Fast sequential multi element analysis of lead and cadmium in canned food samples using effervescent tablet-assisted switchable solvent based liquid phase microextraction (EA-SS-LPME) coupled with high-resolution continuum source flame atomic absorption spectrometry (HR-CS-FAAS).

An effervescent tablet-assisted switchable solvent based liquid phase microextraction (EA-SS-LPME) was developed for multi-element determination of Pb and Cd in various samples using high-resolution continuum source flame atomic absorption spectrometry (HR-CS-FAAS). The effervescent tablets were used for improving the extraction efficiency. Triethylamine as a hydrophobic solvent was switched to protonated triethylamine carbonate by CO2 and used to extract dithizone complexes from samples. Calibration linearities were obtained from 0.06 to 10.0 mg L-1 (Pb) and 0.02 to 1.50 mg L-1 (Cd). LODs of the proposed method were 0.0195 (Pb) and 0.0068 (Cd). LOQs were 0.0649 mg L-1 (Pb) and 0.0228 mg L-1 (Cd) with %RSDs of 1.25%-1.69% (Pb) and 1.07%-1.64% (Cd). The proposed method was applied for the determination of Pb and Cd in water and canned food samples. The spiked recoveries were 82.3-119.0% (Pb) and 81.7-120.0% (Cd). In addition, the PF was 3.3, with EF at 1.4 (Pb) and 2.6 (Cd) obtained after extraction for under 8 min.

Magnetic Dispersive Solid Phase Extraction Using Recycled-graphite for GO-Fe3O4-dithizone Composite Combined with FAAS for Determination of Lead in Environmental Samples.

Magnetic dispersive solid phase extraction (MdSPE) was developed to determine the concentration of lead (Pb) in real water samples, while graphene oxide-magnetite-dithizone (GO-Fe3O4-DTZ) from the used graphite tubes (recycled graphite) of electrothermal technique was simply employed as a new sorbent to improve extraction efficiency, separated by external magnetic field and analyzed with FAAS. The synthesized sorbent was evaluated for its surface property, functional group and surface morphology by Zeta potential, Fourier transform infrared spectrophotometer (FTIR), and scanning electron microscope (SEM), respectively. The relevant measurement parameters, such as pH, extraction time, type and concentration of eluent, sample volume and reusability, were optimized. Under the optimal conditions, preconcentration factor was 13.33. The limit of detection (LOD) and limit of quantitation (LOQ) obtained were 0.070 and 0.23 mg/L, respectively. The relative standard deviation (%RSD) was 3.41%. Recovery values were 90.1 - 123%. In addition, the robustness of the method was affirmed in terms of tolerance limit obtained from interference studies.

Alginate-based magnetic nanosorbent immobilized with aptamer for selective and high adsorption of Hg2+ in water samples.

Alginate-coated magnetic nanocluster (MNC) immobilized with Hg2+-specific aptamer was synthesized to obtain the nanosorbent with high adsorption capacity and high selectivity for trace analysis of inorganic mercury (Hg2+) in water samples. Magnetite nanoparticle was first synthesized by a co-precipitation of iron precursors in the presence of alginate to obtain alginate-coated MNC, followed by immobilization with avidin. Hg2+-Specific DNA aptamer labeled with biotin was then conjugated on the MNC surface via specific avidin-biotin interaction to form aptamer-immobilized MNC. Coating the MNC with alginate can improve its water dispersibility and also increase its adsorption capacity toward Hg2+ (350 mg/g). It exhibited high selectivity through thymine-Hg2+-thymine (T-Hg2+-T) interaction with high tolerance to other foreign ions. This nanosorbent showed linearity over the Hg2+ concentration range of 0.2-10 µg/L with a correlation coefficient of 0.9977, limit of detection of 0.46 µg/L, and enrichment factor of 13. Moreover, it also showed a potential for detection of Hg2+ in drinking and tap water samples with satisfactory recoveries.

Immobilized Activated Carbon as Sorbent in Solid Phase Extraction with Cold Vapor Atomic Absorption Spectrometry for the Preconcentration and Determination of Mercury Species in Water and Freshwater Fish Samples.

A new preconcentration method using solid phase extraction (SPE) was developed by immobilizing dithizone (DZ) and 1,4-diphenylsemicarbazide (DPC) on oxidative activated carbon and then using this for the speciation and preconcentration of mercury species (Hg(II) and MeHg(I)) by flow injection cold vapor atomic absorption spectrometry (FI-CVAAS). The SPE experimental conditions were investigated including pH, amount of adsorbent and flow rate. The elution parameters and effect of foreign ions were also elucidated. Under the optimized conditions, the calibration graph was linear in the ranges of 0.015 - 3.0 µg L-1 of Hg(II), with a detection limit (LOD) of 0.0155 µg L-1, corresponding to three times the standard deviation (3SD, n = 20). The precision of the method, defined as percentage relative standard deviation (%RSD) for mercury was 1.25 - 3.79% at concentrations of 0.1 - 1.0 µg L-1, for which a preconcentration factor of 20 was obtained for Hg(II). The proposed method was validated by determining the mercury concentration in standard reference materials, and successfully applied to the speciation of mercury in several water and freshwater fish samples.

Speciation of mercury in water and biological samples by eco-friendly ultrasound-assisted deep eutectic solvent based on liquid phase microextraction with electrothermal atomic absorption spectrometry.

A simple, fast, sensitive and eco-friendly ultrasound-assisted deep eutectic solvent liquid phase microextraction (UA-DES-LPME) was developed for preconcentration and speciation of Hg2+ and CH3Hg+ combined with ETAAS. Choline-phenol based DES (1:3, molar ratio) was used as an extractant for the determination of species of mercury, Hg2+ formed hydrophobic complexes with dithizone and complexes were then extracted using DES. For CH3Hg+ determination, CH3Hg+ can be extracted directly into DES phase because of its hydrophobic property. Under optimized conditions, the detection limits of Hg2+ and CH3Hg+ were 0.073 and 0.091 ng mL-1, respectively. %RSD (n = 7) were less than 4.1% and the enrichment factor (10 mL sample volume) were 34 and 18.3 for Hg2+ and CH3Hg+, respectively. The accuracy of the developed method was verified by analysis of SRM-1566b oyster tissue. The proposed method was applied to the speciation of mercury in several water and fresh water fish samples.

Speciation of mercury in water and freshwater fish samples by a two-step solidified floating organic drop microextraction with electrothermal atomic absorption spectrometry.

A new and simple two-step SFODME using 4-nitro-o-phenylenediamine (4-NOPD) as a chelating agent was developed for mercury speciation in water and fish samples by ETAAS. For the first step, methylmercury was extracted into 1-undecanol and for the second step, the Hg(II) remaining in the sample solution was complexed with 4-NOPD and then extracted into 1-undecanol. Under the optimized conditions, the calibration graphs of Hg(II) and methylmercury were linear in the range of 0.83-8.0 µg L-1 and 0.78-8.0 µg L-1, with the LOD of 0.25 µg L-1 and 0.24 µg L-1 and the enrichment factor were 25.7 and 32.2, respectively. The %RSDs was in the range of 2.0-4.4% at concentrations of 0.5 and 4.0 µg L-1 (n = 5). The proposed method was successfully applied to mercury speciation in water and fish samples. The accuracy of method, tested by the analysis of SRM 1566b and DORM-4 was in good agreement with the certified values.

Surfactant-assisted emulsification dispersive liquid-liquid microextraction using 2-thenoyltrifluoroacetone as a chelating agent coupled with electrothermal atomic absorption spectrometry for the speciation of chromium in water and rice samples.

A novel method was developed by SAE-DLLME for chromium speciation in water and rice samples using 2-thenoyltrifluoroacetone (TTA) as a chelating reagent by ETAAS. The speciation of Cr(III) and Cr(VI) was achieved by complexation of Cr(III)-TTA and the total Cr was measured after reduction of Cr(VI) to Cr. The calibration graph was linear in the range of 0.02-2.50 µg L-1, with a detection limit of 0.0052 µg L-1. The %RSD was in range of 2.90-3.30% at 0.5, 1.5 and 2.5 µg L-1 of Cr(III), n = 5 and the EF was 54.47. The method was applied to chromium speciation and total chromium determination in real samples and gave recoveries in the range of 96.2-103.5% and 97.1-102.7% for Cr(III) and Cr(VI) in water samples and 93.7-103.5% of total Cr in rice samples. The accuracy of the method was evaluated by analysis of SRM 1573a with good agreement compared to the certified value.

Determination of cadmium in herbs by SFODME with ETAAS detection.

A method for the determination of cadmium in herb samples based on solidified floating organic drop microextraction (SFODME) using 1-(2-Pyridylazo)-2-naphthol (PAN) as a chelating reagent and detection by electrothermal atomic absorption spectrometry (ETAAS) was developed in the present work. The effects of pH, extraction solvent, extraction time, stirring rate, and extraction temperature were investigated. Under the optimized conditions, the calibration graph was linear in the range of 0.017-3.0µgL-1, with a detection limit (LOD) of 0.0052µgL-1. The relative standard deviation (%RSD) for 6 replicate measurements of 1.0µgL-1 cadmium was ±2.67%. The method was applied to the analysis of 10 types of Thai herb samples. Percentage recoveries were in the range 94.5-110.2%. It was found that cadmium concentrations in all Thai herb samples were less than the maximum residue level.

Polyacrylamido-2-methyl-1-propane sulfonic acid-grafted-natural rubber as bio-adsorbent for heavy metal removal from aqueous standard solution and industrial wastewater.

Bio-adsorbent modified natural rubber (modified NR) was prepared, by placing the sulfonic acid functional group on the isoprene chain. This modification was carried out with the aim to prepare material capable to remove heavy metals from aqueous solution. The structures of modified NR materials were characterized by FT-IR and NMR spectroscopies. Thermal gravimetric analysis of modified NR showed that the initial degradation temperature of rubber decreases with increasing amount of polyacrylamido-2-methyl-1-propane sulfonic acid (PAMPS) in the structure. In addition, water uptake of the rubber based materials was studied as a function of time and content of PAMPS. The influence of the amount of PAMPS grafted onto NR, time, pH, concentration of metal ions, temperature, and regeneration were studied in terms of their influence on the adsorption of heavy metals (Pb(2+), Cd(2+) and Cu(2+)). The adsorption isotherms of Pb(2+) and Cd(2+) were fitted to the Freundlich isotherm model, while Cu(2+) was fitted to the Langmuir isotherm. However, the results from these two isotherms resulted in a similar behavior. The adsorption capacity of the modified NR for the various heavy metals was in the following order: Pb(2+)∼Cd(2+)>Cu(2+). The maximum adsorption capacities of Pb(2+), Cd(2+), and Cu(2+) were 272.7, 267.2, and 89.7 mg/g of modified rubber, respectively. Moreover, the modified natural rubber was used for the removal of metal ions in real samples of industrial effluents where the efficiency and regeneration were also investigated.