Abstract
BackgroundDirect determination of metal ions, in particular at ultra-trace concentration, cannot be easily achieved in complex systems by analytical techniques because of the lack of sensitivity and selectivity of these methods. Therefore, an efficient separation step is often required prior to the determination of metal ions for sensitive, accurate, and interference-free determination of metal ions. In accordance, a new solid phase extractor based on silica gel functionalized with ionic liquid (SG-N-PhenacylPyrNTf2) was developed for a selective separation of La(III) prior to its determination by inductively coupled plasma-optical emission spectrometry.MethodsImmobilization of the ionic liquid on activated silica gel surface was confirmed by both Fourier transform infrared spectroscopy and scanning electron microscope. The concentration of ionic liquid on the surface of activated silica gel was determined based on thermal desorption method. The uptake behavior of the new SG-N-PhenacylPyrNTf2 adsorbent toward metal ions was studied under static conditions by batch mode. The supernatant concentrations of metal ions were directly determined after filtration by inductively coupled plasma-optical emission spectrometry.ResultsFourier transform infrared spectroscopy and scanning electron microscopy results strongly confirmed the formation of SG-N-PhenacylPyrNTf2 phase. Adsorption isotherm study revealed the preference of SG-N-PhenacylPyrNTf2 over activated silica gel for a selective separation of La(III) prior to its determination by inductively coupled plasma-optical emission spectrometry. Adsorption isotherm data were well fit the Langmuir adsorption model with a maximum adsorption capacity of 165.39 mg g−1 for La(III), which was consistent with that (167.08 mg g−1) experimentally obtained from adsorption isotherm study. Kinetic study demonstrated that the adsorption of La(III) on the SG-N-PhenacylPyrNTf2 phase followed the pseudo second-order kinetic model.ConclusionsUltimately, the developed method can be applied and effectively utilized for the determination of La(III) in natural water samples with acceptable and reliable results.
Highlights
Direct determination of metal ions, in particular at ultra-trace concentration, cannot be achieved in complex systems by analytical techniques because of the lack of sensitivity and selectivity of these methods
The ICP-OES spectrometer was used with the following parameters: FR power, 1,300 kW; frequency, 27.12 MHz; demountable quartz torch, Ar/Ar/Ar; plasma gas (Ar) flow, 15.0 L min−1; auxiliary gas (Ar) flow, 0.2 L min−1; nebulizer gas (Ar) flow, 0.8 L min−1; nebulizer pressure, 2.4 bar; glass spray chamber according to Scott (Ryton), sample pump flow rate, 1.5 mL min−1; integration time, 3 s; replicates, 3; and wavelength range of monochromator 165 to 460 nm
In order to evaluate the effect of pH on the adsorption of Silica gel (SG)-N-PhenacylPyrNTf2 toward Co(II), Fe(II), Fe(III), La(III), and Ni(II), pH values of the sample solution were studied in the range of 1.0 to 9.0 for all metal ions, except with Fe(II) and Fe(III) whose pH values were investigated in the range 1.0 to 4.0 in order to avoid any precipitation with buffer solutions at a pH value higher than 4.0
Summary
Direct determination of metal ions, in particular at ultra-trace concentration, cannot be achieved in complex systems by analytical techniques because of the lack of sensitivity and selectivity of these methods. The most convenient way to overcome these problems is to apply selective extraction techniques, when they exist at ultra-trace concentration level in complex matrix (Zang et al 2010). Solid-phase extraction (SPE) has been widely used as a separation tool for the speciation of metal ions in environmental samples and has received much attention because of its advantages, such as absence of emulsion, high enrichment factor, disposal cost due to low consumption of reagent, and more importantly environment-friendly (Aydin and Soylak 2007; Simpson 2000). Different surface modification methods have been applied to classical SPE adsorbents (such as silica (Shin and Choi 2009) and polymer (Qiao et al 2012)) in order to increase the selectivity
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