocol) involved magnetite (Mag) and magnetic carbon nanotube (MCNT) modified by citric acid (cit), aspartic acid (asp) and ascorbic acid (asc). The magnetic adsorbents (MCNT, Mag, cit-MCNT, asp-MCNT, asc-MCNT, cit-Mag, asp-Mag, asc-Mag) were characterized using FTIR. Among all of the modified magnetic sorbents, cit-MCNT and asp-MCNT could be used for simultaneous extraction of metals at pH 8.2. The second protocol (organic acid addition protocol) involved Mag and MCNT in which citric acid, aspartic acid and ascorbic acid were added into the extraction medium. It was found that addition of any of the organic acids to the extraction medium reduced the performance of Mag towards Cd(II) but slightly improved its performance towards Pb(II). Addition of citric acid to the extraction medium using MCNT as extractant has a negative influence on Pb(II) extraction but has no influence on Cd(II) extraction. It was recommended to follow the first protocol using cit-MCNT as extractant. The optimum MSPE-FAAS method was achieved at pH 8.2 using 0.050 g cit-MCNT, shaking for 30 min, elution with 10 mL of 0.3 M HNO3. The figures of merit of the method were estimated. Application on real water samples gave the following spiked recovery (Cd(II) and Pb(II), respectively): tap water 73.3 ± 3.1 and 79.4 ± 6.9%; well water 72.2 ± 3.7 and 81.8 ± 3.4%.