An on-line system employing switchable-hydrophilicity solvent-based liquid-phase microextraction (SHS-LPME) is described in this work. The method is based on the preconcentration of the species formed between cobalt and the reagent 1-nitroso-2-naphthol (NN), with subsequent detection by digital image colorimetry. The system's operation begins with the on-line mixture of sample, switchable solvent, and an alkaline agent in a reaction coil. Then the mixture is transported to an extraction chamber. The introduction of a proton donor leads to the passage of the solvent to its hydrophobic form, which allows phase separation. The rich phase is then directed to a glass tube, where detection is performed. Octanoic acid, sodium carbonate, and sulfuric acid were used as the extraction solvent, the alkaline agent, and the proton donor, respectively. Under optimized conditions, the method presented a detection limit of 0.8 μg L⁻¹ and an enrichment factor of 41. The precision obtained was 4.8% (20 μg L⁻¹). The accuracy of the method was tested by the analysis of Tomato Leaves certified reference material (NIST 1573a). The method was applied to the determination of cobalt in food, dietary supplements, and water samples. The method is presented as a green alternative and very accessible to the determination of cobalt in the analyzed samples.

A new bio-MSPE sorbent based on the use of C. micaceus and γ-Fe₂O₃ magnetic nanoparticle was prepared for the preconcentrations of Co(II) and Hg(II). Critical parameters including pH, flow rate, quantity of C. micaceus, quantity of γ-Fe₂O₃ magnetic nanoparticle, eluent (type, concentration and volume), sample volume, and foreign ions were examined. Surface structure and variations after interaction with Co(II) and Hg(II) of bio-MSPE sorbent were investigated by FT-IR, SEM, and EDX. The impact of bio-MSPE column reusage was also tested. The biosorption capacities were determined as 24.7 mg g⁻¹ and 26.2 mg g⁻¹, respectively for Co(II) and Hg(II). Certified reference materials were utilized to find out the accuracy of the prepared bio-MSPE method. This novel bio-MSPE method was accomplished by being applied to real food and water samples. In particular, it will be possible to make use of C. micaceus as new alternatives, in environmental biotechnology applications.

A new, efficient, and sensitive cloud point methodology was developed for preconcentration of trace quantities of cobalt and nickel in water and food samples prior to their determination by flame atomic absorption spectrometry (FAAS). The metals react with 2-(benzothiazolylazo)-4-nitrophenol (BTANP) at pH 7.0 and micelle-mediated extraction using the nonionic surfactant Triton X-114 medium. The surfactant-rich phase was diluted with acidified methanol and the cobalt and nickel content was determined by FAAS. The optimum conditions (e.g. pH, reagent and surfactant concentrations, temperature and centrifugation times) were evaluated and optimized. The proposed CPE method showed linear calibration within the ranges 5.0–100 and 5.0–150 ng mL⁻¹ of cobalt and nickel, respectively, and the limits of detection of the method was 1.4 and 1.0 ng mL⁻¹ of cobalt and nickel, respectively. The interference effect of some cations and anions was also studied. The method was applied to the determination of both metals in water and food samples with a recovery from the spiked water samples in the range of 95–102%. The validation of the procedure was carried out by analysis of a certified reference material.

A novel method based on ultrasound-assisted surfactant-enhanced emulsification microextraction (UASEME) has been developed for the preconcentration of cobalt prior to its determination by graphite furnace atomic absorption spectrometry. In the UASEME technique, chloroform was used as the extraction solvent, sodium dodecyl sulfate was adopted as emulsifier, and ultrasound was applied to assist emulsification. There is no need of using organic dispersive solvent which is typically required in conventional dispersive liquid–liquid microextraction method. Several parameters that affect the extraction efficiency, such as the kind and volume of the extraction solvent, the type and concentration of the surfactant, pH of sample solution, concentration of the chelating agent, and extraction time and temperature were investigated and optimized. Under the optimal conditions, the linearity of calibration curve was in the range of 0.1–5 ng mL⁻¹with a correlation coefficient (R²) of 0.9992. An enrichment factor of 58 was achieved with a sample volume of 5.0 mL. The detection limit of this method for Co was 15.6 ng L⁻¹, and the relative standard deviation (RSD) was 4.3 % at 1.0 ng mL⁻¹concentration level of Co. The accuracy of the developed method was evaluated by analysis of the certified reference materials GBW07605 tea leaf and GBW10015 spinach. The method was successfully applied to determine trace cobalt in food and water samples with satisfactory results.

In this research, a facile synthesis route was used for preparation of cobalt ferrite@SiO2@polyethyleneimine magnetic nanoparticles (Co-Fe2O4@PEI) as a new sorbent in the service of ultrasound assisted dispersive micro-solid phase extraction (UA-DMSPME) for influential clean-up, preconcentration, and determination of tartrazine (TA) prior to UV–Vis spectrophotometric detection. The understudy sorbent was fully characterized by transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), Energy dispersive X-ray analysis (EDX), and vibrating sample magnetometer (VSM). Different operating parameters which affected the extraction efficiency of TA viz. sorbent dosage, extraction time, pH, and volume of eluent were investigated and optimized by using central composite design (CCD). Under optimal conditions, the enrichment and preconcentration factor, limit of detection (LOD), quantification (LOQ), and precision were obtained 98.01, 66.67, 5.09, and 16.96 ng mL−1, and <5.5% respectively. Good linear response (20–4000 ng mL−1) over the tested concentration range was achieved with the value of R2 = 0.9977. Satisfactory recoveries (>99.5%) of TA in complicated samples including saffron spray, cotton candy and water samples were achieved. This superior validation implies high applicability of the purposed method in terms of it being simple, fast, effective, and accessible: all of these allow for accurate analysis at the trace level.

A new, simple, and rapid separation and preconcentration procedure, for determination of Pb(II), Cd(II), Zn(II), and Co(II) ions in environmental real samples, has been developed. The method is based on the combination of coprecipitation of analyte ions by the aid of the Mo(VI)–diethyldithiocarbamate–(Mo(VI)-DDTC) precipitate and flame atomic absorption spectrometric determinations. The effects of experimental conditions like pH of the aqueous solution, amounts of DDTC and Mo(VI), standing time, centrifugation rate and time, sample volume, etc. and also the influences of some foreign ions were investigated in detail on the quantitative recoveries of the analyte ions. The preconcentration factors were found to be 150 for Pb(II), Zn(II) and Co(II), and 200 for Cd(II) ions. The detection limits were in the range of 0.1–2.2 μg L⁻¹ while the relative standard deviations were found to be lower than 5 % for the studied analyte ions. The accuracy of the method was checked by spiked/recovery tests and the analysis of certified reference material (CRM TMDW-500 Drinking Water). The procedure was successfully applied to seawater and stream water as liquid samples and baby food and dried eggplant as solid samples in order to determine the levels of Pb(II), Cd(II), Zn(II), and Co(II) ions.

A new, sensitive, and simple combined method including ionic liquid (IL)-based dispersive liquid–liquid microextraction and partial least squares method (PLS) was developed for simultaneous preconcentration and determination of cobalt and nickel in water and food samples. In this work, a small amount of an IL 1-hexyl-3-methylimmidazolium bis (trifluormethylsulfonyl)imid ([Hmim][Tf₂N]) as an extraction solvent was dissolved in ethanol as a disperser solvent and then the binary solution was rapidly injected by a syringe into the water sample containing Co²⁺ and Ni²⁺, which were complexed by 1-(2-pyridylazo)-2-naphthol. After preconcentration, the absorbance of the extracted ions was measured in the wavelength range of 200–700 nm. The partial least squares method was then applied for simultaneous determination of each individual ion. The parameters controlling the behavior of the system were investigated and optimum conditions were selected. Eleven binary mixtures of cobalt and nickel were selected as the calibration set. The calibration models were validated with four synthetic mixtures containing the metal ions in different proportions, which were randomly designed. The best calibration model was obtained by using PLS-1 regression. Calibration graphs were linear in the range of 2.0–20.0 and 2.0–15.0 ng mL⁻¹ with a limit of detection of 0.65 and 0.32 ng mL⁻¹ for cobalt and nickel, respectively. The root mean square errors of prediction for cobalt and nickel were 0.4032 and 0.2980, respectively. Satisfactory results were reported for simultaneous determination of trace levels of cobalt and nickel in water, food, and geological certified reference material samples.