Graphene-based solid-phase extraction combined with flame atomic absorption spectrometry for a sensitive determination of trace amounts of lead in environmental water and vegetable samples

The control efficiency and mechanism of heavy metals by permeable pavement system in runoff based on enhanced infiltration materials

As one of the commonly used stormwater management measures, permeable pavement system (PPS) played a prominent role in controlling runoff pollution and alleviating urban waterlogging. In this study, new enhanced infiltration materials (construction waste brick, coal gangue, activated carbon, multi-walled carbon nanotube, multi-layer graphene) were applied in PPS and the control efficiency and mechanism of typical heavy metals (HMs, Mn²⁺, Pb²⁺, Zn²⁺, Cu²⁺, Cd²⁺, Ni²⁺) was investigated in runoff. Furthermore, the influences of different rainfall intensities and antecedent dry periods on HMs removal by PPS were evaluated. The results showed that all PPS with enhanced infiltration materials have little leaching effect on HMs (＜3 μg/L). All the selected enhanced infiltration materials meet the requirements of PPS. The concentration of HMs in the effluent of PPS dropped sharply first, followed rebounded and then maintained at a stable range. Activated carbon PPS (AC), Multi-walled carbon nanotube PPS (MCN), and Multi-layer graphene PPS (MG) could significantly improve the control effect of PPS on nearly all selected HMs. The average removal rates of AC, MCN and MG for six HMs were 75.48%-99.35%, 81.30%-97.59%, and 73.03%-99.33%, respectively. Compared with Traditional PPS (TR), the effluent concentrations of HMs in construction waste brick PPS (CW) and coal gangue PPS (CG) were relatively higher and unstable. AC, CN and MG could adapt to different rainfall conditions and the maximum removal rates of most HMs exceed to 99%. With antecedent dry periods increased, the control effect of HMs was significantly improved. The influences of the antecedent drying period on HMs removal followed as: CW＞CG＞TR＞MG＞CN＞AC. This study provided novel methods to eliminating HMs in runoff and provides implications for the design of PPS.

Synthesis and Surface Modification of Iron Oxide Nanoparticles for the Extraction of Cadmium Ions in Food and Water Samples: A Chemometric Study

In this project, a prompt, efficient, and effective method for Cd2+ ions extraction from different food and water samples using magnetic dispersion-based solid phase extraction by functionalized iron oxide nanoparticles was proposed. Iron oxide nanoparticles were synthesized through the co-precipitation method followed by functionalization with tetraethyl orthosilicate (TEOS) and 3-aminopropyl silane (APTES) to obtain Fe3O4@SiO2@APTES. This composite was characterized through different techniques, including vibrating sample magnetometer, dynamic light scattering, zeta potential, FTIR, SEM, XRD, and BET. Variables studied were pH, temperature, sorbent amount, sonication time, and sample and eluent volume affecting the sorption efficacy of freshly synthesized sorbent. Plackett–Burman design was utilized for the identification of significant factors for microextraction of target analyte, while the central composite design was utilized for the optimization of significant factors. Detection and quantification limits obtained were 0.17 and 0.58 μgL−1, respectively, with an enhancement factor of 83.5. Under optimum conditions, Fe3O4@SiO2@APTES showed good stability even after >80 adsorption/desorption cycles run while maintaining over 96% analyte recoveries. The developed method was validated by assessing certified reference materials and standard addition methodology for Cd2+ detection in real samples. To confirm the precision, repeatability (RSDr) and reproducibility (RSDR) were calculated and found as <3.0 (n = 7) and <7.5 (n = 15), respectively. Furthermore, in accordance with the ISO/IEC 17025 recommendations, the validation was also confirmed through a “bottom-up” approach while considering all possible uncertainties in data.

Nickel hydroxide nanoflower-based dispersive solid-phase extraction of copper from water matrix

In this work, a dispersive solid-phase extraction method based on Ni(OH)₂ nanoflowers (Ni(OH)₂-NFs-DSPE) was developed to separate and preconcentrate copper ions from tap water samples for determination by flame atomic absorption spectrometry (FAAS). Ni(OH)₂-NFs was synthesized using a homogeneous precipitation technique and used as sorbent for copper preconcentration. X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy were used to characterize the synthesized sorbent. All experimental variables were carefully optimized to achieve a high enhancement factor of 107.5-folds with respect to the detection sensitivity of the conventional FAAS. The proposed method's analytical parameters including LOD, LOQ, and linear range were determined as 1.33 μg/L, 4.42 μg/L, and 3.0-40 μg/L, respectively. To assess the applicability and reliability of the developed method, optimal conditions were applied to tap water samples and satisfactory percent recoveries (94-103%) were obtained for the samples spiked at 20 and 30 μg/L. This validated the accuracy and feasibility of the developed method to real samples. The developed method can be described as a simple, efficient, and rapid analytical approach for the accurate determination of trace copper ions in water samples.

A new Fe/N doped carbon dot naocatalytic amplification-aptamer SERS/RRS/Abs trimode assay platform for ultratrace Pb2

Nanocatalytic amplification of carbon dots is a new way to improve sensitivity. The preparation of the high catalytic activity and stable iron/nitrogen-doped carbon dot (CD_BFe) sol and its application in aptamer (Apt) assay have not been reported yet. In this paper, a simple hydrothermal procedure for the preparation of CD_BFe derived from Fe²⁺-2,2'-bipyridine complex has been developed. It is found that CD_BFe has a strong catalytic effect on the indicator reaction of glyoxal (C₂H₂O₂) reduction of HAuCl₄ to produce gold nanoparticle (AuNP) probe with strong surface enhanced Raman scattering (SERS) at 1617 cm^-1, resonance Rayleigh scattering (RRS) effect at 370 nm and absorption (Abs) at 550 nm. A rapid and sensitive CD_BFe catalytic amplification Apt method for SERS/RRS/Abs trimode detecting ultratrace lead ions was established, based on the Apt reaction mediated the nanocatalytic indicator reaction. The results show that the SERS intensity and Pb(II) concentration have a good linear relationship in the range of 1.3-16 pM, and the detection limit is the lowest. In addition, Hg(II) and As(III) can also be measured by this naocatalytic amplification- Apt assay platform.

Single step carbonating and activating fir sawdust to activated carbon by recyclable molten carbonates and steam

Molten carbonate pyrolysis with steam on fir sawdust was conducted to produce activated carbon, in which physical and recycling chemical activation was combined with carbonization as a single step process. The effects of temperature, molten carbonate pyrolysis and steam flow rate on the activated carbon were investigated. The BET results showed an excellent specific surface area of 822.02 m²/g and a pore diameter of 2.39 nm. The adsorption capacities of the activated carbon achieved ideal values on methylene blue and iodine and reached a removal capacity of 196.5 mg/g for the elimination of Cr(VI) in wastewater. There were four stages in developing the porous structure of activated carbon by the joint effects of molten carbonates and steam as the temperature rising. The activated carbon had abundant micropores inside the macropore structure at temperatures ranging from 700 °C to 750 °C. Molten carbonates promoted the formation of mesopores and macropores and reduced the reaction temperature as a catalyst and heat transfer medium, while steam promoted micropore generation by water-gas shift reactions. A recycling study indicated that the Cr(VI) adsorption capacity of the activated carbon generated after five recycling cycles of molten carbonates was still reached 195 mg/g.

From waste to value-added products: Evaluation of activated carbon generated from leather waste for supercapacitor applications

Leather tanning operations create a large amount of solid and liquid waste from tanning, wherein Cr(III) compounds are used to produce wet blue leather. In this study, activated carbon (AC) generated from leather waste (LW) was evaluated for supercapacitor (SC) applications. AC was produced through carbonization at a temperature range of 700°C-900 °C, followed by chemical activation. The morphological characteristics of the AC samples revealed a certain degree of porosity and a maximum surface area of 381 m² g^-1. X-ray diffraction and EDX examination showed the existence of graphitic planes in the LW-derived AC. Raman, FT-IR, and XPS confirmed the defect nature and surface functional groups of the AC samples. A three-electrode approach was employed to assess the electrochemical characteristics of the AC samples. The supreme capacitance of a sample (LW700) at 1 A/g was 550 F g^-1 (237 C g^-1) in a 6 M KOH electrolyte. All the electrochemical results (CV, GCD, and Nyquist curves) demonstrated that the LW carbon possessed a high specific capacitance and electrochemical cycle constancy, and hence is appropriate for SC fabrication. These desirable capacitive performances enable solid leather waste-derived carbons as a source of new materials for low-cost energy storage supercapacitors. This work put forwards a new concept of 'waste to value-added products' that can be a helping hand for leather industries and its solid waste management disposal problems.

The Gate-Modified Solution-Gated Graphene Transistors for the Highly Sensitive Detection of Lead Ions

Lead ions are heavy metal ions that are extremely harmful to the human body and ecological environment. They can cause irreversible damage to the human nervous system and blood system at low concentrations. It is very important to develop a simple, rapid, and sensitive detection method of Pb²⁺. Solution-gated graphene transistors (SGGTs) have been widely studied in recent years due to their ultra-high sensitivity in chemical sensing. Herein, we have demonstrated a sensitive sensor of Pb²⁺ based on the SGGTs through the glutathione gate modification. When Pb²⁺ are added into the electrolyte solution, the electrical double layer capacitance near the gate electrode changes because Pb²⁺ can be strongly chelated, leading to the channel current change. The detection of Pb²⁺ can be realized. The detection limit of sensors for Pb²⁺ can reach 1 × 10^-18 M, and the response time is about 1 s. The channel current change and the logarithm of Pb²⁺ concentration exhibit a good linear relationship in the concentration range of 1 × 10^-18 and 1 × 10^-6 M. Because the glutathione molecule can well recognize Pb²⁺, the devices also demonstrate good selectivity to Pb²⁺. Compared with the convention detection, our method shows easy operation, high sensitivity, and high selectivity. Therefore, it has great potential in the analysis of trace samples for health and environment monitoring.

Hit Multiple Targets with One Arrow: Pb2+ and ClO- Detection by Edge Functionalized Graphene Quantum Dots and Their Applications in Living Cells

Recently, multimodal detection of analytes through a single nanoprobe has become an eminent approach for researchers. Herein a fluorescent nanoprobe, functionalized-GQD (F-GQD), has been designed through edge functionalization of graphene quantum dots (GQDs) by 2,6-diaminopyridine molecules. The fluorescence of F-GQD is quite sensitive to medium pH, making it a suitable pH sensor within the pH range 2-6. Interestingly, F-GQD shows dual sensing of Pb²⁺ and ClO^- by entirely different pathways; Pb²⁺ exhibits fluorescence turn-on performance while ClO^- triggers turn-off fluorescence quenching. The fluorescence enhancement may originate from the Pb²⁺-induced aggregation of the nanodots. The limit of detection (LOD) was also impressive, 1.2 μM and 12.6 nM for Pb²⁺ and ClO^-, respectively. The detailed mechanistic investigations reveal that both dynamic and static quenching effects operate together in the F-GQD-ClO^- system. The dynamic quenching was attributed to the energy migration from F-GQD to ClO^- through hydrogen bonding interaction (static quenching) between the amine group at the F-GQD surface and ClO^-. The F-GQD nanodot reveals excellent sensitivity toward the detection of ClO^- in real samples. Moreover, the F-GQDs also serve as multicolor fluorescent probes for cell imaging; the probe can easily penetrate the cell membrane and successfully detect intracellular ClO^-.

Ultra-thin graphene oxide membrane deposited on highly porous anodized aluminum oxide surface for heavy metal ions preconcentration

Analyte extraction using graphene oxide (GO) can be challenging owing to the stochastic behavior of the permeation of water molecules and heavy metal ions, imperfect pore structures, and irregular distribution of multi-layer sheets. We prepared a free standing, through-hole graphene oxide membrane deposited on porous anodic aluminum oxide (AAO) substrate. The hydrophilicity of the GO membrane was improved via oxygen plasma treatment. The resulting AAO-GO membrane was used as novel adsorbent for the heavy metal ions preconcentration prior to their determination using inductively coupled plasma optical emission spectroscopy. This sub-micrometer-thick membrane allowed unimpeded permeation of water molecules via two-dimensional capillaries formed across the pores and in between the closely spaced GO sheets. The proposed method shows good detection limit of 1.2 ng L^-1, and the co-existing ions did not affect the extraction efficiency of the adsorbent. The accuracy of the method was assessed by analyzing standard reference materials, where the Student's t-test values were less than the critical Student's t-value of 4.303 (95% confidence level). Good precision was achieved, as coefficients of variation ranged between 4% and 5%. The developed SPE adsorbent is a promising alternative for bulk adsorbents owing to the wide variety of available 2D materials and deposition methods.

Rapid Speciation of Lead in Human Blood and Urine Samples Based on MWCNTs@DMP by Dispersive Ionic Liquid-Suspension-Micro-Solid Phase Extraction

An efficient sorbent based on 2,3-dimercapto-1-propanol immobilized on multi-wall carbon nanotubes (MWCNTs@DMP) was developed for separation/speciation of organic and inorganic lead (alkyl-Pb, Pb²⁺) in human blood, urine, and water samples by dispersive ionic liquid-suspension-micro-solid phase extraction (DIL-S-μ-SPE). By procedure, the MWCNTs@DMP as solid phase, acetone, and ionic liquid (IL, [HMIM][PF₆]) were mixed and injected to 10 mL of the liquid phase at pH = 6.5. After shaking, the Pb(II) was extracted in MWCNTs@DMP and settled down in a conical tube with IL by centrifuging (Pb²⁺→: SH-SiO₂@CNTs). The lead (Pb²⁺) was back-extracted from sorbent/IL in acidic pH and measured by atom trap atomic absorption spectrometry (AT-AAS). In addition, the organic lead (R-Pb, alkyl lead) converted to Pb(II) and total lead (T-Pb) was determined in the same conditions by UV radiation in 95 °C. Under the optimal conditions, the linear range (9.5-480 μg L^-1), LOD (3.2 μg L^-1), and enrichment factor (10.4) were obtained (RSD < 5%). The adsorption capacity of the MWCNTs@DMP and MWCNTs was achieved as 191.6 mg g^-1 and 25.8 mg g^-1, respectively. The method was validated by standard reference materials (SRM 1643d, SRM 955, and SRM 2668), ET-AAS, and ICP-MS analysis in real samples. Graphical abstract.

A Fluorescence Sensor for Pb2+ Detection Based on Liquid Crystals and Aggregation-Induced Emission Luminogens

Heavy metals, such as lead ions, are regarded as the main environmental contaminants and have a negative impact on human bodies, making detection technologies of lead ions critical. However, most existing detection methods suffer from time consumption, complicated sample pretreatment, and expensive equipment, which hinder their broad use in real-time detection. Herein, we show a new fluorescence sensor for detecting lead ions derived from liquid crystals doped with an aggregation-induced emission luminogen. The mechanism is based on the variation of fluorescence intensity caused by the disturbance of an ordered liquid crystal configuration in the presence of Pb²⁺, induced by DNAzyme and its catalytic cleavage. The proposed fluorescence sensor exhibits a low detection limit of 0.65 nM, which is 2 orders of magnitude lower than that previously reported in an optical sensor based on liquid crystals. The detection range of the Pb²⁺ fluorescence sensor is broad, from 20 nM to 100 μM, and it also selects lead ions from numerous metal ions exactly, resulting in a highly sensitive, highly selective, simple, and low-cost detection strategy of Pb²⁺ with potential applications in chemical and biological fields. This approach to designing a liquid crystal fluorescence sensor offers an inspiring stage for detecting biomacromolecules or other heavy metal ions by varying decorated molecules.

Flexible Type Symmetric Supercapacitor Electrode Fabrication Using Phosphoric Acid-Activated Carbon Nanomaterials Derived from Cow Dung for Renewable Energy Applications

Porous-activated carbon (PAC) materials have been playing a vital role in meeting the challenges of the ever-increasing demand for alternative clean and sustainable energy technologies. In the present scenario, a facile approach is suggested to produce hierarchical PAC at different activation temperatures in the range of 600 to 900 °C by using cow dung (CD) waste as a precursor, and H₃PO₄ is adopted as the nonconventional activating agent to obtain large surface area values. The as-prepared cow dung-based PAC (CDPAC) is graphitic in nature with mixed micro- and mesoporous textures. High-resolution scanning electron microscopy depicts the morphology of CDPAC as nanoporous structures with a uniform arrangement. High-resolution transmission electron microscopy reveals spherical carbon dense nanoparticles with dense tiny spherical carbon particles. N₂ adsorption-desorption isotherms show a very high specific surface area of 2457 m²/g for the CDPAC 9 (CD 9) sample with a large pore volume of 1.965 cm³/g. Electrochemical measurements of the CD 9 sample show a good specific capacitance (C _s) of 347 F/g at a lower scan rate (5 mV/s) with improved cyclic stability, which is run up to 5000 cycles at a low current density (0.5 A/g). Hence, we choose an activated carbon prepared at 900 °C to fabricate the modified electrode material. In this regard, a flexible type symmetric supercapacitor device was fabricated, and the electrochemical test results show a supercapacitance value (C _s) of 208 F/g.

Separation and preconcentration of arsenite and other heavy metal ions using graphene oxide laminated with protein molecules

The graphene oxide surface was laminated with bovine serum albumin (BSA) followed by the directional flow through a membrane to prepare a free-standing PLGO (protein laminated GO) composite. BSA immobilization increased the interlayer spacing of GO and led to the formation of capillaries. The column packed with PLGO adsorbent permeated water faster as much as ca. 5 fold as compared to only GO packed column. The PLGO composite was used to develop a solid phase extraction method for the selective preconcentration of As(III) in the presence of As(V), prior to their determination. As(III) binding to sulfhydryl groups of BSA in PLGO plays a key role in the speciation. The coexisting heavy metal ions did not hinder the recovery of trace As(III). The method was advantageously employed for the preconcentration of As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) from water and food samples. A 3 mL of 1 M hydrochloric acid would be adequate for the complete desorption (recovery > 99%) of the adsorbed metal ions. The preconcentration limit achieved for As(III), Pb(II), Cd(II), Zn(II), Cu(II) and Ni(II) were 1.7, 2.0, 2.0, 2.0, 1.8 and 2.0 μg L^-1 respectively, with an optimized sample flow rate of 10 mL min^-1.

An electrochemical aptasensor for lead ion detection based on catalytic hairpin assembly and porous carbon supported platinum as signal amplification

A novel electrochemical aptasensor for lead detection based on catalytic hairpin assembly and PtNPs@PCs as signal amplification.

Applications of Graphene and Its Derivatives in Chemical Analysis

In this review, the applications of graphene and its derivatives in the chemical analysis have been described. The properties of graphene materials which are essential for their use in chemical and biochemical analysis are characterized. The materials are used in sensors and biosensors, in electrochemistry, in chromatography and in the sample preparation techniques. Chemical and electrochemical sensors containing graphene materials are useful devices for detecting some chemical and biochemical compounds. Chromatographic columns for HPLC with graphene containing stationary phases may be used for separation of polar and nonpolar components of some specific mixtures. Graphene materials could be successfully employed during sample preparation for analysis with SPE, magnetic SPE, and SPME techniques. HighlightsThe review of the applications of graphene (G) and its derivatives, graphene oxide (GO) and reduced graphene oxide (rGO), in chemical and biochemical analysis is proposed.The electron donor-acceptor and proton donor-acceptor interactions for the graphene based materials - analytes systems and their impact on the analysis results are discussed, particularly:    i) in electrochemistry,ii) in chromatography,iii) in modern sample preparation techniquesiv) in sensors of different types.The essence of the thermal stability and the nomenclature of the graphene based materials in their different applications in chemical systems of different classes was discussed (and suggested).The benefits of using SPME fibers with immobilized graphene materials have been presented in detail.

Innovative Configurations of Sample Preparation Techniques Applied in Bioanalytical Chemistry: A Review

Background:

Recently, in all fields of analytical chemistry, increased attention has been paid to extraction procedures and instrumental methods, which are easily scalable and are able to automate in order to improve the “high-throughput” capability.

Introduction:

The main goal of these applications relates to an improvement of the precision in the quantitative analysis, reduction of different sources of errors, decrease the analysis time and, in general, improve the analytical performances. Often these points can be in contrast to each other, not allowing to achieve the expected result but forcing a compromise between the objectives of the method and the analytical performance.

Methods:

In this review, following the evolution of the (micro)extraction procedures and instrument configurations, the recent procedures used in bioanalytical chemistry are critically evaluated. The aim of this paper is providing an overview of the approaches available in order to perform on-line coupling of various extraction techniques with chromatographic methods for the analysis of different compounds in various samples. Furthermore, a comparison between off-line and on-line systems, advantages of on-line systems applied on major extractive techniques and future perspectives are described.

Result:

The extraction methods suitable for on-line coupling covered in this review are: liquid-liquid extraction (LLE), solid phase extraction (SPE), solid phase microextraction (SPME), dispersive liquid- liquid microextraction (DLLME), microextraction by packed sorbent (MEPS), supercritical fluid extraction (SFE) and fabric phase sorptive extraction (FPSE).

Conclusion:

An overview of the micro-extraction techniques mentioned above was provided, making a comparison between them and focusing attention on future perspectives.

Highly sensitive and selective optical sensor for lead ion detection based on liquid crystal decorated with DNAzyme

Lead ions (Pb²⁺) are one of the major environmental pollutants that are dangerous for human health, thus the detection methods of Pb²⁺ become very important as well. However, most reported techniques suffer from drawbacks such as long time, expensive equipment and complicated testing process, which prevent the use of real-time application. Herein, we demonstrate a novel liquid crystal optical sensor for detection of Pb²⁺ based on DNAzyme and its combined strand. The ordered and disordered configuration of liquid crystals, induced by complementary DNA strand and catalytically cleaved DNA in presence of lead ion separately, leads to dark and bright optical image under POM. The proposed naked-eye optical sensor possesses an extremely broad detection range of Pb²⁺ from 50 nM to 500 µM, with a low detection limit about 36.8 nM. The sensor also demonstrates high selectivity of Pb²⁺ from many other metal ions. The proposal LC sensor is highly sensitive and selective for Pb²⁺ detection, which provides a novel platform for other heavy metal, DNAs or antigen in biological and chemical fields by modifying sensing molecules.

Graphene Oxide/Polyethylene Glycol-Stick for Thin Film Microextraction of β-Blockers from Human Oral Fluid by Liquid Chromatography-Tandem Mass Spectrometry

A wooden stick coated with a novel graphene-based nanocomposite (Graphene oxide/polyethylene glycol (GO/PEG)) is introduced and investigated for its efficacy in solid phase microextraction techniques. The GO/PEG-stick was prepared and subsequently applied for the extraction of β-blockers, acebutolol, and metoprolol in human oral fluid samples, which were subsequently detected by liquid chromatography tandem mass spectrometry (LC-MS/MS). Experimental parameters affecting the extraction protocol including sample pH, extraction time, desorption time, appropriate desorption solvent, and salt addition were optimized. Method validation for the detection from oral fluid samples was performed following FDA (Food and Drug Administration) guidelines on bioanalytical method validation. Calibration curves ranging from 5.0 to 2000 nmol L⁻¹ for acebutolol and 25.0 to 2000 nmol L⁻¹ for metoprolol were used. The values for the coefficient of determination (R²) were found to be 0.998 and 0.996 (n = 3) for acebutolol and metoprolol, respectively. The recovery of analytes during extraction was 80.0% for acebutolol and 62.0% for metoprolol, respectively. The limit of detections (LODs) were 1.25, 8.00 nmol L⁻¹ for acebutolol and metoprolol and the lower limit of quantifications (LLOQ) were 5.00 nmol L⁻¹ for acebutolol and 25.0 nmol L⁻¹ for metoprolol. Validation experiments conducted with quality control (QC) samples demonstrated method accuracy between 80.0% to 97.0% for acebutolol and from 95.0% to 109.0% for metoprolol. The inter-day precision for QC samples ranged from 3.6% to 12.9% for acebutolol and 9.5% to 11.3% for metoprolol. Additionally, the GO/PEG-stick was demonstrated to be reusable, with the same stick observed to be viable for more than 10 extractions from oral fluid samples.

Graphene oxide chemically modified with 5-amino-1,10-phenanthroline as sorbent for separation and preconcentration of trace amount of lead(II)

Graphene oxide (GO) was chemically functionalized with 5-amino-1,10-phenanthroline. The resulting conjugate (phen-GO) was characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. The experiments show that phen-GO has a high affinity for extraction of Pb(II) ions. Isotherms and kinetics fit the Langmuir model and pseudo-second-order equations. By using phen-GO as a sorbent, Pb(II) ions can be quantitatively adsorbed at pH 6.0. The adsorption capacity is 548 mg g^-1. Following desorption with 2 mol L^-1 HNO₃, Pb(II) was quantified by inductively coupled plasma optical emission spectrometry. The effects of pH value, eluent type, sorption time, sample volume, and matrix ions were optimized. The accuracy of the method was validated by analysis of the reference materials DOLT-3 (dogfish liver) and SRM 1640a (natural water). Under optimal conditions, the calibration plots cover the 0.25 to 500 ng mL^-1 Pb(II) concentration range. The method was successfully applied to the analysis of spiked water and biological samples. Other figures of merit include a preconcentration factor of 250, a detection limit of 46 ng L^-1, and a relative standard deviation of <5%. Graphical abstract Schematic presentation of the dispersive solid-phase extraction of lead(II) ions using graphene oxide modified with 5-amino-1,10-phenanthroline, followed by their determination by inductively coupled plasma optical emission spectrometry (ICP OES).

High-efficiency adsorption of tetracycline by the prepared waste collagen fiber-derived porous biochar

Porous biochar (PBC) derived from Cr-containing waste collagen fibers was prepared by two-step pyrolysis to 800 °C (PBC-800) and alkali activation.

Efficacy of engineered GO Amberlite XAD-16 picolylamine sorbent for the trace determination of Pb (II) and Cu (II) in fishes by solid phase extraction column coupled with inductively coupled plasma optical emission spectrometry

Graphene oxide (GO) was immobilized innovatively through azo spacer arm onto the surface of polymeric Amberlite XAD-16 resin in order to expose all oxygen functionalities freely available for metal ions coordination and further modification with picolylamine which governs selectivity. The GO Amberlite XAD-16 picolylamine enables the development of SPE column coupled with ICP-OES for preconcentration and determination of Pb (II) and Cu (II) in water and fish samples. Elution was performed by mild acid (2M HCl) no other carcinogenic organic solvent was used, prevents ligand leaching. Under optimized conditions, the preconcentration factors of 150 and detection limits 1.434 and 0.048 µg L⁻¹ for Pb (II) and Cu (II)  were obtained respectively.

A new combination for the determination of ultratrace cadmium: solid-phase microextraction by stearic acid-coated magnetic nanoparticles prior to batch-type hydride generation atomic absorption spectrometry

Solid-phase microextraction method based on stearic acid-coated magnetic nanoparticle has been combined with batch-type hydride generation atomic absorption spectrometry (BT-HGAAS) system to determine cadmium at ultratrace levels. After the adsorption of cadmium ions onto stearic acid-coated magnetic nanoparticles, they were easily separated from the aqueous phase by means of a magnet. All the instrumental and experimental parameters such as pH of buffer solution, interaction period, concentration, and volume of NaBH₄ were optimized. Under the optimal conditions, limit of quantification (LOQ) and limit of detection (LOD) for the solid-phase microextraction (SPME) based on stearic acid-coated magnetic nanoparticles-BT-HGAAS (SACMNP-BT-HGAAS) method were obtained as 270.8 ng/L and 81.7 ng/L, respectively. The matrix-matching calibration method was performed in order to improve the accuracy of cadmium quantification in tap water and the recovery results obtained were as follows: 88.56 ± 8.92 and 97.43 ± 9.76, for 6.0 and 8.0 ng/mL of cadmium-spiked tap water samples, respectively. Graphical abstract ᅟ.

In-syringe solid-phase extraction for on-site sampling of pyrethroids in environmental water samples

On-site sampling is an analytical approach that can ensure the accuracy of monitoring data and enhance the effectiveness of environmental protection measures. In the present work, an in-syringe solid-phase extraction (SPE) device was designed for on-site sampling of trace contaminants in environmental water samples followed by gas chromatography-mass spectrometry (GC-MS) analysis. Template assisted freeze casting followed by hydrazine vapor reduction approach was used to synthesize a hierarchical porous graphene aerogel (HPGA), which was used as the sorbent in the in-syringe SPE device. Environmental degradable pyrethroids were selected as the model analytes. Owing to the large specific surface area and hydrophobicity of HPGA, the target molecules could be completely extracted during one aspirating/dispensing cycle. The analytes were stable on the sorbent for at least 72 h when the device was stored under airtight and light-free conditions, and were not affected by the pH value of sample solution. All results demonstrated that the device could meet the requirements of on-site sampling. For practical application, the limits of detection were found to be in the range of 0.012-0.11 ng mL^-1 under the optimized conditions, and satisfactory recoveries in the range of 65.7-105.9% were obtained for the analysis of real samples. The results of this study demonstrate the immense potential of HPGA for the enrichment of trace environmental pollutants, and meanwhile promote the application of the in-syringe SPE technique as a promising candidate for on-site sampling.