Electromembrane extraction-preconcentration followed by microvolume UV–Vis spectrophotometric determination of mercury in water and fish samples

The role of nanomaterials in tailoring electromembrane extraction performance: A review

Electromembrane extraction (EME) is a membrane-based miniaturized microextraction technique used to extract ionized analytes from complex mixtures. EME extracts can be analyzed using all major analytical instrumental techniques. The major advantages of EME include short extraction time, low consumption of organic solvents and chemicals, high extraction capability, high selectivity, and efficient sample cleanup. Numerous modifications to EME, such as the use of microfluidic devices, green solvents, biobased renewable membranes, and hyphenation with other separation techniques, have increased the selectivity and sensitivity of EME. Furthermore, nanomaterials have been used to improve the efficiency, selectivity, and stability of EME systems. Various nanomaterials have been proposed for the modification of EME-based separation systems. The larger surface area, high porosity, and various interactions with the target analytes are the most important properties of nanomaterials and nanocomposites in improving the figures of merit of EME. Nanomaterials have mainly been used to modify the chemical composition of the liquid membrane in EME, but modifications of the polymeric support membrane and the electrodes have also been reported. Therefore, this review highlights the transformative role of nanomaterials in EME, focusing on their application in enhancing extraction efficiency, selectivity, and stability. Key advancements include modifying supported liquid membranes (SLMs), membrane decoration, and optimizing electrode performance. The review also critically examines challenges, such as pore blockage and electrolysis-induced instability, offering insights into future directions for nanomaterial-enhanced EME. Despite of the numerous benefits of nanomaterials, their environmental toxicity cannot be overlooked and should be carefully examined for each new case. A bio-based and biopolymer-based nanomaterials in future EME studies can significantly address these issues while remaining aligned with green chemistry principles. Artificial intelligence-based models should be applied to predict effective nanomaterials in EME, thus significantly reduce chemical costs and consumption while also increasing the greenness level of developed EME approaches. Finally, long-term stability of new developed solutions should be an obligatory part of each new research in this field.

Electromembrane extraction of multi-class prohibited/restricted veterinary drugs from food samples - Exploring liquid membrane composition

Effective monitoring of veterinary drug residues in food is essential for legislation compliance and food safety, yet remains challenging due to low concentrations and complex matrices. This study introduced a miniaturized 96-well electromembrane extraction (EME) technique for pre-concentration and isolation 80 prohibited/restricted veterinary drugs from honey samples. Three liquid membranes were developed and characterized: V1 ("V" for veterinary), a mixture of 2-undecanone and 0.5 % 2-nitro-p-cymene, was optimal for extraction of quinolones, tetracyclines, and β-agonists. V2, a mixture of 2-nitrophenyl octyl ether and a deep eutectic solution (formed upon mixing 6-methylcoumarin with thymol in a 1:1 w/w ratio) in a 1:1 v/v ratio, with the addition of 0.5 % di(2-ethylhexyl) phosphate (DEHP), was suitable for macrolides and sulfonamides extraction. V3, a deep eutectic solvent formed upon 1-decanoic acid and camphor in a 1:1 w/w ratio with 1 % DEHP, was suitable for aminoglycosides and β-lactams. Operational parameters were fine-tuned to achieve optimal extraction efficiencies, with recoveries ranging from 20.1-117.5 %, 20.3-91.9 %, and 20.1-118.8 % for V1, V2, and V3, respectively. High precision was observed for compounds with recoveries over 40 % (intra-day: 0.4-27.7 %; inter-day: 2.6-33.0 %), and matrix effects were generally within 80-120 %. This work established a theoretical framework for EME in food analysis, highlighting its potential as a powerful sample pretreatment method for the detection of veterinary drug residues. The results demonstrated the feasibility and advantages of using EME for ensuring food safety and regulatory compliance.

An Efficient Fluorescent Chemosensing Probe for Total Determination and Speciation of Ultra-Trace Levels of Mercury (II) Species in Water

The current study reports a novel fluorescent chemosensor based on the tagging agent 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein (Rose Bengal, RB) for detection of trace levels of Hg2+in environmental water. The established probe has been based upon liquid-liquid extraction (LLE) of the developed ternary complex ion associate {[Hg (bpy)2]2+.[RB]2-} of Hg2+ -2,2- bipyridyl complex [Hg (bpy)2]2+ and RB at pH 9.0 onto chloroform and measuring the resulting fluorescence enhancement signal intensity at λex/em = 570/ (580-600) nm. The limits of detection (LOD) and quantification (LOQ) of for Hg2+ was calculated to be 6.06 and 20 nM with a linear dynamic range (LDR) of 0.02-20µM, respectively. The stability constant, stoichiometry, chemical equilibria, and the thermodynamic parameters (ΔH, ΔS, and ΔG) of the developed ion associate were evaluated and assigned. Student's t and F tests at 95% confidence were fruitfully used for validation of the proposed methodology for Hg2+ detection in water samples with the aid of inductively coupled plasma-optical emission spectrometry (ICP-OES). The established strategy was successfully applied for detection of trace levels of Hg2+ in water samples with acceptable results. The proposed probe was satisfactorily applied for total determination and speciation of Hg in various water samples. Integrating the functional chelating agent onto associate formation to improve the selectivity and sensing properties of the LLE combining sensing probe towards target analyte in water represent the main interest.

Environmental Applications of Electromembrane Extraction: A Review

Electromembrane extraction (EME) is a miniaturized extraction technique that has been widely used in recent years for the analysis and removal of pollutants in the environment. It is based on electrokinetic migration across a supported liquid membrane (SLM) under the influence of an external electrical field between two aqueous compartments. Based on the features of the SLM and the electrical field, EME offers quick extraction, effective sample clean-up, and good selectivity, and limits the amount of organic solvent used per sample to a few microliters. In this paper, the basic devices (membrane materials and types of organic solvents) and influencing factors of EME are first introduced, and the applications of EME in the analysis and removal of environmental inorganic ions and organic pollutants are systematically reviewed. An outlook on the future development of EME for environmental applications is also given.

Ultra-trace determination of cadmium in water and food samples by a thin-film microextraction using a supported liquid membrane combined with smartphone-based colorimetric detection

A mixture of n-octanol and dithizone was introduced as an effective and novel extraction agent in a thin-film microextraction technique for the pre-concentration of cadmium ions. The extraction agent was immobilized on small pieces of porous polypropylene flat membrane as a supported liquid membrane. The analyte extraction was performed by immersing the modified film in the sample solution, and via a complex formation between the immobilized dithizone on the film and cadmium ions. After the thin-film microextraction process, the colored cadmium-dithizone complex was directly measured by a smartphone colorimetric analysis. Under optimized conditions, the linear dynamic range, the limit of detection, and the limit of quantification were 0.5-300.0, 0.1, and 0.4 μg L^-1, respectively. The developed technique was successfully employed to quantify cadmium ions in water and food samples. The high relative recovery values (95.0-103.0%) along with relative standard deviations of less than 2.5% were obtained for the spiked samples.

Improvement of Advanced Sample Preparation Systems for the Determination of Trace Ni in Seawater by Electro-Membranes

Due to its important environmental role, the analysis of trace metals in natural waters is attracting increasing attention; consequently, faster and more accurate analytical methods are now needed to reach even lower limits of detection. In this work, we propose the use of electro-membrane extraction (EME) to improve analytical methods based on hollow fiber liquid phase micro-extraction (HFLPME). Specifically, an EME-based method for the determination of trace Ni in seawater has been developed, using an HFLPME system with di-2-ethylhexyl phosphoric acid (DEHPA) in kerosene as a chemical carrier, followed by instrumental determination by graphite furnace atomic absorption spectroscopy (GFAAS). Under optimum conditions, Ni was pre-concentrated 180 ± 17 times after 15 min, using sample pH = 5.5, the concentration of DEHPA 0.9 M in the liquid membranes, and 1.9 M HNO₃ in the acceptor solution, as well as an electric potential of 25 V with the sample being stirred at 500 rpm. When compared with other HFLPME systems for pre-concentration of trace Ni in seawater in the absence of electric potential, the enrichment factor was improved 2.2 times, while the time of extraction was reduced an 89%. The limit of detection of the new method was 23.3 ng L^-1, and both its applicability and accuracy were successfully evaluated by analyzing Ni concentration in a seawater-certified reference material (BCR-403), showing the reliability of EME for sample preparation in the determination of trace metals in marine water samples.

Recruiting chemical grafting method for surface modification of stainless steel to fabricate a selective sorbent for solid phase microextraction of mercury metal ion

Keeping selectiveness and efficiency in view with solid-phase microextraction (SPME) of metal ions, this work was aimed at synthesis of a novel modified sorbent on a stainless-steel surface to fabricate a selective and efficient fiber for SPME of mercury ions from real food and biological samples. After the confirmation of sorbent structure grafted on the stainless-steel surface, by different techniques, the synthesized fiber was utilized for extraction and preconcentration of mercury before its measurement by an inductively coupled plasma-optical emission spectroscopy (ICP-OES). For optimizing the efficiency, the influences of various factors on the extraction of Hg (II) ion were scrutinized. The optimized values used for extraction were pH 7.0, adsorption time 8 min, desorption time 5 min, 5 mL of eluent solvent containing nitric acid with concentration of 0.5 mol L^-1, and stirring rate of 300 rpm. Underneath optimum condition, the relative standard deviation for 30 extractions, done by one synthesized fiber, was calculated to be 2.89% and for five extractions, done by 5 synthesized fibers, was calculated to be 1.78%. The high performance of the synthesized fiber was checked with high recoveries obtained from 30 successive sorption-desorption cycles, using a unique synthesized fiber. Finally, the suggested procedure was triumphally exploited for extraction and pre-concentration of Hg (II) ion in real food and biological samples.

Analytical Performance of Electromembranes as a Tool for Nanoconcentrations of Silver in Waters

Electromembranes increase the efficiency of metal transport in liquid-phase microextraction systems by applying an electric potential, which accelerates the transport. Nevertheless, to get high extraction percentages in short extraction times it is necessary to take into account a great variety of factors, and multivariate optimization techniques are the best alternative to determine the most influential variables and to optimize the extraction process. In this work, a fractional factorial design was applied to determine the most influential variables in the extraction of silver by electromembranes. Thus, the effect of tri-isobutylphosphine sulphide (Cyanex 471x) concentration in the organic solution, sodium thiosulphate concentration in the acceptor solution, nitrate concentration in the sample solution, extraction time, stirring rate and electric potential on the enrichment factor were studied. Once the most important variables were selected, a small composite design (Draper-Lin) was used to obtain their optimal values to maximize the enrichment factor. Under these conditions, an experimental enrichment factor of 49.91 ± 3.95 was achieved after 22 min. Finally, the effect of saline matrix on the enrichment factor was tested and the optimized system was successfully applied to analyse silver concentrations at ultratrace levels, within the range of 7-29 ng·L^-1 in different real seawater samples.

Recent applications and novel strategies for mercury determination in environmental samples using microextraction-based approaches: A review

The growing need to monitor Hg levels in the environment to control its emissions and evaluate the effectiveness of reduction policies is driving the scientific community to focus efforts on creating analytical methods that are simpler, lower cost, more performing, and environmentally sustainable. In this context, an important contribution is provided by microextraction techniques, which have long proven to be simple, reliable, and to ensure an environmentally responsible sample preparation. This manuscript reviews the recent progress in the determination of environmental Hg using microextraction techniques. The considered studies involve all environmental compartments (i.e., air, water, soil, and biota) and have been discussed by grouping them according to the employed technique while pointing out the main advances achieved and the most important limitations. The ultimate goal is to provide an up-to-date overview of the analytical potential of microextraction techniques that can be exploited in various investigation fields and to highlight the most important knowledge gaps that should be addressed in the coming years, such as in-situ sampling, the use of natural materials, and the value of metrological support to obtain data SI-traceable and comparable.

Ultrasound-assisted deep eutectic solvent-based liquid-liquid microextraction for simultaneous determination of Ni (II) and Zn (II) in food samples

A new approach was developed for the simultaneous pre-concentration and determination of Ni (II) and Zn (II) in food samples. This method is based on ultrasound-assisted liquid-liquid micro extraction using hydrophobic deep eutectic solvent (DES) and 1,10-phenanthroline as chelating agent. The effect of several parameters, such as pH, selection and volume of DES, amount of chelating agent, time of sonication and centrifugation, was studied. Under optimized conditions, the developed procedure offered exceptional sensitivity and linearity. The limit of detection was approximately 0.029 µg/Kg and 1.5 µg/Kg for Ni (II) and Zn (II), respectively. The proposed method was applied for the pre-concentration and determination of Ni (II) and Zn (II) in hydrogenated edible oils, fishes, and milk samples. The results of this study were compared with reported methods in the literature revealing its advantages.

Versatile Integration of Liquid-Phase Microextraction and Fluorescent Aptamer Beacons: A Synergistic Effect for Bioanalysis

Fluorescent aptamer beacons (FABs) are a major category of biosensors widely used in environmental analysis. However, due to their low compatibility, it is difficult to use the common FABs for biological samples. To overcome this challenge, construction of FABs with complex structures to adapt the nature of biological samples is currently in progress in this field. Unlike previous works, we moved our range of vision from the FAB itself to the biological sample. Inspired by this idea, in this work, flat membrane-based liquid-phase microextraction (FM-LPME) with sufficient sample cleanup and preconcentration capacities was integrated with FABs. With the merits of both FM-LPME and FABs, the integrated LPME-FAB system displayed a clear synergistic enhancement for target analysis. Specifically, LPME in the LPME-FAB system provided purified and enriched Hg²⁺ for the FAB recognition, while the FAB recognition event promoted the extraction efficiency of LPME. Due to superior performances, the LPME-FAB system achieved highly sensitive analysis of Hg²⁺ in urine samples with a detection limit of 27 nM and accuracies in the range of 98-113%. To the best of our knowledge, this is the first time that an integrated LPME-FAB system was constructed for target analysis in biological samples. We believe that this study will provide a new insight into the next generation of biosensors, where the integration of sample preparation with detection probes is as important as the design of complex probes in the field of bioanalysis.

Selective extraction and determination of Cr(VI) in food samples based on tandem electromembrane extraction followed by electrothermal atomic absorption spectrometry

In this study, electromembrane extraction (EME) combined with micro-EME (µ-EME) was used for the selective extraction of Cr(VI) from food samples (milk powder, Ocimum basilicum, and fish samples). Electrothermal atomic absorption spectrometry was used for the quantification of Cr(VI). Under the optimized extraction conditions, the extraction recovery of Cr(VI) was 73.7%. This proposed method provided a linear range from 0.01 to 5.0 ng/mL and the limit of detection (LOD) and limit of quantification (LOQ) were 0.003 and 0.010 ng/mL. The %RSD (n = 5) was in the range of 11.2-11.8% at 0.05, 1.0 and 2.5 ng/mL of Cr(VI), and the enrichment factor was 584. The accuracy of the method was evaluated by analysis of SRM 2700 as a certified reference material (CRM) and result was in good agreement with the certified value.

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.

Determination of Total Mercury in Solid Samples by Anodic Stripping Voltammetry

The anodic stripping voltammetry (ASV) was investigated to determine total mercury in solid samples using a gold electrode. The mercury was deposited on the gold electrode in a preconcentration step. The oxidation peak of mercury was irreversible. The optimal conditions of the procedure were found to be as follows: 0.05 mol L−1 HCl solution, deposition potential −0.5 V vs. Ag/AgCl/KCls, deposition time 40 s, and sweep rate 0.04 V s−1. Under the optimal conditions, the peak current showed a linear dependence on Hg2+ concentration in the range from 0.01 to 0.1 mg l−1. The detection limit and quantification limit were 4.28 µg L−1 and 12.98 µg L−1, respectively. The mean recovery and relative standard deviation were 91.2% and 2.4% (n = 9). The procedure was successfully applied for determining total mercury in samples collected from Hanoi light bulb warehouse—The Rang Dong Light Source and Vacuum Flask JSC. The results were compared with cold vapor atomic absorption spectrometry (CV-AAS).

A portable selective electrochemical sensor amplified with Fe3O4@Au-cysteamine-thymine acetic acid as conductive mediator for determination of mercuric ion

Mercury ion (Hg²⁺) is considered to be one of the most toxic heavy metal ions and can cause adverse effects on kidney function, the central nervous system, and the immune system. Therefore, it is important to develop a fast and simple method for sensitive and selective detection of Hg²⁺ in the environment. This research proposes a portable electrochemical sensor for rapid and selective detection of Hg²⁺. The sensor platform is designed based on thymine acetic acid anchored with cysteamine-conjugated core shell Fe₃O₄@Au nanoparticles (Fe₃O₄@Au/CA/T-COOH) immobilized on a sensing area of a screen-printed carbon electrode (SPCE) with the aid of an external magnetic field embedded in a homemade electrode holder for ease of handling. In the presence of Hg²⁺, the immobilized thymine combines specifically with Hg²⁺ and forms a thymine-Hg²⁺-thymine mismatch (T-Hg²⁺-T). The resulting amount of Hg²⁺ was determined by differential pulse anodic stripping voltammetry (DPASV). Under optimal conditions, the sensor exhibited two wide linearities in a range from 1 to 200 μg L^-1 and 200-2200 μg L^-1 with the reliability coefficient of determination of 0.997 and 0.999, respectively. The detection limit (LOD) and the quantification limit (LOQ) were also determined to be 0.5 μg L^-1 and 1.0 μg L^-1, respectively. The sensor was further applied for determination of Hg²⁺ in water samples, a certified reference material and fish samples. The results were compared with flow injection atomic spectroscopy-inductively coupled plasma-optical emission spectroscopy (FIAS-ICP-OES) systems as a reference method. Results obtained with the proposed sensor were relatively satisfactory, and they showed no significant differences at a 95% confidence level by t-test from the standard method. Therefore, considering its fast and simple advantages, this novel strategy provides a potential platform for construction of a Hg²⁺ electrochemical sensor.

Hollow fiber-based liquid phase microextraction followed by analytical instrumental techniques for quantitative analysis of heavy metal ions and pharmaceuticals

Hollow-fiber liquid-phase microextraction (HF-LPME) and electromembrane extraction (EME) are miniaturized extraction techniques, and have been coupled with various analytical instruments for trace analysis of heavy metals, drugs and other organic compounds, in recent years. HF-LPME and EME provide high selectivity, efficient sample cleanup and enrichment, and reduce the consumption of organic solvents to a few micro-liters per sample. HF-LPME and EME are compatible with different analytical instruments for chromatography, electrophoresis, atomic spectroscopy, mass spectrometry, and electrochemical detection. HF-LPME and EME have gained significant popularity during the recent years. This review focuses on hollow fiber based techniques (especially HF-LPME and EME) of heavy metals and pharmaceuticals (published 2017 to May 2019), and their combinations with atomic spectroscopy, UV-VIS spectrophotometry, high performance liquid chromatography, gas chromatography, capillary electrophoresis, and voltammetry.

Superhydrophilic graphene oxide/electrospun cellulose nanofibre for efficient adsorption of organophosphorus pesticides from environmental samples

Superhydrophilic graphene oxide/electrospun cellulose nanofibre (GO/CNF) was synthesized, characterized and successfully used in a solid-phase membrane tip adsorption (SPMTA) as an adsorbent towards a simultaneous analysis of polar organophosphorus pesticides (OPPs) in several food and water samples. Separation, determination and quantification were achieved prior to ultra-performance liquid chromatography coupled with ultraviolet detector. The influence of several parameters such as sample pH, adsorption time, adsorbent dosage and initial concentration were investigated. SPMTA was linear in the range of 0.05 and 10 mg l^-1 under the optimum adsorption conditions (sample pH 12; 5 mg of adsorbent dosage; 15 min of adsorption time) for methyl parathion, ethoprophos, sulfotepp and chlorpyrifos with excellent correlation coefficients of 0.994-0.999. Acceptable precision (RSDs) as achieved for intraday (0.06-5.44%, n = 3) and interday (0.17-7.76%, n = 3) analyses. Low limits of detection (0.01-0.05 mg l^-1) and satisfactory consistency in adsorption (71.14-99.95%) were obtained for the spiked OPPs from Sungai Pahang, Tasik Cheras, cabbages and rice samples. The adsorption data were well followed the second-order kinetic model and fits the Freundlich adsorption model. The newly synthesized GO/CNF showed a great adsorbent potential for OPPs analysis.

Formation of functionalized silica-based nanoparticles and their application for extraction and determination of Hg (II) ion in fish samples

An isonicotinic acid hydrazide (INAH) chemically modified fumed silica, as a novel adsorbent, was designed for the preconcentration and determination of Hg (II) ions in fish samples via the solid phase extraction followed by the hydride generation atomic absorption spectrometry (HG-AAS). In this work, the efficiency of the synthesized adsorbent was investigated to determine its ability for the extraction of the Hg (II) ions from the aqueous solutions. The extraction efficiency was investigated by optimizing of different experimental conditions, such as pH, sample volume, flow rate, adsorbent dosage, and eluent type. Under the optimal conditions, a linear calibration curve for the solid phase extraction method was obtained in the range of between 0.12 and 16.5 μg L-1. The obtained detection limit and preconcentration factor were 0.018 μg L-1 and 25, respectively (RSD > 3%). The proposed optimized method was successfully applied to fish samples.

Hollow fiber liquid-phase microextraction based on the use of a rotating extraction cell: A green approach for trace determination of rhodamine 6G and methylene blue dyes

In this work, a novel mode of hollow fiber liquid-phase microextraction (HF-LPME) technique namely rotating extraction cell solvent bar microextraction (REC-SBME) was introduced. The proposed method was applied for the preconcentration of methylene blue (MB) and rhodamine 6G (RG) in some real samples, including soft drink, lipstick, environmental water, and wastewater samples. In the extraction setup, two pieces of hollow fibers were fixed on a mechanical support and immersed in a rotating extraction cell containing the sample solution during the extraction process. The rotation of the extraction cell by using an electric motor led to an enhancement in the mass transfer of the dyes from the sample solution into the organic acceptor phase. In the developed procedure, the UV-Vis spectrophotometry and HPLC-UV/Vis were employed as detection methods for the analysis of the acceptor phase and the obtained results were compared. Optimization of the extraction factors affecting the method, including organic solvent type, sample solution pH, extraction time, rotational rate, the volume of sample and acceptor solutions, salt addition, and temperature was performed in order to obtain the best preconcentration factor. Linear dynamic range obtained by HPLC-UV/Vis and spectrophotometry was observed in the ranges of 2.5-1200 ng mL^-1 for RG and 1.6-600 ng mL^-1 for MB with R² more than 0.9971. Also, relative standard deviation (RSD) values (n = 3) less than 3.8% were obtained. The good conformity of the obtained results makes UV-Vis spectrophotometric method an ideal tool for routine analysis of trace dyes in the complex matrices after REC-SBME.

Metal organic framework assisted in situ complexation for miniaturized solid phase extraction of organic mercury in fish and Dendrobium officinale

Zirconium-based metal-organic frameworks, namely Zr-based MOF, was employed as adsorbent material in the miniaturized solid phase extraction of organic mercury compounds in food prior to capillary electrophoresis-diode array detector analysis. The synthesized adsorbent was characterized by different spectroscopic techniques. Parameters influencing the extraction and complexation of methylmercury chloride, ethylmercury chloride and phenylmercury chloride such as type of eluent solvent, type and amount of adsorbent were investigated. In addition, linear ranges contained 2.00-300.00 ng mL^-1 for MeHg⁺, 5.00-500.00 ng mL^-1 for EtHg⁺ and PhHg⁺, and the established method presented good linearity (R² ≥ 0.998). Under the optimized experimental conditions, the ranges of detection limit and quantitation limit were 0.022-0.067 ng mL^-1 and 0.073-0.220 ng mL^-1, respectively. The relative standard deviations of intra- and inter-day analysis were less than 3.2 and 3.1%, respectively. Trueness of the present method was successfully accomplished by means of the recovery assays (81.4-98.5%) in the blank samples with two concentration levels. The repeatability %RSD of the method was lower than 2.7%. Overall, the developed approach proved to have the latent capability to be utilized in routine analysis of organic mercury compounds in fish and Dendrobium officinale.

Solvent stir bar microextraction technique with three-hollow fiber configuration for trace determination of nitrite in river water samples

In this work, trace determination of nitrite in river water samples was studied using solvent stir bar microextraction system with three-hollow fiber configuration (3HF-SSBME) as a preconcentration step prior to UV-Vis spectrophotometry. The obtained results showed that the increase in the number of solvent bars can improve the extraction performance by increasing the contact area between acceptor and sample solutions. The extraction process relies on the well-known oxidation-reduction reaction of nitrite with iodide excess in acidic donor phase to form triiodide, and then its extraction into organic acceptor phase using a cationic surfactant. Various extraction parameters affecting the method were optimized and examined in detail. Detection limit of 1.6 μg L^-1 and preconcentration factor of 282 can be attained after an extraction time of 8 min under the optimum conditions of this technique. The proposed method showed a linear response up to 1000 μg L^-1 (r² = 0.996) with relative standard deviation values less than 4.0%. The accuracy of the developed method was assessed using the Griess technique. Finally, the proposed method was successfully employed for quantification of nitrite in river water samples (Ghezelozan, Zanjan, Iran).

Developing a miniaturized setup for in-tube simultaneous determination of three alkaloids using electromembrane extraction in combination with ultraviolet spectrophotometry

Herein, electromembrane extraction was combined with ultraviolet spectrophotometry using a customized manifold for preconcentration and simultaneous determination of morphine, codeine, and papaverine in water and human urine samples. Absorption spectra of the extracts were recorded inside the lumen of the hollow fiber using two fiber optics connected to a miniature spectrophotometer. Partial least squares regression was applied to resolve the overlapped spectra of the analytes. Performance of the model was validated by an independent test set. Central composite design was applied to optimize the extraction parameters. The optimized extraction conditions are as follows; supporting liquid membrane: 2-nitrophenyl octyl ether containing 15% v/v bis(2-ethylhexyl) phosphate, applied voltage: 80 V, donor pH: 3.0, acceptor pH: 1.0, extraction time: 20 min. Finally, the optimized extraction method was validated for determination of the mentioned alkaloids in human urine samples. The method showed good linearity (R²  > 0.995) for all of the mentioned alkaloids. The limits of detection for morphine, codeine, and papaverine in diluted human urine were found to be 0.6, 1.1, and 0.6 ng/mL, respectively with acceptable relative standard deviations. Enrichment factors of 104, 108, and 102 were achieved for morphine, codeine, and papaverine, respectively.

A cytosine-rich hairpin DNA loaded with silver nanoclusters as a fluorescent probe for uranium(IV) and mercury(II) ions

A dually responsive fluorescent probe for determination of U(IV) and mercury(II) ions was synthesized. The probe consists of a cytosine-rich hairpin DNA loaded with silver nanoclusters (DNA-AgNCs). The fluorescence of the AgNCs is found to be quenched by UO₂(II) at pH 5.0 and Hg(II) at pH 7.0 due to combined static and dynamic quenching. Under the optimal conditions, the green fluorescence of the DNA-AgNCs, best measured at excitation/emission wavelengths of 420/525 nm, decreases in the 4.0 to 75 pM UO₂(II) concentration range, and in the 0.3 to 8.0 nM Hg(II) concentration range. The respective detection limits are as low as 1.8 pM and 0.1 nM. The method was successfully applied to the determination of UO₂(II) and Hg(II) in (spiked) pond and taps waters and in soil extracts. Graphical abstract A label-free DNA was designed to synthesize green-fluorescent silver nanoclusters (AgNCs) and used for rapid dual detection of uranyl ions (UO₂(II)) at pH 5.0 and of mercury ions (Hg(II)) at pH 7.0 in environmental samples.

Development of Cellulosic Paper-Based Test Strips for Mercury(II) Determination in Aqueous Solution

Titration method (dropping-on method) was introduced as an efficient approach for determining the mercury ion (Hg²⁺) concentration in aqueous solution by using fabricated cellulosic paper-based test strips. In this study, dithizone used as a recognition reagent was physically loaded on cellulosic paper-based test strips for Hg²⁺ selective recognition. The sensing mechanism was established on the spectral absorption rate of the coordination compound that was formed by dithizone and Hg²⁺ under strong acidic conditions. The calibration curve was obtained by the absorbency of Hg²⁺-dithizone complexes from different Hg²⁺ concentration solutions, and the correlation coefficient (R ²) reached 0.9971. The detection range of the test trip for Hg²⁺ was obtained at 0.1 μg/mL to 30 μg/mL. Moreover, these superior cellulosic paper-based test strips have a rapid color-forming time (1.5 min) and low volume demand (3.7 μL samples at 0.0127 g/L dithizone recognition concentration). This portable paper-based test strip can give potential applications for field screening or on-site semiquantitative analysis.

Utility of ultrasound assisted-cloud point extraction and spectophotometry as a preconcentration and determination tool for the sensitive quantification of mercury species in fish samples

The current study reports, for the first time, the development of a new analytical method employing ultrasound assisted-cloud point extraction (UA-CPE) for the extraction of CH₃Hg⁺ and Hg²⁺ species from fish samples. Detection and quantification of mercury species were performed at 550nm by spectrophotometry. The analytical variables affecting complex formation and extraction efficiency were extensively evaluated and optimized by univariate method. Due to behave 14-fold more sensitive and selective of thiophene 2,5-dicarboxylic acid (H₂TDC) to Hg²⁺ ions than CH₃Hg⁺ in presence of mixed surfactant, Tween 20 and SDS at pH5.0, the amounts of free Hg²⁺ and total Hg were spectrophotometrically established at 550nm by monitoring Hg²⁺ in the pretreated- and extracted-fish samples in ultrasonic bath to speed up extraction using diluted acid mixture (1:1:1, v/v, 4molL^-1 HNO₃, 4molL^-1 HCl, and 0.5molL^-1 H₂O₂), before and after pre-oxidation with permanganate in acidic media. The amount of CH₃Hg⁺ was calculated from difference between total Hg and Hg²⁺ amounts. The UA-CPE method showed to be suitable for the extraction and determination of mercury species in certified reference materials. The results were in a good agreement (with Student's t-test at 95% confidence limit) with the certified values, and the relative standard deviation was lower than 3.2%. The limits of detection have been 0.27 and 1.20μgL^-1, for Hg²⁺ from aqueous calibration solutions and matrix-matched calibration solutions spiked before digestion, respectively, while it is 2.43μgL^-1 for CH₃Hg⁺ from matrix-matched calibration solutions. A significant matrix effect was not observed from comparison of slopes of both calibration curves, so as to represent the sample matrix. The method was applied to fish samples for speciation analysis of Hg²⁺ and CH₃Hg⁺. In terms of speciation, while total Hg is detected in range of 2.42-32.08μgkg^-1, the distribution of mercury in fish were in range of 0.7-11.06μgkg^-1 for CH₃Hg⁺ and in range of 1.72-24.56μgkg^-1 for Hg²⁺.

Sample preparation for polar metabolites in bioanalysis

Sample preparation is a primary step of any bioanalytical workflow, especially in metabolomics where maximum information has to be obtained without spoiling the analytical instrument. The sample extraction of polar metabolites is still challenging but strategies exist to enable the phase transfer of hydrophilic metabolites from the biological phase to a clean interference-free phase.

A novel label-free fluorescence assay for one-step sensitive detection of Hg2+ in environmental drinking water samples

A novel label-free fluorescence assay for detection of Hg²⁺ was developed based on the Hg²⁺-binding single-stranded DNA (ssDNA) and SYBR Green I (SG I). Differences from other assays, the designed rich-thymine (T) ssDNA probe without fluorescent labelling can be rapidly formed a T-Hg²⁺-T complex and folded into a stable hairpin structure in the presence of Hg²⁺ in environmental drinking water samples by facilitating fluorescence increase through intercalating with SG I in one-step. In the assay, the fluorescence signal can be directly obtained without additional incubation within 1 min. The dynamic quantitative working ranges was 5–1000 nM, the determination coefficients were satisfied by optimization of the reaction conditions. The lowest detection limit of Hg²⁺ was 3 nM which is well below the standard of U.S. Environmental Protection Agency. This method was highly specific for detecting of Hg²⁺ without being affected by other possible interfering ions from different background compositions of water samples. The recoveries of Hg²⁺ spiked in these samples were 95.05–103.51%. The proposed method is more viable, low-costing and simple for operation in field detection than the other methods with great potentials, such as emergency disposal, environmental monitoring, surveillance and supporting of ecological risk assessment and management.