Isolation and preconcentration of Cd(II) from environmental samples using polypropylene porous membrane in a hollow fiber renewal liquid membrane extraction procedure and determination by FAAS

A Green Method for the Determination of Cadmium in Natural Waters Based on Multi-Fibre Supported Liquid Membranes

Supported liquid membranes have been used to implement a hollow fibre liquid-phase microextraction (HF-LPME) method for the preconcentration of Cd(II) in natural waters as a sample preparation step for its determination by high-resolution continuum source graphite furnace atomic absorption spectrometry (HR-CS-GFAAS). This system was designed to use four hollow fibres simultaneously with the same sample, thus improving the simplicity, speed and reproducibility of the results. The organic liquid membrane bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex^® 272) dissolved in dihexylether (DHE) was immobilised into the pores of the walls of polypropylene hollow fibres. After extraction, the cadmium-enriched acidic phases were recovered and analysed by triplicate. To optimise the extraction process, the effect of both physical and chemical variables was studied, and optimum results with an enrichment factor (EF) of 292 were obtained for a fibre length of 6 cm, 1.06 M Cyanex 272, 0.04 M HNO₃, stirring rate of 600 rpm and an extraction time of 4.26 h. For practical applications, extraction time was reduced to 2 h, keeping the EF as high as 130. Under these conditions, a detection limit of 0.13 ng L^-1 Cd(II) was obtained, with a reproducibility of 3.3 % and a linear range up to 3 µg L^-1 being achieved. The proposed method was successfully applied to the determination of cadmium in mineral, tap and seawater samples.

Comparison Studies on Several Ligands Used in Determination of Cd(II) in Rice by Flame Atomic Absorption Spectrometry after Ultrasound-Assisted Dispersive Liquid-Liquid Microextraction

Ligands plays an important role in the extraction procedures for the determination of cadmium in rice samples by using flame atomic absorption spectrometry (FAAS). In the present study, comparative evaluation of 10 commercially available ligands for formation of Cd(II)-ligand complex and determination of cadmium in rice samples by ultrasound-assisted dispersive liquid–liquid microextraction (UADLLME) combined with FAAS was developed. Sodium diethyldithiocarbamate (DDTC) provided a high distribution coefficient as well as a good absorbance signal, therefore DDTC was used as a ligand in UADLLME. A low density and less toxic solvent, 1-heptanol, was used as the extraction solvent and ethanol was used as the disperser solvent. In addition, the experimental conditions of UADLLME were optimized in standard solution first and then applied in rice, such as the type and volume of extractant and dispersant, pH, extraction time, and temperature. Under the optimal experimental conditions, the detection limit (3σ) was 0.69 μg/L for Cd(II). The proposed method was applied for the determination of Cd(II) in three different rice samples (polished rice, brown rice, and glutinous rice), the recovery test was carried out, and the results ranged between 96.7 to 113.6%. The proposed method has the advantages of simplicity, low cost, and accurate and was successfully applied to analyze Cd(II) in rice.

Synthesize of silver-nanoparticles by plant extract and its application for preconcentration of cadmium followed by flame atomic absorption spectrometry

In this paper, Mentha pulegium leaves extract was used as a green reducing agent for the synthesis of silver-nanoparticles. The synthesized silver-nanoparticles were characterized by UV-VIS spectrophotometry, transmission electron microscopy, X-ray spectroscopy and used as an adsorbent for preconcentration of trace levels of cadmium (ІІ). After the desorption of cadmium (ІІ) in 5 mol L^-1 formic acid, the desorbent solution was aspirated into the flame atomic absorption spectrometry for the determination of cadmium. In order to optimize the experimental condition, a response surface methodology based on central composite design was used. The optimum conditions are: pH: 8.6, amounts of adsorbent: 30 mg, 10 min extraction time and desorption time of 2 min. Under the optimum condition, the calibration curve was linear in the range of 5-200 μg L^-1 cadmium (ІІ) ion with a correlation coefficient of 0.9995. The limit of detection was 1.1 μg L^-1 and the relative standard deviation for 25 μg L^-1 cadmium (ІІ) ion was 3.0% (n = 5). In order to check the applicability of the proposed method, different real samples were analyzed. Also, the accuracy of this method was successfully checked by the analysis of certified reference material and spike tests.

Performance evaluation of hollow fiber renewal liquid membrane for extraction of uranium(VI) from acidic sulfate solution

The performance of the hollow fiber renewal liquid membrane (HFRLM) in the continuous and recycling modes for the extraction of uranium(VI) from the acidic sulfate solution has been investigated. Alamine 336 diluted in kerosene was used as a carrier in liquid membrane (LM) phase. In the batch experiments, the effects of sulfuric acid, extractant and uranium(VI) concentration were studied and the optimum concentration of the donor and LM phases were determined 0.15 mol L−1and 0.0125 mol L−1, respectively. Various parameters affecting the HFRLM performance including the lumen and shell side flow rate, organic/aqueous volume ratio, acceptor phase type and concentration of carrier and acceptor phase were studied. The mass transfer flux increases with increasing the lumen side flow rates and the shell side flow rate did not have any significant effect. The uranium transfer flux increases with increasing O/A ratio, acceptor and Alamine 336 concentration, and reaches a maximum value at 1/20, 0.5 mol L−1and 0.0125 mol L−1, respectively. Further increase in these parameters result in uranium transfer decrement. The results show that liquid membrane phase is a rate-controlling step. Among the investigated acceptor phases, 0.5 mol L−1NH4Cl result in 60.35% uranium(VI) recovery in the recycling mode.

Ionic liquid solvent bar micro-extraction of CdCln(n-2)- species for ultra-trace Cd determination in seawater

Water analysis of trace metals has been benefited by recent studies on sample preparation by liquid micro-extraction. However, there are still limitations for its application to seawater, such as the need of additives to preserve the sample or the availability of chemical extractants for the selective extraction from highly saline samples. In this work, a three phase solvent bar micro-extraction (3SBME) system containing the ionic liquid trioctylmethylammonium chloride (Aliquat^® 336) has been used for isolation and pre-concentration of Cd from seawater samples, due to its ability for ionic exchange of CdCl_n^(n-2)-. The system was optimized to work at the natural pH of seawater, and conditions for application to real samples were 0.18 M Aliquat^® 336 dissolved in kerosene with 0.25 M dodecan-1-ol as organic solution, 1.5 M HNO₃ as acceptor solution, 60 min extraction time, and 800 rpm stirring speed in the sample. Loss of organic solution into the sample during extraction was evaluated and revealed its dependence on stirring rate and extraction time. Under optimum conditions samples containing Cd 0.09-0.90 nM were pre-concentrated 65 times. GF-AAS was used for metal quantification with a limit of detection of 0.04 nM. Accuracy was successfully evaluated measuring Cd in a seawater certified reference material BCR-403.

Methods of liquid phase microextraction for the determination of cadmium in environmental samples

Liquid phase microextraction (LPME) has been widely used in extraction and preconcentration systems as an excellent alternative to conventional liquid phase extraction. In this work, a critical review is presented on liquid phase microextraction techniques used in the determination of cadmium in environmental samples. LPME techniques are classified into three main groups: single-drop liquid phase microextraction (SDME), hollow fiber liquid phase microextraction (HF-LPME), and dispersive liquid-liquid microextraction (DLLME). Methods involving these liquid phase microextraction techniques are described, addressing advantages and disadvantages, samples, figures of merit, and trends.

Vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction with solidification of floating organic droplet combined with flame atomic absorption spectrometry for the fast determination of cadmium in water samples

A novel vortex-assisted surfactant-enhanced-emulsification liquid-liquid microextraction with solidification of floating organic droplet (VSLLME-SFO) was developed for the fast, simple and efficient determination of cadmium (Cd) in water samples followed by flame atomic absorption spectrometry (FAAS). In the VSLLME-SFO process, the addition of surfactant (as an emulsifier), could enhance the mass transfer from the aqueous solution into the extraction solvent. The extraction solvent could be dispersed into the aqueous phase under vigorous shaking with the vortex. In this paper, we investigated the influences of analytical parameters, including pH, extraction solvent type and its volume, surfactant type and its volume, concentration of chelating agent, salt effect and vortex time, on the extraction efficiency of Cd. Under the optimized conditions, the limit of detection was 0.16 μg/L. The analyte enrichment factor was 37.68. The relative standard deviation was 3.2% (10 μg/L, n = 10) and the calibration graph was linear, ranging from 0.5 to 30 μg/L. The proposed method was successfully applied for the analysis of ultra-trace Cd in river water and wastewater samples.

Spectroscopic and Thermogravimetric Investigation of Cd(II) Dinonyldithiophosphate: Removal of Cadmium from Aqueous Solutions

Dinonyldithiophosphoric acid (HDDTP) was synthesised from the reaction of phosphorus pentasulphide and nonyl alcohol. Dinonyldithiophosphate complex of cadmium [Cd(DDTP)2] was prepared by mixing solutions of Cd(II) with HDDTP in ethanol at room temperature. The acid and its complex were characterised by elemental analysis and spectroscopy. The thermal behaviour of Cd(DNDTP)2was investigated by thermogravimetric analysis. Removal of Cd(II) from aqueous media by HDDTP solution was also studied. The optimum conditions for removal of Cd(II) were investigated for effects of solvent, pH, contact time, concentration, and inorganic anions. Cd(II) was quantitatively removed from aqueous solutions at the pH range of0.5<pH<6, under the conditions that the stoichiometric ratio of HDDTP/Cd(II) ≥2/1. It can be stated that contact of the Cd(II) with HDDTP was sufficient for quantitative removing of cadmium from acidic aqueous solutions.

Vortex-assisted ionic liquid microextraction coupled to flame atomic absorption spectrometry for determination of trace levels of cadmium in real samples

A simple and rapid vortex assisted ionic liquid based liquid-liquid microextraction technique (VALLME) was proposed for preconcentration of trace levels of cadmium. According to this method, the extraction solvent was dispersed into the aqueous samples by the assistance of vortex agitator. Cadmium preconcentration was mediated by chelation with the 8-hydroxyquinoline (oxine) reagent and an IL, 1-octyl-3-methylimidazolium hexafluorophosphate ([Omim][PF6]) was chosen as the extraction solvent to extract the hydrophobic complex. Several variables such as sample pH, concentration of oxine, volume of [Omim][PF6] and extraction time were investigated in details and optimum conditions were selected. Under the optimum conditions, the limit of detection (LOD) was 2.9 μg L(-1) for Cd (ІІ) and relative standard deviation (RSD%) for five replicate determinations of 125 μg L(-1) was 4.1%. The method was successfully applied to the determination of cadmium in tap water, apple and rice samples.