Gravitational field-flow fractionation in combination with flow injection analysis or electrothermal AAS for size based iron speciation of particles

A simple gravitational field-flow fractionation (GrFFF) system was used for size separation of micron sized silica particles coated with hydrous iron oxide (geothite). The amount of iron on the particles was monitored either on-line by reverse-flow injection analysis (r-FIA) with chemiluminescence detection using luminol or off-line by electrothermal atomic absorption spectrophotometry (ETAAS). The combination of GrFFF with reverse FIA or with ETAAS has been demonstrated to be a cost-effective tool for size based iron speciation of particles.     

Size fractionation of marine sediments by pinched inlet gravitational split-flow thin fractionation and the study of size dependent PCDD/Fs concentrations from different bay areas

Pinched inlet gravitational split-flow thin fractionation (PI-GSF) has been applied to the continuous size fractionation of marine sediments in order to study the difference in sediment size distribution and the concentration of PCDD/Fs contained in different particle sizes. A PI-GSF channel, known to improve the separation efficiency by reducing the sample inlet thickness, was utilized to fractionate sediments collected from three different bay areas (Geoje, Ulsan, and Pohang) in Korea into 5 different sub-populations (<2.0, 2.0-5.0, 5.0-10, 10-20, 20-63 microm in diameter). The sorted sediment fractions from PI-GSF were examined using electron microscopy to obtain size distribution and the results showed a variation in particle size distribution between bay areas. When the collected particle fractions were examined for size dependent levels of PCDD/Fs, the concentrations of total PCDD/Fs were shown to be much greater for samples collected close to heavy industry complexes than sediments from bay areas without major industry.     

A simple method for assessment and minimization of errors in determination of electrophoretic or electroosmotic mobilities and velocities associated with the axial electric field distortion

It is commonly accepted that the modern CE instruments equipped with efficient cooling system enable accurate determination of electrophoretic or electroosmotic mobilities. It is also often assumed that velocity of migration in a given buffer is constant throughout the capillary length. It is simultaneously neglected that the noncooled parts of capillary produce extensive Joule heating leading to an axial electric field distortion, which contributes to a difference between the effective and nominal electric field potentials and between velocities in the cooled and noncooled parts of capillary. This simplification introduces systematic errors, which so far were however not investigated experimentally. There was also no method proposed for their elimination. We show a simple and fast method allowing for estimation and elimination of these errors that is based on combination of a long‐end and short‐end injections. We use it to study the effects caused by variation of temperature, electric field, capillary length, and pH.     

Study of the abnormal late co-elution phenomenon of low density polyethylene in size exclusion chromatography using high temperature size exclusion chromatography and high temperature asymmetrical flow field-flow fractionation

The elution behaviour of linear and branched polyethylene samples in SEC was studied. For the branched samples an abnormal late co-elution of large and small macromolecules manifests itself as an abnormal re-increase of the molar mass and the radius of gyration values detected with multi angle light scattering at high elution volumes in SEC. The late co-elution of small and large macromolecules cannot be explained by the SEC mechanism alone. The influence of several experimental parameters on the late co-elution was studied. It was found that the type of SEC column and the flow rate have a significant influence. The late eluting part of the sample was fractionated and separated by HT-SEC- and HT-AF4-MALS. The different results of both methods have been discussed with the aim to find possible explanations for the late elution. The experiments indicate that especially large branched structures show an increased tendency for the phenomenon.     

Asymmetric flow field flow fractionation of aqueous C60 nanoparticles with size determination by dynamic light scattering and quantification by liquid chromatography atmospheric pressure photo-ionization mass spectrometry

A size separation method was developed for aqueous C₆₀ fullerene aggregates (aqu/C₆₀) using asymmetric flow field flow fractionation (AF4) coupled to a dynamic light scattering detector in flow through mode. Surfactants, which are commonly used in AF4, were avoided as they may alter suspension characteristics. Aqu/C₆₀ aggregates generated by sonication in deionized water ranged in size from 80 to 260 nm in hydrodynamic diameter (D_h) as determined by DLS in flow through mode, which was corroborated by analysis of fractions by DLS in batch mode and by TEM. The mass of C₆₀ in each fraction was determined by LC–APPI–MS. Only 5.2 ± 6.7% of the total aqu/C₆₀ mass had D_h less than 80 nm, while 58 ± 32% of the total aqu/C₆₀ mass had D_h between 80 and 150 nm and 14 ± 9.2% of the total aqu/C₆₀ were between 150 and 260 nm in D_h. With the optimal fractionation parameters, 77 ± 5.8% of the aqu/C₆₀ mass eluted from the AF4 channel, indicating deposition on the AF4 membrane had occurred during fractionation; use of alternative membranes did not reduce deposition. Channel flow splitting increased detector response although channel split ratios greater than 80% of the channel flow led to decreased detector response. This is the first report on the use of AF4 for fractionating a colloidal suspension of aqu/C₆₀.     

Study of the interaction between polyphenol,quercetin and three micelles with different electric charges in acidic and aqueous media

The interactions between the polyphenol quercetin, Q, with three surfactant aggregates with different electric charges named micelles, were studied in aqueous solutions with pH values 4.7 and 7.0, to determine the following parameters: critical micellar concentration (CMC), micelle size and binding constant of the complex (Q-Micelle) proposing interaction sites for the formation of the complex. The surfactants used were: hexadecyltrimethyl ammonium bromide (cationic surfactant), CTAB, sodium dodecyl sulfate (anionic surfactant), SDS, and triton X-100 (non-ionic surfactant), TX100, used as Q fluorescence promoters to determine the CMC. The CMC values of the above surfactants at pH 4.7 were: 0.80 ± 0.10, 1.39 ± 0.07 and 0.59 ± 0.05 mM respectively, being lower than those reported in the water. With dynamic light scattering measurements, the hydrodynamic diameters of each micelle were calculated resulting in values of: 2.4 ± 0.5, 5.0 ± 1.1 and 8.4 ± 4.3 nm at pH 4.7 and: 2.1 ± 0.4, 4.9 ± 1.1 and 11.5 ± 4.1 nm at pH 7.0 respectively. In addition, the binding constants of the complex (Q-Micelle) with 1:1 stoichiometry were calculated from emission fluorescence data giving Log K values: 2.94 ± 0.02, 2.54 ± 0.02, and 3.63 ± 0.05 M^-1 respectively. Finally, from the experimental data by UV–Vis spectrophotometry, the change in the behavior of the Q spectrum upon the addition of each of the surfactants to the system was analyzed, showing a decrease in absorbance when SDS and TX100 were added in an acidic medium, as a consequence of the photo-instability of the drug, suggesting that Q interacts with the outside of these micelles and is not fully incorporated inside them.     

Synthesis of asymmetric star-branched polymers consisting of three or four different segments in composition by means of living anionic polymerization with a new dual-functionalized 1,1-bis(3-chloromethylphenyl)ethylene

A series of four-armed A₂BC, AB₂C, and ABC₂ asymmetric star-branched polymers with a three-component system, the A, B, and C segments of which are polystyrene, polyisoprene, and poly(4-trimethylsilylstyrene), respectively, have been successfully synthesized with a methodology based on living anionic polymerization with dual-functionalized 1,1-bis(3-chloromethylphenyl)ethylene ( 1 ). These star-branched polymers have well-defined architectures and precisely controlled chain lengths, as confirmed by size exclusion chromatography, ¹H and ¹³C NMR, vapor pressure osmometry, and static light scattering analyses. A simple and convenient one-pot process for star-branched polymer synthesis is an additional advantage of this methodology. One problem to be solved is that the synthetic route is limited in some cases by the inherently low reactivity of polyisoprenyllithium toward the 1,1-diphenylethylene functionality of in-chain-functionalized polymers. A new four-armed ABCD star-branched polymer, the A, B, C, and D segments of which are polyisoprene, poly(4-methoxystyrene), polystyrene, and poly(4-trimethylsilylstyrene), could also be synthesized through the extension of the methodology using 1 to a four-component system. The successful results strongly demonstrate the synthetic versatility and potential of this methodology for a wide variety of well-defined asymmetric star-branched polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4535–4547, 2004     

H/D isotope effect on charge‐inverted hydrogen‐bonded systems: Systematic classification of three different types in H3XH…YH3 (X = C,Si, or Ge,and Y = B,Al, or Ga) with multicomponent calculation

Three different H/D isotope effect in nine H₃XH(D)^…YH₃ (X = C, Si, or Ge, and Y = B, Al, or Ga) hydrogen‐bonded (HB) systems are classified using MP2 level of multicomponent molecular orbital method, which can take account of the nuclear quantum nature of proton and deuteron. First, in the case of H₃CH(D)^…YH₃ (Y = B, Al, or Ge) HB systems, the deuterium (D) substitution induces the usual H/D geometrical isotope effect such as the contraction of covalent R(C? H(D)) bonds and the elongation of intermolecular R(H(D)^…Y) and R(C^…Y) distances. Second, in the case of H₃XH(D)^…YH₃ (X = Si or Ge, and Y = Al or Ge) HB systems, where H atom is negatively charged called as charge‐inverted hydrogen‐bonded (CIHB) systems, the D substitution leads to the contraction of intermolecular R(H(D)^…Y) and R(X^…Y) distances. Finally, in the case of H₃XH(D)^…BH₃ (X = Si or Ge) HB systems, these intermolecular R(H(D)^…Y) and R(X^…Y) distances also contract with the D substitution, in which the origin of the contraction is not the same as that in CIHB systems. The H/D isotope effect on interaction energies and spatial distribution of nuclear wavefunctions are also analyzed. © 2015 Wiley Periodicals, Inc.