Further study on a flow injection on-line multiplexed sorption preconcentration coupled with flame atomic absorption spectrometry for trace element determination

A further study on a newly developed flow injection (FI) on-line multiplexed sorption preconcentration (MSP) using a knotted reactor coupled with flame atomic absorption spectrometry (FAAS) was carried out to demonstrate its applicability and limitation for trace element determination. For this purpose, Cr(VI), Cu(II), Ni(II) and Co(II) were selected as the analytes, and detailed comparison was made between the MSP-FAAS and conventional FI on-line sorption preconcentration FAAS in respect to retention efficiency and linear ranges of absorbance versus sample loading flow rate and total preconcentration time. Introduction of an air-flow for removal of the residual solution in the KR after each sub-injection in the MSP procedure played a decisive role in the improvement of retention efficiency. The linearity of absorbance versus sample loading flow rate or total preconcentration time was extended to a more degree for the metal ions with less stability of their PDC (pyrrolidine dithiocarbamate) complexes than those with more stable PDC complexes. It seems that the MSP procedure behaves advantages beyond the inflection points in the diagrams of absorbance versus total preconcentration time and sample loading flow rate obtained by conventional (a single continuous) preconcentration procedure. With a sample loading flow rate of 6.0 ml min⁻¹ and a total preconcentration time of 180 s, the retention efficiencies were increased from 25, 46, 41 and 63% with a single continuous sorption preconcentration to 44, 78, 65 and 75% with a six sub-injection preconcentration procedure for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The detection limits were 0.40, 0.33, 0.31 and 0.26 μg l⁻¹ for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The precision (R.S.D.) for eleven replicate determination of 2 μg l⁻¹ Cr(VI), Co(II) and Ni(II), and 1 μg l⁻¹ Cu(II), was 2.1, 4.1, 2.6 and 1.7%, respectively.     

Sorption Characteristics of Polymer Concrete during Long-Term Exposure to Water

The moisture sorption characteristics of polymer concrete and its components (polyester resin, unfilled and filled with diabase flour) on long-term (up to 15-year) exposure to water at different temperatures are studied. It is established that, during the long-term sorption and subsequent desorption at 20°C, the ratio of diffusion coefficients of the polymer concrete and the corresponding resin is equal to the value of time-moisture reduction function, which characterizes changes in the creep compliance of the materials. The evaluation of the diffusion coefficient of the composite from the properties of its components, by using various known heat-and-mass-transfer models, shows that most acceptable is the Kerner model. With account of volume content of pores, an estimate for the limiting moisture content in the composite is proposed. An analysis of sorption curves of the composite and the corresponding resin reveals that Fick's law does not describe the experimental results in the range of large times and/or elevated temperatures. In the case of polyester resin filled with diabase flour, the composite effect is expressed in a linear increase in the specimen mass (the rate of the increase is temperature-dependent. In the case of polymer concrete, the composite effect is expressed in mass losses, which can be described by Fick's law with a diffusion coefficient and a limiting moisture content both depending on temperature.     

Condensation and isothermal water transfer in cement mortar Part I — Pore size distribution,equilibrium water condensation and imbibition

The pore size distribution of cement mortar is studied in relation to water sorption experiments with the help of mercury intrusion and nitrogen sorption. The importance of adsorbed water is pointed out. Isothermal imbibition experiments at four temperatures are presented. The temperature-dependence of the mass transfer coefficients is compared to the one predicted by the classical model. Significant discrepancies are noticed. On the basis of the knowledge of the pore structure, a modelisation of the transfer process at moderate water content is proposed. It particularly takes into account Knudsen's vapor diffusion and effects of the presence of a discontinuous capillary phase interacting with vapor diffusion.     

The absorption of organic liquids in poly(aryl-ether-ether-ketone) [PEEK]

The absorption and subsequent desorption of benzene, toluene, carbon disulfide, and chloroform in amorphous and 27% crystalline poly (aryl-ether-ether-ketone) (PEEK) were determined. At 35°C, the equilibrium weight gain (solubility) of benzene, toluene, chloroform, and CS₂ are 23.5, 19.8, 51.2, and 21.2 wt%, respectively. The initial weight gain is linear with root-time and pseudodiffusion constants for absorption into amorphous PEEK ranging from 0.35 to 9.85 x 10^-12m²/s were calculated. The desorption processes are two-step and are controlled by the T_g of the penetrant-resin mixture. The rate of diffussion into the crystalline material is extremely slow; crystalline PEEK reaches saturation (12.5 wt%) after immersion in CS₂ (35°C) for several hundred hours but, even after 1300 h immersion, the other fluids do not reach saturation.     

The binding energy of an adsorbed atom

Summary We discuss the effect of substrate vibrations on the binding of an adsorbed atom. At zero temperature, we compute the binding energyD ₀-E, whereD ₀ is the surface well depth (classical binding energy) andE is the quantum correction. For several simple models, we find thatE is surprisingly model independent. We compareD ₀-E with the binding energies to a rigid substrate,D ₀-E _rs, and to a vibrationally averaged substrate,D ₀-E _va. We prove thatE _va≥E≥E _rs and that similar relations hold at finite temperature for the free energy of binding. We find that in most casesE _rs is better thanE _va as an approximation toE. In honour of Prof. Fausto Fumi on the occasion of his retirement from teaching.     

Sorption,diffusion, and partial molar volumes of C4 hydrocarbons in rubbery polymers

Sorption and dilation isotherms and diffusion coefficients for seven hydrocarbons (n-butane, isobutane, 1-butene, cis-2-butene, trans-2-butene, isobutylene, and 1,3-butadiene) in two rubbery polymers, 1,2-polybutadiene (PB) and poly(ethylene-co-vinyl acetate) (EVAc), were measured at 25°C. Dissolution parameters (Henry's law coefficient and Flory-Huggins interaction parameter), partial molar volumes, and diffusion coefficients were determined. PB exhibited greater affinity and lower diffusivity than EVAc to the C₄ gases, although the gases showed nearly the same partial molar volumes in the two polymers. The diffusivity of such elongated molecules as trans-2-butene in both polymers was higher than that of bulky molecules with similar partial molar volume, such as cis-2-butene and isobutylene. Pressure-dependent permeabilities of PB and EVAc films to the hydrocarbons were predicted and discussed based on the dissolution parameters and the diffusivities. © 1995 John Wiley & Sons, Inc.     

Gravimetric characterisation of the surface properties of a porous drug carrier

The gas adsorption method is the most common means to characterise the topology of solid surfaces with regard to its use as an adsorbent. Adsorption isotherms are determined advanta-geously using a vacuum microbalance: Thermogravimetric techniques allow the observation of sample degassing and its optimization. The dry mass is determined in situ, the mass of gas adsorbed is measured directly and different gases can be used without calibration. From the isotherm the pore size distributions, specific surface area, fractal dimension and density can be derived. Commercially available gravimetric sorption apparata and vacuum balances as well as software for data evaluation are reviewed in tables. The sorption analysis of an aluminum oxide is presented. The porous material was used as a matrix for a slow drug release.     

Dithiocarbamate functionalized or surface sorbed Merrifield resin beads as column materials for on line flow injection-flame atomic absorption spectrometry determination of lead

This article describes the preparation of dithiocarbamate immobilized/functionalized and diethylammonium dithiocarbamate (DDTC) sorbed Merrifield Chloromethylated Resin (MCR) beads and comparison of these materials for on-line flow injection (FI)–flame atomic absorption spectrometry (FAAS) determination of lead. The above two materials enrich lead quantitatively over an identical optimal pH range (8.0–9.0), a preconcentration/loading time (up to 4 min) and elution with acidified methanol (a minimum of 0.01 mol L⁻¹ HNO₃ in methanol). However, the detection limit for lead using dithiocarbamate functionalized MCR beads is 1.3 μg L⁻¹ compared to 3 μg L⁻¹ for DDTC sorbed MCR beads. Again, the sensitivity enhancement over direct FAAS signal is 48- and 27-fold, respectively. In addition, dithiocarbamate functionalized MCR beads offers better precision compared to DDTC sorbed MCR beads as the corresponding relative standard deviation (R.S.D.) values for five successive determinations of 0.20 μg mL⁻¹ are 1.44 and 4.36%, respectively. The accuracy of the developed on-line FI–FAAS procedure employing dithiocarbamate functionalized MCR beads as column material was tested by analyzing Certified Reference Material (CRM) of soil (IAEA soil-7) and marine sediment reference material (MESS-3) supplied by International Atomic Energy Agency (IAEA), Vienna and National Research Council (NRC), Canada, respectively. Furthermore, the developed procedure has been successfully tested for the analysis of surface, pond, ground and effluent water and soil samples collected from the vicinity of lead acid battery industry in India.     

Biosorption kinetics, thermodynamics and isosteric heat of sorption of Cu(II) onto Tamarindus indica seed powder

Biosorption of Cu(II) by Tamarindus indica seed powder (TSP) was investigated as a function of temperature in a batch system. The Cu(II) biosorption potential of TSP increased with increasing temperature. The rate of the biosorption process followed pseudo second-order kinetics while the sorption equilibrium data well fitted to the Langmuir and Freundlich isotherm models. The maximum monolayer Cu(II) biosorption capacity increased from 82.97 mg g(-1) at 303 K to 133.24 mg g(-1) at 333 K. Thermodynamic study showed spontaneous and endothermic nature of the sorption process. Isosteric heat of sorption, determined using the Clausius-Clapeyron equation increased with increase in surface loading showing its strong dependence on surface coverage. The biosorbent was characterized by scanning electron microscopy (SEM), surface area and porosity analyzer, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy. The results of FTIR analysis of unloaded and Cu(II)-loaded TSP revealed that -NH(2), -OH, -C=O and C-O functional groups on the biosorbent surface were involved in the biosorption process. The present study suggests that TSP can be used as a potential, alternative, low-cost biosorbent for removal of Cu(II) ions from aqueous media.     

Water transport in aluminium oxide-poly(ethylene-co-butyl acrylate) nanocomposites

Polymer composites with metal oxide nanoparticles are emerging materials for use as insulation in electrical applications. However, the extensive interfacial surfaces and the presence of polar groups on the particle surfaces make these composites susceptible to water sorption. Water sorption kinetics were studied at 23 °C and different relative humidities (18–90%) for composites based on poly(ethylene-co-butyl acrylate) and aluminium oxide (?12 wt.%); the latter being in three different forms: uncoated and coated with either octyltriethoxysilane or aminopropyltriethoxysilane. The equilibrium water uptake increased linearly with increasing overall concentration of polar groups on the nanoparticle surfaces. Composites with well-dispersed nanoparticles showed Fickian diffusion (constant diffusivity and invariant boundary conditions) with a diffusivity that decreased with increasing filler content; the maximum factorial decrease in diffusivity was 300 with reference to that of the pristine polymer. This effect was most pronounced for composites with accessible polar groups on the particle surfaces, suggesting that water saturation of the composites is retarded by dual water sorption. Composites that contained a sizeable fraction of large nanoparticle agglomerates showed a two-stage sorption process: a rapid process associated with the saturation of the matrix phase and a slow diffusion process due to water sorption by the large nanoparticle agglomerates.