Characterization of triacontyl (C-30) liquid chromatographic columns.

Differences in the characteristics of seventeen commercial C-30 liquid chromatographic columns were studied for the separation of carotenoid isomers. A mixture consisting of nine xanthophyll and hydrocarbon carotenoids were separated under conditions carefully chosen to reveal changes in selectivity. The influence of the mobile phase composition, column temperature, and mobile phase flow rate were evaluated. Shape selectivity was characterized with Standard Reference Material (SRM) 869b Column Selectivity Test Mixture, for correlation with carotenoid retention behavior. Regular changes were observed across a broad spectrum of shape selectivity characteristics as indicated by SRM 869b. Better separations of carotenoid isomers were achieved with C-30 columns than were possible with C-18 columns, even after optimization of separation conditions.

Characterization of cross-linked cellulosic ion-exchange adsorbents: 2. Protein sorption and transport.

Adsorption behavior in the HyperCel family of cellulosic ion-exchange materials (Pall Corporation) was characterized using methods to assess, quantitatively and qualitatively, the dynamics of protein uptake as well as static adsorption as a function of ionic strength and protein concentration using several model proteins. The three exchangers studied all presented relatively high adsorptive capacities under low ionic strength conditions, comparable to commercially available resins containing polymer functionalization aimed at increasing that particular characteristic. The strong cation- and anion-exchange moieties showed higher sensitivity to increasing salt concentrations, but protein affinity on the salt-tolerant STAR AX HyperCel exchanger remained strong at ionic strengths normally used in downstream processing to elute material fully during ion-exchange chromatography. Very high uptake rates were observed in both batch kinetics experiments and time-series confocal laser scanning microscopy, suggesting low intraparticle transport resistances relative to external film resistance, even at higher bulk protein concentrations where the opposite is typically observed. Electron microscopy imaging of protein adsorbed phases provided additional insight into particle structure that could not be resolved in previous work on the bare resins.

Evaluation of different adsorbents for large-volume pre-concentration for analyzing atmospheric persistent organic pollutants at trace levels.

This paper investigates the performance of some adsorbents, Carbopack B, Tenax-GC, and XAD-2, in a SPE and GC analytical method for sampling and determining some persistent organic pollutants such as benzene, toluene, o-, m-, and p-xylenes, naphthalene, anthracene, fluorene, fluoranthene, benzo(i,k)fluorene, pyrene and benzo(a)pyrene, aldrin, dieldrin, endrin, endosulfan, and PCB congeners (nos. 1, 15, 44, 77, and 209). Adsorbents evaluated in this study are Carbopack B, Tenax-GC, and XAD-2. Before applying the analytical method to air samples, it was widely investigated in laboratory: the sampler is constituted by a glass pyrex vial home-filled with 300 mg (sampling section) and 50 mg of adsorbent material (backup section). The re-extraction is performed by CS(2) (1-2 mL) and analysis is performed by GC-FID and GC-ECD. The evaluation of breakthrough volumes and desorption efficiencies shows the XAD-2 performance in the enrichment of different organic species present in atmosphere at trace levels (ppt) to be more advantageous than the other two materials in terms of analytical and technical parameters. One of the advantages is the high volume of sampled air with high concentration factor and limited loss of analytes (breakthrough volumes are higher than 5,000 L g(-1) for high-boiling compounds and higher than 400 L g(-1) for low-boiling solutes). Another advantage is the possibility of easy and speed re-extraction of analytes using small volumes of solvent (a few milliliters). The recoveries are about 100% with a RSD ≤ 2.3 for low-boiling compounds, and between 77% and 109% with a RSD ≤ 5.7% for high-boiling species. The XAD-2 adsorbent was applied to real air samples collected in different polluted areas (urban, industrial, rural, and remote locations) demonstrating the wide application of such methodology in various environmental situation.

Evaluation of chelating ion-exchange resins for separating Cr(III) from industrial effluents.

In this study two chelating resins containing iminodiacetic acid groups (Amberlite IRC 748 and Diaion CR 11) and a chelating resin based on sulfonic and diphosphonic acid groups (Diphonix) were investigated in order to separate Cr(III) from industrial effluents produced in hard and decorative electroplating. Samples of two industrial plants were characterized during a period of about one year and a half in terms of the metals content (Cr, Cu, Na, Ca, Fe and Ni), Total Suspended Solids (TSS), Total Dissolved Solids (TDS), Chemical Oxygen Demand (COD) and pH. Some of the physical properties of the resins, namely the moisture content, apparent density, intraparticle porosity and the particle size distribution were also evaluated. To quantify the sorption capacity of the resins, batch experiments were performed using synthetic solutions of Cr(III), as well as solutions of Fe in the case of Diphonix. The Langmuir and Langmuir-Freundlich isotherms enabled a good description of the ion-exchange equilibrium data, and the maximum sorption capacity determined for Amberlite and Diaion was 3.6 mequiv./g(dry resin). For Diphonix that parameter was 3.4 mequiv./g(dry resin). The Diphonix resin exhibits a high selectivity for transition metals (Fe, Ni) over the chromium trivalent. Therefore, it was screened as the most suitable for selectively removing those metal impurities from chromium electroplating effluents. For this resin, the sorption capacity is strongly dependent on the initial pH of the solution. Though, high regeneration efficiencies of Diphonix for stripping Cr(III) were found by using a mixture of NaOH/H(2)O(2). The mathematical model tested for describing the dynamics of the process allowed a good fitting to the experimental data and enabled the estimation of effective pore diffusivity of Cr(III). The saturations of Diphonix with industrial effluents demonstrated that the breakthrough capacity of the resin is affected by the presence of other species in solution, such as Fe and Ni. Nevertheless, these effluents may be treated with this resin, being possible to separate Cr(III) from other transition metallic ions in solution.

Kinetics and equilibrium studies for the removal of nickel and zinc from aqueous solutions by ion exchange resins.

Removal of heavy metals from wastewater is obligatory in order to avoid water pollution. In the present study, performance of Dowex HCR S/S cation exchange resin was evaluated for removal of nickel and zinc from aqueous solutions. Batch shaking adsorption experiments were performed in order to examine the effects of pH, dosage of resin and contact time on removal process. It was observed that more than 98% removal efficiency was achieved under optimal conditions for nickel and zinc. The experimental equilibrium data were tested for the Langmuir, Freundlich and Temkin isotherms. Correlation coefficients indicate the following order to fit isotherms: Langmuir>Freundlich>Temkin for both nickel and zinc ions. Pseudo-first- and -second-order kinetic models were used for describing kinetic data. It was determined that removal of Ni(2+) and Zn(2+) was well-fitted by second-order reaction kinetic. Furthermore, separation factors and distribution coefficients of nickel and zinc for Dowex HCR S/S were calculated.

Studies on the adsorption behavior of trace amounts of 90Sr2+, 140La3+, 60Co2+, Ni2+ and Zr4+ cations on synthesized inorganic ion exchangers.

Three inorganic ion exchangers namely potassium zinc hexacyanoferrate(II) (PZF), magnesium oxide-polyacrylonitrile composite (MgO-PAN) and ammonium molybdophosphate (AMP) were synthesized. The physicochemical properties of these ion exchangers were determined using different techniques including inductively coupled plasma (ICP), CHNSO elemental analysis, infrared spectroscopy (IR), X-ray diffraction (XRD), thermogravimetric (TGA) and pH - titration curve analysis. The solubility of the synthesized ion exchangers in different acidic and alkaline media, their thermal stability and the effect of gamma irradiation were investigated. It was observed that the exchange capacity of the ion exchangers depend upon the pH value of the solution used. Furthermore, the adsorption of (90)Sr(2+), (140)La(3+), (60)Co(2+) and the distribution coefficient of these ion exchangers for Ni(2+)and Zr(4+) were studied. The effect of parameters such as pH and contact time on the adsorption was also investigated and the optimum conditions for separation of these ions were determined.

A flow-through solid-phase spectroscopic sensing device implemented with FIA solution measurements in the same flow cell: determination of binary mixtures of thiamine with ascorbic acid or acetylsalicylic acid.

A continuous and simple UV-photometric flow-through optosensor has been developed for the simultaneous determination of a binary mixture of two species with different electric charges present at very different concentrations - ascorbic acid (or acetylsalicylic acid) and thiamine. The sensing device is based on the selective sorption and determination of a cationic analyte on a cation-exchange gel (Sephadex SP-C25) while the other, anionic, analyte is determined in the solution among the interstices of the cation-exchange gel in the same flow cell. The analytes arrive in sequence at the sensing zone, which detects their intrinsic absorbance at 253 nm, as a result of on-line separation by use of a minicolumn filled with the same cation-exchange gel as in the cell, and placed before the flow cell. Thiamine is retained in the minicolumn whereas ascorbic acid or acetylsalicylic acid pass through it and produce their signal as a result of absorbance in the interstitial solution among the resin beads. Thiamine is then eluted from the precolumn, transported to the flow cell, and temporarily retained in the sensing zone from this eluted solution. Calibration graphs were linear over the range 3-50, 25-400, and 300-3000 microg mL(-1) (600 microL sample volume) and the relative standard deviations were 2.56, 1.85, and 1.25 % for thiamine, ascorbic acid, and acetylsalicylic acid, respectively. The proposed method was satisfactorily applied to the determination of binary mixtures of thiamine with ascorbic acid or acetylsalicylic acid in pharmaceutical preparations and semi-synthetic samples.