Determination of some trace metal ions in various samples by FAAS after separation/preconcentration by copper(II)-BPHA coprecipitation method

A green and simplified approach for the quantitative and sensitive analysis of heavy metal ions in sea and stream waters

Elimination of the matrix effect is a major challenge in developing a method for the quantification of heavy metals (HMs) in water samples. In this regard, the current research describes the simultaneous analyses of Cu(II), Cd(II), and Ni(II) ions in water matrices through flame atomic absorption spectrophotometry (FAAS) after preconcentration with carrier element-free co-precipitation (CEFC) technique by the help of an organic co-precipitant, 3-{[5-(4-Chlorobenzyl)-3-(4-chlorophenyl)-1H-1,2,4-triazol-1-yl]-methyl}-4-[2,4-(dichlorobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (CCMBATT). Based on our literature research, CCMBATT was employed for the first time in this study as an organic co-precipitant for the preconcentration of HMs. Factors such as solution pH, concentration of co-precipitant, sample volume, standing time, centrifugation rate, and time were thoroughly examined and optimized to achieve the highest efficiency in terms of HM recovery. The limits of detection (LODs) (with 10 number of tests) of 0.54, 0.34, and 1.95 μg L-1 and the relative standard deviations (RSD %) of 2.1, 3.3, and 3.0 were determined for Cu(II), Cd(II) and Ni(II) ions, respectively. Recovery results of HMs for the spiked samples were in the range of 92.8-101.0%, demonstrating the trueness of the method and its applicability to the water samples matrix.

Inhibition of CRISPR-Cas12a trans-cleavage by lead (II)-induced G-quadruplex and its analytical application

In this work, the inhibition of clustered regularly interspaced short palindromic repeats (CRISPR) - CRISPR associated protein (Cas) trans-cleavage by Pb²⁺-induced G-quadruplex has been firstly explored to detect Pb²⁺ in tea beverage and milk. In absence of Pb²⁺, the Na⁺-induced G-quadruplex can be cleaved by CRISPR-Cas12a. In contrast, Pb²⁺ can competitively combine with G-quadruplex, resulting in its conformational changes and resistance to trans-cleavage of CRISPR-Cas12a. Therefore, the fluorescence resonance energy transfer can happen. Pb²⁺ can be detected in a linear range from 100 nM to 5 µM with a lowest detection limit of 2.6 nM and a relative standard deviation of 4.32%. In summary, this work not only provides a new method for Pb²⁺ detection based on its induced G-quadruplex inhibition on CRISPR-Cas12a trans-cleavage, but also broadens the application of CRISPR-Cas system for heavy metal analysis in the field of food safety.

Magnetic dispersive solid-phase extraction based on graphene oxide/Fe3 O4 @polythionine nanocomposite followed by atomic absorption spectrometry for zinc monitoring in water, flour, celery and egg

BACKGROUND

Magnetic graphene oxide nanocomposite has been proposed as a promising and sustainable sorbent for the extraction and separation of target analytes from food matrices. Sample preparation based on nanocomposite presents several advantages, such as desired efficiency, reasonable selectivity and high surface-area-to-volume ratio.

RESULTS

A new graphene oxide/Fe₃ O₄ @polythionine (GO/Fe₃ O₄ @PTh) nanocomposite sorbent was introduced for magnetic dispersive solid-phase extraction and flame atomic absorption spectrometric detection of zinc(II) in water, flour, celery and egg. To fabricate the sorbent, an oxidative polymerization of thionine on the surface of magnetic GO was applied, while polythionine was simply employed as a surface modifier to improve extraction yield. The properties of the sorbent were characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, energy-dispersive X-ray analysis, vibrating sample magnetometry and Fourier transform-infrared spectroscopy. The calibration curve showed linearity in the range of 0.5-30 ng mL^-1 . Limits of detection (S/N = 3) and quantification (S/N = 10) were 0.08 and 0.5 ng mL^-1 , respectively.

CONCLUSION

The method was applied for trace-level determination of Zn(II) in water and food samples, and its validation was investigated by recovery experiments and analyzing certified reference material. © 2018 Society of Chemical Industry.

A new turn-on fluorimetric method for the rapid speciation of Cr(III)/Cr(VI) species in tea samples with rhodamine-based fluorescent reagent

A new fluorimetric method with rhodamine-based fluorescent agent was developed for the rapid speciation of Cr(III)/Cr(VI) in tea, soil and water samples. The system, which utilizes a fluorescent reagent, was used for the first time after synthesis/characterization of 3',6'-bis(diethylamino)-2-{[(1E)-(2,4-dimethoxyphenyl)methylene] amino}spiro[isoindole-1,9'-xanthen]-3(2H)-one (BDAS). The reagent responds instantaneously at room temperature in a 1:1 stoichiometric manner to the amount of Cr(III). The selectivity of this system for Cr(III) over other metal ions is remarkably high, and its sensitivity is below 0.01mgL^-1 in aqueous solutions which enables a simplification without any pretreatment of the real sample. The method has a wide linear range of 0.1-10mgL^-1 and a detection limit of 0.15μgL^-1 for Cr(III) while the relative standard deviation was 0.1% for 0.1mgL^-1 Cr(III) concentration. The results of detection and recovery experiments for Cr(III) in tea, soil and water were satisfactory, indicating that the method has better feasibility and application potential in the routine determination and speciation of Cr(III)/Cr(VI). The results of analysis of the certified reference material (INCT-TL-1 tea sample and CWW-TM-D waste water) are in good agreement with the certified value.

Synthesis, characterization and application of a new chelating resin for solid phase extraction, preconcentration and determination of trace metals in some dairy samples by flame atomic absorption spectrometry

In this study, a simple and rapid solid phase extraction/preconcentration procedure was developed for determination of Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Pb(II), and Zn(II) trace metals by flame atomic absorption spectrometry (FAAS). A new chelating resin, poly(N-cyclohexylacrylamide-co-divinylbenzene-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (NCA-co-DVB-co-AMPS) (hereafter CDAP) was synthesized and characterized. The influences of the analytical parameters such as pH of the sample solution, type and concentration of eluent, flow rates of the sample and eluent, volume of the sample and eluent, amount of chelating resin, and interference of ions were examined. The limit of detection (LOD) of analytes were found (3s) to be in the range of 0.65-1.90μgL(-1). Preconcentration factor (PF) of 200 and the relative standard deviation (RSD) of ⩽2% were achieved (n=11). The developed method was applied for determination of analytes in some dairy samples and certified reference materials.

Determination of some metal ions in various meat and baby food samples by atomic spectrometry

In this paper, we report a simple and rapid solid phase extraction system for the separation/preconcentration and determination of Cd(II), Co(II), Cu(II), Fe(III), Cr(III), Pb(II), and Zn(II) ions by flame atomic absorption spectrometry (FAAS). This method is based upon the retention of metal ions on a column packed with poly[N-(3-methyl-1H-indole-1-yl)]-2-methacrylamide-co-2-acrylamido-2-methyl-1-propane sulphonic acid-co divinylbenzene] (MMAD) resin as a solid-phase extraction (SPE) sorbent at pH 8. At the optimized conditions, the limits of detection (3 s/b) between 0.12 and 1.6 μg L(-1), preconcentration factor of 100, and the relative standard deviation of ⩽1.8% were achieved (n=10). The accuracy of the method was verified by analyzing certified reference materials (CRMs) and performing recovery experiments. The developed method was successfully applied to the various natural water, meat products and baby food samples. The recoveries of analyte ions were found in added real samples and CRMs from 95% to 102%.

A new coprecipitation method without carrier element for separation and preconcentration of some metal ions at trace levels in water and food samples

A new simple and sensitive preconcentration, separation and environmentally friendly method based on carrier element free coprecipitation (CEFC) was developed using 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (APSAL) as a new organic co-precipitant to precipitate Cr(3+), Cu(2+), Fe(3+), Pb(2+) and Zn(2+) ions from water and food samples. The levels of the studied elements were detected by flame atomic absorption spectrometry (FAAS). The impact of several analytical parameters, such as pH, sample volume and coprecipitant amount as well as centrifugation rate and time was investigated to recover the examined metal ions. The influence of matrix ions was also tested, and no interferences were observed. The recovery values of the analyte ions were calculated and found to be in the range of 95-101%. The detection limits, corresponding to three times the standard deviation of the blank (N=10), were found to be in the range of 0.2-1.2 μg L(-1). The relative standard deviation (RSD) was calculated to evaluate the precision of the proposed method and was found to be ≤5.0%. The calculated preconcentration factor was 100. The proposed method was successfully applied to separate and preconcentrate trace amounts of ions in several water and food samples. To confirm the accuracy and validate the proposed method, certified reference materials were analyzed with satisfactory results.

Determination of lead in soybean sauces by the diffusive gradients in thin films technique

A diffusive gradients in thin films (DGT) device with sodium poly (aspartic acid) (PASP) as a novel binding agent (PASP DGT) combined with graphite furnace atomic absorption spectrometry (GFAAS) was developed for the sampling and measurement of lead in soybean sauce samples. The performance of PASP DGT was independent of pH in the range of 3-6 and salinity in the range from 4 to 14 g/L (as NaCl). There was no significant difference between PASP DGT technique and hydride generation atomic fluorescence spectrometry (HG-AFS) method for the measurement of lead in soybean sauce samples. The recoveries of lead in spiked soybean sauce samples determined by PASP DGT coupled with GFAAS were 94.3-97.2% with the relative standard deviations of 2.52-3.09%. The concentrations of Pb in twelve soybean sauce samples determined by PASP DGT coupled with GFAAS were in the range of 0.09-0.71 mg/L.

Resting eggs as new biosorbent for preconcentration of trace elements in various samples prior to their determination by FAAS

In this study, the resting eggs of aquatic creatures living in freshwater (Daphnia, Cladocera, Crustacean) ecosystems were used as a novel biosorbent extractant for synchronous preconcentration of trace Cd(II), Co(II), Cu(II), Mn(II), and Ni(II) previous to measurement by flame atomic absorpiton spectrometry (FAAS). Using column procedures, optimization studies were conducted to realize the effective adsorption of the analyte ions such as the solution pH, amount of the biosorbent, volume of the sample, interfering ions, etc. A high preconcentration factor of 67 and low relative standard deflection of ≤4.1% (n=8) were obtained. The invention constrains based on the 3 s/b criterion were 2.4 for Cd(II), 41.4 for Co(II), 4.2 for Cu(II), 3.0 for Mn(II), and 9.6 μg L(-1) for Ni(II). The accuracy of the method was verified by analysis of a certified standard reference material. The used procedure was applied to the definition of the analytes in diverse environmental samples with convincing results. Consequently, the resting eggs of Daphnia can be used as a biosorbent for preconcentration and biosorption studies.

Tris(2-Aminoethyl)Amine-Functionalized Fe3O4Magnetic Nanoparticles as a Selective Sorbent for Separation of Silver and Gold Ions in Different pHs

The usage of tris(2-aminoethyl)amine-functionalized Fe3O4nanoparticles as a novel magnetic sorbent for rapid extraction, preconcentration, and determination of trace amounts of silver and gold ions was investigated. The optimum conditions for sample pH, eluent parameters (type, concentration and volume) were obtained. The effect of various cationic interferences on the adsorption of silver and gold was evaluated. The analytical efficiency values of both silver and gold ions were higher than 98.0% in the optimum conditions. The limits of detection (LOD) were less than 0.8 and 0.5 ng mL−1for silver and gold, respectively. The linear ranges for silver and gold were 1.5–1000 ng mL−1and 1.0–1000 ng mL−1respectively. The maximum capacity of the modified magnetic nanoparticles was more than 97.3 mg g−1and 167 mg g−1for silver, and gold ions, respectively. The presented method was used to determine silver and gold ions in real samples. Finally, the method accuracy was confirmed by standard reference materials.

Chelating agent free-solid phase extraction (CAF-SPE) of Co(II), Cu(II) and Cd(II) by new nano hybrid material (ZrO2/B2O3)

New nano hybrid material (ZrO(2)/B(2)O(3)) was synthesized and applied as a sorbent for the separation and/or preconcentration of Co(II), Cu(II) and Cd(II) in water and tea leaves prior to their determination by flame atomic absorption spectrometry. Synthesized nano material was characterized by scanning electron microscope, transmission electron microscope and X-ray diffraction. The optimum conditions for the quantitative recovery of the analytes, including pH, eluent type and volume, flow rate of sample solution were examined. The effect of interfering ions was also investigated. Under the optimum conditions, adsorption isotherms and adsorption capacities have been examined. The recoveries of Co(II), Cu(II) and Cd(II) were 96 ± 3%, 95 ± 3%, 98 ± 4% at 95% confidence level, respectively. The analytical detection limits for Co(II), Cu(II), and Cd(II) were 3.8, 3.3, and 3.1 μg L(-1), respectively. The reusability and adsorption capacities (32.2 mg g(-1) for Co, 46.5 mg g(-1) for Cu and 109.9 mg g(-1) for Cd) of the sorbent were found as satisfactory. The accuracy of the method was confirmed by analyzing certified reference material (GBW-07605 Tea leaves) and spiked real samples. The method was applied for the determination of analytes in tap water and tea leaves.