Silica-based Strong Anion Exchange Research Articles

Silica-based strong anion exchange media for protein purification

The main objective of our research was to develop silica-based, polymer-functionalized ion exchange materials for single-use bioprocess applications, with the ultimate goal of achieving maximal binding capacity for target proteins. Herein we report the utilization of Grace® wide pore silica gel and bonding the silica with cationic polymers. The strong anion exchange materials have been prepared by a two-step process involving initial bonding with two trimethoxysilanes and subsequent aqueous solution radical polymerization with quaternary ammonium ion containing monomers and an azo initiator. Using the binding capacities for bovine serum albumin (BSA), a model protein for the evaluation of the new materials, we optimized the processes with regard to the median pore size of the silica gel, as well as polymer composition and ratios, which were determined by reagent ratios and reaction conditions. The products were also characterized by both chemical and physical methods. It has been found that higher binding capacities are associated with lower ligand density and higher molecular weight for the attached polymers, with over 20% higher in both static and dynamic binding capacity values with the same amount of attached polymers. The advantages of a large pore size distribution and optimal median pore size for the base silica are discussed. Optimal pore size range of 500–1500Å and distribution of Span 90 for over 1.0 give the highest BSA binding capacities. Silica-based strong anion exchange materials showed excellent flow characteristics when packed into a column and were superior to commercial agarose-based strong anion exchange material with respect to dynamic binding capacity, elution of proteins, and baseline separation of a mixture of three model proteins.

SPE speciation of inorganic arsenic in rice followed by hydride-generation atomic fluorescence spectrometric quantification

Due to high toxicity, inorganic arsenic (iAs) species are the focus of monitoring effort worldwide. In this work arsenic was first extracted from rice by microwave-assisted digestion in HNO3-H2O2, during which As(III) was oxidized to As(V). Silica-based strong anion exchange cartridges were used to separate As(V) from organic forms. After prereduction by iodide, iAs was quantified by hydride-generation atomic fluorescence spectrometry (HG-AFS). This method achieved 1.3 ng g(-1) limit of detection (LOD), and 94 ± 3% and 93 ± 5% recoveries, respectively, for As(III) and As(V) at 100 ng g(-1). Validation was performed using standard reference material NIST 1568a (102 ng g(-1)) and ERM BC211 (124 ng g(-1)) rice flour. By eliminating chromatography, SPE speciation gained throughput and cost advantages. HG-AFS, at 10% budget and operation cost of a typical inductively-couple plasma mass spectrometer (ICPMS), proved highly sensitive and specific for iAs quantification.

SPE of 5-lipoxygenase metabolites and the effect of head-column field-amplified sample stacking in MEKC

The SPE of leukotrienes and eicosatetraenoic acids using anion exchange materials was compared to the classical extraction with C18 columns. A silica-based strong anion exchanger, a polymer-based weak anion exchanger, and a polymer-based mixed-mode strong anion exchanger were studied. All anion exchange materials displayed a higher recovery of the analytes with values between 70 and 90% when extracting standard solutions and analyzing by HPLC. The effect was less pronounced for the analysis of the compounds in incubations of polymorphonuclear leukocytes. Using MEKC with head-column field-amplified sample stacking for analyte quantification, much lower values of the peak areas were observed compared to the determination of the recovery of the analytes by HPLC. Using MEKC analysis, the highest values were found for the polymer-based weak anion exchange material, while values below 10% were found for the polymer-based mixed mode strong anion exchanger. This could be attributed to the presence of electrolytes in the eluates that compromised the stacking efficiency. The extent of residual electrolytes depended on the SPE protocol, resulting in large differences of the amount of analyte determined by MEKC when applying head-column field-amplified sample stacking for online analyte concentration.

Polyelectrolyte functionalized multi-walled carbon nanotubes as strong anion-exchange material for the extraction of acidic degradation products of nerve agents

Extraction, enrichment and gas chromatography mass spectrometric analysis of degradation products of nerve agents from water is of significant importance for verification of Chemical Weapons Convention (CWC) and gathering forensic evidence of use of nerve agents. Multi-walled carbon nanotubes (MWCNTs) were non-covalently functionalized with poly(diallyldimethylammonium chloride) (PDDA) to afford the cationic functionalized nano-tubes, which were used as solid-phase anionic-exchanger sorbents to extract the acidic degradation products of nerve agents from water. Extraction efficiencies of MWCNTs-PDDA were compared with those of mixed mode anion-exchange (HLB) and silica based strong anion-exchange (Si-SAX) cartridges. Optimized extraction parameters included MWCNTs-PDDA 12 mg, washing solvent 5 mL water and eluting solvent 3 mL of 0.1M aqueous HCl followed by 3 mL methanol. At 1 ng mL(-1) spiking concentration of mono- and di-basic phosphonic acids, MWCNTs-PDDA exhibited higher extraction efficiencies in comparison to Si-SAX and HLB. The limits of detection were achieved down to 0.05 and 0.11 ng mL(-1) in selected ion and full scan monitoring mode respectively; and limits of quantification in selected ion monitoring mode were achieved down to 0.21 ng mL(-1).

Ionic liquid-functionalized silica for selective solid-phase extraction of organic acids, amines and aldehydes

Three ionic liquid (IL)-functionalized silica materials, imidazolium, N-methylimidazolium and 1-alkyl-3-(propyl-3-sulfonate) imidazolium, were synthesised and applied in solid-phase extraction (SPE) of organic acids, amines and aldehydes, which are important compound families in atmospheric aerosol particles. 1-Alkyl-3-(propyl-3-sulfonate) imidazolium-functionalized silica was tested as sorbent for SPE for the first time. The analytes were separated and detected by liquid chromatography–mass spectrometry (LC–MS). To confirm the results achieved by LC–MS, the acids were additionally determined by gas chromatography–mass spectrometry (GC–MS). The stability of the IL-functionalized silica materials was tested at low and high pH. The effect of the pH on the extraction was also informative of the retention mechanism of the materials. The results showed anion exchange to be the main interaction, but hydrophobic and π interactions and hydrogen bonding also played a role in the extraction. Extraction efficiencies for organic acids ranged from 87 to 110%, except for cis-pinonic acid (19–29%). Lower extraction efficiencies for amines and aldehydes confirmed that anionic exchange was the predominant interaction. Comparisons made with two commercial SPE materials—silica-based strong anion exchange (SAX) and polymer-based mixed-mode anion exchange and reverse-phase (MAX)—showed the IL-functionalized materials to offer different selectivity and better extraction efficiency than SAX for aromatic compounds. Finally, the new materials were successfully tested in the extraction of an atmospheric aerosol sample.

A polar-copolymerized method to prepare silica-based anion exchanger for ion chromatography

A novel silica-based strong anion exchanger was developed for ion chromatography by copolymerizing methyltrichlorosilane and 3-chloropropyltrichlorosilane. The method allows the column capacity to be easy control simply by adjusting the ratio of silanes. The unwanted residual silanol groups onto the surface of silica gel could also be greatly reduced by this strategy. The effective column capacity of the column used was measured to be 50.8μequiv/column (2.03μequiv/cm). The exchanger was characterized by solid state CP/MAS 13C NMR and elemental analysis and its separation performance was evaluated for the separation of common inorganic anions. The results showed that the column had good separation efficiency (e.g. the plate number of nitrite is 80,000/m) and the separation mechanism was observed to be dominantly governed by ion exchange mechanism. The utility of the column was demonstrated for the determination of nitrite and nitrate in saliva sample.

Simultaneous Determination of Ionic Liquid Cations and Anions Using Ion Chromatography with Tandem Ion Exchange Columns: a Preliminary Assessment

The usefulness of a cation exchange system followed by conductometric detection for alkylimidazolium cations separation and analysis was found for the first time. Furthermore, the possibility of simultaneously separating cations and anions typically used in ionic liquids in one chromatographic run was tested. A tandem of columns containing silica-based strong anion exchange and strong cation exchange packings was used. The study's objective was to find the optimal mobile phase: the best results were obtained with one consisting of potassium hydrogen phthalate and phthalic acid modified with acetonitrile. The method is simple and selective, and is believed to be applicable to numerous ionic liquids based on a similar design.

Improved tert-butyldimethylsilylation gas chromatographic/mass spectrometric detection of nerve gas hydrolysis products from soils by pretreatment of aqueous alkaline extraction and strong anion-exchange solid-phase extraction.

In the analysis of tert-butyldimethylsilyl derivatives (IBDMS) of alkyl methylphosphonic acids (RMPA) and methylphosphonic acid (MPA), from soils by gas chromatography/mass spectrometry (GC/MS), the detection yields are generally low, due to the suppression of TBDMS derivatization by the soil matrix components and the adsorption of RMPA and MPA to the soils. An ion-exchange pretreatment of the aqueous soil extract can be used to overcome the former factor by removing interfering compounds. A pretreatment method is described for improving the detection yields due to the latter factor, using an alkaline extraction procedure. The recovery was estimated quantitatively using capillary electrophoresis. The soil samples tested included volcanogenous immature soils and showed a low aqueous extraction recovery and GC/MS detection yields. The inclusion of sodium hydroxide in the extraction solvent dramatically increased the recovery. Using a 0.1 M sodium hydroxide solution, the recovery was in excess of 68%. Interfering components were removed from the alkaline soil extract by solid-phase extraction of the acids on a silica-based strong anion exchanger. The alkaline soil extract was neutralized with hydrofluoric acid and applied to the cartridge in the fluoride form. After washing with water, MPA and RMPA could be eluted with methanolic ammonia nearly quantitatively. Using the established pretreatment method, MPA and RMPA were detected from all the soil samples in more than 67% yield.

Speciation of arsenic using solid phase extraction cartridges.

Various solid phase extraction (SPE) cartridges were investigated for speciation of arsenite [As(III)], arsenate [As(v)], monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA). Cartridges containing different types of sorbent materials were tested for arsenic retention and elution characteristics. Alumina cartridges were found to completely retain all the four target arsenic species, and are suitable for removal and preconcentration purposes. For speciation analysis, different arsenic species were separated on the basis of their selective retention on and elution from specific cartridges. DMA was retained on a resin-based strong cation exchange cartridge and eluted with 1.0 M HCl. MMA and As(v) were both retained on a silica-based strong anion exchange cartridge and sequentially eluted with 60 mM acetic acid (for MMA) and 1.0 M HCl [for As(v)]. As(III) was not retained on either cartridge and remained in solution. Arsenic species in solution and those eluted from the cartridges were subsequently quantified by using flow injection with hydride generation atomic fluorescence spectrometry (FI-HGAFS) and hydride generation atomic absorption spectrometry (FI-HGAAS). A detection limit of 0.05 microg L(-1) arsenic in water sample was achieved using HGAFS. An application of the method was demonstrated at a drinking water treatment facility. As(III) and As(v) species were determined in water at various stages of treatment. The method is suitable for routine determination of trace levels of arsenic in drinking water to comply with more stringent environmental regulations.

Simultaneous analysis of anthranilic acid derivatives in pharmaceuticals and human urine by high-performance liquid chromatography with isocratic elution

A high-performance liquid chromatographic (HPLC) method for simultaneous determination of mefenamic acid (MFA), flufenamic acid (FFA) and tolfenamic acid (TFA) is presented for application to pharmaceuticals and human urine. Isocratic reversed-phase HPLC was employed for quantitative analysis using tetra-pentylammonium bromide (TPAB) as an ion-pair reagent. Urine samples were purified by solid-phase extraction using a silica-based strong anion-exchanger, Bond-Elut SAX cartridge. The HPLC assay was carried out using a Wakosil ODS 5C 18 column (5 μm, 150×4.6 mm I.D.). The mobile phase consisted of 1.9 g of TPAB dissolved in 1 l of a mixture of acetic acid–sodium acetate buffer solution, pH 5.0, and acetonitrile (11:9, v/v). The calibration curves of MFA, FFA and TFA showed good linearity in the concentration range of 33–167 μg/ml with a wavelength of 280 nm for pharmaceuticals, and in the low concentration range (1.7–30.1 μg/ml) with a wavelength of 230 nm for biological fluids. The correlation coefficients were better than 0.9999 in all cases. The lower limits of detection (defined as a signal-to-noise ratio of about 3) were approximately 2 ng for MFA, 3.5 ng for FFA and 2.5 ng for TFA. The procedure described here is rapid, simple, selective and is suitable for routine analysis of pharmaceuticals and pharmacokinetic studies in human urine samples.

Retention of some glucosinolates in anion exchange chromatography. Part I: Qualitative study on a silica-trialkylammonium exchanger

The retention and separation of glucosinolates, as organic anions, were studied on a silica-based strong anion exchanger under isocratic elution conditions. All glucosinolates carry the same functional ionic group (-OSO 3 − ), however they do not have the same retention in anion exchange chromatography. The plots of capacity factors of organic anions versus the reciprocal of eluent ion concentration show good linearity. From the slope and y-intercept data the major retention mechanisms are interpreted as ion exchange and reversed-phase interactions. The effects of nature and concentration of the eluent ion and the influence of organic modifier addition to the aqueous buffered mobile phase are also investigated. Direct and indirect UV detection were used. Our results open the way for the development of new systems for intact glucosinolate analysis which are easier to use than the present ion-pairing chromatographic method.

Novel silica-based strong anion exchanger for single-column ion chromatography

A novel silica-based anion exchanger for single-column ion chromatography was prepared by immobilizing a quaternary ammonium salt of cyanuric chloride onto the surface of silane-modified silica-gel. A stationary phase with low capacity (0.38 mequiv./g) was obtained and effective separation of monovalent anions was achieved with a concentration of tartaric acid or o-phthalic acid lower than 0.5 m M on a short column prepared using a conductometric detector. Factors that can affect the retention behaviour, such as eluent species, eluent concentration and eluent pH, were examined. The results demonstrate that the retention of anions is dominantly governed by ion-exchange interactions. However, the matrix effect due to the interaction between the stationary phase and the eluent may also play an important role.