https://doi.org/10.1007/s44211-022-00181-9
“For the first time, air-assisted cloud point extraction (AACPE) was presented to preconcentrate metal ions. The procedure was conjugated with inductively coupled plasma-optical emission spectroscopy for determination of samarium. In this procedure, samarium ions were complexed with aluminon and extracted into Triton X-114 in the presence of potassium iodide. The mixture was repeatedly sucked and dispersed with a syringe (three times) to create cloud solution. Experimental factors that affect the extraction competence of the AACPE procedure, such as pH, amount of aluminon and Triton X-114, salt addition, number of suction/injection cycles, and centrifugation rate and time, have been investigated and optimized. A linear calibration curve from 0.2 to 200.0 μg L−1 with enrichment factor and detection limit of 102 and 0.06 μg L−1, respectively, was established under the optimum experimental conditions. The approach was used to determine samarium in wastewater and rock samples, with recoveries ranging from 98% to 99%.”
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Apparatus
A Genway 7300 spectrophotometer (Cole-Parmer Ltd., Staffordshire, UK) was used to record UV–visible spectra. ICP-OES analysis was performed with an Agilent 5100 ICP-OES (Agilent Technologies, Melbourne, Australia). Table 1 shows the operating conditions of ICP-OES for Sm3+ determination. A digital pH meter was used to take the readings (Hanna Instruments Inc, RI, USA). To speed up the phase separation, a commercial centrifuge (Hinotek Technology Co., Ningbo, China) was used.
Chemicals
Ultrapure chemicals were used in the study and purchased from Merck (Darmstadt, Germany) or Sigma-Aldrich (St. Louis, MO, USA). The stock standard solution of Sm3+ (1000 mg L−1) was prepared by dissolving 0.2956 g of Sm(NO3)3·6H2O (99.9%) in 5.0 mL of HNO3 (1.0 mol L−1) and the volume was made up to 100 mL with double distilled water. The stock solution of aluminon (10–2 mol L−1) was prepared by dissolving 0.4734 g in 100 mL of double distilled water. The pH was controlled using the following solutions: HCl/KCl (pH 1.0–2.0), acetate buffer (pH 3.0–6.0), and hexamine buffer (pH 7.0–8.0). Hard Rock Mine Waste standard reference material (SRM 2780a) from the National Institute of Standards and Technology (NIST, Gaithersburg, MD, USA) was processed to evaluate the accuracy.
General procedure for AACPE
To aqueous solution of standard or sample, 2.0 mL buffer solution (pH 2.5), 0.5 mL of 10–2 mol L−1 aluminon, 1.0 mL of 5.0% (v/v) Triton X-114 and 1.0 mL of 1 mol L−1 KCl were added in the same sequence and the volume was adjusted to 50 mL by double distilled water. The contents were then rapidly sucked into a 50-mL syringe and injected into the tube (3 times) using a needle. To increase the viscosity of the surfactant-rich phase, the tubes were first placed in ice bath for 10 min before being centrifuged at 3000 rpm for 5 min. The upper aqueous phase was decanted, and the residual surfactant-rich phase was removed by micro-syringe and its volume was made up to 0.5 mL by 1.0 mol L−1 of HNO3 prior to aspiration into ICP-OES. The extraction recovery (R), which may be computed using the following formula, was used to measure the extraction efficiency.
where Cs is the concentration of Sm3+ in the surfactant-rich phase of volume Vs, Ci is its initial concentration and Vi is the initial volume.
Environmental samples
Rock samples were taken from Abu-Tartour phosphate mine (New Valley, Egypt) and collected in polyethylene bags. Rock samples were crushed and powdered to less than 120 mesh using agate mortar. In Teflon vessels, accurately weighed samples or SRM (0.2–0.3 g) were mixed with a mixture of HF, HNO3 and double distilled water (2.0 mL each). The microwave digestion was proceeded based on our previously optimized program: 145 °C (5 min), 165 °C (5 min) and 170 °C (20 min) [31]. Following cooling, 20 mL of boric acid (5% w/v) was added to neutralize the excess HF and the volume was completed to 50 mL with double distilled water. Industrial wastewater samples, from Sinmar Chemicals Factory (Port-Said, Egypt), were collected in acid-washed polyethylene vessels. The water samples were filtered through 0.45 μm cellulose nitrate membrane (Millipore, Bedford, MA, USA), acidified to pH 2 with HNO3.
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