Application of ion chromatography to qualitative and quantitative determination of the main inorganic ionic components of samples from a production process of potassium sulphate

This review presents the possibility to use ion chromatography (IC) to analyse solids and brines deriving from treatment procedures of potassium salts. Qualitative and quantitative determination of ions samples has been used to make their chemical reconstruction. By using conventional calibration methods covering the whole concentration interval, analysis were not suitably accurate. During this process, the analysis is considered acceptable when the difference between the sum of the equivalents of cations and anions (ΔE) is ≤2%. For the process, a calibration method has been used employing four reference curves; each defined by three points corresponding to three standards purposely devised in our laboratory. The composition of the standards matched that expected for the samples from the different stages of the process reaction, after their usual sampling, dissolution and dilution. By comparing the conductivity of the analyte in the real sample to the conductivity of the same analyte in a standard, the effects of other analytes present in the medium are practically cancelled and need not be considered. The IC method results are in good agreement with conventional analysis methods (potentiometric titration, atomic absorption, gravimetric analysis).     

Polyaniline‐coated cigarette filters as a solid‐phase extraction sorbent for the extraction and enrichment of polycyclic aromatic hydrocarbon in water samples

Polyaniline coated cigarette filters were successfully synthesized and used as a solid‐phase extraction sorbent for the extraction and preconcentration of polycyclic aromatic hydrocarbons in water samples. The polyaniline helped to enhance the adsorption ability of polycyclic aromatic hydrocarbons on the sorbent through π–π interactions. The high porosity and large surface area of the cigarette filters helped to reduce backpressure and can be operated with high sample flow rate without loss of extraction efficiency. The developed sorbent was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy. The parameters that affected the extraction efficiencies, i.e. polymerization time, type of desorption solvent and its volume, sample flow rate, sample volume, sample pH, ionic strength, and organic modifier were investigated. Under the optimal conditions, the method was linear over the range of 0.5–10 μg/L and a detection limit of 0.5 ng/L. This simple, rapid, and cost‐effective method was successfully applied to the preconcentration of polycyclic aromatic hydrocarbons from water samples. The developed method provided a high enrichment factor with good extraction efficiency (85–98%) and a relative standard deviation <10%.     

Zinc underpotential deposition at Pt(111) and Pt(110) under the influence of boric acid and chloride anions

Zinc underpotential deposition (Zn UPD) was studied by cyclic voltammetry in solutions of various pH and composition, where the effects of the presence of boric acid or chloride in the solution were observed. We have found that the cyclic voltammograms of Zn UPD at Pt(111) were dependent on boric acid concentrations, zinc ion concentrations, and pH in acidic solutions. These suggest that the induced adsorption of borate by releasing of H⁺ is accompanied with Zn UPD. The preadsorbed chloride species on Pt(110) accelerate the UPD process by their removal just before the UPD, making the surface sites available for the process, and the UPD remains at identical electrode potentials, while the chloride ions do not take part in the induced adsorption on UPD Zn at Pt, as clearly found by the radiotracer method. These show that the anions play versatile roles in the process of adlayer formation by their different but essential chemical characteristics. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 745–751 The text was submitted by the authors in English.     

An atmospheric pressure chemical ionization study of the positive and negative ion chemistry of the hydrofluorocarbons 1,1-difluoroethane (HFC-152a) and 1,1,1,2-tetrafluoroethane (HFC-134a) and of perfluoro-n-hexane (FC-72) in air plasma at atmospheric pressure

A report is given on the ionization/dissociation behavior of the title compounds within air plasmas produced by electrical corona discharges at atmospheric pressure: both positive and negative ions were investigated at different temperatures using atmospheric pressure chemical ionization mass spectrometry (APCI-MS). CHF(2)CH(3) (HFC-152a) undergoes efficient ionic oxidation to C(2)H(5)O(+), in which the oxygen comes from water present in the plasma. In contrast, CF(3)CH(2)F (HFC-134a) does not produce any characteristic positive ion under APCI conditions, its presence within the plasma being revealed only as a neutral ligand in ion-molecule complexes with ions of the background (H(3)O(+) and NO(+)). Analogously, the perfluorocarbon FC-72 (n-C(6)F(14)) does not produce significant positive ions at 30 degrees C: at high temperature, however, it undergoes dissociative ionization to form many product ions including C(3)F(6)(+), C(2)F(4)(+), C(n)F(2n+1)(+) and a few families of oxygen containing cations (C(n)F(2n+1)OH(2)(+), C(n)F(2n)OH(+), C(n)F(2n-1)O(+), C(n)F(2n-1)O(2)H(2)(+), C(n)F(2n-2)O(2)H(+)) which are suggested to derive from C(n)F(2n+1)(+) in a cascade of steps initiated by condensation with water followed by steps of HF elimination and H(2)O addition. Negative ions formed from the fluoroethanes CHF(2)CH(3) and CF(3)CH(2)F (M) include complexes with ions of the background, O(2)(-)(M), O(3)(-)(M) and some higher complexes involving also water, and complexes of the fluoride ion, F(-)(H(2)O), F(-)(M) and higher complexes with both M and H(2)O also together. The interesting product O(2)(-)(HF) is also formed from 1,1-difluoroethane. In contrast to the HFCs, perfluoro-n-hexane gives stable molecular anions, M(-), which at low source temperature or in humidified air are also detected as hydrates, M(-)(H(2)O). In addition, in humidified air F(-)(H(2)O)(n) complexes are also formed. The reactions leading to all major positive and negative product ions are discussed also with reference to available thermochemical data and relevant literature reports. The effects on both positive and negative APCI spectra due to ion activation via increasing V(cone) are also reported and discussed: several interesting endothermic processes are observed under these conditions. The results provide important information on the role of ionic reactions in non-thermal plasma processes.