Abstract
Direct detecting of trace amount Al(III) in aqueous solution by stripping voltammetry is often frustrated by its irreversible reduction, resided at −1.75 V (vs. Ag/AgCl reference), which is in a proximal potential of proton reduction. Here, we described an electroanalytical approach, combined with liquid phase microextraction (LPME) using ionic liquid (IL), to quantitatively assess trace amount aluminum in environmental samples. The Al(III) was caged by 8-hydroxyquinoline, forming a superb hydrophobic metal–chelate, which sequentially transfers and concentrates in the bottom layer of IL-phase during LPME. The preconcentrated Al(III) was further analyzed by a square-wave anodic stripping voltammetry (SW-ASV). The resulting Al-deposited electrodes were characterized by scanning electron microscopy and powder X-ray diffraction, showing the intriguing amorphous nanostructures. The method developed provides a linear calibration ranging from 0.1 to 1.2 ng L−1 with a correlation coefficient of 0.9978. The LOD attains as low as 1 pmol L−1, which reaches the lowest report for Al(III) detection using electroanalytical techniques. The applicable methodology was implemented for monitoring Al(III) in commercial distilled water.
Highlights
Spectrometric techniques, such as atomic absorption spectrometry [1], inductively coupled plasma atomic emission spectrometry [2], fluorometry [3], and inductively coupled plasma–mass spectrometry (ICP-MS) [4], are widely applied in detecting metals in aqueous samples
The samples were obtained by diluting the stock standard sample with proper solvents. 1-octy-3-methylimidazolium hexafluorophosphate [C8 mim][PF6 ] (Chengjie Chemical Reagent Co., Shanghai, China) was employed as an extracting agent without further purification. 8-hydroxyquinoline was purchased from Merck (Darmstadt, Germany)
These results proved we were not over-valuating the sensitivity of the method by using ethanol to simulate water without Al(III) and the limit of detection (LOD) obtained is reasonable
Summary
Spectrometric techniques, such as atomic absorption spectrometry [1], inductively coupled plasma atomic emission spectrometry [2], fluorometry [3], and inductively coupled plasma–mass spectrometry (ICP-MS) [4], are widely applied in detecting metals in aqueous samples. Electroanalytical techniques offer important advantages, such as good sensitivity, high selectivity, cost-effective, easy for automation and suitable for portable devices [5,6]. In aqueous solutions, direct voltammetric determination of metal ions with high electronegativity, such as aluminum, potassium, sodium and barium, is limited due to the parallel hydrogen evolution reaction. Polarographic determination of Al(III) was achieved by reducing aluminum di-o-hydroxyazo complex [7].
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