阳离子交换富集/ICP-MS测定高纯硒中13种杂质

研究了阳离子交换富集预处理/ICP-MS法测定高纯硒中多种杂质,建立了高纯硒中Mg、Al、Ti等13种杂质的分析方法.测定下限达到0.02～0.2μg/g.测定高纯硒样品,相时标准偏差2.5％ ～22％;加标回收率为80％～110％.     

pH-based cation exchange chromatography in the capture and elution of monoclonal antibodies

Cation exchange chromatography separates adsorbed proteins by controlling the salt concentration or the mobile phase pH. This study examines the pH‐based method for binding and elution of monoclonal antibodies (MAbs). Five different clones with isoelectric points from 6 to 9 were evaluated. We performed our studies using a new chromatography resin (Nuvia? S), which has high binding capacity. A three‐column process incorporating Nuvia S as a capture step was also demonstrated for the purification of MAb from tissue culture fluid. Chromatography performance of Nuvia S was demonstrated in a 50‐cycle study.     

Electrical conductivity and cation exchange kinetic studies on poly-o-toluidine Th(IV) phosphate nano-composite cation exchange material

An advanced organic–inorganic cation exchange material poly-o-toluidine Th(IV) phosphate nano-composite was synthesized by a modified sol–gel technique by incorporating Th(IV) phosphate precipitate with the matrix of poly-o-toluidine. The material showed good ion-exchange behavior and used successfully in separation of metal ions. The conductivity of the composite was found within the range of 10⁻² to 10⁻³ S/cm; measured by 4-in-line-probe dc electrical conductivity measuring technique. The conductivity is at the border of metallic and semiconductor region. Ion-exchange kinetics for few divalent metal ions was evaluated by particle diffusion-controlled ion-exchange phenomenon at four different temperatures. The particle diffusion mechanism is confirmed by the linear τ (dimensionless time parameter) versus t (time) plots. The exchange processes thus controlled by the diffusion within the exchanger particle for the systems studies herein. Some physical parameters like self-diffusion coefficient (D₀)_, energy of activation (E_a) and entropy of activation (ΔS⁰) have been evaluated under conditions favoring a particle diffusion-controlled mechanism.     

Electrolysis of sodium chloride using composite poly(styrene-co-divinylbenzene) cation exchange membranes

Composite cation exchange membranes are prepared from cross-linked styrene-divinylbenzene copolymers for the electrolysis of sodium chloride to produce sodium hydroxide and chlorine by selective removal of sodium ions. It is prepared from a syrup of the polymer using dual initiating system and is modified with chloroacetic acid to introduce acid functional groups (COO⁻) on its surface. The effect of the modification is confirmed by FTIR, SEM, contact angle, water content, and ion exchange capacity measurements. The performance of the membrane has been evaluated in terms of current efficiency and power consumption and the effect of current density, salt concentration and flow rate on efficiency has been studied. Our membrane has an ion exchange capacity of 0.833 meq./g which is close to that of the commercially available Nafion-117 membrane having an ion exchange capacity 0.9 meq./g. The Nafion-117 used for electrodialysis of sodium sulfate has a current efficiency of around 90% and specific energy consumption of 0.1 kW/mol at 2N concentration of the salt at 1000 A/m². Our membrane used for electrodialysis of sodium chloride has a current efficiency of 93% and a power consumption of around 0.3122 kW/mol at the same concentration of salt and at a current density of 254 A/m². The two-dimensional space-charge model in cylindrical coordinates has been solved semi-analytically to obtain the effective wall potential and pore size of the membrane which are difficult to measure directly. The experimentally obtained solute flux and current density have been fitted to the model and optimum values of effective wall potential and pore diameter have been determined to be 98.5 mV and 0.8 nm, respectively.     

Separation of exenatide analogue mono-PEGylated with 40 kDA polyethylene glycol by cation exchange chromatography

Random PEGylation usually resulted in product mixtures composed of mono-PEGylated isomers and multi-PEGylated attachments. Generally in PEGylation research, separation of the mono-PEGylated isomers was the prerequisite for finding the optimal PEGylation site. However, when peptides or proteins were PEGylated with polyethylene glycol as large as 40 kDA, the physicochemical properties like hydrophobicity and molecular size of the isomers would become too similar to make the routine separation methods, like RP-HPLC, size-exclusion chromatography, SDS-PAGE and capillary isoelectric focusing invalid. This article presented a useful method of successfully separating exenatide analogue (an incretin for diabetic therapy) isomers mono-PEGylated with 40 kDA polyethylene glycol by cation exchange chromatography, which would be a powerful tool for the PEGylation research.     

Octadecyltrimethylammonium surfactant-immobilized cation exchange membranes for solid-phase extraction of phenolic compounds

In this study, octadecyltrimethylammonium surfactant was immobilized onto a cation exchange membrane for the application in solid-phase extraction of phenolic compounds. The results indicate that an HCl prewashing step and the use of hydroxide (or methoxide) counter ion could greatly improve the immobilized surfactant capacity. Through elemental and thermogravimetric analyses, the resulted immobilization percentage on the membrane (compared to membrane ion exchange capacity) was about 50, 100, and 150%, respectively, for the feed surfactant amount of 150, 2000, and 5000 μmol (volume = 20 mL). Phenol, 4-nitrophenol, 2,4-dimethylphenol, 2,4-dichlorophenol, 4-chloro-3-methylphenol, and bisphenol A were the tested compounds in a breakthrough volume experiment. The order of the obtained breakthrough volume values is similar to that of K_ow values of the phenolic compounds. In the solid-phase extraction process from a feed mixture of 0.1 ppm for 4-nitrophenol, 2,4-dichlorophenol, and 4-chloro-3-methylphenol, high concentration factors and almost complete recoveries were achieved. Moreover, by increasing the membrane volume, a larger sample volume could be processed without any deterioration in performance.     

Simultaneous recovery of EDTA and lead(II) from their chelated solutions using a cation exchange membrane

Factors affecting the efficiency of electrochemical recovery of EDTA and Pb(II) from their chelated solutions were systematically examined using a cation exchange membrane Neosepta CM-1. The catholyte contained an equimolar amount of Pb(II) and EDTA, and the anolyte contained 0.1 M NaNO₃. The iridium oxide coated on titanium (IrO₂/Ti) and stainless steel were used as anode and cathode, respectively. Experiments were carried out at different current densities (46.3–185 A/m²), initial catholyte pH values (1.47–6.02) and Pb(II) concentrations (0.005–0.03 M). An economically feasible current efficiency and recovery percentages of Pb(II) and EDTA could be achieved if the concentration of the chelated Pb(II) was sufficiently high.     

Trimerization of isobutene over cation exchange resins: Effect of physical properties of the resins and reaction conditions

Oligomerization of isobutene has been investigated using several cation exchange resins in order to produce triisobutenes that are useful feedstock for heavy alkylates and neo-acids. Trimers selectivity increases with increasing isobutene conversion. High isobutene conversion is obtained at high temperature and low space velocity by using macroporous cation exchange resins that have high concentration of sulfonic acid groups. Under selected conditions (viz., isobutene WHSV: 10 h⁻¹; temperature: 70 °C; catalyst: Amberlyst-35), the isobutene is quantitatively oligomerized with higher than or equal to 70% selectivity for trimers. The wet resin catalysts containing water or ethanol are very stable for the oligomerization up to about 70 h contrary to the gradual decrease in the conversion with dehydrated catalysts.     

Hydrophobic and cation exchange mechanisms in the retention of basic compounds in a polymeric column

A cation exchange retention mechanism concomitant with the well-known hydrophobic partition mechanism in a polymeric column has been observed and investigated. This exchange process is attributed to ionization of some acidic sites present in the polymer column at basic mobile phase pH values. Several drugs of different basicity have been chromatographed on a polymeric PLRP-S column with methanol-water and acetonitrile-water mobile phases. The cation exchange between the protonated basic drug and the buffer cations (Na+, K+ and BuNH4+) is observed at the pH range where the protonated drug and the ionized sites of the column coexist. This process produces a shift of the retention versus pH plot of the base to pH values lower than those expected from the pKa of the base as well as a maximum in the plot at basic pH values. These effects are more pronounced for acetonitrile-water mobile phases.     

Behavior of human serum albumin on strong cation exchange resins: I. Experimental analysis

Experiments with human serum albumin on the strong cation exchange resin Fractogel EMD SE Hicap (M) were carried out. Even though human serum albumin was used at high purity, two peaks in gradient elution experiments occurred. The obtained data can be explained by considering that human serum albumin binds to Fractogel EMD SE Hicap (M) in two different binding conformations: the protein adsorbs instantaneously in the first conformation and then changes into the second one with a kinetic limitation. The two-peak behavior of human serum albumin was analyzed in detail, especially at various gradient lengths, concentrations and temperatures. Breakthrough curves were performed at four modifier concentrations and three velocities. The characteristic adsorption behavior, found for gradient experiments, was confirmed by the breakthrough curves. The two-peak elution pattern of human serum albumin was also found for other strong cation exchange resins, but not for weak cation exchange resins. It is concluded that the described behavior is peculiar for the interaction of human serum albumin with the strong cation exchange ligand of the resin.     

The rôle of countercurrent chromatography in the fractionation of complex mixtures

The biologically active pricipals in nature are frequently present as only a few parts per million of complex mixtures of non-volatile components and often have limited stability. Their isolation often requires the application of all available techniques, such as adsorption chromatography, ion exchange procedures, size exclusion techniques, and solvent partition methods consistent with their physical properties and stability. The process of countercurret chromatography is essentially liquid-liquid chromatography in which the stationary liquid bed is retained in the column by a force field rather than by a solid supporting matrix. Adsorption effects are thereby eliminated. The technique is particularly advantageous in the preparative separation of milligram to gram quantities of polar and labile organic compounds and bio-particulate materials such as cells and cell fragments. Virtually any twophase solvent system, either aqueous or non-aqueous may be employed. Countercurrent chromatography (CCC) provides a convenlent alternative to adsorption chromatography for fractionation of natural products or other complex mixtures. In some cases, this high resolution method offers advantages with regard to the avoidance of contamination from solid adsorbents, versatility, and relatively inexpensive operation. The article covers some of the applications, selection of solvents, and advantages of CCC.     

Enrichment and low‐level determination of glyphosate,aminomethylphosphonic acid and glufosinate in drinking water after cleanup by cation exchange resin

For the determination of glyphosate, aminomethylphosphonic acid and glufosinate in drinking water, different procedures of enrichment and cleanup were examined using anion exchange or SPE. In many cases interactions of, e.g. alkaline earth metal ions especially calcium could be observed during enrichment and cleanup resulting in loss of analytes. For that reason, a novel cleanup and enrichment procedure for the determination of these phosphonic acid herbicides has been developed in drinking water using cation‐exchange resin. In summary, the cleanup procedure with cation‐exchange resin developed in this study avoids interactions as described above and is applicable to calcium‐rich drinking water samples. After derivatization with 9‐fluorenylmethylchloroformate followed by LC with fluorescence detection, LOD of 12, 14 and 12 ng/L and mean recoveries from real‐world drinking water samples of 98±9, 100±16 and 101±11% were obtained for glyphosate, aminomethylphosphonic acid and glufosinate, respectively. The low LODs and the high precision permit the analysis of these phosphonic acid herbicides according to the guidelines of the European Commission.     

Selective separation and purification of highly polar basic compounds using a silica-based strong cation exchange stationary phase

Compared to moderately and weakly hydrophilic bases, highly polar basic compounds are even more difficult to separate due to their poor retention in reversed phase (RP) mode. This study described the successful applications of a strong cation exchange (SCX) stationary phase to achieve symmetric peak shape, adequate retention and selectivity in the separation of very polar basic compounds. Salt and acetonitrile concentrations were adjusted to optimize the separation. Good correlations (R² = 0.998–1.000) between the logarithm of the retention factor and the logarithm of salt or acetonitrile concentration were obtained. Gradients generated by changing salt or acetonitrile concentration were compared for the analysis of different highly polar bases. Although all of the analytes were eluted more quickly with an acetonitrile gradient, the effect of the gradients tested on peak width and peak shape varied with respect to analyte. In addition, the effects of different types of cation and anion additives were also investigated. After separation parameters were acquired, the SCX-based method was utilized to analyze highly hydrophilic alkaloids from Scopolia tangutica Maxim with high separation efficiency (plate numbers > 32,000 m⁻¹). Concurrently, one very polar alkaloid fraction was purified with symmetric peak shape using the current method. Our results suggest that SCX stationary phase can be used as an alternative to RP stationary phase in the analysis and purification of highly hydrophilic basic compounds.     

Pre-concentration of trace elements in short chain alcohols using different commercial cation exchange resins prior to inductively coupled plasma-optical emission spectrometric detection

Chelex-100, Dowex 50W-x8 and Dowex MAC-3 exchange resins were investigated for separation and pre-concentration of trace amounts of Cd, Cr, Cu, Fe, Mn, Pb, Ti and Zn in alcohols with respect to retention and desorption characteristics. Dowex 50W-x8 was found to be the best sorbent with percentages recoveries >95%. In addition, Chelex-100 appeared to be suitable for the pre-concentration of Cu, Fe and Zn, whereas Dowex MAC-3 was selective for Cu and Fe. Therefore, Dowex 50W-x8 was used for further investigations. The relative standard deviations <4% (n = 20), limits of detection and quantification were 0.1–1.2 μg L⁻¹ and 0.3–1.5 μg L⁻¹, respectively. The SPE method was validated against a certified reference material and the results were in agreement with certified values. The accuracy of the optimized method was verified by the recovery test in the spiked alcohol samples. The accuracy and spike recovery test for different metal ions were in the range 98–102% and 95–105%, respectively. The optimized method was applied to the separation and pre-concentration of metal ions in different commercial alcohol samples.     

Behavior of human serum albumin on strong cation exchange resins: II. Model analysis

Experiments with human serum albumin on a strong cation exchange resin exhibit a peculiar elution pattern: the protein elutes with two peaks in a modifier gradient. This behavior is modeled with a general rate model, where the two elution peaks are modeled with two binding conformations, one of which is at equilibrium conditions, while for the other, the adsorption process is rate limited. Isocratic experiments under nonadsorbing conditions were used to characterize the mass transfer process. The isotherm of both adsorption conformations as well as the kinetic of adsorption and desorption for the second conformation are functions of the modifier concentration. They are evaluated with linear modifier gradient experiments and step experiments with various adsorption times. All experimental features are well reproduced by the proposed modified general rate model.     

Kinetics and mechanism of ion exchange of Fe3+, Cd2+ and Na+/H+ on Lewatite S-100 cation exchanger in aqueous and aqueous-detergent media

Sorption mechanism of Fe (III), Cd (II) and Na (I) on cation exchange resins in H-form was investigated from aqueous and aqueous-detergent media by a modified limited batch technique. The cation exchange studies involved the sorption of metallic ions onto a Lewatite S-100 exchanger. Effects of mesh size of the exchanger, temperature and detergent on the exchange rate have been investigated. The mechanisms of cation exchanges have been determined in the temperature range of 25–65°C. In all cases of the reactions ions, diffusion is found to be the rate determining step in the exchange process. The exchange rate in the exchange process was found to increase with a decrease of particle size and an increase of temperature. However, in case of the influence of detergent, the exchange reactions are dependent on the reaction technique. The effective-diffusion coefficients have been evaluated at three different temperatures. The energy barriers (ΔE_a), entropies of activation (ΔS*), (ΔH*) and (ΔG*) for various sorption systems have also been calculated. The results are discussed in terms of size and valences of the counter ions. No change in the internal structure of Lewatite S-100 is inferred due to the sorption of counter ions.     

Separation behavior of U(VI) and Th(IV) on a cation exchange column using 2,6-pyridine dicarboxylic acid as a complexing agent and its application for the rapid separation and determination of U and Th by ion chromatography

The retention behavior of U and Th as their 2,6-pyridine dicarboxylic acid (PDCA) complexes on a cation exchange column was investigated under low pH conditions. Based on the observed retention characteristics, an ion chromatographic method for the rapid separation of uranium and thorium in isocratic elution mode using 0.08 mM PDCA and 0.24 M KNO(3) in 0.22 M HNO(3) as the eluent was developed. Both uranium and thorium were eluted as their PDCA complexes within 2 min, whereas the transition and lanthanide metal cations were eluted as an unresolved broad peak after thorium. Under the optimized conditions both U and Th have no interference either from alkali and alkaline earth elements up to a concentration ratio of 1:500 or from other elements up to 1:100. The detection limits (LOD) of U and Th were calculated as 0.04 and 0.06 ppm, respectively (S/N=3). The precision in the measurement of peak area of 0.5 ppm of both U and Th was better than 5% and a linear calibration in the concentration range of 0.25-25 ppm of U and Th was obtained. The method was successfully applied to determine U and Th in effluent water samples.     

New functionalised silicas for highly selective cation exchange SPE purification in medicinal chemistry

Functionalised silicas 2 and 3 are effective for the cation exchange SPE purification of basic molecules containing acid-sensitive functionalities, the selective separations of mixtures of basic compounds and accelerated reaction work-ups/product isolations.     

Exploration of overloaded cation exchange chromatography for monoclonal antibody purification

Cation exchange chromatography using conventional resins, having either diffusive or perfusive flow paths, operated in bind-elute mode has been commonly employed in monoclonal antibody (MAb) purification processes. In this study, the performance of diffusive and perfusive cation exchange resins (SP-Sepharose FF (SPSFF) and Poros 50HS) and a convective cation exchange membrane (Mustang S) and monolith (SO(3) Monolith) were compared. All matrices were utilized in an isocratic state under typical binding conditions with an antibody load of up to 1000 g/L of chromatographic matrix. The dynamic binding capacity of the cation exchange resins is typically below 100 g/L resin, so they were loaded beyond the point of anticipated MAb break through. All of the matrices performed similarly in that they effectively retained host cell protein and DNA during the loading and wash steps, while antibody flowed through each matrix after its dynamic binding capacity was reached. The matrices differed, though, in that conventional diffusive and perfusive chromatographic resins (SPSFF and Poros 50HS) demonstrated a higher binding capacity for high molecular weight species (HMW) than convective flow matrices (membrane and monolith); Poros 50HS displayed the highest HMW binding capacity. Further exploration of the conventional chromatographic resins in an isocratic overloaded mode demonstrated that the impurity binding capacity was well maintained on Poros 50HS, but not on SPSFF, when the operating flow rate was as high as 36 column volumes per hour. Host cell protein and HMW removal by Poros 50HS was affected by altering the loading conductivity. A higher percentage of host cell protein removal was achieved at a low conductivity of 3 mS/cm. HMW binding capacity was optimized at 5 mS/cm. Our data from runs on Poros 50HS resin also showed that leached protein A and cell culture additive such as gentamicin were able to be removed under the isocratic overloaded condition. Lastly, a MAb purification process employing protein A affinity chromatography, isocratic overloaded cation exchange chromatography using Poros 50HS and anion exchange chromatography using QSFF in flow through mode was compared with the MAb's commercial manufacturing process, which consisted of protein A affinity chromatography, cation exchange chromatography using SPSFF in bind-elute mode and anion exchange chromatography using QSFF in flow through mode. Comparable step yield and impurity clearance were obtained by the two processes.     

Lanthanide N,N′-piperazine-bis(methylenephosphonates) (Ln=La, Ce, Nd) that display flexible frameworks, reversible hydration and cation exchange

Hydrothermal syntheses of lanthanide bisphosphonate metal organic frameworks comprising the light lanthanides lanthanum, cerium and neodymium and N,N′-piperazine bis(methylenephosphonic acid) (H₂L(1) and its 2-methyl and 2,5-dimethyl derivatives (H₂L(2) and H₂L(3)) gives three new structure types. At elevated starting pH (ca. 5 and above) syntheses give ‘type I’ materials with all metals and acids of the study (MLnLxH₂O, M=Na, K, Cs; Ln=La, Ce, Nd; x≈4: KCeL(1)·4H₂O, C2/c, a=23.5864(2) Å, b=12.1186(2) Å, c=5.6613(2) Å, β=93.040(2)°). The framework of structure type I shows considerable flexibility as the ligand is changed, due mainly to rotation around the -N-CH₂- bond of the linker in response to steric considerations. Type I materials demonstrate cation exchange and dehydration and rehydration behaviour. Upon dehydration of KCeL·4H₂O, the space group changes to P2₁/n, a=21.8361(12) Å, b=9.3519(4) Å, c=5.5629(3) Å, β=96.560(4)°, as a result of a change of the piperazine ring from chair to boat configuration. When syntheses are performed at lower pH, two other structure types crystallise. With the ‘non-methyl’ ligand 1, type II materials result (LnL(1)H₂L(1)·4.5H₂O: Ln=La, P−1, a=5.7630(13) Å, b=10.213(2) Å, c=11.649(2) Å, α=84.242(2)°, β=89.051(2)°, γ=82.876(2)°) in which one half of the ligands coordinate via the piperazine nitrogen atoms. With the 2-methyl ligand, structure type III crystallises (LnHL(2)·4H₂O: Ln=Nd, Ce, P2₁/c, a=5.7540(9) Å, b=14.1259(18) Å, c=21.156(5) Å, β=90.14(2)°) due to unfavourable steric interactions of the methyl group in structure type II.