Desorption Agent Research Articles

Cr(III) removal and recovery from Saccharomyces cerevisiae

Heavy metal recovery from biosorbents is of major importance in the assessment of competitiveness of biosorption processes. Several desorption agents (H 2SO 4, HNO 3, HCl, CH 3COOH and EDTA) were tested for the selection of the optimal elution conditions for Cr(III) recovery from Saccharomyces cerevisiae cells. Sorption time was optimised as it plays an important role in the sorption–desorption process, being shown that a 30 min sorption period is the best option to ensure metal removal from solution and good recovery from biosorbent. The optimal contact time with desorption agents was also studied, as long exposures to these ones may cause cell damage, affecting biosorbent metal uptake capacity in subsequent sorption cycles. Each eluant was analysed in terms of its desorption capacity and its effect on the biomass metal uptake capacity in multiple sorption–desorption cycles. Considering the effectiveness of chromium desorption from loaded biomass, it was possible to conclude that H 2SO 4 (pH ≈ 1) was the most effective eluant tested, accomplishing the highest Cr(III) recovery from S. cerevisiae in three consecutive sorption/desorption cycles. Regarding the damage caused by acid treatment on S. cerevisiae cells, assessed by the reduction on metal uptake capacity after elution, it was possible to observe that sulphuric acid was the most harmful eluant causing long term negative effects in metal uptake. By the time the experiments were interrupted (nearly 26 h of continuous cycles) biomass uptake capacity was reduced to about 77% of the value reached before acid treatment.

Sorption of gold and silver on carbon adsorbents from thiocyanate solutions

Sorption recovery of thiocyanate gold and silver complexes on different carbon adsorbents has been studied using model solutions with concentrations 0.08–0.82 mmol/l and 0.16–1.06 mmol/l for gold and silver, respectively. The potassium thiocyanate concentration in these solutions was 0.25 mol/l and the pH of the contacting solution was ∼2. The degree of recovery exceeded 90% for gold and 80% for silver. The separate step-by-step desorption of thiocyanate gold and silver complexes was carried out by varying the initial concentration of thiocarbamide (desorption agent). The degree of recovery of noble metals can be increased up to 95% using basic thiocarbamide solutions (in 0.1–0.2 M NaOH) at the higher temperature of the process (up to 150 °C).

Differences in retention of dioxin‐like compounds and organochlorinated insecticides on an immunochromatographic column. Interpretation and applicability

The retention of organochlorinated compounds on an immunochromatographic column is studied. The compounds considered are usually found together in real samples of environmental concern, and include chlorinated biphenyls, chlorinated dibenzo-p-dioxins, chlorinated dibenzofurans, and organochlorinated insecticides. The different retention observed for different compounds is interpreted in light of the structural similarities of the compound studied with that used as a hapten to raise the antibodies employed as ligands in the immunochromatographic column. Differences in retention of the organochlorinated compounds on the immunocolumn make it possible to fractionate them. Mixtures of phosphate buffer solution and ACN in different ratios were used as desorption agents. Depending on the percentage of ACN employed, different fractionations of the organochlorinated compounds are obtained. The use of 20% ACN allows fractionation of most insecticides from chlorinated biphenyls, dioxins, and furans. Besides, chlorinated biphenyls of different chlorination degree can be separated. Moreover, pentachlorinated dioxins and pentachlorinated furans are separated from hexachlorinated biphenyls. Fractionation is of critical importance from a practical point of view, as it avoids some of the interferences that otherwise take place during the subsequent gas chromatography/mass spectrometry (GC/MS) analysis of these compounds. In this way, immunochromatography makes it possible to perform in a single step all the processes (extraction, clean-up, concentration, and fractionation) that are needed prior to the GC/MS analysis of these analytes in aqueous samples. An additional advantage of this method is the reusability of the immunoaffinity chromatography column for more than 500 times.

Use of immunodotting to select the desorption agent for immunochromatography

In immunochromatography, a technique of increasing use, the sample containing the antigen (Ag) to be purified or determined is introduced into a chromatographic column containing an antibody (Ab) bound to the packing material. The antigen is retained based on antigen–antibody recognition. To reuse the immunocolumn for subsequent assays, the antigen has to be eluted without causing irreversible damage of antibodies. Selection of conditions for performing immunochromatography is usually made by trial and error. This way of working is time consuming and it may ruin the column. In this article, the feasibility of using immunodotting to select the conditions to be employed in one immunochromatographic assay is shown. An immunodotting method is developed to select the best desorption agent for an enzyme-linked immunoaffinity chromatography (ELIAC) assay to determine β-lactoglobulin (β-LG). The effect of several factors on the immunodotting performance is studied. The way of performing solvent exchange to treat the antibody with different solutions considered as potential desorption agents to check their effect is shown. Effectiveness of the solution chosen by immunodotting (4 M MgCl 2 in 20 mM Tris, pH 5.9) as desorption agent is demonstrated by immunochromatographic assays. The immunodotting and solvent exchange methods developed should be useful to choose solvents and conditions for any other kind of assay.

Arsenic Removal Using Mesoporous Alumina Prepared via a Templating Method

The health threat of arsenic is well-known, and the U.S. EPA recommends the maximum contaminant level to be 0.01 ppm or less for arsenic in drinking water. Therefore, advanced treatment processes are needed for finished water to meet the required regulations. Adsorption is considered to be a less expensive procedure that is safer to handle than precipitation, ion exchange, and membrane filtration. Activated alumina (AA) is the most commonly used adsorbent for the removal of arsenic from aqueous solutions. However, conventional porous solids including AA have ill-defined pore structures and, typically, low adsorption capacities and act in a kinetically slow manner. An ideal adsorbent should have uniformly accessible pores, an interlinked pore system, a high surface area, and physical and/or chemical stability. To meet this requirement, mesoprous alumina (MA) with a wide surface area (307 m2/g) and uniform pore size (3.5 nm) was prepared, and a spongelike interlinked pore system was developed through a post-hydrolysis method. The resulting MA was insoluble and stable within the range of pH 3-7. The maximum uptake of As(V) by MA was found to be 7 times higher [121 mg of As(V)/g and 47 mg of As(III)/ g] than that of conventional AA, and the kinetics of adsorption were also rapid with complete adsorption in less than 5 h as compared to the conventional AA (about 2 d to reach half of the equilibrium value). A desorption study using sodium hydroxide solutions (0.01-1 M) was conducted, and 0.05 M NaOH was found to be the most suitable desorption agent. More than 85% of the arsenic adsorbed to the MA was desorbed in less than 1 h. Several other activated aluminas with different pore properties were also tested. The results show that the surface area of the adsorbents does not greatly influence on the adsorption capacity. In fact, the key factor is a uniform pore size and an interlinked pore system. These studies show that MA with a wide surface area, uniform pore size, and interlinked pore system can be used as an efficient adsorbent for the removal of arsenic.

Characterization and electrodialytic treatment of wood combustion fly ash for the removal of cadmium

Due to a high content of macronutrients and a potential liming capacity, recycling of ashes from biomass combustion to agricultural fields as fertilisers and/or for soil improvement is considered in Denmark and other countries utilising biomass as an energy source. However, the fly ash fractions especially contain amounts of the toxic heavy metal cadmium that may exceed the limiting values for agricultural utilisation given by the Danish Environmental Protection Agency. In this work the advances of using an electrodialytic remediation method to reduce the Cd content in wood combustion fly ash—for the aim of recycling—was described. Initial characterisation of the experimental ash showed that the Cd content exceeded the limiting values for agricultural use and therefore needed treatment before being recycled. The pH in the ash was very high (13.3), and the Cd was not soluble at these alkaline conditions. However, significant amounts of Cd could be extracted at neutral to alkaline conditions using an ammonium citrate solution as a desorption agent. Electrodialytic remediation experiments showed that, under optimised remediation conditions using a mixture of ammonium citrate ( 0.25 M ) and NH 3 (1.25%) as an assisting agent, more than 70% of the initial Cd could be removed from the wood fly ash. The results also indicated that a continuous out-separation of Cd from the aqueous process solutions is possible. Thereby, recycling of the (nutrient rich) process solutions as well as of the remediated ash seems achievable.

Desorption behaviour of regular adsorbed polyampholytic layers

The desorption behaviour of the diblock polyampholyte PMAA-b-PDMAEMA, poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), preadsorbed on silicon substrates was investigated under the influence of several desorption agents. The investigated polyampholyte is known to adsorb in regular structures directly from aqueous solutions onto silicon substrates. While the adsorption process is mainly determined by electrostatic interactions, two kinds of desorption mechanism should be assumed. The first mechanism is based on changed electrostatic conditions caused for instance by a strong change in pH of the aqueous solution. The other mechanism is observed after treatment with hydrophobic organic solvent, which leads to the desorption of hydrophobic adsorbed polyampholyte chains, while the electrostatically attached ones will not be influenced. To complete the desorption experiments with organic solvents also adsorption experiments from analogous polyampholytic solutions in the same organic solvents were performed. The amount of polymer at the substrate surface after adsorption or desorption experiments was determined using ellipsometry. Atomic force microscopy (AFM) was used to investigate the surface topography of dried samples after the desorption process.

Enzyme-linked immunofiltration assay used in the screening of solid supports and immunoreagents for the development of an azinphos-methyl flow immunosensor

Azinphos-methyl (AM), O, O-dimethyl S-[(4-oxo-1,2,3-benzotriazin-3(4 H)-yl)methyl] phosphorodithioate, is a dithiophosphorous insecticide extensively used for the control of fruit culture pests. In this work the ELIFA system, initially developed and marketed to substitute conventional ELISA methods, was used for the screening of supports and immunoreagents in the development of a flow immunosensor to AM. The objective was to find the optimal antibody concentration, support quantity and enzymatic tracer concentration to develop a sensitive and reusable immunosensor. The influence of chitosan as protein stabilizing agent was also investigated. We observed that, on the basis of immunosorbent characterization, chitosan-modified silica with immobilized LIB-MFH14 monoclonal antibody (MAb) showed the best sensitivity, with a I 50 value of 6 nM AM. All of the immobilized MAbs either in alkylaminated or chitosan-modified silica showed I 50 values between 10 and 36 nM. Regarding the regeneration capability, the best desorption agent tested was 0.1 M glycine/HCl, pH 2.0, performing in most cases a 100% desorption after just one wash and maintaining the antibody activity even after 20 cycles of regeneration. The chitosan-modified silica seemed to be the best support for this purpose.

The effect of water desorption and organosilane coupling agents on the adhesion of poly(p-xylylene) films to a silicon wafer surface

The adhesion strength of a poly(p-xylylene) (PPX) film to a silicon wafer surface deposited from the vapor was studied using a peel test method. It was found that, within the time and the temperature range studied in this work, the adhesion strength increases with the time and the temperature of the vacuum desiccation of the surface prior to the deposition of the film. This shows that the presence of water adsorbed on the surface strongly decreases the adhesion strength of the film. The effect of organosilane coupling agents on the adhesion of the film to the silicon wafer surface was studied for organosilane derivatives of different chemical compositions. It was found that the adhesion strength can be significantly improved by the presence of 3-(trimethoxysilyl)propyl methacrylate vapor before or during the poly(p-xylylene) deposition. No significant effect on PPX film adhesion was observed for other organosilanes having the propylmethacrylate group replaced by phenyl or alkyl groups. It was found that, in contrast to the other organosilanes, the recrystallization of the PPX from solution did not remove the methacrylate organosilane which remained bonded to the PPX crystals. It is suggested that chemical bonding between the methacrylic group and the PPX chain end radicals is responsible for the improved adhesion of the PPX films.

Procion Red MX-3B-Derived Poly(HEMA/EGDMA) Microspheres for Removal of Cadmium Ions

Poly(hydroxyethyl methacrylate/ethylene glycol dimethacrylate) [poly(HEMA/ EGDMA)]-Procion Red MX-3B microspheres were used for removal of Cd(II) ions from aqueous solutions containing different amounts of Cd(II) ions (5–60 ppm). Dye-derived microbeads carrying 8.95 μmol Procion Red MX-3B/g polymer were used in the adsorption-desorption of Cd(II) ions. High adsorption rates were observed at the beginning of adsorption and then equilibrium was achieved in about 5–10 min. The maximum adsorption of Cd(II) ions onto the Procion Red MX-3B-derived microspheres (i.e., by chelate formation of Cd(II) ions with dye molecules) was about 4.2 mg Cd(II) ions/g polymer, which was observed at pH 7.0. While non-specific adsorption onto the underived microspheres was 0.93 mg Cd(II) ions/g polymer. More than 96% of the adsorbed Cd(II) ions was desorbed in 15 min by using 0.1 M HNO3 as an desorption agent. The regenerability of the dye-derived microspheres was also sufficient.

Discussion

Water purification provides a feasible way to relieve the pressure of water shortage and water pollution which we are facing and adsorption is one of the most effective ways to turn polluted water into clean water. Here, we prepared graphene-tannic acid hydrogel using graphene oxide and tannic acid, a natural green reducer and adsorbent, through one-step hydrothermal method. The composition, structure, and morphology of the compounds were systematically examined. The adsorption of dyes was mainly influenced by the morphology and chemical properties of gel. The addition of tannic acid, a molecule rich in oxygen containing functional groups, changed the surface chemistry of graphene sheets and microstructures of gels, which was beneficial for contaminate adsorption. Compared with reduced graphene oxide hydrogel, the graphene-tannic acid hydrogel showed an outstanding adsorption capacity for organic dye methylene blue, more than 500 mg/g at pH 10 and the maximum adsorption capacity was up to 714 mg/g. After adsorption, ethanol and inorganic acid solution can be used as desorption agent and there was no significant adsorption capacity loss after 5 cycles.

New Dye-Ligand: Procion Red MX-3B Carrying Poly(EGDMA-HEMA) Microbeads for Removal of Copper Ions

ABSTRACT Procion Red MX-3B-attached poly(ethylene glycol dimethacrylate-hydroxy-ethyl methacrylate [poly(EGDMA-HEMA)] microbeads were prepared for removal of Cu2+ ions from aqueous media containing different amounts of Cu2+ ions (2–50 ppm). Procion Red MX-3B-attached microbeads were characterized by FTIR, optical microscopy and elemental analysis. Dye-attached microbeads with a swelling ratio of 55% and carrying 8.95 μmol Procion Red MX-3B/g polymer were used in the adsorption-desorption of Cu2+ ions. Very high adsorption rates were observed at the beginning of adsorption process and then equilibrium was achieved in about 5–10 minutes. The maximum adsorption of Cu2+ ions onto the Procion Red MX-3B-attached poly(EGDMA-HEMA) microbeads (i.e., by chelate formation of Cu2+ ions with dye molecules) was about 4.6 mg Cu2+ ions/g polymer, which was observed at pH 7.5. Adsorption onto the plain poly(EGDMA-HEMA) microbeads (i.e., nonspecific adsorption) was about 0.36 mg Cu2+ ions/g polymer under the same experimental conditions. More than 90% of the adsorbed Cu2+ ions was desorbed in 15 minutes by using 0.1 M HNO3 as an desorption agent.

Studies about the desorption of volatile halocarbons from activated carbon by application of static headspace gas chromatography.

The analysis of volatile halocarbons (VHCs) in air or ground air is often performed after their adsorption and enrichment on activated carbon. The current procedure for their subsequent determination is based on their extraction from the activated carbon with a volatile organic solvent such as n-pentane, followed by gaschromatographic (GC) analysis. In order to avoid extraction steps, the static headspace method in combination with GC analysis using diphenylmethane as a desorption agent has been applied. Satisfactory desorption rates for the chloromethanes, for 1,1,1-trichloroethane, trichloroethene and for tetrachloroethene have been obtained after a sample equilibration of 45 min at 120 degrees C in the presence of diphenylmethane. The results have shown a higher recovering rate especially of the unsaturated VHCs compared to the extraction with n-pentane, whereby a potential loss of analytes by the latter procedure has been avoided.

Preconcentration of lead, cadmium and zinc on silica gel loaded with diethyldithiocarbamate prior to their determination by flame-atomic absorption spectrometry

A silica gel sorbent loaded with sodium diethyldithiocarbamate has been developed for the preconcentration of lead, cadmium and zinc prior to their determination by flameatomic absorption spectrometry (FAAS). The sorption and desorption of the metal ions was studied under both static and dynamic conditions. The metal ions were quantitatively retained on the silica gel sorbent based on an equilibrium time of less than 1 min. In case of the batch method, the effects of pH, shaking time, amount of sorbent, and desorption time were investigated. Among the desorption agents studied, only EDTA in ammonium chloride/ammonia buffer yielded quantitative recoveries. Freundlich's sorption isotherms determined for each metal show that sufficient sorption ability is obtained. The column method allows the preconcentration of metal ions from large sample volumes (e.g. 200 mL) using a flow rate of 5 mL min−1. The influence of foreign ions present in natural waters and saline solutions was examined. The reproducibility of the total analytical method, expressed as relative standard deviation (RSD) is 1.8, 0.5 and 0.6%, for lead, cadmium and zinc, respectively.

Availability of radiocaesium in soils: a new methodology

Two issues are addressed in this paper: (a) the partitioning of radiocaesium between the micaceous specific site pool and the reversible ion exchange pool in mineral soils characterized by relatively low contents of organic matter; (b) the presentation of a new methodology for measuring radiocaesium availability in soils. The partitioning of radiocaesium between specific sites and reversible ion exchange sites is predicted on the basis of soil characterization: specific sites and overall ion exchange capacity. It is predicted that, in mineral soils, only very small fractions of radiocaesium can be expected to be present in readily reversible ion exchange sites. Such predictions are confirmed by an experimental screening study on radiocaesium desorption in a sandy, loamy sand, loam and clay soil, using a variety of desorption agents. A new methodology is presented for measuring radiocaesium availability, using an infinite bath scenario. The method is illustrated by a series of radiocaesium desorption protocols on humic acid, a reference illite clay, a sand loam, loam and clay soil and a set of podzolic soils, including samples from the Chernobyl 30-km zone. It is demonstrated that the (Ca + Mg)/K ratio in soils may play a key role in accelerating the radiocaesium fixation process in the specific sites. The implications of the positive effect of a high CaMg status in the soil on its fixation potential are discussed in terms of the long-term effects of possible countermeasures.

Sorption-desorption dynamics of radiocaesium in organic matter soils

A systematic study has been carried out on the radiocaesium sorption properties of 25 soils (forest, peat) covering organic matter (OM) contents in the range of 10–97%. Predictions are made for radiocaesium partitioning between micaceous Frayed Edge Sites (FES) and regular exchange sites (RES) on the basis of specific radiocaesium interception potentials of the soil and overall exchange capacity. It is shown that for soils with a very high OM content (> 80%), significant fractions are present in a readily reversible form in the OM phase. In soils of low-medium OM content (< 40%), only a very minor fraction is present in the OM exchange complex. Experimental findings, based on a desorption screening with a variety of desorption agents are in agreement with these predictions. On the basis of a study of sorption kinetics, some additional tools are available for identifying problem soils. In cases of very high OM content, radiocaesium adsorption is completed within hours demonstrating the involvement of the OM sites. In soils for which interception occurs in the FES, sorption continues to proceed for periods of 2–3 weeks. In conclusion, some examples are presented on radiocaesium desorption using ion exchangers as radiocaesium sinks in promoting desorption. For a peaty soil, near quantitative desorption is accomplished. For forest soils with OM contents in a range of 10–40%, fixation levels of 30–50% are demonstrated.

Accumulation of zirconium by microalgae and cyanobacteria

The accumulation of zirconium (Zr) as [Zr4-(OH)8(H2O)16]8+ by cyanobacteria and microalgae has been characterized. In all the cyanobacterial and microalgal species examined, accumulation consisted of a single rapid energy-independent phase (“biosorption”) and no energy-dependent accumulation was observed. Biosorption of Zr was concentration-dependent, followed a Freundlich adsorption isotherm, and was dependent on pH, showing decreased accumulation with decreased pH. Prior treatment with Na+, K+, Cs+, Ca2+, Mg+ and Sr2+ (added as chlorides) also decreased Zr accumulation by cyanobacteria and microalgae, probably a result of competition between Zr ions and other cations, including H+, for available binding sites on the cell walls. Zr desorption from microalgae and cyanobacteria was increased by increasing external cation concentrations or by decreasing the pH of the desorption agent.

Accumulation of technetium by cyanobacteria

Accumulation of pertechnetate ions (99TcO4 −) by the cyanobacterial speciesSynechocystis PCC 6803,Synechococcus PCC 6301,Plectonema boryanum,Anabaena variabilis and a redOscillatoria sp. consisted solely of a single rapid energy-independent phase (biosorption); no energy-dependent uptake was detected. Biosorption of TcO4 − was concentration-dependent and could be described by a Freundlich adsorption isotherm for each cyanobacterial species examined. Decreasing pH increased the accumulation of TcO4 − by all the species as did an increase in external NaCl concentration. Accumulation of TcO4 − was also increased inA. variabilis, P. boryanum and the redOscillatoria by an increased external osmotic potential. Concentrations of cations affected TcO4 − accumulation; K+ increased accumulation in all the species, Mg2+, Ca2+, Sr2+ and Cs+ increased accumulation inSynechococcus PCC 6301 and Ca2+ increased accumulation by the redOscillatoria. Some anions decreased TcO4 − accumulation; CO3 2− inA. variabilis and the redOscillatoria, SO4 2− inSynechocystis PCC 6803, and HCO3 − inP. boryanum. The majority of TcO4 − accumulated by all the cyanobacteria was easily desorbed, with no difference in the amounts desorbed between desorption agents of different pH or cation concentration.

Uptake of technetium by freshwater green microalgae

Accumulation of [99Tc]pertechnetate ions (99TcO4−) by the freshwater microalgae Chlorella emersonii, Chlamydomonas reinhardtii and Scenedesmus obliquus has been characterized. In all three species, accumulation consisted of a single rapid energy-independent phase (biosorption), and no energy-dependent accumulation was observed. Biosorption of 99TcOinf4sup−by all three species was concentration dependent, followed a Freundlich adsorption isotherm, and was dependent on pH with increased accumulation by cells with decreasing external pH. Elevated external NaCl concentrations also caused increased accumulation of 99TcOinf4sup−by the cells, as did increased external osmotic potential. Concentrations of K+, Mg2+ and Ca2+ increased accumulation of 99TcOinf4sup−, but concentrations of HCOinf3sup−, SOinf4sup2−and COinf3sup2−decreased 99TcOinf4sup−accumulation by the cells. Most of the 99TcOinf4sup−accumulated by all three species was easily desorbed by 10 mm buffers at various pH values, 0.5 m NaCl, 10 mm Na2CO3 or 10 mm Na2SO4. No differences in the amount of desorption were observed between the various desorption agents used.

Specific Removal of Transthyretin from Plasma of Patients with Familial Amyloidotic Polyneuropathy: Optimization of an Immunoadsorption Procedure

Familial amyloidotic polyneuropathy is characterized by the presence in patients plasma of a genetic variant of transthyretin. No specific treatment has been found and extracorporeal immunoadsorption on immobilized anti-transthyretin antibodies appears as a potentially attractive procedure. Parameters involved in specific immunoadsorption of transthyretin were studied and optimized. Several monoclonal anti-TTR antibodies were compared as affinity ligands and one of them was found to be suitable for such purposes. Optimum quantities of antibodies to be immobilized on the gel were determined. Three desorption agents were tested for regenerating immunoadsorbents and best results were obtained with basic variation of pH, allowing total desorption of TTR and possibility of multiple use without loss of adsorption capacity. Simulation of an immunoadsorption procedure in well-defined conditions showed efficiency and specificity of adsorption to remove TTR and the system thus should be subjected to clinical trials.