In situ-produced CO2-assisted dispersive liquid–liquid microextraction for extraction and preconcentration of cobalt, nickel, and copper ions from aqueous samples followed by graphite furnace atomic absorption spectrometry determination

Determination of Ultra-Trace Amounts of Copper in Environmental Water Samples by Dispersive Liquid-Liquid Microextraction Combined with Graphite Furnace Atomic Absorption Spectrometry

A new method of dispersive liquid-liquid microextraction (DLLME) combined with graphite furnace atomic absorption spectrometry (GFAAS) was proposed for the determination of ultra-trace copper. It was based on the reaction of Cu(II) with the laboratory-prepared chelating agent 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA) in a HAc-NaAc buffer solution at pH 5.0 to form stable hydrophobic chelates, which were separated and enriched by DLLME with chlorobenzene (C6H5Cl) and acetonitrile (CH3CN) as extraction and disperser solvents, respectively. The sedimented phase containing the chelates was then determined with GFAAS. Various operating variables that may be affected by the extraction process such as the pH of the solution, the concentration of the chelating agent 5-Br-PADMA, the types and volumes of extraction and disperser solvents, the extraction time, and the centrifugation time were investigated. Under optimum conditions, the calibration curve was linear in the range from 0.02 ng/mL to 0.16 ng/mL of copper with a correlation coefficient of r = 0.9961, and the detection limit was 0.01 ng/mL based on 3Sb. The relative standard deviation for six replicate measurements of 0.05 ng /mL of copper was 3.9%. An enrichment factor (EF) of 110 was obtained. The method has the advantages of low detection limit, high sensitivity, simple operation, less consumption of organic solvents, higher enrichment factor, and environmental friendliness and was applied to the determination of trace copper in environmental water samples with satisfactory results.

Surface-Active Ionic Liquid-Assisted Cloud Point Extraction for Pre-Concentration and Determination of Cobalt Ions in Pharmaceutical Preparations

: Herein we describe an efficient, simple, and precise micelle-mediated microextraction strategy based on the aggregation behavior of surface-active ionic liquids (SAILs) for the preconcentration and determination of cobalt ions in pharmaceutical preparations. Unlike the commonly used hydrophobic ionic liquids in IL-based microextraction methods, a water-soluble surface-active ionic liquid [1-hexadecyl 3-methylimidazolium chloride (C16MeImCl)] was used. A modified cloud point extraction (CPE) procedure based on the C16MeImCl-Triton X-114 mixed micellar system was proposed as an efficient extracting phase. A comparison of the analytical features of the extraction process with and without SAILs revealed the benefits of the proposed method. Advantages such as a wider linear range, lower detection limit, higher reproducibility, and improved extraction efficiency highlighted the proposed method over the conventional CPE method. These attractive specifications are due to the higher extraction efficiencies achieved in the presence of the SAIL and its favorable effects at the phase separation stage. Various parameters affecting the extraction efficiency were optimized by univariate and multivariate (Box-Behnken design) approaches. The calibration curve was obtained in the optimal experimental conditions with a linear range from 0.01 to 5.5 mg L-1 of cobalt ion concentration (R = 0.9992) and a detection limit of about 0.005 mg L-1. The RSD% for 10 replicate determinations of 1.0 mg L-1 Co was 0.9%. The proposed method was successfully applied to determine cobalt ions in vitamin B12 ampoules and tablets.

Determination of Ultra-Trace Cobalt in Water Samples Using Dispersive Liquid-Liquid Microextraction Followed by Graphite Furnace Atomic Absorption Spectrometry

A novel method for the determination of ultra-trace cobalt by dispersive liquid–liquid microextraction (DLLME) coupled with graphite furnace atomic absorption spectrometry has been developed. It is based on the color reaction of Co²⁺ with 2-(5-bromo-2-pyridylazo)-5-dimethylaminoaniline (5-Br-PADMA) in a Britton–Robinson buffer solution at pH 6.0 to form stable hydrophobic chelates, which were separated and enriched by DLLME with 1,2-dichloroethane (CH₂ClCH₂Cl) as extraction and acetonitrile (CH₃CN) as a dispersive solvent. The sedimented phase containing the chelates is then determined with GFAAS. Parameters that affect extraction efficiency, such as types and volumes of extraction and disperser solvents, pH of sample solution, extraction time, concentration of the chelating agent 5-Br-PADMA, and salt effect, were investigated. Under optimal conditions, the calibration graph was linear over the range 0.05–1.0 ng/mL, with a correlation coefficient of 0.9922 and a detection limit of 0.03 ng/mL. Preconcentration factor (PF) is calculated as the ratio of the aqueous solution volume (5 mL) to that of the organic phase volume (40 μL), and enrichment factor (EF) is calculated as the ratio of the slopes of the calibration graphs obtained with and without DLLME for 5.0 mL of sample solution, which were 120 and 112.5, respectively. The extraction efficiency, calculated by EF/PF·100, was 93.8%. The relative standard deviation (RSD) at the 0.5 ng/mL Co²⁺ level was 3.8% (n = 6). The method has been applied to the determination of trace cobalt in water samples with satisfactory results.

Ionic hydrophobic deep eutectic solvents in developing air-assisted liquid-phase microextraction based on experimental design: Application to flame atomic absorption spectrometry determination of cobalt in liquid and solid samples

This paper reports a new and simple microextraction procedure for cobalt determination using green ionic hydrophobic deep eutectic solvent in developing air-assisted liquid-phase microextraction and flame atomic absorption spectrometry. Thecomplexationof Co(II) ions was carried out by using dithizone solution as complexing agent at pH5.The key variables affecting microextraction steps were optimized by response surface methodology (RSM) based on central composite design. Under the optimum microextraction conditions, calibration graph was linear in the range of 0.1-500 µg L^-1 Co(II) with correlation coefficient of 0.9985. Additionally, detection limit, quantitation limit and enrichment factor were found to be 0.04 µg L^-1, 0.1 µg L^-1 and 175, respectively. The reproducibility and repeatability were ≤ 2.9% and ≤ 3.6%, respectively. Based on the results obtained, the proposed methodology has been successfully employed for Co analysis in liquid and solid samples with recovery range of 94.2-105%.

Determination of Vitamin B12 and cobalt in egg yolk using vortex assisted switchable solvent based liquid phase microextraction prior to slotted quartz tube flame atomic absorption spectrometry

A switchable solvent based liquid phase microextraction (SS-LPME) has been proposed for the determination of cobalt in egg yolk and Vitamin B12 at trace levels. N,N-Dimethylbenzylamide (DMBA) was used as a switchable solvent and converted to protonated DMBA form by the addition of dry ice. Cobalt was complexed with 1,5-diphenylcarbazone (DPC) and extracted into the DMBA phase. After the extraction, HNO₃ was added to increase nebulization efficiency of the DMBA phase. Slotted quartz tube (SQT) was combined with FAAS to enhance the detection power of the system when compared to the conventional FAAS. Under the optimum conditions, limit of detection values were recorded as 75 µg L^-1 for FAAS, 33 µg L^-1 for SQT-FAAS, 7.6 µg L^-1 for SS-LPME-FAAS, and 2.3 µg L^-1 for SS-LPME-SQT-FAAS. The developed method was applied for the determination of cobalt in egg yolk and Vitamin B12 and the recovery results were found in the range of 105-114% with 0.30-7.6 standard deviation values (n = 3).