Abstract

Background: Cobalt is one of the most important essential trace metals of human nutrition. Low doses of cobalt are needed for many humans and animals to stay healthy. Cobalamine (named vitamin B12) is a cobalt-containing essential vitamin. The direct detection of metal ions in various matrices by AAS may be difficult due to matrix interferences and extremely low levels of metal ions. Thus, a preconcentration and separation step is normally demanded. In this report, a two-step microextraction technique, combining room temperature ionic liquid based dispersive liquid-liquid microextraction (ILDLLME) and dispersive magnetic solid-phase microextraction (MSPME) was prepared for the flame atomic absorption spectrometric determination (FAAS) of trace cobalt ions in water samples.

Methods: In this study, a two-step microextraction technique based on a new combined approach of ILDLLME/ M-SPME was discussed and the proposed method was applied to the rapid determination of trace cobalt ions in various water samples. In this study, room temperature IL-1-ethyl-2,3- dimethylimidazolium bis(trifluoromethyl sulfonyl)imide [EMIM][Tf2N] was employed as an extractant in the first extraction step (i.e. DLLME). This combined technique offers low limits of detection and high preconcentration factors resulting in high sensitivity. The reported method described an amazing and innovative approach of combining different microscope sample preparation methods to solve some analytical problems.

Results: In the first microextraction step, room temperature ionic liquid (RTIL) was employed to extract cobalt-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) complexes from aqueous solution with ultrasound. In the second step, magnetic Fe3O4 NPs was added as an adsorbent and employed to collect the analytes in the organic solvent. After magnetic solid phase separation, the concentrated analyte complexes were eluted with 0.1 M HCl. As a consequence, the linear working range was 0.1-250 µg/L, and the detection limit of the method (LOD) was estimated to be 0.05 µg/L. The proposed twostep extraction procedure was employed by analysis of a certified reference and real water samples.

Conclusion: In the current study, a simple two-step extraction method, namely ionic liquid DLLME combined with magnetic SPME was developed. The magnetic Citrate-Fe3O4 (Cit-Fe3O4) nanocomposite was synthesized and can be easily separated by a powerful magnet. In addition, this technique does not require clean-up steps and the magnetic sorbent material (i.e. after extraction, IL adsorbed onto the magnetic material) can often be easily regenerated and reused. This new extraction methodology offers various features such as sensitivity, cost-effective, easy to operate, short extraction time, low detection limit, and use less-toxic organic solvents. In fact, the preconcentration method was successfully applied for Co determination in water samples, with good accuracy and good reproducibility. The calibration graph of two-step microextraction method was linear in the range of 0.1-250 µg/L and the percent recovery of Co was in the range of 95-102%. This is an applicable method for cobalt trace assay in various types of matrices in order to diminish its hazardous effects on ecosystem and environment.

Keywords: Cobalt, liquid-liquid microextraction, magnetic solid phase microextraction, atomic spectroscopy, water analysis, (LOD).

Graphical Abstract