Quantification of arsenic in real samples using a spectrophotometric cloud point extraction of the formed ion pair with astrazon orange G.

A novel cloud-point extraction (CPE) procedure for the determination of ultra-trace amounts of arsenic species in real samples, purchased from the local market by spectrophotometer was developed. Inorganic arsenic species analysis in water, beverages, and foods has become increasingly important in recent years, as arsenic species are considered carcinogenic and are assessed at significant levels in samples. The technique is established on a selective ternary complex of As(V) with astrazon orange G (AOG+) in the presence of tartaric acid and polyethylene glycol tertoctylphenyl ether (Triton X-114) at pH 4.0. The calibration curve developed within range 3.0-160 ng/mL with a correlation coefficient of 0.9988 for As(V) provided a preconcentration factor of 200 and a limit of detection (3S blank/m) of 0.88 ng/mL under optimum investigation conditions. The results of molar absorptivity and Sandell sensitivity are calculated and found to be 4.38 × 105 L/mol cm and 0.018 ng cm-2, respectively. The statistical treatment of data obtained from the proposed and GF-AAS procedures are compared in terms of Student's t-tests and variance ratio F-tests has revealed no significant differences. The methodology has been effectively confirmed by assessing real samples and comparing it to the GF-AAS method statistically.

The highly selective green colorimetric detection of yttrium ions in biological and environmental samples using the synergistic effect in an optical sensor.

A new eco-friendly method for creating an optical sensor membrane specifically designed to detect yttrium ions (Y3+) has been developed. The proposed sensor membrane is fabricated by integrating 4-(2-arsonophenylazo) salicylic acid (APASA), sodium tetraphenylborate (Na-TPB), and tri-n-octyl phosphine oxide (TOPO) into a plasticized poly(vinyl chloride) matrix with dimethyl sebacate (DMS) as the plasticizer. In this sensor membrane, APASA functions dually as an ionophore and a chromoionophore, while TOPO enhances the complexation of Y3+ ions with APASA. The composition of the sensor membrane has been meticulously optimized to achieve peak performance. The current membrane exhibits a linear dynamic range for Y3+ ions from 8.0 × 10-9 to 2.3 × 10-5 M, with detection and quantification limits of 2.3 × 10-9 and 7.7 × 10-9 M, respectively. No interference from other potentially interfering cations and anions was observed in the determination of Y3+. The membrane showed strong stability and a swift response time of about 3.0 minutes, with no signs of APASA leaching. This sensor is highly selective for Y3+ ions and can be renewed by treating it with 0.15 M HNO3. It has been effectively applied to measure Y3+ in nickel-based alloys, as well as in biological and environmental samples.

Eco-friendly optical sensor for precise detection of gold ions in diverse matrices through the integration of ß-2-hydroxybenzyl-3-methoxy-2-hydroxyazastyrene in a PVC membrane.

An environmentally conscious methodology is investigated for the precise and discerning identification of trace concentrations of gold ions in diverse matrices. A novel optical sensor membrane is proposed for the determination of Au3+ ions, utilizing the immobilization of ß-2-hydroxybenzyl-3-methoxy-2-hydroxyazastyrene (HMHS) entrapped in polyvinyl chloride (PVC). The sensor incorporates sodium tetraphenylborate (Na-TPB) as the ionic additive and dibutyl phthalate (DBP) as a plasticizer. Under optimal conditions, the suggested sensor exhibits a linear calibration response to Au3+ ions within a concentration range of 5.0 to 165 ng mL-1. Detection and quantification limits are specified as 1.5 and 4.8 ng mL-1, respectively, with a rapid response time of 5.0 min. Upon presentation, this optical sensor not only affirms high reproducibility, stability, and an extended operational lifespan but also showcases exceptional selectivity for Au3+ ions. Notably, no discernible interference is observed when assessing the potential influence of other cations and anions on Au3+ ion detection. The adaptability of this optical sensor is validated through its successful application in determining Au3+ ion concentrations across various sample types, including water, environmental, cosmetics, and soil matrices.

Revolutionizing scandium detection in real samples: Unleashing the power of sol-gel-based optical sensor.

The development of a highly selective and ultra-sensitive optical sensor for detecting scandium (Sc3+) ions involves incorporating the reagent 2,3-dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline (DCHNAQ) into a silica sol-gel thin film on a glass substrate. This innovative approach utilizes tetraethoxy-silane (TEOS) as the precursor, maintaining a sol-gel pH level of 4.5, a water-to-alkoxide ratio of 5:1, and a DCHNAQ concentration of 5.0 × 10-4 M. A detailed exploration of the impact of sol-gel parameters on the sensing capabilities of the developed sensor has been meticulously undertaken. This innovative sensor demonstrates remarkable selectivity in evaluating Sc3+ ions over a dynamic range of 7.5-170 ng/mL, with limits of quantification and detection recorded at 7.3 and 2.20 ng/mL, respectively. Consistent results are achieved with a minimal RSD of 1.47 and 0.94% for Sc3+ ions at 50 and 100 ng/mL, respectively, coupled with a swift response time of three min. Assessments of interference demonstrate a noteworthy preference for Sc3+ions, accomplished by enclosing DCHNAQ within the sol-gel framework and making optimal structural modifications to the doped sol-gel. The sensor offers straightforward regeneration using a 0.25 M EDTA solution, exhibiting complete reversibility. Comparative analysis with other methodologies underscores the efficacy in determining Sc3+ions in various reference materials, including plant leaves, fish, water, alloys, ores, and monazite samples.

Innovative assembled optode device for enhanced in-situ ceric ions (Ce4+) evaluation and preconcentration in its real human, foods, water, and alloy samples.

Cerium (Ce) are the most widely distributed rare earth element. However, humans exposed to Ce through inhalation have been reported to experience heat sensitivity, itching, and heightened taste and odour perception. The present study aims to develop an optical sensor device with a short response time and high selectivity for Ce amongst other ions in various environments. The potential applicability of a 6-hydroxy-5-((4-hydroxy-2-methylphenyl)diazenyl)pyrimidine-2,4(1H,3H)-dione (HHMDPD) assembled ligand as aceric ion (Ce4+)-selective caption optode was examined. After generating an ion pair with Tetra-n-octylammonium bromide (TOABr) and immobilizing on a tri-acetyl cellulose (TAC) membrane, the solubility of the HHMDPD ligand is improved. The constructed optode membrane reacts with Ce4+ by turning its orange colour to violet in Thiel buffer (pH of 5.5), which can be detected spectrophotometrically at λmax 667 nm. The measurement linearity was in the range of 0.70 - 18.7 × 10-6 mol/L of Ce4+ concentration with detection and quantification limits of 0.23 × 10-6 and 0.70 × 10-6 mol/L, respectively. Whatever the Ce4+ concentration in its real samples, the response time of the constructed device was 5.0 min. Additionally, it recorded repeatability and reproducibility with a %RSD of 1.37 and 2.55, respectively (n = 3). The proposed optode device exhibited complete reversibility, for multiple measurements, which could be easily achieved with the aid of a solution of HCl, 0.01 mol/L. The applicability of the proposed device has been effectively extended to analyze synthetic mixes corresponding to different Ce4+ real human, foods, water, and magnesium-based Ce4+ alloys.

Exploring the design and performance of a tellurium optical sensor utilizing a plasticizer-free polymer inclusion membrane.

A highly responsive, discerning, and uncomplicated technique has been devised for immobilizing reagents onto a plasticizer-free optical sensor membrane, employing polymer inclusion membranes (PIMs). This procedural strategy relies on a physical immobilization approach, specifically encapsulation, resulting in the creation of an optical sensing membrane. The responsive PIM is composed of poly(vinyl chloride) (PVC) as the fundamental polymer, Aliquat 336 as an extractant, and 4-(4 -chlorobenzylideneimino)-3-methyl-5-mercapto-1,2,4-triazole (CBIMMT) as the reagent. The optimized sensor demonstrates a linear range of 6.00-156 ng/mL for Te(IV), along with detection and quantification limits of 1.75 and 5.60 ng/mL, respectively. The sensor response time is 3.0 min, confirming its reproducibility. Effective regeneration of the sensor is achieved using a 0.2 mol/L HCl solution. The sensor membrane's selectivity is evaluated against various interfering ions, underscoring minimal interference. The sensor membrane efficacy is demonstrated through successful applications in quantifying Te(IV) levels, including natural water, chalcogenides, milk, vegetables, and soil samples.

A modified selective optical sensor for selenium determination based on incorporating xylenol orange in a poly(vinyl chloride) membrane.

A novel optical sensor has been developed to measure selenium ions. The sensor membrane was created by mixing xylenol orange (XO) and sodium tetraphenylborate (NaTPB) with a plasticized poly(vinyl chloride) membrane that contained o-nitrophenyl octyl ether (o-NPOE) as a plasticizer. XO was previously established for use in a colorimeter to measure selenium in water and other media. At pH 6.6, the color of the detecting membrane changed from orange to pink when in contact with Se4+ ions. Various variables affecting the uptake efficiency were evaluated and optimized. Under optimum conditions (i.e., 30% PVC, 60% o-NPOE, and 5.0% of both XO and NaTPB for 5.0 min as the response time), the proposed sensor displayed a linear range 10-175 ng mL-1 with the detection and quantification limits of 3.0 and 10 ng mL-1, respectively. Also, the precision (RSD%) was better than 2.2% for six replicate determinations of 100 ng mL-1 Se4+ in various membranes. For the detection of Se4+, the selectivity of the sensor membrane was investigated for a number of possible interfering inorganic cations, but no appreciable interference was found. With the use of a 0.3 M HCl solution, the sensor was successfully restored, and the response that may have been reversible and reproducible exhibited an RSD% of less than 2.0%. The sensor has been successfully used to analyze Se4+ ions in environmental and biological materials.

Construction of an optical sensor for copper determination in environmental, food, and biological samples based on the covalently immobilized 2-(2-benzothiazolylazo)-3-hydroxyphenol in agarose.

An optical chemical sensor has been developed for the quantitative spectrophotometric analysis of copper. The optode is dependent on covalent immobilization of 2-(2-benzothiazolylazo)-3-hydroxyphenol (BTAHP) in a transparent agarose membrane. The absorbance variation of immobilized BTAHP on agarose as a film upon the addition of 5 × 10-3 M aqueous solutions of Mn2+, Zn2+, Hg2+, Cd2+, Pb2+, Co2+, Ni2+, Fe2+, La3+, Fe3+, Cr3+, Zr4+, Se4+, Th4+, and UO22+ revealed substantially higher changes in the Cu2+ ion content compared to other ions investigated here. The effects of various experimental parameters, such as the solution pH, the reaction time, and the concentration of reagents, on the quality of Cu2+ sensing were examined. Under ideal experimental circumstances, a linear response was achieved for Cu2+ concentrations ranging from 1.0 × 10-9 to 7.5 × 10-6 M with an R2 value of 0.9988. The detection (3σ) and quantification (10σ) limits of the procedure for Cu2+ analyses were 3.0 × 10-10 and 9.8 × 10-10 M, respectively. No observable interference was recorded in the detection of Cu2+ due to other inorganic cations. With no indication of BTAHP leaching, the membrane demonstrated good durability and quick response times. The optode was effectively used to determine the presence of Cu2+ in environmental water, food, and biological samples.

Ultrasensitive and highly selective detection of nickel ion by two novel optical sensors.

Novel optical sensors for nickel determination by incorporation of 5-(2`-bromo-phenylazo)-6-hydroxypyrimidine-2,4-dione (I), 5-(2`,4`-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (II), dibutylphthalate (DBP) and sodium tetra-phenylborate (Na-TPB) to the plasticized polyvinyl chloride matrices were prepared. The introduction of DBP in the membrane substantially increased the ability of both ionophores I and II to function as chromo ionophores. The advantages of the reported sensors include great stability, reproducibility, and relatively long lifespan, as well as excellent selectivity for Ni2+ ion detection across a wide range of alkali, alkaline earth, transition, and heavy metal ions.Under optimized membrane compositions and experimental parameters, the response of both sensors was linear throughout a concentration range of 3.5 × 10-8 to 8.1 × 10-5 and 2.0 × 10-8 to 5.1 × 10-5 M for I and II, respectively. Sensor detection and quantification limits based on the definition that the concentration of the sample leads to a signal equal to the blank signal plus three and ten times its standard deviation were determined to be 1.15 × 10-8 and 3.45 × 10-8 M when utilizing I, whereas they were 0.61 × 10-8 and 1.95 × 10-8 M when utilizing II, respectively. The reaction time of optodes is defined as the period required achieving 95% of based sensors and found to be 8.0 and 5.0 min using I and II, respectively. Ni2+ ion concentrations in water, food, and environmental samples were effectively determined using the proposed optical sensors. Representative diagram for preparation of the sensing Ni2+ sensor.

Sensitive ratiometric sensor for Al(III) detection in water samples using luminescence or eye-vision.

A facile, quick, and sensitive ratiometric luminescence sensor is designed for detection aluminum ions in water samples using luminescence or eye-vision. This approach relies on the emission change of the europium(III) complex with 3-(2-naphthoyl)-1,1,1,-trifluoro acetone (3-NTA) after interaction with various concentration of aluminum ions. The addition of aluminum ions suppressed the Eu(III) emission at 615 nm under 333 nm excitation, while simultaneously enhancing the ligand emission at 480 nm. Optimum detection was obtained in methanol. The quantification of aluminum ions using ratiometric method was determined by plotting the luminescence ratio (F480nm/F615nm) versus aluminum ions concentration. The calibration plot was obtained within the range 0.1-100 µM with LOD = 0.27 µM. Additionally, the concentration of aluminum ions can be estimated semi-quantitatively by visually observing the luminescence colour change of the probe from red to light green and then to dark green after being excited by a UV lamp with 365 nm. As far as we are aware, this is the first luminescent lanthanide complex-based ratiometric probe for the detection of aluminum ions. The probe showed remarkable aluminum ions selectivity relative to that of other metal ions. The suggested sensor was used effectively to identify aluminum ions in water samples with good results.

Optical chemical sensor of Gd(iii) based on 5-(2'-bromophenyl- azo)-6-hydroxypyrimidine-2,4-dione immobilized on poly(methyl methacrylate) and 2-nitrophenyloctylether matrix.

A novel optical chemical sensor (optode) was fabricated for the determination of Gadolinium ions. The optical sensor was prepared by incorporating a recently synthesized ionophore, 5-(2'-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (BPAHPD), and 2-nitrophenyloctylether (NPOE) as a plasticizer in poly(methyl methacrylate) (PMMA) membrane. The color of the sensing membrane in contact with Gd(iii) ions changed from yellow to red-orange due to the adsorption of Gd(iii) with the maximum absorbance (λ max) at 563 nm. The chemical sensor responds optimally towards Gd(iii) ions at the optimum conditions of pH 7.5, contact time 10 min, 150 ng mL-1 Gd(iii), and 5.0 mL solution. The linear regression equation achieved was A = 4.36C (µg mL-1) - 0.15 (r = 0.9976). A linear Gd(iii) calibration curve can be established in the concentration range of 5.0-250 ng mL-1 with R 2 = 0.9976. Detection and quantification limits are 1.47 and 4.75 ng mL-1, respectively. The molar absorptivity and Sandell sensitivity are found to be 6.86 × 107 L mol-1 cm-1 and 0.023 ng cm-2, respectively. In addition to its stability and reproducibility, the optode revealed a great selectivity toward Gd(iii) ions as compared to other coexisting ions in real samples. The recovery of Gd(iii) ions from the sensor material was achieved using 0.4 M HNO3 . The offered optode sensor membrane has been employed to monitor Gd(iii) in soil, sediments, river water, and urine with an internal standard addition method and compared statistically with the ICP-OES method. The results revealed calculated t-values between 1.11-1.85, whereas F values were in the range of 2.46-3.77 which did not exceed the theoretical values, indicating no significant difference at 95% confidence level. The observed percent recovery is in the range of 97.24-102.52%.

A novel sensor for the selective monitoring of trace ytterbium ions using an agarose-based optical membrane.

A novel highly selective sensitive optical sensor was prepared via the chemical immobilization of ß-2-hydroxybenzyl-5-bromo-2-hydroxyazastyrene (HBBHAS) on an epoxy-activated agarose membrane pieces. The absorbance variation of the immobilized azastyrene film on agarose upon the addition of 1.5 × 10-5 M aqueous solutions of La3+, Y3+, Al3+, Sc3+, Sm3+, Eu3+, Lu3+, Fe3+, Ce3+, Cr3+, S2O3 2-, Tb3+, Mn2+ and KIO3 revealed substantially higher changes for the Yb3+ ion compared to the other considered ions. Thus, using HBBHAS as an appropriate ionophore, a selective optical sensor for Yb3+ was prepared via its chemical immobilization on a transparent agarose membrane. The effects of pH, reagent concentration, and time duration of the reaction of immobilizing the reagent were examined. A distinct change in the maximum absorbance of the reagent was established on contact of the sensing membrane with Yb3+ ions at pH = 4.25. For the membrane sensor, a linear relationship was observed between the variation in membrane absorbance (ΔA) at 424 nm and Yb3+ concentrations in the range of 4.75 × 10-5 to 6.20 × 10-10 M with a detection limit of 1.9 × 10-10 M for Yb3+. The effects of some potentially interfering ions on the assessment of Yb3+ were analyzed, and no substantial interference was found. The sensor showed a short response time and decent durability with no reagent leaching. The recovery of Yb3+ ions from the sensor material was performed using 0.3 M HNO3 and its response was reversible and reproducible with RSD ≥ 1.95%. This study reports a non-toxic, economical, stable, accurate, easy-to-use, and novel optical sensor material to assess Yb3+ in synthetic and environmental water samples.

Fluorescence determination of Fe(iii) in drinking water using a new fluorescence chemosensor.

A new fluorescence chemosensor based on (Z)-2-(1-(3-oxo-3H-benzo[f]chromen-2-yl)ethylidene)hydrazine-1-carbothioamide (CEHC) has been developed for the determination of Fe(iii) in drinking water. The optimum conditions were acetate buffer solution with a pH 5.0. In this approach, the determination of Fe(iii) is based on static quenching of the luminescence of the probe upon increasing concentrations of Fe(iii). The CEHC sensor binds Fe(iii) in a 1 : 1 stoichiometry with a binding constant K a = 1.30 × 104 M-1. CEHC responds to Fe(iii) in a way that is more sensitive, selective, and quick to turn off the fluorescence than to other heavy metal ions. Selectivity was proved against seven other metal ions (Mn(ii), Al(iii), Cu(ii), Ni(ii), Zn(ii), Pb(ii), and Cd(ii)). The calibration curve was constructed based on the Stern-Volmer equation. The linear range was 2.50-150 µM with the correlation coefficient of 0.9994, and the LOD was 0.76 µM. The method was successfully applied to determine Fe(iii) in drinking water samples, and the accuracy of the chemosensor was validated by atomic absorption spectrometry.

A highly selective bulk optode based on 6-{4-(2,4-dihydroxy-phenyl)diazenyl)phenyl}-2-oxo-4-phenyl-1,2-dihydro-pyridine-3-carbonitrile incorporating chromoionophore V for determination of nano levels of cadmium.

A novel optical sensor has been fabricated for highly accurate, simple and selective determination of nanomolar levels of cadmium ions. The sensor depends on the interaction of 6-{4-(2,4-dihydroxyphenyl)diazenyl)phenyl}-2-oxo-4-phenyl-1,2-dihydropyri-dine-3-carbonitrile (DDPODC) with Cd(II) in plasticized (2-nitrophenyloctyl ether) (o-NPOE) polyvinylchloride (PVC) membrane incorporating chromoionophore V as a lipophilic H+-selective indicator. It would seem that the higher Cd(II) concentration, the lower absorbance of chromoionophore V in the membrane at 668 nm, whereas the absorbance at 586 nm increased. The developed sensor at pH 4.7 has a linear range of 5.0 × 10-12 - 2.5 × 10-5 M with limits of detection and quantification of 1.62 × 10-12 and 4.95 × 10-12 M, respectively. The relative standard deviation (RSD) for eight determination of 1.0 × 10-7 M Cd(II) was 1.67%. Finally, the proposed sensor gives good results for applications in the direct determination of cadmium ions in water, food, and biological samples. Additionally, we compared the obtained results with the data obtained from the flame atomic absorption spectrometry (FAAS).

Utilization of a plasticized PVC optical sensor for the selective and efficient detection of cobalt(ii) in environmental samples.

A novel sensitive, selective, and reversible cobalt(ii) ion optical sensor was prepared by the incorporation of 5-[o-carboxyphenylazo]2,4-dihydroxybenzoic acid [CPDB] and sodium tetraphenylborate (NaTPB) in a plasticized polyvinyl chloride (PVC) membrane containing dioctyl adipate (DOA) as a plasticizer. The influence of several parameters such as pH, base matrix, solvent mediator and reagent concentration was optimized. A comparison of the obtained results with those of previously reported sensors revealed that the proposed method, in addition to being fast and simple, provided a good linear range (0.05-45.20 µM) and low detection limit (0.015 µM). Low detection and quantification limits and excellent selectivity in the presence of interfering ions such as Fe3+, Cu2+, Ni2+, Ag+, Au3+, Cr3+, Cd2+, Zn2+, Hg2+, and SO4 2- make it feasible to monitor Co2+ ion content accurately and repeatedly in environmental samples with complicated matrices. The optode was regenerated successfully using 0.3 M nitric acid (HNO3) solution while its response was reversible with a relative standard deviation (RSD) lower than 1.9% for seven replicate determinations of 20 µM Co2+ in various membranes. The optode was stable and was stored for at least 15 days without observing any change in its sensitivity.

Sensitive optical thin film sensor based on incorporation of 2-(2'-hydroxynaphthylazo)-benzothiazole in a sol-gel matrix for detection of manganese(II) in environmental samples.

A novel selective and precise optical thin film sensor reliant on the incorporation of synthesized 2-(2'-hydroxynaphthylazo)-benzothiazole (HNABT) as a selective ionophore into the nonporous of a clear glass like material via the sol-gel process is examined for its ability to assess Mn(II) ions in aqueous solutions. The sensor was constructed by spin-coating prepared sol onto a glass plate and the influence of sonication time on immobilization of HNABT into silica matrix was demonstrated through calculation of leaching percentage. The results designated that a sonication time of 25 min is the optimum to accomplish more stable thin films without fluctuation in sensitivity and response time of the introduced sensor for a wide period. The offered sensor can be employed to evaluate Mn(II) ions within the range of 6.0 × 10-8 - 1.5 × 10-5 M with detection and quantification limits of 1.7 × 10-8 and 5.5 × 10-8 M, respectively. The relative standard deviation of 2.1 and 0.83% for reproducibility and repeatability, are assessed, along with a rapid response time of ≈3.0 min. The constructed optode is stable in wet circumstances and should be kept for at least four weeks without detecting any variation in its sensitivity. The recommended sensor was successfully performed to estimate Mn(II) in food, saline effluents, tea leaves, biological and water samples, and the results were established by the GFAAS method.

Utility of 5-(2',4'-dimethylphenylazo)-6-hydroxy-pyrimidine-2,4-dione in PVC membrane for a novel green optical chemical sensor to detect zinc ion in environmental samples.

In plasticized (2-nitro-phenyloctyl ether (o-NPOE)) and polyvinyl chloride (PVC) membrane incorporating (N,N-diethyl-5-(octadecanoylimino)-5H-benzo[a] phenolxazine-9-amine (ETH 5294) and sodium tetraphenyl borate (NaTPB), an ionophore 5-(2',4'-dimethylphenylazo)-6-hydroxy-pyrimidine-2,4-dione (DMPAHPD) form an optical chemical sensor for zinc determination is ascribed. The sensor response is based on selective complexation of Zn2+ with DMPAHPD in the designed membrane phase, resulting in an ion exchange process between H+ in the membrane and Zn2+ in the sample solution. The influences of several experimental parameters, as membrane composition, pH, and type and concentration of the regenerating reagent, were demonstrated. The sensor has a response range of 5.0 × 10-9 to 2.5 × 10-5 M Zn2+ with detection and quantification limits of 1.6 × 10-9 and 4.9 × 10-9 M, respectively. The response time of 1 min at 0.1 M phosphate buffer solution of pH 5.0 with recording repeatability and sensor-to sensor reproducibility is reported. The proposed sensor signifies high selectivity for Zn2+ over various transition metal ions, alkali, and alkaline earth ions. The sensor membrane can be simply regenerated with 0.5 M HNO3. The sensor has been used to assess Zn2+ in river, waste, tap, sea, well, and spring waters samples, serum of diabetic patients, powdered milk, hair, red meat, pharmaceutical formulations, and talc powder samples.

Fast and Reliable Synthesis of Melanin Nanoparticles with Fine-Tuned Metal Adsorption Capacities for Studying Heavy Metal Ions Uptake.

PURPOSE: Adsorption and uptake of heavy metals by polymeric nanoparticles is driven by a variety of physicochemical processes. In this work, we examined heavy metal uptake by synthetic melanin nanoparticles and analyzed physicochemical properties that affect the extent of metal uptake by the nanoparticles. METHODS: Eumelanin nanoparticles were synthesized in a one-pot fast process from a 5,6-diacetoxy indole precursor that is hydrolyzed in situ into dihydroxy indole (DHI). The method allows the possibility of changing the level of sodium ions that ends up in the nanoparticles. Two variants of synthetic DHI-melanin (low-sodium and high sodium variants) were evaluated and demonstrated different relative adsorption efficiencies for heavy metal cations. RESULTS AND DISCUSSION: For the low-sodium DHI-melanin and in terms of percentages of metal ion removal, the relative order of extraction from 50 ppm solutions was Zn2+ > Cd2+ > Ni2+ > Co2+ > Cu2+ > Pb2+, with the extraction percentages ranging from 90% down to 76%, for a 30-minute adsorption time before equilibrium. The lower-sodium DHI-melanin consistently removed more Zn2+ than the higher-sodium variant. Electron microscopy (SEM) showed an increase in melanin particle size after metal ions uptake. In addition, X-ray photoelectron spectroscopy (XPS) of DHI-melanin particles with depth profiling after Zn ions uptake supported particle swelling and ion transport within the particles. CONCLUSION: These initial studies showed the potential of this straightforward synthesis to obtain synthetic DHI-melanin nanoparticles similar to those from biological sources with the possibility to fine-tune their metal adsorption capacity. These synthetic nanoparticles can be used either for the removal of a variety of metal ions or to mimic and study mechanisms of metal uptake by melanin deriving from biological sources, with the potential to understand, for instance, differential heavy metal uptake by various melanic pigments.

Quantification of silver in several samples using a new ionophore polymer membrane as an optical sensor.

Growing concerns about the possible toxicity of silver to aquatic organisms, bacteria, and humans have led to newly issued regulations by the United States Environmental Protection Agency (US EPA) and the Food and Drug Administration (FDA) regarding the use of silver. However, the increase in bacterial resistance to antibiotics has led to a resurgence in the use of silver as a biocidal agent in applications ranging from washing machine additives to the drinking water treatment system on the International Space Station (ISS). For Ag+ ion detection, a highly sensitive and reversible optical sensor has been established. The optode relies on a novel Schiff base, namely 2-[(benzo[d]thiazol-2-ylimino)methyl]phenol (BTMP) immobilized within PVC film and also incorporated with tris(2-ethylhexyl)phosphate (TEHP) and Aliquat 336 as an ion carrier. Under optimum conditions (i.e. pH 8.5), the proposed sensor displayed a linear response to Ag+ over 4.8 × 10-9 to 1.0 × 10-5 M (0.8494-1698.7 µg L-1) with limits of detection and quantification of 1.5 × 10-9 and 4.8 × 10-9 M (0.2548 and 0.8494 µg L-1), respectively. The sensor's response time was found to be 8.0 min. The sensor was applied successfully to determine Ag+ ion in some real samples, including food, biological, water, and environmental samples.

Use of cloud-point preconcentration for spectrophotometric determination of trace amounts of antimony in biological and environmental samples.

This work presents a cloud-point extraction process using the micelle-mediated extraction method for simultaneous preconcentration and determination of Sb(III) and Sb(V) species in biological and environmental samples as a prior preconcentration step to their spectrophotometric determination. The analytical system is based on the selective reaction between Sb(III) and 3-dichloro-6-(3-carboxy-2-hydroxy-1-naphthylazo)quinoxaline (DCHNAQ) in the presence of cetyltrimethylammonium bromide (CTAB) and potassium iodide at pH 4.5. Total Sb concentration was determined after reduction of Sb(V) to Sb(III) in the presence of potassium iodide and ascorbic acid. The optimal reaction conditions and extraction were studied, and the analytical characteristics of the method (e.g., limits of detection and quantification, linear range, preconcentration, improvement factors) were obtained. Linearity for Sb(III) was obeyed in the range of 0.2-20 ng ml(-1). The detection and quantification limits for the determination of Sb(III) were 0.055 and 0.185 ng ml(-1), respectively. The method has a lower detection limit and wider linear range, inexpensive instrument, and low cost, and is more sensitive compared with most other methods. The interference effect of some anions and cations was also studied. The method was applied to the determination of Sb(III) in the presence of Sb(V) and total antimony in blood plasma, urine, biological, and water samples.