Weak Anion Exchange Research Articles

Simultaneous qualitative and quantitative analysis of fluoroalkyl sulfonates in riverine water by liquid chromatography coupled with Orbitrap high resolution mass spectrometry

In this study, a robust method for quick screening, confirmation and quantification analysis of eight fluoroalkyl sulfonates in surface riverine samples was developed using ultra-high performance liquid chromatography-high resolution mass spectrometer (LC-Orbitrap Tribrid HRMS). Weak anion exchange solid phase extraction was optimized to maximum recover perfluoroalkyl sulfonates (PFSAs), fluorotelomer sulfonates and the emerging 6:2 chlorinated polyfluoroalkyl ether sulfonate at the same time. Both qualitative and quantitative purposes could be achieved by simultaneous acquiring full-scan mass spectrum (MS1) and data-dependent MS2 data. The LC-Orbitrap Tribrid HRMS method showed competent method detection limits for all analytes (7.1–62pg/L) compared with the triple quadrupole mass spectrometry (LC–MS/MS) quantification method (12–54pg/L), and satisfactory method validation results were also obtained in linearity (R2>0.999), trueness (88–118%), precision (2–17%) and recovery (63–103%). A good correlation (R>0.999) was found between the sets of quantified PFSA residue concentrations in thirteen estuary river samples by both the LC-Orbitrap Tribrid HRMS (0.2–440ng/L) and LC–MS/MS (0.1–424ng/L) methods, indicating that Orbitrap Tribrid HRMS could be used for reliable quantitative analysis purpose. Moreover, the LC-Orbitrap Tribrid HRMS method could also benefit from its high mass resolution characteristic to eliminate potential environment interferents (e.g., taurodeoxycholate) and to quantify all PFSA isomers based on full-scan MS1 chromatogram at a narrow MS window (5 part per million).

A Case-control Study in an Orcadian Population Investigating the Relationship between Human Plasma N-glycans and Metabolic Syndrome

Background: Alterations in glycosylation patterns have long been known to reflect changes in cell metabolism. In this study, we investigated the relationship between human N-glycan profiles and metabolic syndrome. Method: Between 2005 and 2011, 2,155 individuals from the Orkney Islands (UK) were recruited and biological material, alongside phenotypic measures were collected. Individual N-glycan profiles were measured in plasma using weak anion exchange high performance liquid chromatography and calibrated hydrophilic interaction liquid chromatography. Pre-specified criteria were used to identify 564 cases with metabolic syndrome and 1475 controls. We applied logistic regression to test for association between this binary outcome against measured plasma N-glycans. We also assessed the correlation between N-glycan traits and individual components of metabolic syndrome and compared this to results found in similar analyses based in Chinese and Croatian populations. Results: 21 N-glycan traits were found to be associated with either an increased or a decreased likelihood of participants having metabolic syndrome, including monosialylated plasma N-glycans (OR of 1.49 (95%CI 1.33, 1.67), q=1.26E-12) and core fucosylated plasma N-glycans (OR of 0.81(95% CI 0.72-0.90), q=7.75E-4). Notably, consistent results in both sections of this analysis demonstrated the protective association of higher levels of core fucosylated N-glycans. Conclusion: Our results demonstrate that metabolic syndrome is associated with an alteration in plasma N-glycosylation patterns. The metabolic role of core fucosylated N-glycans is of particular interest for future study.

Development and validation of a specific method to quantify intact glucosinolates in honey by LC–MS/MS

Glucosinolates (GLSs), which are secondary plant metabolites, have been scarcely investigated in honey. Recently, research has been conducted into the potential of GLSs as botanical biomarkers or as a parameter to establish honey freshness, but the employed methodologies were not specifically developed for intact GLSs quantification in honey. The aim of this study was to develop a new method to quantify twelve intact GLSs in honey, by using liquid chromatography with tandem mass spectrometry. An efficient extraction procedure was proposed; this involved dissolution of the honey with heated water, followed by solid-phase extraction with a weak anion exchange sorbent. Chromatography was performed on a C18 analytical column with a mobile phase of formic acid in water (0.5%, v/v) and formic acid in acetonitrile (0.5%, v/v). The method was fully validated in terms of selectivity, limits of detection (LOD) and quantification (LOQ), linearity, carry-over effect, reinjection reproducibility, precision and accuracy. The LOD and LOQ values were below 4μgkg−1 and 10μgkg−1, respectively. The proposed method was applied to analyze intact-GLSs in honey from different botanical origins. Four of the intact GLSs studied were identified at low concentration levels (<25μgkg−1) in several of the samples analyzed.

Phosphate removal from aqueous solutions using a hybrid fibrous exchanger containing hydrated ferric oxide nanoparticles

This study presents the evaluation of a fibrous ion exchanger impregnated with nanoparticles of hydrated ferric oxide (HFO) as a selective sorbent for phosphate. The hybrid impregnated anion exchanger (FIBAN-As) combines the durability and mechanical strength of a polymeric weak base anion exchange resin with the high sorption affinity of HFO towards phosphate species. The phosphate loading capacity at the common pH of waste waters treatment plant secondary effluents was 162±12mg PO43−/g sorbent. Dynamic experiments were carried out and data obtained was fitted to fixed-bed sorption models. The theoretical sorption capacities reported by the Thomas model were in good agreement to the breakthrough experimental capacities determined from the sorption data. The sorption capacity decreased in multicomponent system due to the faster ion exchange of competing anions compared to phosphate ions. The loaded FIBAN-As was efficiently regenerated by using a sodium hydroxide solution, reporting up to 90% of recovery. Finally, reuse of FIBAN-As was evaluated in three successively sorption–desorption cycles by using two regeneration solutions. A sorption capacity reduction of 23% and 30% was observed for acid and alkaline solutions, respectively after the third cycle.

Evaluation of glycidyl methacrylate-based monolith functionalized with weak anion exchange moiety inside 0.5 mm i.d. column for liquid chromatographic separation of DNA

In this study, the organic polymer monolith was developed as a weak anion exchanger column in high performance liquid chromatography for DNA separation. Methacrylate-based monolithic column was prepared in microbore silicosteel column (100 × 0.5 mm i.d.) by in-situ polymerization reaction using glycidyl methacrylate as monomer; ethylene dimethacrylate as crosslinker; 1-propanol, 1,4-butanediol, and water as porogenic solvents, with the presence of initiator α,α′-azobisisobutyronitrile (AIBN). The monolith matrix was modified with diethylamine to create weak anion exchanger via ring opening reaction of epoxy groups. The morphology of the monolithic column was studied by SEM. The properties of the monolithic column, such as permeability, mechanical stability, binding capacity and pore size distribution, were characterized in detail. From the results of the characterization, monoliths poly-(GMA-co-EDMA) with total monomer percentage (%T) 40 and crosslinker percentage (%C) 25 was found to be the ideal composition of monomer and crosslinker. It has good mechanical stability and high permeability, adequate molecular recognition sites (represented with binding capacity value of 36 mg ml−1), and has relatively equal proportion of flow-through pore and mesopores (37.2% and 41.1% respectively). Poly-(GMA-co-EDMA) with %T 40 and %C 25 can successfully separate oligo(dT)12–18 and 50 bp DNA ladder with good resolution.

Bar adsorptive microextraction (BAμE) coated with mixed sorbent phases-Enhanced selectivity for the determination of non-steroidal anti-inflammatory drugs in real matrices in combination with capillary electrophoresis.

The present work proposes the application of bar adsorptive microextraction coated with mixed sorbent phases (n-vinylpyrrolidone and divinylbenzene polymers with strong and weak anion exchangers), combined with liquid desorption followed by capillary electrophoresis with diode array detection (BAμE(PMIX)-LD/CE-DAD) for the determination of trace levels of non-steroidal anti-inflammatory drugs (NSAIDs: salicylic acid, mefenamic acid, diclofenac and naproxen as model compounds) in urine and water matrices. Assays performed on 25mL of water samples spiked at the 80.0μg/L level, yielded average recoveries between 86.6 and 104.% for all the NSAIDs under study using optimized experimental conditions. The proposed analytical methodology demonstrated suitable detection limits (0.3μg/L) and good linear dynamic ranges (2.5-320.0μg/L) with determination coefficients higher than 0.9981. By using the standard addition methodology, the present analytical approach was applied on urine and water samples, where good selectivity and sensitivity were achieved. The proposed method, which operated under the floating sampling technology, proved to be a suitable sorption-based static microextraction alternative for monitoring trace levels of NSAIDs in urine and water samples. The methodology showed to be easy to implement, demonstrating good reproducibility and robustness, allowing the possibility to choose the most selective sorbent, or mixed sorbent phases, according to the compounds of interest.

Kinetic modeling and error analysis for zinc removal on a weak base anion exchange resin

The efficiency of Purolite A103S resin for zinc removal (as zinc chloride complexes) has been studied using different resin quantities and temperatures in a batch adsorption system. The experimental data were analyzed using pseudo-first-order, pseudo-second-order forms, Elovich, and intra-particle diffusion models. Kinetic studies showed that the adsorption followed type 1 pseudo-second-order reaction model. The results obtained from the kinetics models were examined by the most common error functions (e.g. ERRSQ/SSE, HYBRID, ARE, EABS, MPSD,rs, sRE, S.E., RMSE, APE, and ∆q). Thermodynamic parameters, enthalpy, entropy, and Gibbs free energy were calculated in order to determine the adsorption behavior. The enthalpy value indicated an exothermic reaction. The activation energy value suggested that the process that rules over the zinc sorption on the Purolite A103S resin is physical.

Purification and characterization of oligonucleotide binding (OB)-fold protein from medicinal plant Tinospora cordifolia.

The oligonucleotide binding fold (OB-fold) is a small structural motif present in many proteins. It is originally named for its oligonucleotide or oligosaccharide binding properties. These proteins have been identified as essential for replication, recombination and repair of DNA. We have successfully purified a protein contains OB-fold from the stem of Tinospora cordifolia, a medicinal plants of north India. Stems were crushed and centrifuged, and fraction obtained at 60% ammonium sulphate was extensively dialyzed and applied to the weak anion exchange chromatography on Hi-Trap DEAE-FF in 50mM Tris-HCl buffer at pH 8.0. Eluted fractions were concentrated and applied to gel filtration column to get pure protein. We observed a single band of 20-kDa on SDS-PAGE. Finally, the protein was identified as OB-fold by MALDI-TOF. The purified OB-fold protein was characterized for its secondary structural elements using circular dichroism (CD) in the far-UV region. Generally the OB-fold has a characteristic feature as five-stranded beta-sheet coiled to form a closed beta- barrel. To estimate its chemical stability, guanidinium chloride-induced denaturation curve was followed by observing changes in the far-UV CD as a function of the denaturant concentration. Analysis of this denaturation curve gave values of 8.90±0.25kcalmol(-1) and 3.78±0.18M for ΔGD° (Gibbs free energy change at 25°C) and Cm (midpoint of denaturation), respectively. To determine heat stability parameters of OB-fold protein, differential scanning calorimetry was performed. Calorimetric values of ΔGD°, Tm (midpoint of denaturation), ΔHm (enthalpy change at Tm), and ΔCp (constant-pressure heat capacity change) are 9.05±0.27kcalmol(-1), 85.2±0,3°C, 105±4kcalmol(-1) and 1.6±0.08kcalmol(-1)K(-1). This is the first report on the isolation, purification and characterization of OB-fold protein from a medicinal plant T. cordifolia.

Determination of organophosphate diesters in urine samples by a high-sensitivity method based on ultra high pressure liquid chromatography-triple quadrupole-mass spectrometry

Organophosphate (OP) diesters in urine samples have potential use as biomarkers of organism exposure to environmentally relevant OP triester precursors and in particular OP triester flame retardants. This present study developed a quantitatively sensitive ultra high pressure liquid chromatography (UHPLC–MS) based method for urine and the determination of OP diesters (i.e. diphenyl phosphate (DPHP), bis(2-chloroethyl) phosphate (BCEP), bis(2-chloroisopropyl) phosphate (BDCIPP), di-n-butyl phosphate (DNBP), di(2-ethylhexyl) phosphate (DEHP), bis(1-chloro-2-propyl) phosphate (BCIPP), and bis(2-butoxyethyl) phosphate (BBOEP)). Fortified with the 7 OP diesters, 1mL of human urine sample was cleaned up using weak anion exchange solid phase extraction and eluted with high ionic strength ammonium acetate buffer. Subsequently, 4 non-chlorinated OP diesters were directly determined using UHPLC–electrospray(−)-triple quadrupole–MS (UHPLC–ESI(−)–QqQ–MS), and UHPLC–ESI(+)–QqQ–MS was used for determination of 3 chlorinated OP diesters after methylation using diazomethane. Recovery efficiencies of OP diesters ranged from 88 to 160% at three spiking levels (0.4, 2 and 10ng/mL urine). Matrix effects (MEs) and method limits of quantification (MLOQs) were 15-134% and 0.10–0.32ng/mL urine, respectively. Concentrations of OP diesters in n=12 urine samples (from 4 Canadian residents, 2014) varied as follows, nd-<0.28 (DNBP), nd-1.29 (DPHP), nd-<0.28 (DEHP), <0.16–12.33 (BCEP), nd-1.17 (BCDIPP) and nd-0.68ng/mL (BCIPP).

Determination of hexavalent chromium in traditional Chinese medicines by high-performance liquid chromatography with inductively coupled plasma mass spectrometry.

An analytical method that combined high-performance liquid chromatography with inductively coupled plasma mass spectrometry has been developed for the determination of hexavalent chromium in traditional Chinese medicines. Hexavalent chromium was extracted using the alkaline solution. The parameters such as the concentration of alkaline and the extraction temperature have been optimized to minimize the interconversion between trivalent chromium and hexavalent chromium. The extracted hexavalent chromium was separated on a weak anion exchange column in isocratic mode, followed by inductively coupled plasma mass spectrometry determination. To obtain a better chromatographic resolution and sensitivity, 75 mM NH4 NO3 at pH 7 was selected as the mobile phase. The linearity of the proposed method was investigated in the range of 0.2-5.0 μg L(-1) (r(2) = 0.9999) for hexavalent chromium. The limits of detection and quantitation are 0.1 and 0.3 μg L(-1) , respectively. The developed method was successfully applied to the determination of hexavalent chromium in Chloriti lapis and Lumbricus with satisfactory recoveries of 95.8-112.8%.

Selective determination of COXIBs in environmental water samples by mixed-mode solid phase extraction and liquid chromatography quadrupole time-of-flight mass spectrometry

The development and performance evaluation of a method for the simultaneous determination of six pharmaceuticals belonging to the class of non-steroidal anti-inflammatory drugs (NSAIDs) which present high selectivity for the cyclooxygenase (COX)-2 isoform of COX (COXIBs) in environmental waters are presented. The method involves an off-line mixed mode (reversed-phase and strong anionic exchange) solid phase extraction (SPE) for the selective concentration of COXIBs in combination with liquid chromatography (LC) quadrupole time-of-flight (QTOF) mass spectrometry (MS). The use of a strong anionic exchange sorbent (Oasis MAX) led to a significant reduction of matrix effects, during electrospray ionization (ESI), in comparison with results obtained for mixed mode weak anionic exchange sorbent (Oasis Wax) and polymeric reversed phase sorbents (Oasis HLB and Strata X).The developed method attained limits of quantification (LOQs) between 0.01 and 0.20ngL−1 for river water and effluent wastewater and, for influent wastewater this limits were ranged between 0.03 and 0.45ngL−1.Among the pharmaceuticals investigated, two of them (celecoxib and etoricoxib) were detected at low levels (ppt) in real samples of treated and raw wastewaters, and two metabolites were also found; the carboxylated celecoxib and the hydroxylated etoricoxib.

Ion exchange recovery of rhenium from industrially relevant sulfate solutions: Single column separations and modeling

In this study, phenomena behind recovery of Re by weak anion exchangers from sulfate solutions containing Mo and As as impurities were investigated. All the metals exist as different kinds of oxyanions or, at some conditions, cations, meaning that several phenomena need to be taken into account. Batch uptake kinetics and dynamic breakthrough experiments were conducted with three commercial resins, and a model based on competitive Langmuir isotherm and an approximate diffusion equation was used to describe competitive sorption of the oxyacids. The separation systems are also discussed in relation to thermodynamic properties of the related oxyanions.The ability of the anion exchangers to adsorb Re from concentrated sulfate solutions is related to the size and degree of hydration of perrhenate anion, ReO4−. Especially high Re equilibrium capacities of the Purolite A170 and gel-type A172 resins are related to their complex amine functional group, which favors less charged and more hydrophobic anions. However, the functionality did not explain the superior Re/Mo selectivity of the A172 resin detected especially in dynamic column experiments. Diffusion coefficients of all components were remarkably low in A172, and the measured moisture content of the resin was also low. These observations lead to a conclusion that the physical structure of the A172 is so dense that Mo species can only enter near the surface of the resin particle, which is the cause to a low uptake. Both of the Purolite resins also had a good Re/As selectivity, and are well suited for recovering Re from acidic sulfate solutions not containing Mo that are common in industrial applications.

Synthesis and evaluation of carboxymethyl chitosan for glycopeptide enrichment

Glycans are known to be involved in a variety of biological processes throughout human physiology. Mass spectrometry has demonstrated itself as powerful analytical tool for quantitative and structural characterization of glycans. Studying these molecules at the glycopeptide level however, offers distinct advantages, namely the ability to characterize both the glycan and peptide fragments simultaneously, and moreover the ability to assign site specific heterogeneity. In light of this, peptides often dominate the spectrum and hinder the ionization efficiency of glycopeptides. For this reason, enrichment protocols prior to downstream MS analysis need to be developed. Here, we discuss the synthesis and use of carboxymethyl chitosan (CMCH) to enrich glycopeptides from a 12 protein mixture for MS analysis. This protocol was compared to a commercially available glycopeptide enrichment kit offered by EMD Millipore through the use of tandem mass tags (TMT) for relative quantification. Using this approach, we identified 98 unique N-linked glycopeptides and observed, that CMCH was able to enrich more sialylation than the commercial kit. In addition, we observed a trend based on TMT reporter ratios with respect to increasing sialylation. This corroborated that this stationary phase was exhibiting a mixed-mode enrichment through both hydrophilic interaction liquid chromatography (HILIC) and weak anion exchange (WAX) principles.

Sulfate removal from brackish water using an anion exchanger with recycled regeneration

The removal of excess sulfate from brackish water was carried out using a weak anion exchanger that was regenerated with a potassium chloride solution. The potassium sulfate was removed from the regeneration solution by adding solid KCl, which reduces the solubility of K2SO4. Dilution of the regenerated solution was substantially reduced by using three displacement solutions with different KCl concentrations. Precipitation of potassium sulfate in the column during regeneration was prevented by heating it to 50–60°C. After the regeneration solution exited the column, it was cooled to achieve maximal precipitation of the K2SO4. The weight of the K2SO4 obtained was about the same as that of the KCl used for regeneration. The volume of the solution disposed to drain approached zero.

Recovery of ReO4− by weakly basic anion exchangers: Modeling of sorption equilibrium and rate

Abstract Equilibria and dynamics of rhenium uptake from nitrate, chloride and sulfate matrices using weak base anion exchangers have been studied. Gel-type IRA-67 containing tertiary amine groups and macroporous WP-1 containing primary, secondary and tertiary groups were used. Experimental equilibrium and batch kinetic data were correlated using various ion exchange and intra-particle diffusion models. For both exchangers, best correlation was found with the exchange/protonation model including Donnan exclusion and with the surface complexation model. Explicit models requiring no iterations are less accurate but correlate the data satisfactorily. Approximate solution of the Nernst–Planck model was found adequate for correlation of the uptake rates in base-form and fully protonated exchangers.

Separation of cannabinoids on three different mixed-mode columns containing carbon/nanodiamond/amine-polymer superficially porous particles.

Three mixed-mode high-performance liquid chromatography columns packed with superficially porous carbon/nanodiamond/amine-polymer particles were used to separate mixtures of cannabinoids. Columns evaluated included: (i) reversed phase (C18 ), weak anion exchange, 4.6 × 33 mm, 3.6 μm, and 4.6 × 100 mm, 3.6 μm, (ii) reversed phase, strong anion exchange (quaternary amine), 4.6×33 mm, 3.6 μm, and (iii) hydrophilic interaction liquid chromatography, 4.6 × 150 mm, 3.6 μm. Different selectivities were achieved under various mobile phase and stationary phase conditions. Efficiencies and peak capacities were as high as 54 000 N/m and 56, respectively. The reversed phase mixed-mode column (C18 ) retained tetrahydrocannabinolic acid strongly under acidic conditions and weakly under basic conditions. Tetrahydrocannabinolic acid was retained strongly on the reversed phase, strong anion exchange mixed-mode column under basic polar organic mobile phase conditions. The hydrophilic interaction liquid chromatography column retained polar cannabinoids better than the (more) neutral ones under basic conditions. A longer reversed phase (C18 ) mixed-mode column (4.6 × 100 mm) showed better resolution for analytes (and a contaminant) than a shorter column. Fast separations were achieved in less than 5 min and sometimes 2 min. A real world sample (bubble hash extract) was also analyzed by gradient elution.

Development and validation of a liquid chromatography-tandem mass spectrometry method to determine intact glucosinolates in bee pollen

A new method was developed to determine twelve intact-glucosinolates (GLSs) (glucoiberin, GIB; glucoraphanin, GRA; glucoerucin GER; gluconapin, GNA; glucotropaeolin, GTL; glucobrassicin, GBC; gluconasturtiin, NAS; glucoalyssin, ALY; 4-hydroxyglucobrassicin, 4OH; 4-methoxyglucobrassicin, 4ME; neoglucobrassicin, NEO; sinigrin, SIN) in bee pollen, by means of liquid chromatography tandem mass spectrometry (LC-MS/MS) with electrospray ionization (ESI). An efficient extraction procedure was proposed (average analyte recoveries were between 85% and 96%); this involved a solid-liquid extraction (SLE) with heated water, followed by a solid phase extraction (SPE) with a weak anion exchange (NH2) sorbent. Chromatography was performed on a Gemini(®) C18 analytical column with a mobile phase of formic acid in water (0.5%,v/v) and formic acid in acetonitrile (0.5%,v/v), in gradient elution mode at 1mL/min, resulted in baseline-separated peaks and a run time of 30min. The method was fully validated in terms of selectivity, limits of detection (LOD) and quantification (LOQ), linearity, carry-over effect, reinjection reproducibility, precision and accuracy. A good selectivity, low LODs and LOQs, ranging from 1 to 16μg/kg, wide linear ranges from LOQ to 1000μg/kg, and satisfactory reinjection reproducibility, precision and accuracy with relative standard deviation and relative error values lower than or equal to 9%; meanwhile, results indicates a negligible carry-over effect. The proposed method was applied to analyze intact-GLSs in bee pollen. Nine of the GLSs studied were identified in certain samples analyzed over a wide concentration range (LOQ-2226μg/kg), and significant differences in GLS content were observed among the samples.

Determination of avibactam and ceftazidime in human plasma samples by LC-MS.

Avibactam, a novel non-β-lactam β-lactamase inhibitor co-administrated with the β-lactam antibiotic ceftazidime, is in clinical development. The need to evaluate its PK and PD requires accurate and reliable bioanalytical methods. We describe LC-MS/MS methods for the determination of avibactam and ceftazidime in human plasma. Avibactam was extracted using weak anionic exchange solid-phase extraction and analyzed on an amide column. Ceftazidime was extracted using protein precipitation and analyzed on a C18 column. Calibration curves were established over 10-10,000 ng/ml (avibactam) and 43.8-87,000 ng/ml (ceftazidime). Method validation, cross-validation between three laboratories and incurred sample re-analysis demonstrated method robustness. The methods were successfully applied to multiple clinical studies.

Preparation of thiacalix[4]arenetetrasulfonate-modified D201 resin and its adsorption of heavy metal ions

A thiacalix[4]arenetetrasulfonate-modified resin has been prepared by loading thiacalix[4]arenetetrasulfonate onto resins for the adsorption of heavy metal ions. Various factors affecting the adsorption capacities such as different resins, resin size, pH, contact time, and temperature were investigated by batch adsorption experiments, and the adsorption isotherms, thermodynamics, kinetics, selectivity, and regeneration were also studied. It was found that the loading capacity of the D201 resin (macroporous strong basic anion exchange resin) for thiacalix[4]arenetetrasulfonate was substantially higher than those of the D301 (macroreticular weak basic styrene anion exchange resin) and the 717 (strong base styrene anion exchange resin) resins and increased with decreasing particle size of the D201 resin. The adsorption kinetics followed the pseudo-second-order rate law for heavy metal ions, indicating that chemical sorption is the rate-limiting step of the adsorption mechanism. The adsorption of heavy metal ions onto the thiacalix[4]arenetetrasulfonate-modified resin was analyzed and was found to fit better to the Langmuir isotherm than to the Freundlich isotherm, and the maximum adsorption capacities were 78.1, 65.8, 54.3, and 49.8 mg/g for Cu2+, Zn2+, Cd2+, and Pb2+ ions, respectively. The prepared modified resin has high adsorption selectivity for heavy metal ions under the co-occurrence of alkali metal and alkaline earth metal ions. The regeneration efficiencies still exceed 90% after five cycles, indicating that the thiacalix[4]arenetetrasulfonate-modified resin could be favorably recycled.

Characterization of Recombinant Monoclonal Antibody Charge Variants Using OFFGEL Fractionation, Weak Anion Exchange Chromatography, and Mass Spectrometry.

Recombinant monoclonal antibody charge heterogeneity has been commonly observed as multiple bands or peaks when analyzed by charge-based analytical methods such as isoelectric focusing electrophoresis and cation or anion exchange chromatography. Those charge variants have been separated by some of the above-mentioned methods and used for detailed characterization. The utility of a combination of OFFGEL fractionation and weak anion exchange chromatography to separate the charge variants of a recombinant monoclonal antibody was demonstrated in the current study. Charge variants were separated into various fractions of high purity and then analyzed thoroughly by liquid chromatography mass spectrometry. Analysis of intact molecular weights identified the presence of heavy chain leader sequence, C-terminal lysine, and C-terminal amidation. The identified modifications were further localized into different regions of the antibody from analysis of antibody fragments obtained from FabRICATOR digestion. Analysis of tryptic peptides from various fractions further confirmed the previously identified modifications in the basic variants. Asparagine deamidation and aspartate isomerization were identified in acidic fractions from analysis of tryptic peptides. Basic variants have been fully accounted for by the identified modifications. However, only a portion of the acidic variants can be explained by deamidation and isomerization, suggesting that additional modifications are yet to be identified or acidic variants are an ensemble of molecules with different structures.