Chemical Species In Aqueous Solution Research Articles

A new version of the Langelier-Ludwig square diagram under a compositional perspective

The Langelier-Ludwig square diagram is a commonly used diagnostic tool in groundwater chemistry. Suitable groupings of cations and anions are selected and plotted as percentages of milliequivalents with the sums of the selected cations and anions plotted on the y- and x-axes, respectively. It displays relative ratios rather than absolute concentration whereby each axis ranges from 0 to 50 meq%. However, the sample space in which data are represented in a Langelier-Ludwig square diagram is indeed given by the simplex. Incorrect conclusions may be drawn when the compositional nature of compositional data is not taken into account, i.e., a change in one value in one component changes all other values due to due to the constant sum constraint of the measured chemical elements. Correlations are thus influenced by the presence of negative bias in the covariance structure and linear or nonlinear patterns on the square diagram can be misinterpreted. A new version of the Langelier-Ludwig square diagram based on a well-chosen coordinate representation of cations and anions is proposed. The advantage of the revised diagram is that all the information is contained in the log-ratios describing the intricate relationship between chemical species in aqueous solutions. It is shown that the geochemical interpretation of this new diagram – based on the relative dominance of major ions and distance from the (robust) barycenter of the data – provides a better and unbiased understanding of water-environment interactions. To further aid interpretation, (robust) tolerance ellipses show the correlation structure in the new version of the Langelier-Ludwig square diagram, and clustering algorithms can be applied to divide the data into groups beforehand. A bunch of different plotting options and interactive representations complete the implementation in free open-source software. It is recommended to replace the classic Langelier-Ludwig diagram with the new version.

Reconciliation of pH, conductivity, total organic carbon with carboxylic acids detected by ion chromatography in solution after contact with multilayer films after γ-irradiation

The impact of γ-irradiation on polymers in multilayer films was studied by means of the study of the diffusion and release (spontaneous migration of the molecules from the container into the product) of chemical species in aqueous solution. A series of different measurements have been performed: pH, conductivity, total organic carbon (TOC) and ion chromatography (IC). Their evolution according to γ-irradiation dose was studied. More several rinsings made over several months allowed to quantify well the impact of the irradiation on these polymers. The samples are irradiated at several γ-doses, up to 270 kGy, and compared with a non-irradiated sample used as reference. It shows that quantity of generated carboxylic acids depends on the film material (PE/EVOH/PE and EVA/EVOH/EVA) and increases with γ-dose.

Differential imaging of the metabolism of bacteria and eukaryotic cells based on light-addressable potentiometric sensors

A light-addressable potentiometric sensor (LAPS) is a field-effect-based potentiometric sensor with an electrolyte/insulator/semiconductor (EIS) structure, which is able to monitor analyte concentrations of (bio-)chemical species in aqueous solutions in a spatially resolved way. Therefore, it is also an appropriate tool to record 2D-chemical images of concentration variations on the sensor surface. In the present work, two differential, LAPS-based measurement principles are introduced to determine the metabolic activity of Escherichia coli (E. coli) K12 and Chinese hamster ovary (CHO) cells as test microorganisms. Hereby, we focus on i) the determination of the extracellular acidification rate (ΔpH/min) after adding glucose solutions to the cell suspensions; and ii) recording the amplitude increase of the photocurrent (Iph) related to the produced acids from E. coli K12 bacteria and CHO cells on the sensor surface by 2D-chemical imaging. For this purpose, 3D-printed multi-chamber structures were developed and mounted on the planar sensor-chip surface to define four independent compartments, enabling differential measurements with varying cell concentrations. The differential concept allows eliminating unwanted drift effects and, with the four-chamber structures, measurements on the different cell concentrations were performed simultaneously, thus reducing also the overall measuring time.

Quality assurance of thermodynamic data

To promote metrology in chemistry, ACQUAL has invited a Topical Issue under the header ‘‘Quality Assurance in Chemical Thermodynamics’’. Chemical thermodynamics is an important field of experimental chemistry. Its results are widely used even outside the chemical field. Data collections of formation quotients of chemical species in aqueous solutions are compiled with the intention to simulate the behavior of ground water constituents; activity coefficients are determined in order to predict the solubility of green house gases in ocean seawater; the thermodynamic properties of newly prepared compounds are tested for their interaction in industrial processes. The initial intention has been to learn how current workers in the field assess the quality of the data published under their name. The number of possible contributors for such an issue is, however, limited. Next to the often protracted experimental work, complex numerical (e.g., chemometric) methods need to be found to obtain an appropriate model or to decide between alternative appropriate models for the interpretation of the observed data. Only a limited number of workers in chemical thermodynamics are at least willing to deal with metrological issues. Therefore, the title of this topical issue has been decided to be ‘‘quality assurance of thermodynamic data,’’ not ‘‘metrology of thermodynamic data.’’ There are multiple possible reasons. The complexity of a thermodynamic study, e.g., of metal ligand interaction in aqueous solution, is but one reason. The application of sophisticated numerical models in the analysis of experimental data confronts the researchers with multiple possible interpretations often without clear criteria to make a decision. Targeting the behavior of chemicals in the environment may raise the problem to define the measurand. Naturally occurring organic materials (NOM), for instance, form important reactants in the environment, however, without allowing a simple separation into chemically identifiable compounds with unambiguous molar masses. As long as there is no real demand, this situation will change with an only low momentum. ‘‘Chemistry is a study of complicated systems and the complexity cannot be understood at an arbitrary level of accuracy. (...) Thus any measured data has noise, uncertainties and variability’s, non-linearity’s and unrecognized features (model-deficiencies). And mainstream chemistry has still great difficulties in recognising these basic facts’’ [1]. These words might be from an ACQUAL editorial but in fact are stated 15 years ago by one of the founding fathers of chemometrics. Statistical and numerical techniques are among those methods also applied by thermodynamicians to assess variability in data. However, the reader should understand that incorporation of metrological concepts into chemical thermodynamics is a process at its beginnings—and not yet a success story. While the complete measurement uncertainty budget is a topic, the important concept of traceability, for instance, is not discussed at all. This issue, nevertheless, consists an interesting fixing point of the current state-of-the-art in metrology in chemistry. It is probably easy to understand that a reviewer from the field of thermodynamics sees little interest in a complex S. Lis (&) Department of Rare Earths, Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland e-mail: blis@amu.edu.pl

Organic-based sensor for chemical detection in aqueous solution

We present a flexible, pentacene-based field-effect device, for the detection of chemical species in aqueous solution. The sensor consists in a double-gate transistor, where the detection is achieved by exploiting the charge sensing capabilities of the floating-gate terminal. To provide the pH-sensitivity, the floating gate is functionalized with thioamine groups as such groups protonize proportionally to the concentration of H3O+ ions in solution. With respect to the existing organic-based devices for pH monitoring, our sensor does not require a counterelectrode and the organic semiconductor is not affected by the contact with the monitored solution.

Rice husk ash (RHA) as cement admixture for immobilization of liquid radioactive waste at different temperatures

Cementitious materials will initially act as a mechanical barrier preventing activated water flow through the waste for a long time, and thus will contribute to the retardation of dissolved radionuclides by the combination of physical and chemical interactions. Most chemical species in aqueous solutions will undergo some kind of (chemical) interactions with any solids of the cementations material. Therefore, it is of great importance to develop a quantitative understanding of the chemical processes involved and to strictly differentiate between physical and chemical aspects of radionuclide transport through such materials. A study is undertaken to determine the waste immobilization performance of (Cs +) wastes in cement–RHA mixtures. In addition to evaluating the effects of RHA on the leaching properties of cemented waste forms, the effect of addition of (RHA) on the strength of the cemented waste form is also investigated. However, RHA addition of 30% causes a significant increase in the hydraulic stability of cemented waste form. RHA enhances the strength; leaching and durability of cement may be through three primary actions which are the filler effect, the acceleration of ordinary Portland cement hydration and the pozzolanic reaction with calcium hydroxide (CH). The results were compared to control sample, and the viability of the RHA addition to concrete was verified. The use of these minerals results in ecological, economic and energy saving considerations.

Simulation of chemical phenomena in the Co(NO 3) 2–Na 2CO 3–H 2O system based on a thermodynamic model

A simulation for the Co(NO 3) 2–Na 2CO 3–H 2O system based on a thermodynamic model was proposed which predicts possible equilibrium states attained among gas, aqueous and solid phases under isothermal and isobaric conditions. Various chemical species such as CoOH + the cobalt complex, carbonate species in aqueous solution, precipitate of basic cobalt carbonate and CO 2 gas were taken into account. By using the Debye–Hückel formula for the activity coefficients of ionic species, apparent equilibrium constants of chemical reactions were well evaluated. A thermodynamic model was constructed by combining mass action law, mass balance, and charge balance equations together with equilibrium conditions among different phases. Simulation was carried out to compute concentrations of various chemical species in aqueous solution, amount of precipitate, and pressure of CO 2. In order to examine the validity of the thermodynamic model, the computed pH values were compared with experimental results and a relatively good agreement between them was obtained.

Rate Constants for Reactions of Radiation-Produced Transients in Aqueous Solutions of Actinides

Rate constants have been critically compiled for reactions of ions of the actinides Am, Cf, Cm, Np, Pu, Th, and U, as well as the element Tc, in different oxidation states with various chemical species in aqueous solution. The reactants include products of the radiolysis of water (hydrated electrons, hydrogen atoms, hydroxyl radicals, hydrogen peroxide) and transient species derived from other solutes (e.g., carbonate radical). The data are useful in the estimation of migration properties of actinides, which are relevant to waste management studies.

Calculation of equilibrium distributions of chemical species in aqueous solutions by means of monotone sequences

A numerical method for the calculation of equilibrium distributions of chemical species in aqueous solutions of electrolytes is presented. This method is constructed by transforming the problem of determining the set of unknown concentrations satisfying the mass balance and mass action equations into the equivalent problem of finding the limits of certain well-behaved mathematical sequences in a multivariable direct iteration scheme. The total (analytical) concentrations are taken as the starting estimates, and the recursive equations are constructed from the starting equations. It is shown that the sequences so constructed are both monotonic and bounded, hence convergent in an orderly fashion by a mathematical axiom. Each unknown free ion concentration (that is, each limit) is approached simultaneously from above and from below, being effectively “sandwiched” in an ever tightening manner. Strict error bounds therefore are easily constructed. The method has been found to be exceedingly efficient in practice, with the error bound (maximum fractional error in taking the upper estimate as the final answer) decreasing in an approximately exponential fashion with respect to iteration number, commonly 0.5–1.5 orders of magnitude per iteration. Correction for nonideality is presented, and the possibility of this giving rise to more than one solution is discussed in connection with three examples of natural waters of low-, medium-, and high-ionic strengths.