The chemical effects of ionizing radiations on fluorinated ethers

The state of knowledge on the mechanism of the radiolysis of poly(perfluoroethers) (PFPE) with the poly(trimethylene oxide), poly(propylene oxide) and poly(ethylene-methylene oxide) structures is reviewed and the results of recent investigations performed using EPR, radiothermal luminescence (RTL), electron scavenging, pulse radiolysis and UV-Vis matrix spectroscopy are reported. The radiolytic degradation of the poly(perfluoroethers) is based on excited species formed presumably via the cation-electron geminate recombination. The excited ether moieties undergo homolytic CO and CC bond cleavage with formation of a variety of neutral free radicals which by coupling and cage disproportionation accounts for the major chemical changes detected in the PFPE chains. As a consequence of the bond cleavages a linear decrease of the average molecular weights with increasing the radiation dose is observed. The CF splitting is also detected from the related free radicals and branching units in the chains; however their incidence is of minor importance with respect of chain scissions and it is significant only in the linear PFPEs. The role of ionic intermediates has been analyzed by matrix EPR and UV-Vis spectroscopy, pulse radiolysis, RTL spectroscopy and electron scavenging experiments: the results strongly suggest that ionic reactions are participating to the radiolysis mechanism but the upper limit estimate of their contribution to free radical yields is <20% for the Demnum™ and Krytox™ and <30% for the more polar Fomblin™ Z. An insight of the stability and decomposition modes of the elusive radical-cations and radical-anions of the perfluoroethers associated to the ionic mechanism was obtained through low-temperature electron loss and electron capture selective experiments coupled with matrix EPR spectroscopy and M.O. calculations; the results suggest that both species are intrinsically unstable at 77 K, the favored decomposition modes being the CO splitting for the anions and the cleavage of the C-C bonds adjacent to oxygen for the cations.     

Effect of gamma radiation on organic ion exchangers

Effects of gamma radiation on indigenous strong cation and anion exchange resins have been studied in HCl medium up to a dosage of 3600 kGy. The ion exchange capacities of cation and anion exchangers decreased by around 20% at 2400 kGy of absorbed dose. Decrease in salt-splitting capacity and total exchange capacity for both cation and anion exchangers were comparable up to 2400 kGy. Above 2400 kGy, a marginal loss in the capacity was observed for cation exchangers whereas a drastic reduction was noticed for the anion exchangers. The distribution coefficients for zirconium, antimony and cobalt, measured in HCl medium, did not change significantly for 2400 kGy of absorbed dose. Crushing strength and moisture retention capacity did not exhibit any specific trend with the absorbed dose.     

Distribution of heteroatoms of synthetic ion exchangers in pyrolysis products

Distribution of sulfur and nitrogen atoms in products of pyrolysis of spent synthetic ion exchangers AV-17 and KU-2 in the temperature range 50–550°C was studied. The compounds containing heteroatoms were identified, and their amounts were determined.     

Potentiometric sensors based on organic ion exchangers for determining tetraalkylammonium salts

Potentiometric sensors with plasticized polymer membranes based on organic ion exchangers, tetraalkylammonium dodecyl sulfates (benzyldimethyldodecylammonium, benzyldimethyltetradecylammonium, dimethyldistearylammonium), have been proposed for the determination of quaternary ammonium salts in model solutions and KATAPAV technical solutions. The thermal stability, composition, and solubility product have been estimated. It has been shown that ion associates are stable to 60?C70°C, K _S varies in the range from 2 × 10^?8 to 5 × 10^?10. The basic electrochemical parameters of the sensors have been determined as well, such as linearity ranges of the electrode function (5 × 10^?5 (5 × 10^?6)?1 × 10^?2 (1 × 10^?3) M) and slopes of the electrode functions (47?C59 mV/pc), response time (60?C90 sec), potential drift (2?C3 mV/day), operation period (3?C4 months), limits of detection for tetramethylammonium salts (1 × 10^?5?4 × 10^?7 M).     

Distribution and catalytic activity of sulfonic acid groups in organic ion exchangers

The existence of inhomogeneities in the polymer structure of ion exchangers was demonstrated and their influence on catalytic properties was shown. The results are based on the differences in catalytic activity of two ion exchangers with low degrees of sulfonation differing in the distribution of active groups within the polymer particles.     

The adsorption behaviour of microamounts of radium on inorganic ion exchangers

The radiochemical method has been used for investigation of the adsorption of radium on eighteen inorganic ion exchangers. The distribution coefficient of radium obtained are as follows: barite 2955, celestite 2420, BaSO₄ 4350, BaCrO₄ 5245, Ba₃(PO₄)₂ 5775, MnO₂·nH₂O 1681, La₂O₃·nH₂O 4150, Zerolit S/F 2920, etc.Presented at the International Conference on Nuclear and Radiochemistry, Beijing, Sept. 1–5, 1986.     

Structural studies on some inorganic ion exchangers

Ferrocyanides of zirconium(IV) and tin(IV), antimonates of cerium(IV) and titanium(IV), and cerium(IV) tungstate, has been shown to be useful materials as inorganic ion exchangers in radio- and analytical chemistry. These materials are sufficiently stable towards high dose of γ-radiations. Attempt is made to study some structural aspects and possible exchange sites of these materials using different techniques like thermal, Mössbauer and infrared spectroscopy.     

Physical quantification of the biological effectiveness of ionizing radiations

The role, and limitations, of the fundamental physical quantities used in our current system of dosimetry for the protection of individuals against the hazardous effects of ionizing radiation is discussed briefly. A major limitation is the inability to correlate biological data, in a unified way, as a function of linear energy transfer with the consequent necessity for quality factors. From consideration of the various interaction processes undergone by charged particles in the equilibrium slowing down spectra generated by the incident radiation field, it is shown that good correlation of biological effects, for all radiation types, can be achieved in terms of linear primary ionization. The implication is that delta-ray effects play at most a very minor role, at moderate fluences, and that, consequently, the absorbed dose is an unsuitable parameter for describing radiation effects. Structure in the radiosensitive targets is observed to have a critical dimension of about 2 nm. It occurs only when double-stranded DNA is present and the magnitude of the inactivation probability is consistent with double-stranded breaks being the significant lesion. Calculation is made of the yield of lesions as a function of the mean free path for primary ionization. Differential spectra of radiation quality are obtained for monoenergetic electrons (0.2 keV to 30 MeV); for characteristic X-rays from carbon, aluminium, neon, potassium, copper, silver, and tungsten; for 50 kV X-rays, 250 kV X-rays, ²⁴¹Am, ¹³⁷Cs, and ⁶⁰Co gamma rays; and for neutrons with energies between 0.1 and 50 MeV. Damage by electrons is shown to be predominant at the ends of their tracks between 50 and 200 eV, whereas this is not so for the proton recoil spectrum generated by neutrons above 1 MeV. Proposals are made for a unified system of dosimetry that is independent of radiation type and that obviates the need for quality factors. The method is thought to be of general applicability to irradiations by nuclides incorporated into mammalian cells, by ingested emitters, and by external sources.     

The chemical precipitation of nickel on ion exchangers and active carbons

The chemical precipitation of nickel in the form of poorly soluble precipitates in ion exchanger matrices and on active carbons from solutions of nickel chloride and chemical nickel plating electrolytes was studied. The sorption of nickel ions from a solution of nickel chloride occurs most effectively on Purolite D24002 macroporous chelate forming ion exchanger, KU-23-15/100 sulfo cation exchanger, and KU-2-8 gel sulfo cation exchanger. Nickel enters sulfo cation exchangers in the form of counterions, and is adsorbed on Purolite D24002 largely because of complex formation. The subsequent precipitation of nickel in the solid state in matrix pores liberates ionogenic centers, which allows repeated sorption cycles to be performed. After three chemical precipitation cycles under static conditions, the amount of nickel is higher by 170–250% than the ion exchange capacity of the sorbents. The electrolyte of chemical nickel plating contains nickel predominantly in the form of negatively charged and neutral complexes with glycine, which cannot form bonds with the matrices under study. It is therefore reasonable to perform sorption at decreased solution pH values.     

Comparison of nonporous silica-based ion exchangers and monolithic ion exchangers in separations of inorganic anions

Low capacity anion exchangers for IC have been prepared by modification of nonporous uniformed silica MICRA microbeads and by modification of the organic polymeric monolithic matrixes prepared in situ in quarz capillary. Due to the small particle size (1.5 microm) high-performance adsorbents were prepared allowing to obtain up to 190,000 tp/m. However, the column possesses a very high back-pressure and can be used in a short length up to 50 mm only to meet the requirements of conventional chromatographic equipment. An analysis of a test mixture of seven anions was completed within 3 min with a back column pressure of about 350 bar (HETP of about 5.5 microm, where HETP is the height equivalent to the theoretical plate). Monolithic capillary columns provide lower efficiency per column unit length than MICRA columns; however, they can be used at a longer length because of their low flow resistance. Monolithic column of ca. 40 cm length has workable pressure below 10 bar and allows separation of a five anions test mixture within less than 10 min. A better efficiency of monolithic column (HETP approximately 75 microm) can be achieved at reduced flow rates when the analysis time is not a critical parameter.     

Computer evaluation of water sorption on ion exchangers

Water sorption on an ion exchanger can be described by formation of several hydrates. The general least squares program WSLET based on the "pit-mapping" approach has been written for evaluating such equilibria. It is written in FORTRAN 77 for use on personal computers. Besides finding the best values for the equilibrium constants of the various hydrates the program also searches for best values of the stoichiometric indices by using the so-called ESI-method. The program is provided with least-squares procedures and blocks for statistical analysis of the residuals as well as for data simulation. It has been tested with data on the strong base resin Dowex 1 as well as on simulated data. In the present paper an illustrative example is given together with data simulation. It is found that in most cases WSLET helps to find a better fit than earlier models quite efficiently, showing the advantage of the ESI method in combination with least-squares methods.     

Sorption properties of nitrogen-containing ion exchangers

Sorption capacity of ion exchangers based on glycidyl derivatives of aromatic compounds and polyamines was studied in relation to pH of solution. The mechanism of sorption of polyvalent metal ions was examined.     

Sorption of gaseous ammonia on sulfonated macroreticular ion exchangers

The amount of gaseous ammonia sorbed on dry sulfonated macroreticular ion exchangers with different contents of divinylbenzene was found to be greater than the number of sulfonic acid groups. The excess ammonia could be removed by washing with water. With ion exchangers containing more than 20% of divinylbenzene a certain amount of chemically bonded ammonia could not be removed, even by elution with strong acid. Sorption of ammonia occurred also on dry ion exchangers fully neutralized with sodium ion, and in that case also, ammonia could only partially be removed by water from higher crosslinked samples. On desorption into a gaseous phase the amount of desorbed ammonia was proportional to the surface area of the ion exchanger, since desorption occurred only from surface layers. The results obtained indicate that ammonia migrates among acid groups located within the mass of the ion exchanger.     

Micellar enhanced cyanide ion determination in samples from synthetic organic processes

A method was developed for the recovery and determination of cyanide ion in organic sample matrices. To facilitate the solubilization of cyanide ions, cetyltrimethylammonium bromide (CTAB) was added at concentrations above the critical micelle concentration. Sample cyanation reaction products consisted of solvent mixtures of a hydroxynitrile in DMF-toluene or DMF-isopropylacetate (IPAC). Spectrophotometric determination of cyanide ion at 578 nm by the pyridine-barbituric acid method was automated by flow injection analysis. Recovery of cyanide ion from spiked samples was 93.2% in DMF-IPAC solvent matrix and 93.9% in DMF-toluene. Low alkali concentration was observed to favor solubilization of cyanide ion in the micellar solution.     

Microanalysis with the aid of ion exchangers

The resin spot test is modified by the use of a high molecular weight amine, Amberlite LA-1, in carbon tetrachloride; 0.2 μg of cobalt(II) can be detected rapidly by shaking an acidic solution containing thiocyanate with a 5% amine solution. Amine-impregnated papers can also be used.     

Hydrolysis of oligosaccharides by sulphonic ion exchangers

The hydrolysis of oligosaccharides by sulphonic ion exchangers has been performed in batch and in column experiments. The rate constants and selectivity are compared with the values obtained in homogeneous phase with H₂SO₄ and polystyrene sulphonic acid. The rate constants are lower in the presence of ion exchangers for dimers and the efficiency decreases as the degree of polymerization of the oligosaccharides increases, because of control by intraparticle diffusion. It is concluded that the ion exchanger process is rather inefficient for higher molecular weight solutes when compared with the corresponding polyelectrolyte or low molecular weight acid.     

Potentiometric sensors based on organic ion exchangers of tetraalkylammonium and silver complexes with ampicillin,oxacillin, and cefazolin

Potentiometric sensors with plasticized polymer membranes based on tetraalkylammonium organic ion exchangers and silver(I) complexes with ampicillin, oxacillin, and cefazolin are proposed for the quantification of antibiotics in model mixtures. The quantitative parameters of complex species of silver with β-lactam antibiotics (β-lac) are established. The complexes (β-lac)₂Ag are shown applicable as electroactive components of membranes of potentiometric sensors with tetraalkylammonium cations as counterions. For the information on potentiometric selectivity coefficients and the parameters of cross-sensitivity of sensors in solutions of β-lactam antibiotics they might be used in multisensor systems of the electronic tongue type. The analytical signals are processed by the method of neural network. The average relative error of the individual quantification of β-lactam antibiotics in three-component model mixtures was 4–6%.     

The use of ligand exchange for the separation of aromatic acids on synthetic cation exchangers

Summary A very good separation of the mixture of eight aromatic acids has been obtained by ion-exchange chromatography using the ligand-exchange technique, on a column containing a synthetic cation exchanger and trivalent metal ion (Al³⁺, Fe³⁺, or Ce³⁺).