Dilute Aqueous Solutions Research Articles

Effect of Ultrahigh Dose Rate on Biomolecular Radiation Damage.

Dose rate is one of the important parameters in radiation-induced biomolecular damage. The effects of dose rate have been known to modify radiation toxicity in biological systems. The rate and extent of sublethal DNA damage (e.g., base damage and single-strand breaks) repair and those of cell proliferation have been manifested by dose rate. However, the recent preclinical application of ultrahigh dose rate [(UHDR) ca. 40 Gy/s and higher] radiation modalities have been shown to lower the type and extent of radiation damage to biological systems. At these UHDR, radiation-induced physicochemical and chemical processes are expected to differ from those observed after irradiation at conventional dose rates (CONV). It is unclear whether these UHDR conditions can affect the quality (type) and quantity (extent) of biomolecular damage such as DNA lesions. Here, we comparatively study the influence of indirect effects of CONV and UHDR on the formation of DNA strand breaks and clustered damage including densely accumulated lesions in an aerated and an anoxic dilute aqueous solution of a plasmid DNA model under low and high hydroxyl radical (•OH) scavenging conditions. Aqueous solutions of purified supercoiled plasmid DNA (pUC19) were prepared in either air- or nitrogen-saturated conditions, with Tris buffer added as the radiation-produced •OH scavenger at low and high scavenging capacities. These DNA samples were irradiated using kV X-ray systems at CONV (0.1 Gy/s) and high dose rate (HDR, 25 Gy/s) as well as UHDR (55 and 125 Gy/s) under different scavenging and environmental conditions. DNA lesions including strand breaks and clustered damage including densely accumulated lesions were quantified by gel electrophoresis and the yields of these lesions were calculated from the dose-response curve. Non-DSB clustered damage including densely accumulated lesions were evaluated by treating DNAs using bacterial endonuclease enzymes (Fpg and Nth) prior to gel electrophoresis. UHDR of 55 and 125 Gy/s induced lower amounts of both isolated strand breaks and clustered DNA damage including densely accumulated lesions at doses >40 Gy in the presence of oxygen, compared to the abundance of these lesions induced by 0.1 and 25 Gy/s irradiation under the same dose conditions. Overall, the strand break and clustered damage including densely accumulated lesions yields decreased by factors of 1.3-3.5 after UHDR. We did not observe these differences either via •OH scavenging or by removing oxygen from the solution. In addition, our results point out that the inter-track recombination reactions did not contribute to the observed dose-rate effects on DNA damage. The effects of dose rate on DNA damage are highly dependent on the total dose, as expected, but also on the •OH scavenging capacity that is employed in the aqueous DNA solutions. These important variables may be relevant in biological systems as well. On a practical level, our in vitro plasmid DNA model, which permits to precisely vary the scavenging capacity and gassing conditions (air saturated vs. N2 saturated) can help to differentiate dose-rate effects on biomolecular damage. Our results indicate that the radical-radical reactions are important in understanding the dose-rate effect on DNA damage.

Copolymers of Vinylphosphonic and p‐Methacrylamidobenzoic Acids and their Complexes with Lanthanide Ions

AbstractNew copolymers of vinylphosphonic and p‐methacrylamidobenzoic acids of varying compositions were synthesized via free radical copolymerization. The structure of the obtained polymers was confirmed by NMR and FTIR spectroscopy. As the proportion of vinylphosphonic acid in the initial reaction mixture increased, the yield of the copolymer and its molecular mass both decreased. The synthesized copolymers were found to form stable soluble luminescent complexes in dilute aqueous solutions, with a concentration range of 0.002 to 0.02 mg/ml. An increase in the concentration of vinylphosphonic acid moieties in copolymers was accompanied by a noticeable decrease in the luminescence intensity. The new copolymers’ ability to bind efficiently with lanthanide ions renders them a promising material for the design of polymeric contrast agents, preparations for radioimmunotherapy and photodynamic therapy.

Influence of iron content in palladium catalysts supported on alumina and their reduction conditions on the hydrodechlorination of diclofenac in aqueous solutions

Using the method of wet impregnation of alumina with iron and palladium nitrates, 1Pd0.5Fe and 1Pd10Fe catalysts modified with iron oxides were prepared with a target content of 1 wt % Pd, 0.5 or 10 wt % iron. The catalysts were compared with each other and with the monometallic catalyst 1Pd in the hydrodechlorination (HDC) of diclofenac (DCF) in dilute aqueous solutions at 30°C in batch and flow reactors after high-temperature (320°C) and mild (30°C) reduction; the latter was carried out in a batch or flow reactor. Using X-ray photoelectron spectroscopy (XPS), it was shown that after reduction at 320°C the surface of catalysts contains mainly Pd0, Fe2+ and Fe3+. The surface Fe2+/Fe3+ ratio increases as the iron content decreases. The reduction of Pd2+ to Pd0 is possible already at 30°C, but it proceeds much worse on the surface of 1Pd0.5Fe compared to 1Pd10Fe. According to XPS data, temperature-programmed reduction and infrared spectroscopy of diffuse reflection of adsorbed CO, modification with iron oxides increases the palladium content on the surface compared to 1Pd, promotes the emergence of new Pd–O–Fe centers, and affects the ability of palladium to be reduced. These effects increase with increasing iron content. Iron-modified catalysts reduced at 320°C showed similar activity and stability in the conversion of DCP in flow-through and batch systems. Unlike 1Pd0.5Fe, the 1Pd10Fe catalyst is highly efficient and stable even after mild reduction at 30°C. Under flow conditions with comparable DCF conversion, it provides increased selectivity in the HDC reaction of diclofenac compared to 1Pd, which is also active in hydrogenation.

Micrometer-Scale Graphene-Based Liquid Cells of Highly Concentrated Salt Solutions for In Situ Liquid-Cell Transmission Electron Microscopy.

In situ liquid-cell transmission microscopy has attracted much attention as a method for the direct observations of the dynamics of soft matter. A graphene liquid cell (GLC) has previously been investigated as an alternative to a conventional SiN x liquid cell. Although GLCs are capable of scavenging radicals and providing high spatial resolutions, their production is fundamentally stochastic, and a significant compositional change in liquids encapsulated in GLCs has recently been pointed out. We found that graphene-based liquid cells were formed in nano- to micrometer sizes with high reproducibility when the concentration of the encapsulated aqueous salt solution was high. In contrast, when we revisited conventional fabrication methods, water-encapsulated GLC was formed with low yield, and any electron diffraction spots from ice were not confirmed by a cooling experiment. The reason for this was the presence of intrinsic defects in the graphene, the presence of which we confirmed by the etch-pit method. The shrinkage of a water-encapsulated cell and a decrease in the bubble area in an aqueous (NH4)2SO4 solution cell suggested that volatile water molecules and gas molecules can leak from the cells during the fabrication and observation processes. Further revision of the conditions for the formation of liquid cells and a reduction in the number of intrinsic graphene defects are expected to lead to the provision of graphene-based liquid cells capable of encapsulating dilute aqueous solutions or pure water.

Supercapacitive behaviors of N/S co-doped biomass porous carbon-based supercapacitors in “water-in-salt” electrolyte

The design of carbon electrode materials and electrolytes is distinct significance for improving the energy density of supercapacitors. Herein, N/S co-doped biomass porous carbon materials based on sustainable resource were prepared by in-situ expansion, heteroatom doping, and subsequent KOH activation strategy by using camellia seed shell as carbon source and ammonium persulfate as dopant and expander. The as-prepared N/S co-doped biomass porous carbon (N/S-CSAC-650) possesses the characteristics of high specific surface area, large pore volume, and suitable heteroatom content. The N/S-CSAC-650 electrode achieves a high specific capacitance of 335.9 F g−1 in the 3 M KOH electrolyte at 0.5 A g−1. The constructed symmetric supercapacitor demonstrates excellent cyclic stability and shows a high retention rate of 98.4 % after 30,000 charge and discharge processes at 2 A g−1. Especially, the energy density of supercapacitors is usually constrained by the narrow electrochemical stability window (ESW) of dilute aqueous solution (1.23 V), in order to effectively widen the ESW of water, herein the “water-in-salt” (WIS) electrolyte strategy is put forward and the ESW of water was extended to 2.94 V by using a 25 M KAc WIS electrolyte. The operating voltage window of the symmetric supercapacitor assembled by 25 M KAc WIS electrolyte and N/S-CSAC-650 electrodes can reach 2.0 V, and a high energy density of 48.86 Wh kg−1 is realized.

Metal-free ring-opening polymerization for the synthesis of biocompatible star-shaped block copolymers with controllable architecture

Star-shaped block copolymers (SBCs) have sparked interest as efficient cargo carriers due to their high loading capacity, decreased burst effects through sustained release, and maintained stability in dilute aqueous solution. Despite these advantages, the practical usage of SBCs is hindered by their challenging synthesis processes that often utilize metal-based catalysts at high temperatures. Herein we report the tailored synthesis of 3-, 4-, and 6-arm polycaprolactone-b-poly(ethylene glycol), PCL-b-PEG, SBCs using diphenyl phosphate as a friendlier, more sustainable non-metallic catalyst. Nuclear magnetic resonance (NMR) analysis confirms the molecular architecture of SBCs and gel permeation chromatography (GPC) is used to elucidate trends in molar mass when the number of arms within the SBCs is tuned, while dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) studies provide insights into aggregation behavior. Critical aggregation concentration (CAC) values, as measured by fluorescence spectroscopy, demonstrated that the 4-arm and 6-arm SBCs have greater stability than the 3-arm SBC. Biocompatibility assessment indicated minimal cytotoxicity of the nanoaggregates, even at high concentration, making these PCL-b-PEG SBCs potentially safe and sustainable vehicles for biomedical release applications.

High Performance and Selective Sequestration of Cd(II) from Water by Layered Thiophosphate.

The extensive use of toxic cadmium (Cd) in energy conversion and industrial applications ranging from solar cells and battery appliances to paints and pigments contaminates water bodies. However, the upper limit of Cd contamination in drinking water is to be only 3 ppb by the WHO and 5 ppb by the USA-EPA, which underscores the need for cost-effective, efficient, and ppb level capture of Cd from contaminated water. Leveraging the selectivity due to Lewis's hard-soft acid-base (HSAB) theory, we have achieved swift and highly selective capture of Cd(II) ions from aqueous mediums using layered potassium manganese thiophosphate (K-MnPS3). K-MnPS3 effectively removes Cd(II) ions from extremely dilute aqueous solutions (ppb levels), achieving a maximum sorption capacity of 405.43 mg/g and a removal rate exceeding 97% within 20 min. Even in the presence of competing ions such as Na+, Mg2+, Ca2+, and Pb2+, K-MnPS3 remains selective. Additionally, it operates efficiently across a wide pH range (1.78-11.19) with a high distribution coefficient (∼104 mL/g). Breakthrough experiments using a 1 wt % K-MnPS3 and 99 wt % sand column showed complete breakthrough of Cd(II) after 62 h, leading K-MnPS3 as a promising candidate for Cd(II) removal from industrial effluents.

Is Passynski's Approach to Hydration Numbers Consistent with Thermodynamics?

Hydrophilic and hydrophobic phenomena occur in aqueous solutions. Despite the complex nature of the molecular interactions, the propensity of molecules and ions to hydration is sometimes characterized by a single "hydration number". Passynski's method for determining the hydration numbers in dilute aqueous solutions belongs to the group of methods based on the analysis of the isentropic compressibility of a mixture. Isentropic compressibility is a thermodynamic material constant; thus, the paper deals with Passynski's approach discussed in terms of thermodynamics. First, Passynski's assumptions were applied to the volume of the mixture. Subsequent strict thermodynamic derivation led to a formula for the hydration number which resembled that of Onori rather than the original one. Passynski's number turned out to be inconsistent with the thermodynamics and mechanics of fluids. This is a rather purely empirical measure of the slope of the dependence of isentropic compressibility on the solute mole fraction in a dilute aqueous solution. Being the quotient of the slope and the isentropic compressibility of pure water, Pasynski's numbers are more convenient to analyze and discuss than the slopes themselves. Conclusions about molecular interactions based on these numbers must be treated with considerable caution.

Self-Assembled Nanostructure of Ionic Sn(IV)porphyrin Complex Based on Multivalent Interactions for Photocatalytic Degradation of Water Contaminants.

[Sn(H2PO4)2(TPyHP)](H2PO4)4∙6H2O (2), an ionic tin porphyrin complex, was synthesized from the reaction of [Sn(OH)2TPyP] (1) with a dilute aqueous solution of a polyprotic acid (H3PO4). Complex 2 was fully characterized using various spectroscopic methods, such as X-ray single-crystal crystallography, 1H NMR spectroscopy, elemental analysis, FTIR spectroscopy, UV-vis spectroscopy, emission spectroscopy, EIS mass spectrometry, PXRD, and TGA analysis. The crystal structure of 2 reveals that the intermolecular hydrogen bonds between the peripheral pyridinium groups and the axially coordinated dihydrogen phosphate ligands are the main driving force for the supramolecular assembly. Simultaneously, the overall association of these chains in 2 leads to an open framework with porous channels. The photocatalytic degradation efficiency of methyl orange dye and tetracycline antibiotic by 2 was 83% within 75 min (rate constant = 0.023 min-1) and 75% within 60 min (rate constant = 0.018 min-1), respectively. The self-assembly of 2 resulted in a nanostructure with a huge surface area, elevated thermodynamic stability, interesting surface morphology, and excellent catalytic photodegradation performance for water pollutants, making these porphyrin-based photocatalytic systems promising for wastewater treatment.

Prediction of Diffusion Coefficients for Organic Compounds in Dilute Aqueous Solutions

Prediction of Diffusion Coefficients for Organic Compounds in Dilute Aqueous Solutions

Physicochemical Characterization and Antimicrobial Properties of Lanthanide Nitrates in Dilute Aqueous Solutions.

This work presents the results of studying dilute aqueous solutions of commercial Ln(NO3)3 · xH2O salts with Ln = Ce-Lu using X-ray diffraction (XRD), IR spectroscopy, X-ray absorption spectroscopy (XAS: EXAFS/XANES), and pH measurements. As a reference point, XRD and XAS measurements for characterized Ln(NO3)3 · xH2O microcrystalline powder samples were performed. The local structure of Ln-nitrate complexes in 20 mM Ln(NO3)3 · xH2O aqueous solution was studied under total external reflection conditions and EXAFS geometry was applied to obtain high-quality EXAFS data for solutions with low concentrations of Ln3+ ions. Results obtained by EXAFS spectroscopy showed significant contraction of the first coordination sphere during the dissolution process for metal ions located in the middle of the lanthanide series. It was established that in Ln(NO3)3 · xH2O solutions with Ln = Ce, Sm, Gd, Yb (c = 134, 100, 50 and 20 mM) there are coordinated and, to a greater extent, non-coordinated nitrate groups with bidentate and predominantly monodentate bonds with Ln ions, the number of which increases upon transition from cerium to ytterbium. For the first time, the antibacterial and antifungal activity of Ln(NO3)3 · xH2O Ln = Ce, Sm, Gd, Tb, Yb solutions with different concentrations and pH was presented. Cross-relationships between the concentration of solutions and antimicrobial activity with the type of Ln = Ce, Sm, Gd, Tb, Yb were established, as well as the absence of biocidal properties of solutions with a concentration of 20 mM, except for Ln = Yb. The important role of experimental conditions in obtaining and interpreting the results was noted.

A Two-Step Intermolecular Interaction Of Molecular Macroions With Multivalent Counterions.

Macroion-counterion interaction is essential for regulating the solution behaviors of hydrophilic macroions, as simple models for polyelectrolytes. Here, we explore the interaction between uranyl peroxide molecular cluster Li68K12(OH)20[UO2(O2)OH]60 (U60) and multivalent counterions. Different from interaction with monovalent counterions that shows a simple one-step process, isothermal titration calorimetry, combined with light/X-ray scattering measurements and electron microscopy, confirm a two-step process for their interaction with multivalent counterions: an ion-pairing between U60 and the counterion with partial breakage of hydration shells followed by strong U60-U60 attraction, leading to the formation of large nanosheets with severe breakage and reconstruction of hydration shells. The detailed studies on macroion-counterion interaction can be nicely correlated to the microscopic (self-assembly) and macroscopic (gelation or phase separation) phase transitions in the dilute U60 aqueous solutions induced by multivalent counterions.

The Gibbs and Butler Equations and the Surface Activity of Dilute Aqueous Solutions of Strong and Weak Linear Polyelectrolyte-Surfactant Mixtures: The Roles of Surface Composition and Polydispersity.

In a previous paper, we applied a combination of direct measurements of both surface tension and surface excess in conjunction with the Gibbs equation to explain features of the adsorption and surface tension of mixtures of surfactants and strong linear polyelectrolytes at the air-water interface. This paper extends that model by including (i) the restrictions of the Butler equation for the behavior of the surface tension of mixed systems and (ii) the surface behavior of surfactant and linear weak polyelectrolyte mixtures, for which the inclusion of measurements of the surface excess and composition is shown to be particularly important. In addition, a closer examination of earlier data at higher concentrations provides evidence that the surface layering that is often observed in polyelectrolyte-surfactant systems is also an average equilibrium phenomenon and is driven by particular aggregation patterns that occur in some systems and not in others. Although the successful application of the Gibbs and Butler equations indicates that strong polyelectrolyte-surfactant systems can be described in terms of an average equilibrium over wide ranges of concentration, we have identified two concentration ranges where polydispersity in either polyelectrolyte molecular weight or composition results in significant time dependence of the surface behavior.

Coacervate Formation in Dilute Aqueous Solutions of Inorganic Molecular Clusters with Simple Divalent Countercations.

We report a complex coacervate formed by a 2.5 nm-diameter, rigid uranyl peroxide molecular cluster (Li68K12(OH)20)[UO2(O2)OH]60, U6060-) and SrCl2 salt in dilute aqueous solutions, including its location in the phase diagram, composition, rheological features, and critical conditions for phase transitions. In this coacervate, the Sr2+ cations are a major building component, and the coacervate phase covers a substantial region of the phase diagram. This coacervate demonstrates features that differ from traditional coacervates formed by oppositely charged long-chain polyelectrolytes, especially in its formation mechanism, dehydration, enhancement of mechanical strength with increasing ionic strength, and the change of salt partition preference into the coacervate and supernatant phases with ionic strength.

A dual-layer solid electrolyte interphase enhances interfacial chemistry stability in aqueous aluminium metal batteries

Aqueous aluminum metal batteries (AAMBs) have garnered significant attention owing to the abundance of aluminum, high volumetric energy density (8040 mAh cm−3, approximately four times that of lithium metal anodes), and chemical inertness. However, profound issues such as surface corrosion and the side reaction of hydrogen evolution severely impede the advancement of AAMBs. Here, we report the in-situ formation of a dense inorganic AlF3 + Al/Zn-CO3 + flexible carbon shell solid-electrolyte interface (SEI) on the surface of an Al electrode through hydrothermal and electrochemical activation in a dilute aqueous solution of Al(OTf)3-Zn(NO3)2. Experimental evidence demonstrates that the electrically insulating Al/Zn-NO3 layer initially forms on the Al negative electrode surface through self-polymerization reactions of Al with Zn2+ and NO3– under sealed heating conditions. Subsequent electrochemical activation leads to the decomposition of CF3SO3- to form conductive AlF3 + Al/Zn-CO3, while in situ generation of a flexible carbon layer occurs internally on the surface. The inorganic inner layer facilitates the diffusion of Al ions, while the organic carbon shell suppresses water permeation and maintains the stability of the SEI structure. The in-situ formed SEI enables the Al//Ti battery to achieve a high Coulombic efficiency (CE) of 98.9 % over 100 cycles. Constructing the Al//β-MnO2 battery yields a high energy density of 216 Wh kg−1, with the capacity retention remaining stable at 83.6 % after 700 cycles.

Structural Characterization of Disulfide-Linked p53-Derived Peptide Dimers.

Disulfide bonds provide a convenient method for chemoselective alteration of peptide and protein structure and function. We previously reported that mild oxidation of a p53-derived bisthiol peptide (CTFANLWRLLAQNC) under dilute non-denaturing conditions led to unexpected disulfide-linked dimers as the exclusive product. The dimers were antiparallel, significantly α-helical, resistant to protease degradation, and easily reduced back to the original bisthiol peptide. Here we examine the intrinsic factors influencing peptide dimerization using a combination of amino acid substitution, circular dichroism (CD) spectroscopy, and X-ray crystallography. CD analysis of peptide variants suggests critical roles for Leu6 and Leu10 in the formation of stable disulfide-linked dimers. The 1.0 Å resolution crystal structure of the peptide dimer supports these data, revealing a leucine-rich LxxLL dimer interface with canonical knobs-into-holes packing. Two levels of higher-order oligomerization are also observed in the crystal: an antiparallel "dimer of dimers" mediated by Phe3 and Trp7 residues in the asymmetric unit and a tetramer of dimers mediated by Trp7 and Leu10. In CD spectra of Trp-containing peptide variants, minima at 227 nm provide evidence for the dimer of dimers in dilute aqueous solution. Importantly, and in contrast to the original dimer model, the canonical leucine-rich core and robust dimerization of most peptide variants suggests a tunable molecular architecture to target various proteins and evaluate how folding and oligomerization impact various properties, such as cell permeability.

Standard partial molar volumes of single aqueous ions composing ionic liquids. Measurement and evaluation of temperature dependent values. Parsing and LSER correlation with molecular descriptors based on DFT/COSMO approach

The densities of highly dilute aqueous solutions (m < 0.2 mol·kg−1) of 50 common ionic liquids (ILs) or related salts were accurately measured at seven equidistant temperatures in the range of (288.15 to 318.15) K and ambient pressure. The examined set of ILs/salts composed of 31 ions was judiciously selected to cover wide ranges of ion sizes and chemical structures and allow reliable evaluation of ionic contributions. The data were duly analyzed to infer related thermodynamic properties and information on the behavior of these systems on a molecular level. Appropriate means of mathematical statistics were used to estimate data uncertainties, assign weights to data correlations, and judge the significance of the results obtained. The standard partial molar volumes V¯∞ of the ILs/salts at infinite dilution were evaluated through fitting the concentration dependence of respective apparent molar volumes to Redlich-Meyer equation and their temperature dependence was correlated to quadratic polynomial. The data presented were compared whenever possible with those available in the literature; good agreement was often found, although some data from the literature were also considerably dispersed or in error. Standard partial molar volumes of ILs/salts obeying ionic additivity were split by least-squares optimization into temperature-dependent single-ion values based on the Conway-Millero extrathermodynamic assumption. The ionic additivity of BV parameter was also identified. Its magnitude for anions is typically greater than that for cations, supporting the fact that an anion dominates the volumetric behavior of aqueous ILs. As the BV,anion and the second temperature derivative ∂2V¯anion∞/∂T2 were found to correlate, the two solute’s water structure making/breaking ability indicators appear to speak consistently. Enhanced values of standard partial molar expansion were observed for both strongly kosmotropic and chaotropic anions and a plausible explanation of this phenomenon was suggested. To correlate and analyze the effect of ionic structure on V¯ion,298∞, Linear Solvation Energy Relationship (LSER) methodology with the recently proposed four quantum chemistry computed descriptors based on DFT/COSMO approach was employed providing excellent fit (SD = 2.48 cm3·mol−1, R2 = 0.9996).

Reactive separation of acrylic acid: Effect of organic phase &design of extraction column

Reactive separation is an intensified method for the separation of carboxylic acids from dilute aqueous solutions. In this respect, separation of acrylic acid was studied employing reactive separation using various combinations of extractants (TBP, TOA and Aliquat336) and diluents (octanol and toluene). The results were compared with the previous published works and it was observed that TOA + octanol system is the most efficient combination (extraction efficiency (η)> 95 %). Synergism was observed when the extractants were used in mixed form (Aliquat336-TOA, TBP-TOA and Aliquat336-TBP), providing equivalent separation to TOA alone and is proposed to be a cost-effective solution for reactive separation of acrylic acid. Also mixed diluents (octanol + toluene) were tried with individual extractants to combat the emulsion problem when toluene was used alone. Mathematical modelling (using the law of mass action) was carried out and loading curves were validated by mathematical models. Binary extractant/diluents combination could be proposed as cheap and effective solution to the high prices of solvents used for acrylic acid recovery. Regeneration of acid from loaded organic phase was carried out by temperature swing (recovery of 69 %) and contact with NaOH (recovery >95 %). Design parameters for the RDC extraction column were also obtained.

Smartphone-Based Colourimetric Detection of Methyl Red, Co(II), Uric Acid, and Topotecan after Pre-concentration onto a Hectorite Clay-Hydroxyethylcellulose Hybrid

Objective:: This paper describes a new, digital image colourimetry-based format for the quantification of analytes in an aqueous solution. Method:: The proposed method is based on analyte pre-concentration by adsorption onto Bentone LT. Bentone LT pellet isolation comes after adsorption, followed by in-situ application of an analyteselective chromogenic reaction. The resulting pellet colouration is captured by the phone’s integrated camera and assessed using the free open-source image processing software, ImageJ. Responses are calibrated and quantified. Results:: We tested the applicability of the proposed methodology for the quantification of specific model analytes which are of concern in environmental matrices (methyl red, Co(II), uric acid, topotecan). The smartphone-based assay was proven reliable in quantifying the model analytes (standard recovery of 82-116%), alone or in mixture, from dilute aqueous solutions and was found to depict accurately the adsorption behaviour followed photometrically in solution. Lower limit of linearity was calculated at 0.05, 0.11, 0.85 and 0.20 μg/mL for methyl red, Co(II), uric acid, and topotecan, respectively. The proposed format was found superior when compared to alternative published photometric/ colourimetric assays in terms of the lower limit of linearity. In the presence of possible adsorption interferents, the lower limit of linear response was shifted to slightly higher concentrations for topotecan i.e. from 0.2 μg/mL to 0.5 μg/mL. Conclusion:: We here demonstrate the extended applicability of the proposed methodology for the smartphone-based quantification of the specific model analytes. The applicability of this analysis format likely extends to other analytes, where analyte-specific colour formation is feasible.

Detection of Salt Content in Canned Tuna by Impedance Spectroscopy: A Feasibility Study for Distinguishing Salt Levels.

The electrical impedance of dilute aqueous solutions containing extracts from five brands of canned tuna is analyzed using impedance spectroscopy in order to analyze their salt content and detect the potential presence of other salts beyond the well-stated NaCl. A complex electrical impedance is modeled with an equivalent electrical circuit, demonstrating good agreement with experimental data. This circuit accounts for the contribution of ions in the bulk solution, as well as those contributing to electrode polarization. The parameters describing the equivalent circuits, obtained through fitting data to the electrical impedance, are discussed in terms of the various ion contributions to both the electrical double layer at the electrode interface and the electrical conductivity of each solution. The ionic contribution to the electrical impedance is compared with that of a pure NaCl solution at the same concentration range. This comparison, when extended to real samples, allows for the development of a model to estimate the electrical conductivity of canned tuna samples, thereby determining the salt concentration in tuna. The model enables differentiation among the various samples of tuna studied. Subsequently, the potential presence of other ions besides Na+ and Cl- and their contribution to the electrical properties of each canned tuna extract is considered, especially for samples with a higher ratio of the sum of K+ and phosphates to Na+ concentration. This analysis shows the potential of impedance spectroscopy for on-site and rapid analysis of salt content and/or detection of additives in canned tuna fish.