Studies on the Authorship of Albumen Vintage Photographs: A Combined Experimental and Chemometric Approach.

The differences in albumen photographs from vintage photographic studios were identified by energy-dispersive X-ray fluorescence spectroscopy and Fourier transform infrared spectroscopy. The results inspired the concept of finding common features characteristic of a given photographic studio. The obtained measurement data (i.e., positions of vibrational bands for characteristic groups of albumen and the mass contents of chosen elements) were analyzed chemometrically by employing the Principal Component Analysis (PCA). The PCA technique allowed us to reduce the number of relevant experimental parameters characterizing the unique features of the photographic objects. The two major components were able to distinguish the photographic objects in terms of their authorship and the time to produce a photograph. The method developed was examined for a selected group of photographs consisting of albumen prints from three Polish photographic ateliers. To validate ED-XRF measurements and, consequently, the chemometric findings, reference albumen photo samples were designed and prepared. The empirical functional relationships between the content of photochemically reduced silver particles on the photographic paper and several physicochemical factors, including time of exposure to UV light, AgNO3 concentration in a fixed bath, and concentrations of other additives, were proposed. These results can be used for the prediction of the experimental conditions under which the investigated photographs were developed.

Electrochemical Determination of Nanoparticle Size: Combined Theoretical and Experimental Study for Matrixless Silver Nanoparticles.

A chronoamperometric procedure for the preparation of silver nanoparticles (AgNPs) in aqueous systems with no extra added stabilizing agents is presented. The uniqueness of the prepared nanoparticle systems was explored by theoretical considerations. The proposed theoretical model predicts the structural parameters of the obtained nanoparticle system. The parameters required for the calculations (the zeta potential, conductivity, and effective diffusion coefficient of ionic silver) are available from independently performed measurements. Chronoamperometry at a microelectrode was employed for the evaluation of the effective diffusion coefficient of ionic silver present in the AgNP solution. The values of AgNP radii predicted by the theoretical model for the selected samples were compared to those obtained by Transmission Electron Microscopy (TEM) and Dynamic Light Scattering (DLS) methods. Because of the high polydispersity of the prepared nanoparticle samples, DLS results were overestimated in comparison to both: the TEM results and some theoretical predictions. By correcting the theoretical predictions by the Debye length, the calculated nanoparticle sizes become comparable (within their expanded uncertainties) to those measured in TEM images, especially for the nanosystems at early stages of their formation via the electrosynthesis process.

Statistical evaluation of the effect of sample preparation procedure on the results of determinations of selected elements in environmental samples. Honey bees as a case study.

Honey bees became a frequently studied environmental research object due to the fact that they are considered as indicators of the environmental contamination with metals. Such studies require reliable methods of sample preparation that allow comparison of the results obtained in different laboratories. In this paper, different variants of sample preparation were examined, including washing, milling and mineralization. Determination of total contents of Cd, Pb, Co, Cr, Cu, and Zn was performed using ICP MS. Each procedure of the sample preparation was characterized in terms of repeatability and recovery and the resulting combined standard uncertainty was evaluated. The relative UNC ranges for the treatment procedures examined are: 11-16% (washing, open digestion), 13-14% (open digestion), 13-51% (washing, closed digestion), 12-37% (washing, milling, closed digestion), 13-68% (closed digestion), and 12-51% (milling, closed digestion). In almost all cases the lower limits of these ranges correspond to Zn determinations while the upper limits to Pb. Analytical results of metal determination obtained for samples prepared according to six different procedures do not differ significantly when compared within the expanded uncertainty (±2×u(c¯M)). The procedures were compared statistically using one-factor analysis of variance (ANOVA) and chemometrically on the basis of Principal Component Analysis (PCA), which allowed to demonstrate some general recommendations regarding environmental monitoring for matrices other than honey bees.

Selective Recovery of Zinc from Metallurgical Waste Materials from Processing Zinc and Lead Ores.

A method for processing of metallurgical waste materials (chemically defined as sulfur-bearing zinc-ferric materials) produced by plants processing zinc ores and their concentrates is proposed. The method proposed is a combination of pyro- and hydrometallurgical treatments of the waste material. The crucial steps in the developed method include: roasting the material at 450 °C to generate sulfur dioxide (SO2), absorption of SO2 in an aqueous system to form sulfuric acid (IV), carbothermic decomposition of zinc ferrite compounds, and leaching of zinc from the roasted material using sulfuric (IV) acid. The method allows one to extract up to 40% of zinc from the waste material and, consequently, to generate a fraction of material with substantially higher content of iron oxides. The proposed method takes advantage of the presence of sulfur in the processed material which upon roasting is converted to sulfuric acid (IV)-a leaching agent for selective extraction of zinc. The properly adjusted pH of the aqueous medium in which the leaching process is carried out is the key factor determining the quantitative and selective separation of zinc. If the amount of sulfur in the processed material is insufficient, it may be supplemented by adding sulfuric acid (VI) to adjust the pH. The method proposed was tested at a laboratory scale and quarter industrial scale using the real samples taken from stockpiles in the vicinity of the plant processing zinc and lead ores in Poland. It may also work for any zinc-ferric materials from various sources.

Highly efficient and selective leaching of silver from electronic scrap in the base-activated persulfate - ammonia system.

A system composed of persulfate salt and ammonia in highly alkaline aqueous solution is developed and examined for leaching metallic silver from elements of the electronic waste materials (e-scrap). Strong base activates persulfate ions providing in situ generation of highly reactive oxygen molecules. The oxidized metal forms then well soluble complex ions with ammonia ligands. The kinetic studies of the leaching process were performed for pure metallic silver. They revealed that the efficiency of the process is affected by the type of the persulfate salt. By employing potassium persulfate one obtains significantly (more than 50% for silver plates and more than 100% for silver powder) increased efficiency of silver dissolution compared to the solution composed of either sodium or ammonium persulfates. In the range of persulfate concentrations between 0.02 and 0.23mol/L the apparent reaction order with respect to the persulfate concentration was similar for all persulfate salts and was estimated to be around 0.5. The room temperature (22±2°C) seems to be an optimal temperature for the leaching process. An increase in the temperature resulted in the significant drop in the silver dissolution rate due to the decreased solubility of oxygen. Based on these results a possible mechanism of dissolving silver is discussed and the optimal composition of the leaching solution is formulated. The obtained formulation of the leaching solution was applied for the extraction of silver coatings of Cu-based e-waste scrap and the obtained results revealed an important effect of copper in the mechanism of the leaching process. The regression analysis of the leaching curve indicated that each gram of base-activated potassium persulfate under the specified conditions may leach almost 100mg of silver coatings in a form of well soluble diamminesilver (I) complex. The silver complex can be relatively easy reduced to metallic silver. The method developed is relatively cheap, low toxic and does not produce harmful by-products.

Electrochemical Examination of the Structure of Thin Hydrogel Layers Anchored to Regular and Microelectrode Surfaces.

For the examination of hydrogel structure, thin layers of thermoresponsive gels based on poly(N-isopropylacrylamide) (pNIPA) and copolymer poly(N-isopropylacrylamide-co-sodium acrylate) (p(NIPA-co-AS)) were successfully anchored to microelectrode and regular electrode surfaces using the electrochemically induced free radical polymerization. The obtained layers were stable and covered the entire surface of the electrodes. Electroactive probes 1,1'-ferrocenedimethanol (Fc(CH2OH)2) and synthesized derivatives of ferrocene modified with polyethylene glycol units (Fc-PEGn) of various length (n = 4, 9, 75, and 135) were employed for studying the volume phase transition of the thin hydrogel layers and for the determination of their structural parameters. The quantitative information on the structural parameters of the hydrogel layers was derived from the obstruction model for diffusion using the voltammetrically determined diffusion coefficients for the model redox probe Fc(CH2OH)2. An approach to the determination of the effective radii of the gel openings (channels) for pNIPA and p(NIPA-co-AS) microlayers was developed. The obtained results were matched with the experimental results and allowed derivation of quantitative conclusions. The voltammograms obtained with modified electrodes in solutions containing Fc-PEG4, Fc-PEG9, and Fc-PEG75 were well defined and of appropriate height. However, the voltammograms recorded for Fc-PEG135, the hydrodynamic radius of which exceeded the size of the gel channels, were at the baseline level.

Quantifying uncertainty of determination by standard additions and serial dilutions methods taking into account standard uncertainties in both axes.

The analytical expressions for the calculation of the standard uncertainty of the predictor variable either extrapolated or interpolated from a calibration line that takes into account uncertainties in both axes have been derived and successfully verified using the Monte Carlo modeling. These expressions are essential additions to the process of the analyte quantification realized with either the method of standard additions (SAM) or the method of serial dilutions (MSD). The latter one has been proposed as an alternative approach to the SAM procedure. In the MSD approach instead of the sequence of standard additions, the sequence of solvent additions to the spiked sample is performed. The comparison of the calculation results based on the expressions derived to their equivalents obtained from the Monte Carlo simulation, applied to real experimental data sets, confirmed that these expressions are valid in real analytical practice. The estimation of the standard uncertainty of the analyte concentration, quantified via either SAM or MSD or simply a calibration curve, is of great importance for the construction of the uncertainty budget of an analytical procedure. The correct estimation of the standard uncertainty of the analyte concentration is a key issue in the quality assurance in the instrumental analysis.

Voltammetric studies of diffusional and migrational transport of ferrocene derivative of tripeptide glutathione.

The transport of mono- and divalent anions of S-ferrocenylmethyl-L-glutathione (FcCH2SG) was investigated voltammetrically at a microelectrode in solutions of low ionic strength. The electrooxidation reactions of the ferrocenyl group attached to biologically active glutathione neutralized with a strong base in two consecutive steps can be represented as FcCH(2)SG(-) --> Fc(+)CH(2)SG(-) + e and FcCH(2)SG(2-) --> Fc(+)CH(2)SG(2-) + e for the mono- and divalent anions of FcCH(2)SG, respectively. The limiting currents due to these electrode processes were investigated under the conditions of varying content of supporting ions. The results obtained for the electrooxidation of the monovalent anion of FcCH(2)SG deviate significantly from the theoretical predictions derived for the charge cancellation electrode processes (i.e., processes producing uncharged species upon electron transfer). The differences observed are attributed to the specific migrational behavior of the generated dipole-like product which formally bears no net charge but in fact contains two oppositely charged moieties within a molecule. To interpret the data obtained for the divalent anion of FcCH(2)SG, a recent model of the theory of migrational voltammetry has been adapted and extended. The agreement between the experimental data and the theory is obtained only for the ratio of diffusion coefficients of the electrode process product (Fc(+)CH(2)SG(2-)) and the substrate (FcCH(2)SG(2-)) smaller than 1. This leads to a conclusion that upon oxidation this molecule undergoes a conformation change and winds up because of the formation of a coordination bond. The conclusion is supported by molecular-mechanics calculations. The presented methodology allows one to study quantitatively the changes in the concentration distribution of biologically active molecules driven by migration and diffusion and to diagnose their possible structural changes upon reduction/oxidation. Both factors are essential for the proper understanding of the functionality of biologically active systems.

Structural changes of polyacids initiated by their neutralization with various alkali metal hydroxides. Diffusion studies in poly(acrylic acid)s.

The changes in the three-dimensional structure of the poly(acrylic acid), PAA, induced by incorporation of various alkali-metal counterions have been evaluated by studying diffusion of an uncharged probe (1,1'-ferrocenedimethanol) in the polymeric media. The studies are supported by the measurements of conductivity and viscosity of the polymeric media. Solutions of linear PAA of four different sizes (molecular weights: 450,000, 750,000, 1,250,000, 4,000,000) were neutralized with hydroxides of alkali metals of group 1 of the periodic table (Li, Na, K, Rb, Cs) to the desired neutralization degree. The transport properties of the obtained polyacrylates were monitored by measuring the changes in the probe diffusion coefficient during the titration of the polyacids. The probe diffusivity was determined from the steady-state current of the probe voltammetric oxidation at disk microelectrodes. Diffusivity of the probe increases with the increase in the degree of neutralization and with the increase in viscosity. It reaches the maximum value at about 60-80% of the polyacid neutralization. The way the probe diffusion coefficients change is similar in all polyacid solutions and gels. The increase in the size of a metal cation causes, in general, an enhancement in the transport of probe molecules. The biggest differences in the probe diffusivities are between lithium and cesium polyacrylates. The differences between the results obtained for cesium and rubidium are not statistically significant due to lack of good precision of the voltammetric measurements. The measurements of the electric conductivity of polyacrylates and the theoretical predictions supplemented the picture of electrostatic interactions between the polyanionic chains and the metal cations of increasing size. In all instances of the PAAs, the viscosity of the solutions rapidly increases in the 0-60% range of neutralization and then becomes constant in the 60-100% region. With the exception of the shortest chain polyacid, the formation of a rigid medium (gel) has been observed in the experiments with all cations. After the end point of the titration was passed, a sudden drop in the viscosity and the disappearance of the gelatinous structure were seen. The largest value of viscosity has been recorded for the longest chain polyacid. The change in the cation of the strong base used did not affect the viscosity of the polymeric system.

General theory for migrational voltammetry. Strong influence of diversity in redox species diffusivities on charge reversal electrode processes.

High sensitivity of the microelectrode response to the difference between the substrate and the product diffusion coefficients is predicted for the charge reversal processes. This effect is anticipated from the general theoretical model developed for the diffusional-migrational transport to microelectrodes. The model predicts the voltammetric wave heights for any type of electrode processes carried out in the presence of any number and concentration of nonelectroactive ions. It involves changes in diffusion coefficients of the redox species and assumes no homogeneous complications. Handy, analytical expressions for the limiting current and limiting potential can be derived for a system of a univalent product and univalent ions of supporting electrolyte. This case covers charge reversal processes of the following type: S(z) --> P(+/-) + ne (n + z = sgn(n), absolute value(n) > or = 2). It has been shown that under migrational conditions the change in the ratio of the product and the substrate diffusivities (D(P)/D(S)) by as little as 10% results in significant changes in the voltammetric wave height. For 2-e charge reversal processes, a 10% increase in D(P) versus D(S) leads to a drop in the voltammetric wave height of 18.3% compared to that calculated for equal diffusion coefficients. The reversed change, i.e., the 10% decrease of the D(P) value with respect to D(S), increases the voltammetric wave height by 30.5% compared to that obtained for equal diffusivities. The theoretical predictions were confronted with our recent experimental results obtained for the 2-e oxidation of sodium (6,8-diferrocenylmethylthio)octanoate, which process can be classified as the charge reversal reaction. The best fit was obtained for D(P)/D(S) equal to 0.71.

Diffusion of uncharged probe reveals structural changes in polyacids initiated by their neutralization: poly(acrylic acids).

The diffusion studies of the uncharged probe (1,1'-ferrocenedimethanol) have been successfully applied for the evaluation of the changes in the three-dimensional structure of poly(acrylic acids) of various molecular weights (ranging from 2000 to 4,000,000 g/mol) during their neutralization with a strong base. The qualitative picture of the macromolecule arrangement during the titration of the polyacids has been obtained from the conductometric measurements. The characteristic changes in the poly(acrylic acid) conductivity are practically the same for all polyacids examined and are in a very good agreement with the predictions of our theoretical model of the polyelectrolyte conductance. The transformation of the polyelectrolyte solution into the gel-like or gel phase has been investigated more quantitatively by tracing the changes in the diffusion coefficient of the uncharged probe redox system. The probe diffusivities, D, were determined using steady-state voltammetry at microelectrodes for a wide range of neutralization degree, alpha, of the polyacids tested. The dependencies of D versus alpha are of similar shape for all poly(acrylic acids). The first parts of the dependencies reflect a rapid increase in D (up to neutralization degree of either 45% for the lowest molecular-weight poly(acrylic acid) or 75-80% for other polyacids). They are followed by the parts of a slight drop in the diffusion coefficient. The changes in the probe diffusivity become stronger as the molecular weight of poly(acrylic acid) increases. The maximum probe diffusion coefficients are greater than the initial values in the pure polyacid solutions by 14, 24, 19, 30, and 28% for poly(acrylic acid) of molecular weights of 2000, 450,000, 1,250,000, 3,000,000, and 4,000,000 g/mol, respectively. The variation in the probe diffusion coefficient qualitatively follows the line of the changes in the macroscopic viscosity of the polyelectrolyte system. This is in contrast to the predictions of the Stokes-Einstein relation and, therefore, suggests that the changes in the probe diffusion rate are mainly due to the structural changes in the polyacrylate medium and the macromolecular rearrangements induced by the chemical, acid-base reaction. By adapting the obstruction model for diffusion in homogeneous gels, the transport characteristics of the probe were converted into the structural characteristics of the polyelectrolytic systems. It has been found that the most ordered structure of the polyelectrolyte, or in other words the most permeable structure, is obtained when poly(acrylic acid) is neutralized at 75-80%.

Generalized theory of steady-state voltammetry without a supporting electrolyte. Effect of product and substrate diffusion coefficient diversity.

A generalized theory of the steady-state voltammetric response of a microelectrode in the absence of supporting electrolyte and for any values of diffusion coefficients of the substrate and the product of an electrode process is presented. The treatment applies to any reasonable combination of the charge numbers of the substrate, its counterion, and the product. A way to incorporate the activation polarization into the model is also demonstrated. It has been shown that the height, position, and shape of the migrational voltammogram are affected by the ratio of the product to substrate diffusivity (theta). In particular, for the electrode processes with sign retention, unequal diffusivities of electroactive species influence both characteristic points of the voltammogram (the limiting current and the half-wave potential). For charge neutralization processes (uncharged product), the changes in theta parameter are accompanied only by a shift in the half-wave potential. The most dramatic changes in the I-E relation can be observed for the charge reversal processes. In this case, a consecutive increase in theta results in the transition of the voltammogram shape from rapid exponential growth (theta < 1), through ramp shape (theta = 1), to common wave shape (theta > 1). On the basis of the expressions derived for the limiting current (exact and linearized), a possibility of the determination of the diffusion coefficient of the electrode reaction product is demonstrated. In addition, the ranges of theta where the assumption of equal diffusivities of the substrate and the product is obeyed within an insignificant error have been determined quantitatively. The theory has been experimentally verified using voltammetric oxidation of hexacyanoferrate(II).

Direct determination of diffusion coefficients of substrate and product by chronoamperometric techniques at microelectrodes for any level of ionic support.

A new method for the determination of the diffusion coefficients of both the substrate, DS, and the product, DP, of an electrode process has been developed. The method proposed is based on the analysis of the transient currents and can be applied to some reactions of the type SzS = PzP + ne and, in contrast to the concept based on the steady-state current, to any ratio of the concentrations of supporting electrolyte and substrate. The diffusion coefficients can be evaluated sequentially from the two parts of the double-potential step chronoamperogram, since the magnitude of the normalized chronoamperometric current of the first step depends on the DS value, while that of the second step is controlled by both DS and DP values. The corresponding, easy-to-use equations and procedures are given in the paper. The equations were derived on the basis of the numerical simulation data. The proposed methods of determination of diffusion coefficients for the substrates and products have been examined experimentally with the charged and uncharged ferrocene derivatives under diffusional and mixed diffusion-migration conditions. Only the chronoamperometric DS values obtained for the substrates could be compared to those determined from the steady-state diffusional current. It was found that for the systems investigated the agreement between these two methods was good. In this limited comparison, the standard deviations for the transient techniques were slightly larger than those obtained for the excess supporting electrolyte steady-state voltammetry.