Role of ionic species and valency on the steady shear behavior of partially hydrolyzed polyacrylamide solutions

Polyacrylamides are anionic polymers with a large number of charges along the polymer chains. The rheological properties of aqueous polyacrylamide solutions can be significantly modified by varying the solvent environment with the addition of salt. The presence of cations substantially reduces the inter- and intra-molecular interactions of the macroions. It was found that the valency of the cation has a strong effect on the rheological behavior of polyacrylamide solutions, but the size and type of salt have a negligible effect.The reduction in the solution viscosity with di-valent salts (e.g., CaCl₂, MgCl₂, BaCl₂, and MgSO₄) can be as high as an order of magnitude compared with mono-valent salt (KI, KC1, NaCl, and NaBr), depending on the salt concentration and shear rate. An identical viscosity function can be obtained for different types of polyacrylamide solutions by varying the salt content in solution. This interesting feature provides a useful means in the development and preparation of certain ideal fluids for simulation studies of complex flow problems.     

The use of a short-end injection procedure to achieve improved performance in capillary electrophoresis

Summary Minimum capillary lengths on commercial instruments are fixed and cannot be decreased further. To effectively reduce the capillary length used for separation the sample can be injected from the end of the capillary nearest the detector. This procedure is known as a short-end injection and can reduces analysis times by at least two-thirds compared to conventional injections. The time reduction benefits are shown in rapid separations of basic drugs, drug-related impurities and chiral compounds. Short-end injections, in combination with both increased electrolyte strength and reduced voltage are an effective approach to reducing the detrimental impact of high sample solution ionic strength. They can also lead to improved resolution by increasing stacking effects and reducing peak tailing. Peak area and migration time precision obtained are shown to be equivalent to those obtained for conventional injection procedures. It is concluded that short-end injections should be considered for routine operation as they are a useful means of reducing analysis time, increasing sensitivity, decreasing buffer depletion effects. They also allow use of higher electrolyte strengths which can improve resolution and reduce peak tailing, and can overcome significant problems which occur when analysing samples containing high salt contents.     

Separation of nitrophenols by capillary zone electrophoresis

Separation conditions suitable to a rapid resolution of a group of eight nitrophenols by capillary zone electrophoresis (CZE) were found. Required differences in their effective mobilities were achieved via host-guest complexation of -cyclodextrin combined with intermolecular interactions involved by polyvinylpyrrolidone. When both additives were present in the carrier electrolyte at pH=9.1 nitrophenols could be separated in the column of a, 300 m I.D. and 180 mm in the length within 8–9 minutes. It is shown that the column of such an I.D. providing enhanced sample load capacity, can operate with high separation efficiencies as maintaining zone dispersions due to Joule heating on a tolerable level. CZE on-line coupled with isotachophoretic sample pretreatment is shown to provide the concentration limits of detection at low ppb concentrations by using an on-column photometric detector operating at 254 and 405 nm detection wavelengths.     

Flow-Injection Determination of Elemental Iodine by Polyvinyl Alcohol

Complex formation between elemental iodine and polyvinyl alcohol was studied under flow conditions. The formation of substances with a weak hyperchromic effect in the UV and visible regions was detected. It was shown that this reaction could be used under flow conditions provided the gel-forming ability and viscosity of the polyvinyl alcohol solution were reduced by adding isopropanol and 6% dimethylsulfoxide. It was found that the reaction efficiency under flow conditions could be monitored using a new method for the determination of the dispersion coefficient of a sample based on comparison between standard and flow absorptivity coefficients. Because of the effect of nonequilibrium factors, it turns out that the best calibration function is a nonlinear one. The throughput capacity of the method is 140 samples per hour, and the limit of detection is 60 ng/mL. The high selectivity for chlorides allows one to determine iodine and its species in seawater and to monitor its concentration in white salt.     

Small-angle X-ray and neutron scattering studies of the morphology of ionomers

Preliminary small-angle neutron scattering (SANS) studies have been made of different ionomers in the dry state and after saturation with water. Scattering from the dry samples arises from differences in the neutron scattering cross sections of the ionic and nonionic units in the polymer. The SANS technique is complementary to previous small-angle x-ray scattering (SAXS) studies since the SANS contrast differences are generally quite different than those for SAXS. A quantitative comparison is made of SANS and SAXS intensities for a dry cesium salt of an ethylene-methacrylic acid (E-MAA) copolymer. For water-saturated samples the technique of isotopic replacement can be used in conjunction with SANS since saturation can be effected with either H₂O or D₂O. In this case information about the chemical composition of the phases is obtained from an analysis of the intensity ratio I/I. Results are consistent with the presence of a separate phase containing water molecules and ions in a matrix of the nonionic units. A Guinier analysis gives a radius of gyration of 17 Å for a water-saturated cesium salt of an E-MAA copolymer.     

Determination of low-level90Sr in environmental materials: A novel approach to the classical method

A method was developed for the separation of strontium from large amounts of calcium which does not depend on fuming nitric acid. A sample in the form of mixed carbonates or oxides is stirred into concentrated nitric acid in the proportion 17 w/v. Strontium forms insoluble nitrates while calcium remains in the solution. Two re-precipitation steps combined with an acetone wash yield a very pure strontium salt which is suitable for gravimetric determination of recovery. The method, devised originally for⁹⁰Sr assay in sea water, can also be applied to solid samples which present analytical problems due to their high calcium content.     

Determination of uranium and thorium in Eskişehir-Beylikahir ore samples by delayed neutron counting technique

The Eskiehir-Beylikahir district has the largest and richest thorium and rare earth elements deposits in Turkey. The uranium and thorium concentrations of samples taken from four different parts of this area have been determined by the delayed neutron counting technique. The results are compared with those of previous analyses by other techniques and found to be in good agreement.     

Studies in inorganic polyelectrolytes — Part II

Viscosity behaviour of several samples ofGraham's salt with varying molecular weight has been studied. Reduced viscosity (η _sp /c) versus concentration curves were found to be characteristic of polyelectrolytes. They are dependent on the molecular weight and can be reduced to straight lines by plotting the reciprocal of the reduced viscosity against the square root of concentration. The intrinsic viscosities obtained by extrapolation were found to be proportional to the square of molecular weights. The value of reduced viscosity at any particular concentration in the concentration range between 0.25% and 4.0% was linearly related to the molecular weight. Reduced viscosities were found to decrease considerably on addition of electrolytes. Reduced viscosity versus added salt concentration curves were remarkably molecular weight dependent. The p_H of the medium seemed to have no effect at all. Bivalent salts reduce the viscosity to a much greater extent than monovalent ones. By keeping the concentration of the added salt constant and varying that ofGraham's salt, curves showing hump which disappeared at higher concentration of the added salt, were obtained. In the action of electrolytes the more important factor is the valency of cation rather than the ionic strength of the medium. Most observations confirm the already well-establishedFolding-Chain Theory of polyelectrolytes developed byKatchalsky, Fuoss and others.     

Rapid determination of90Sr by Compton suppression gamma-ray spectrometry

This work presents a low-level background gamma spectrometry system capable of achieving rapid determination of⁹⁰Sr without chemical separation, in a soil sample when the⁹⁰Sr to -ray emitting nuclide concentration ratio exceeds 10. The system consists of a highly efficient HPGe central detector operated in coincidence or anticoincidence with a NaI(Tl) guard detector and a NaI(Tl) backscatter detector. Experimental results indicate that the bremstrahlung radiation from a pure -emitter can be distinguished with respect to the differences in normal and coincidence spectra. The⁹⁰Sr activity can be directly detemined in the sample in less than 1 hour with a minimum detectable concentration (MDC) estimated at 0.002 Bq·g^–1 for a sample containing no appreciable -ray nuclides or other high energy, -emitting nuclides. In actual measurement, a 0.06 Bq·g^–1 MDC for contaminated soils is achieved.     

Computer simulation of the aggregation of ion pairs in the polymerization of styrene initiated by RCl/SnCl4/NRCl− systems

Computer simulations show that ion pair aggregation can be responsible for the unusual dependence of the initial rate of polymerization on the concentration of added salt in the cationic polymerization of styrene initiated by RCl/SnCl₄/NRCl⁻. Addition of small amounts of tetraalkylammonium chloride to the system reduces the rate of polymerization due to the decrease of the concentration of propagating free cations. Subsequent salt addition leads to a small rate increase, and then the rate decreases at higher [salt]₀/[SnCl₄]₀ ratio. The simulations show that the rate increase can be ascribed to the formation of aggregates of ion pairs and thus to a higher overall proportion of carbocations resulting in faster polymerization. The decrease of the polymerization rate at higher concentrations of added salt can be explained by the conversion of free SnCl₄ to SnCl anions which are weaker Lewis acids. The effect of various equilibrium constants on the total concentration of carbocations as a function of added salt is simulated.     

The validation of a method for determining the migration of trace elements from food packaging materials into food

A new radiotracer method has been developed to measure the migration of trace elements from food contact packaging into four standard food simulants; acetic acid, ethanol, olive oil, deionised water. A sample of material is irradiated in a thermal neutron flux of 10¹⁶n·m^–2·s^–1 to activate the trace elements and produce a range of radionuclides. The sample is then placed in the food simulant and the migration of the radionuclides is monitored by performing -ray spectrometry on a sample of the simulant. Any radionuclides measured must be due entirely to the migration of the elements present in the plastic, since the simulant itself is not radioactive. Preliminary studies have shown that detection limits of around 0.2g·dm^–2 (0.002 mg/kg) can be achieved for antimony in a sample of polyethylene terephthalate. This method can now been extended to measure migration into real foods. This will highlight any differences between the standard simulants currently used and real foods. Since the method only involves irradiation of the packaging material, any food matrix can be studied.     

High-Level Production of DNA-Specific Endonuclease AsEndI with Synonymous Codon and its Potential Utilization for Removing DNA Contamination

Endonuclease I is a widely distributed periplasmic or extracellular enzyme. A method for the high-level production of recombinant AsEndI (endonuclease I from Aliivibrio salmonicida) in Escherichia coli with secretion expression is investigated. The coding sequence of AsEndI gene was assembled according to the E. coli codon usage bias, and AsEndI was expressed in the periplasm of E. coli TOP10 with a C-terminal 6× His-tagged fusion. The recombinant AsEndI (His-AsEndI) was purified by Ni-NTA resin with a yield of 1.29?×?10⁷ U from 1-L LB medium. His-AsEndI could be classified into Ca²⁺/Mg²⁺-dependent nucleases and showed highest nuclease activity to dsDNA at pH 8.0 and 37 °C. His-AsEndI is highly active in a broad range of salt concentration range up to 1.0 M with optimal NaCl concentration at 0.4 M. His-AsEndI can effectively remove DNA contamination in RNA sample or in PCR reagents to the level that cannot be detected by highly sensitive nested PCR and without adverse effects on the subsequent PCR reaction. His-AsEndI can remove DNA contamination at high salt conditions, especially for the DNA that may be shielded by DNA-binding protein at low salt conditions.     

Salt Bridge Rearrangement (SaBRe) Explains the Dissociation Behavior of Noncovalent Complexes

Native electrospray ionization-mass spectrometry, with gas-phase activation and solution compositions that partially release subcomplexes, can elucidate topologies of macromolecular assemblies. That so much complexity can be preserved in gas-phase assemblies is remarkable, although a long-standing conundrum has been the differences between their gas- and solution-phase decompositions. Collision-induced dissociation of multimeric noncovalent complexes typically distributes products asymmetrically (i.e., by ejecting a single subunit bearing a large percentage of the excess charge). That unexpected behavior has been rationalized as one subunit “unfolding” to depart with more charge. We present an alternative explanation based on heterolytic ion-pair scission and rearrangement, a mechanism that inherently partitions charge asymmetrically. Excessive barriers to dissociation are circumvented in this manner, when local charge rearrangements access a lower-barrier surface. An implication of this ion pair consideration is that stability differences between high- and low-charge state ions usually attributed to Coulomb repulsion may, alternatively, be conveyed by attractive forces from ion pairs (salt bridges) stabilizing low-charge state ions. Should the number of ion pairs be roughly inversely related to charge, symmetric dissociations would be favored from highly charged complexes, as observed. Correlations between a gas-phase protein’s size and charge reflect the quantity of restraining ion pairs. Collisionally-facilitated salt bridge rearrangement (SaBRe) may explain unusual size “contractions” seen for some activated, low charge state complexes. That some low-charged multimers preferentially cleave covalent bonds or shed small ions to disrupting noncovalent associations is also explained by greater ion pairing in low charge state complexes.

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Graphical Abstract ?

     

High pressure nebulization: a new way of sample introduction for atomic spectroscopy

Summary The solution to be investigated is nebulized by a pressure of 50 to 400 bar. The liquid sample (5 l to 2 ml) to be analyzed is fed into a sample loop — as is common procedure in HPLC techniques. But instead of being pressed through HPLC columns, the liquid is now pressed through a special nozzle with an opening of a few micrometers. An aerosol results which is then submitted to a spectroscopical source (flame-AAS; ICP/OES). The aerosol yield is more than 50%; even a saturated solution of cooking salt can be nebulized. The sensitivity of flame-AAS increases by about one order of magnitude (signal area). In addition, an effective on-line coupling of HPLC and atomic spectrometric determination methods is possible.

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Hochdruck-ZerstÄubung: eine neue Art der Probeeinführung für die Atomspektroskopie

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Dedicated to Prof. Dr. W. Fresenius on the occasion of his 75th birthday     

Overcoming Selectivity and Sensitivity Issues of Direct Inject Electrospray Mass Spectrometry via DAPNe-NSI-MS

Direct inject electrospray mass spectrometry offers minimal sample preparation and a “shotgun” approach to analyzing samples. However, complex matrix effects often make direct inject an undesirable sample introduction technique, particularly for trace level analytes. Highlighted here is our solution to the pitfalls of direct inject mass spectrometry and other ambient ionization methods with a focus on trace explosives. Direct analyte-probed nanoextraction coupled to nanospray ionization mass spectrometry solves selectivity issues and reduces matrix effects while maintaining minimal sample preparation requirements. With appropriate solvent conditions, most explosive residues can be analyzed with this technique regardless of the nature of the substance (i.e., nitroaromatic, oxidizing salt, or peroxide).

Highly Sensitive Determination of microRNA Using Target‐Primed and Branched Rolling‐Circle Amplification

One‐nucleotide differences in microRNAs (miRNAs) can be discriminated in an assay based on a branched rolling‐circle amplification (BRCA) reaction and fluorescence quantification. With the proposed method miRNA can be detected at concentrations as low as 10 fM , and the miRNA in a total RNA sample of a few nanograms can be determined.

     

Free energy perturbation simulations of cation binding to valinomycin

Experimental values of the free energies of cation binding to the cyclic depsipeptide molecule, valinomycin, obtained from Pedersen-type salt extraction measurements, provide data against which it is possible to test the adequacy of the procedures and force fields of the molecular dynamics algorithms, MOLARIS and GROMOS. These data are then used to assess appropriate values for the partial charges of the ester carbonyl oxygen and carbon. Valinomycin was chosen because it has only one kind of ion-binding ligand and because the cation is sufficiently enfolded by the molecule in the ion-complexes that the overall size and shape of the complex is virtually the same regardless of the species of cation bound. For such an isosteric complex, the experimentally measured selectivities are sufficiently similar in a wide variety of solvent environments that thedifferences in free energies measured between the different ion-valinomycin complexes by two-phase salt extraction experiments into dichloromethane can be taken as equivalent to the differences in free energies in vacuo. Thesedifferences were therefore compared with those computed for ion-valinomycin complexationin vacuo by Free Energy Perturbation/Molecular Dynamics (FEP/MD) simulations using the MOLARIS and GROMOS programs. Starting with a set of Lennard-Jones 6–12 parameters for the monovalent cations assessed for aqueous solution we explored the effect of varying the partial charges of the ester carbonyl ligands on binding free energy differences (i.e. the selectivity) among Na, K, Rb, and Cs. The computed selectivity was found to depend strongly on the value of partial charge, following a typical Eisenman Selectivity Pattern in which the correct selectivity sequence and magnitude occurred only over a very narrow range of partial charge (around 0.33 and 0.6 for the standard carbonyls of MOLARIS and GROMOS, respectively). Using MOLARIS we explored the effect of varying the size of the ester carbonyl ligands by comparing the standard carbonyl of MOLARIS with the somewhat smaller carbonyls of GROMOS and found an equally satisfactory ability to reproduce the experimental data with a partial charge value of 0.41. These results validate the use of both the MOLARIS and GROMOS force fields as starting points for quantitative calculations of ion-binding in more complex molecules (e.g., ion-binding sites and channels in proteins).This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Critical comparison of ICP-OES, XRF and fluorine volatilization-FTIR spectrometry for the reliable determination of the silicon main constituent in ceramic materials

For the optimization of preparation processes for ceramic powders and compacts by pyrolysis of inorganic polymers, the intermediate and final products have to be monitored by in-situ analysis (in its original place) for main, subsidiary and trace components. In the determination of silicon in Si-N-C- based ceramic samples by ICP-OES after pressurized decomposition at temperatures between 220°–250°C too low concentrations of Si were found. Completely independent analytical procedures were applied to trace systematic errors, i.e. XRF after decomposition of the sample in a metaborate/boric acid melt and FTIR-spectrometry after reaction of the sample with fluorine. The low recoveries of Si were found to be due to losses, which amount up to 25% depending on the temperature and time applied for the pressurized decomposition. With the latter two procedures Si can be determined in the %-range with a relative standard deviation of 0.4% and 0.2%, respectively.     

Preparation and characterization of the double potassium salt of sulfosalicyclic acid as a standard substance in alkalimetry

Summary The utility of the double potassium acid salt of sulfosalicylic acid as an alkalimetric standard substance has been studied. To this end an appropriate preparative procedure has been elaborated. This procedure includes partial neutralization of sulfosalicylic acid with potassium carbonate in a hot water-ethanol solution followed by four crystallizations of a crude product from a water-ethanol mixture, 11 by volume. The preparations of the salt prepared according to this procedure are well reproducible and homogeneous. The average content of the pure compound in 6 preparations assayed, based on 36 independent precise titrations was found to be equal to 100.008%±0.030%. The salt proved to be stable up to 280°C, and well soluble in water.These results allow to recommend the double potassium acid salt of sulfosalicylic acid as a primary standard in alkalimetry.Presented at Euroanalysis V, Kraków, August, 26–31, 1984.     

Micro and two-dimensional NIR FT raman spectroscopy

The former major problem in conventional Raman spectroscopy in the visible range, the disturbing fluorescence of impurities, has now been eliminated: Raman spectra can be excited by light quanta in the near-infrared range, the energy of which is too low to excite fluorescence spectra. An inherent disadvantage of this technique, the v ⁴-dependence of the intensity of the Raman radiation, is compensated for by using interferometers, which are more powerful, by a factor of several hundred, than grating spectrometers. Raman spectroscopy can now be applied to analyses of real world samples bio materials, food, paintings, micro electronics and new materials, as well as to quality control of raw materials, to production and product control without special sample preparation. By using fiber bundles, Raman spectra can be recorded on line at the sample site, in containers and in real time. For successful recording of NIR FT Raman spectra of small samples a compromise between large lateral resolution and a large signal/noise ratio has to be found. Its theoretical base and practical approach is discussed. Confocal microscopes allow recording of NIR FT Raman spectra of small particles or inclusions. They can be coupled to the spectrometer by fiber optics, so that they may be placed at some distance from the spectrometer. By using computer-driven x-y stages, systematic mapping of the distribution of specific compounds on the surface of different samples is possible with the FT Raman microscope, as well as with the ordinary sample arrangement.