Simultaneous chromatographic separation of the anomers of saccharides on a polymer sulfobetaine zwitterionic stationary phase.

Simultaneous chromatographic separation of the anomers of saccharides was achieved by using a polymer zwitterionic stationary phase functionalized by acrylamide-type sulfobetaine. By optimization of separation parameters including column temperature, pH, and flow rate, the column operated in hydrophilic interaction chromatography mode exhibited excellent separation selectivity toward five monosaccharides and their anomers (including ribose, xylose, galactose, glucose, and arabinose) and two disaccharides (lactose and maltose). Baseline separation could be achieved at mild operation conditions such as 20-30°C of column temperature or typical mobile phase composition (85% acetrontrile-15% 20 mM ammonium formate [NH4 FA]) with wide pH tolerance range of 2-8. This offers a rapid way to determine the configuration of α or ß anomer of the saccharides.

A hyperbranched polyethylenimine functionalized stationary phase for hydrophilic interaction liquid chromatography.

A hyperbranched stationary phase for hydrophilic interaction liquid chromatography (HILIC) has been prepared by grafting polyethylenimine (PEI) onto silica gel (termed as PEI-Sil). Rich primary, secondary, and tertiary amino groups associated with PEI render its good hydrophility. More importantly, the hyperbranched structure of PEI molecule is greatly helpful in improving interaction with polar analytes. For several kinds of model polar compounds, including organic acids, nucleosides, nucleic acid bases, amino acids, cephalosporins, and non-reducing sugars, PEI-Sil demonstrated excellent separation performance in terms of running stability, reproducibility, and separation efficiency (e.g., plate count ~74,000/m). In addition, PEI-Sil also exhibited much better separation selectivity toward inorganic anions when operated in the mode of ion chromatography relative to a commercial amino propyl-bonded column.

A polyvinyl alcohol-coated silica gel stationary phase for hydrophilic interaction chromatography.

Multiple layers of polyvinyl alcohol (PVA) coating are generated onto silica gel by thermal immobilization to form a stationary phase applied for hydrophilic interaction liquid chromatography (HILIC). It offers an easy way to manipulate the thickness of PVA coating and the obtained stationary phase demonstrated high efficiency and high chemical stability.

An open tubular ion chromatograph.

We describe an open tubular ion chromatograph (OTIC) that uses anion exchange latex coated 5 µm radius silica and 9.8 µm radius poly(methyl methacrylate) tubes and automated time/pressure based hydrodynamic injection for pL-nL scale injections. It is routinely possible to generate 50,000 plates or more (up to 150,000 plates/m, columns between 0.3 and 0.8 m have been used), and as such, fast separations are possible, comparable to or in some cases better than the current practice of IC. With an optimized admittance detector, nonsuppressed detection permits LODs of submicromolar to double digit micromolar for a variety of analytes. However, large volume injections are possible and can significantly improve on this. A variety of eluents, the use of organic modifiers, and variations of eluent pH can be used to tailor a given separation. The approach is discussed in the context of extraterrestrial exploration, especially Mars, where the existence of large amounts of perchlorate in the soil needs to be confirmed. These columns can survive drying and freezing, and small footprint, low power consumption, and simplicity make OTIC a good candidate for such a mission.

Facile preparation of polyvinyl alcohol coated SiO2 stationary phases for high performance liquid chromatography.

A facile method to prepare a polar stationary phase for hydrophilic interaction chromatography (HILIC) was proposed by coating polyvinyl alcohol onto silica particles (PVA-Sil). A water or organic solvent-insoluble permanent PVA coating on the silica particle surface can be formed simply by dipping silica particles into a hot PVA solution and then settled from this solution, leaving a thin layer of PVA coating and frozen in a freezer. The PVA-Sil shields the silica core from solution erosion to some degree and the pH tolerance range was extended to 9.5 from 8.0 for bare silica. PVA-Sil demonstrated a good hydrophilic property for several kinds of polar compounds and ∼57000 m(-1) of plate count was achieved. This method can also be extended as a universal method to prepare various stationary phases with exchangeable functionalities by doping the desired ingredient in a PVA solution.

Fabrication and application of a continuously regenerated cationic impurity removal device for ion chromatography.

A continuously regenerated cationic impurity removal device (CR-CRD) has been fabricated and applied for ion chromatography (IC). The removal of cationic impurities is realized by electrodialytically replacing the cationic impurities with hydronium ions. The device is configured in a sandwich structure and the central eluent channel is respectively isolated from both electrodes by stacked cation exchange membranes and a bipolar membrane (BPM) plus stacked anion exchange membranes. The eluent channel is packed with cation exchange resins in hydronium form and their continuous regeneration can be achieved by electrodialysis. A desirable feature of the device is gas-free, and no degasser is required. It showed sufficient ability to remove cationic impurities, as indicated by > 99.9 % removal of 10 mL of 1 mM LiOH solution injected (∼10 µmol) or continuous removal of 1 mM LiOH solution at the flow rate of 1 mL/min (1 µmol/min). A useful application was for sample pretreatment in nuclear power industry, by eliminating strong matrix interference of the sample containing LiOH (1 mM) and boric acid (2000 mg/L) with trace anion analysis.

Polymethylmethacrylate open tubular ion exchange columns: nondestructive measurement of very small ion exchange capacities.

We describe an approach to prepare an open tubular ion exchange (OTIE) column by coating a monolayer of anion exchange nanoparticle to a 16-20 µm bore polymethylmethacrylate (PMMA) capillary. The latex nanoparticle was electrostatically attached to carboxylate groups on the inner wall of capillary, pretreated with strong base for hydrolyzing the ester. Several approaches to nondestructively measure ion exchange capacities (IEC) of the columns were examined: (a) adsorption-desorption of an intensely fluorescent ion, e.g. fluorescein, and off-line fluorometry, (b) loading a weakly retained ion (e.g., IO3(-)), frontal displacement by a strongly bound ion (e.g., Cl(-)), and online optical or conductometric boundary detection, and (c) similar to the above except displacement being accompanied by reaction (e.g., acid-base titration). To our knowledge, this is the first time on-column titration has been used to measure capacities. By using different pH displacer solutions, we demonstrate for the first time the possibility of pKa-differentiated ion exchange capacity measurements. The cation exchange capacity of bare PMMA capillaries was on the order of 1 pequiv/mm(2) with little dependence on time and temperature of hydrolysis conditions. After AS18 latex coating, the strong base anion exchange capacity was on the order of 10 pequiv/mm(2), very close to what would be estimated on the basis of monolayer coverage of the surface by individual latex particles. The latex used contained a significant, additional amount of weak base character, about the same as the strong base ion exchange capacity.

A polyethyleneimine-functionalized polymer substrate polar stationary phase.

A polyethyleneimine (PEI)-functionalized polymer substrate polar stationary phase was prepared for hydrophilic interaction chromatography (HILIC) by grafting PEI onto poly(styrene-divinylbenzene) (PS-DVB) microspheres. The phase shows a U-shape retention profile and it exhibits typical hydrophilic characteristic when the organic solvent fraction in the mobile phase is > 60%. Hydrogen bonding, anion exchange, and hydrophobic interaction are involved in the retention mechanism. Good separation and unique selectivity for acidic, basic and neutral polar analytes were achieved. It showed extremely low column bleed (comparable to that of blank) under gradient elution mode (even to 50% fraction of water) and wide pH tollerance range (at least 1-13).

A hyperbranched polyglycerol-functionalized polymer polar stationary phase.

A polymer polar stationary phase functionalized with hyperbranched polyglycerol for hydrophilic interaction chromatography (HILIC) is described. It is prepared via surface-initiated ring-opening polymerization of hyperbranched polyglycerol onto hydrolzed poly(glycidyl methacrylate-divinylbenzene) microspheres. The capacity of the functional groups can be maniputed by repeating hyperbranch layers. The phase showed typical HILIC character with good separation performance towards tested polar analytes. It also exhibited wider pH tolerance range (e.g. at least 2 to 12) and as well negligible bleed level under gradient elution mode (even to 50% fraction of water).

A novel silica based click lysine anion exchanger for ion exchange chromatography.

Ion chromatography (IC) is one of the most powerful analysis technologies for the determination of charged compounds. A novel click lysine stationary phase was prepared via Cu(I) catalyzed alkyne-azide 1,3-dipolar cycloaddition (CuAAC) and applied to the analysis of inorganic ions. The chromatographic evaluation demonstrated good performance (e.g. the plate number of thiocyanate is ∼50,000 plates m(-1)) and effective separation ability for the common inorganic anions with aqueous Na(2)SO(4) eluent. The separation mechanism was observed to be mainly dominated by ion exchange interaction. The retention of these analytes is highly dependent on the pH value of eluent. Compared with the lysine stationary phase prepared via the conventional manner, the click lysine exchanger demonstrated shorter retention time and better ion separation characteristics under the same chromatographic conditions, which is a great advantage for rapid separation and analysis of inorganic ions.

Preparation and evaluation of a polymer-based sulfobetaine zwitterionic stationary phase.

We describe a polymer-based sulfobetaine zwitterionic stationary phase for hydrophilic interaction liquid chromatography (HILIC). It was prepared by grafting acrylamide-type sulfobetaine monomer instead of common methacrylate-type sulfobetaine onto hydrolysed poly (glycidyl methacrylate-divinylbenzene) (GMA-DVB) microspheres via pendant double bonds of DVB. The phase has been characterized by elemental analysis, scanning electron micrograph and N2 adsorption-desorption experiment. It shows wider pH tolerance range (from 2 to 12) and excellent separation ability towards common strong polar analytes such as nucleosides and nucleic bases, water-soluble vitamins, amino acids, inorganic anions and cations. Notably, it exhibits negligible baseline noise level (~0.15 pA) under typical HILIC mobile phase. Excellent selectivity in separation of α- and ß-anomers of reducing sugars and lactose/lactulose has also been observed.

Preparation of a polymer-based weak cation exchanger for ion chromatography via atom transfer radical polymerization.

A novel polymer-based weak cation exchanger (WCX) for ion chromatography has been described. It was prepared by grafting tert-butyl acrylate and maleic anhydride onto the surface of poly(glycidyl methacrylate-divinylbenzene) microspheres via atom transfer radical polymerization, followed by hydrolytic treatment to produce acrylic and maleic acid groups. The obtained WCX showed better separation and higher selectivity for model cations relative to solely acrylic or maleic acid. Simultaneous separation of alkali and alkaline earth cations (including NH4+) was achieved in a single isocratic run under suppressed mode, and ion exchange was found to dominate the separation process. Its utility was demonstrated for determination of several cations in a beer sample and the recovery was ranging from 98.4 to 109.9%.

Sulfonamide-Selective Ambient Mass Spectrometry Ion Source Obtained by Modification of an Iron Sheet with a Hydrophilic Molecularly Imprinted Polymer.

We have described a sulfonamide-selective ambient ion source coupled with electrospray ionization mass spectrometry (ESI-MS) for selective extraction and determination of trace sulfonamide antibiotics. It is obtained by modifying an iron sheet with a sulfadiazine-templated hydrophilic molecularly imprinted polymer (SF-HMIP). It behaves as both an online extractor and a MS ion source. Five sulfonamide antibiotics, including sulfamethoxazole (SMZ), sulfamerazine (SMR), sulfisoxazole (SIZ), sulfathiazole (ST), and sulfameter (SMD), were chosen to evaluate SF-HMIP coupled with ESI-MS, which showed good linearity in the range of 0.2-1000 ng/mL with correlation coefficient values (R2) over 0.9946. The limits of detection (LODs) for analysis of pure water and honey were in the range of 0.1-0.2 and 0.2-1.5 ng/mL, respectively. Limits of quantitation (LOQs) for analysis of pure water and honey were in the range of 0.3-0.5 and 1.0-5.0 ng/mL, respectively. The results demonstrated that SF-HMIP combined with ESI-MS could be applied for the direct analysis of five trace sulfonamide compounds in honey and pure water with recoveries ranging from 76 to 129%.

A bipolar membrane-based cation electrolytic membrane suppressor for ion chromatography.

A bipolar membrane (BPM)-based cation electrolytic membrane suppressor (CEMS) for ion chromatography is described. It has a sandwiched configuration, similar to that of commercial CEMS, except that a BPM and an anion exchange membrane (AEM) are respectively used to isolate the central eluent channel from two outer regenerant chambers. The AEM side of BPM is facing the central channel, contactless with the cathode. The suppression hydroxide ions are generated by enhanced water splitting at the junction layer of BPM. The suppressor showed comparable performance to common one in terms of suppressed background conductivity (∼0.38 µS/cm) and very low noise level (∼0.6 nS/cm). Possible electrochemically induced reductive deamination of AEM when immersed into the alkaline solution at the cathode can be avoided.

On-line preconcentration of protein in capillary electrophoresis with an end-column cellulose acetate-based porous membrane.

A simple on-line preconcentration method of protein for capillary electrophoresis (CE) using a cellulose acetate (CA)-coated porous membrane was proposed. CA membrane is fabricated at one of the ends of the column that allows the passage of buffer ions but excludes larger protein molecules. Protein sample is continuously electrokinetically loaded and trapped by the membrane. When injection is completed, the direction of the electric field is switched and the trapped proteins are then separated by conventional CE procedure. The results achieved showed that the preconcentration mechanism of this method was based on size-exclusion effect. Bovine serum albumin (BSA) was used for model protein sample, and signal enhancement of 550-fold with 15 min injection time was achieved.

A highly selective hydrophilic sorbent for enrichment of N-linked glycopeptides.

Selective enrichment and purification of N-glycopeptides from complex biological samples is often a necessary step for effective identification of low abundance glycopeptides. A polyethylenimine functionalized sorbent described here demonstrates good enrichment ability and excellent selectivity towards acidic glycopeptides (e.g. sialylated glycopeptides), even at 1:3000 mass ratio of target glycopeptides and non-glycopeptides, which is much more superior to commercial ZIC-HILIC and other reported sorbents. It also shows effective enrichment for neutral glycopeptides (IgG). Another desirable feature of such sorbent is its large binding capacity (∼220mg/g for fetuin).

A polyvinyl alcohol-functionalized sorbent for extraction and determination of aminoglycoside antibiotics in honey.

A novel highly hydrophilic sorbent simply prepared by coating polyvinyl alcohol (PVA) onto silica gel was used for extraction and determination of aminoglycoside antibiotics (AAs). The fabricated PVA coating is aimed to effectively protect core silica gel inside and offers good hydrophilic property. In combination of hydrophilic interaction chromatography tandem mass spectrometry, the performance of the sorbent was evaluated by selecting four model AAs (dihydrostreptomycin, streptomycin, kanamycin, spectinomycin). The sorbent was found to have effective adsorption ability to hydrophilic AAs, which was superior or comparable to those of commercial ones. Good recoveries (84-112%) of model AAs spiked in honey were obtained with good precision (<12.4%) and the limit of quantitation for the proposed method was in the range of 7.8-19.4ng/mL.

Simple preparation of solid-phase microextraction fiber with cation exchange capacities using poly(butadiene-maleic acid).

A simply way was proposed to prepare solid-phase microextraction (SPME) fiber with cation-exchange functional groups by the thermally initiated radical polymerization of poly(butadiene-maleic acid) (PBMA) copolymer onto a silica capillary. The capacity of the fiber coating could be easily controlled by fabricating successive layers of PBMA. The performance of the fiber combined with ion chromatography was evaluated by choosing Mg(2+) and Ca(2+) as model analytes; ∼13 and ∼51-fold enrichment factors for Mg(2+) and Ca(2+) were obtained, respectively.

Synthesis of molecularly imprinted polymer sorbents and application for the determination of aminoglycosides antibiotics in honey.

Aminoglycoside antibiotic (AA)-selective molecularly imprinted polymer (MIP) sorbent was synthesized by polymerization of methacrylic acid and ethylene glycol dimethacrylate in the presence of streptomycin as template molecule. The MIP sorbent was in detail characterized and its performance was evaluated by selecting four model AAs including streptomycin, gentamicin, spectinomycin and dihydrostreptomycin. Relative to non-imprinted polymer (NIP), the MIPs exhibited much higher recognizable capacity and specificity to the AAs and negligible adsorption for non-AAs as well. In combination of hydrophilic interaction liquid chromatography-tandem mass spectrometry (HILIC-MS/MS), the MIP sorbent-based solid phase extraction (SPE) was able to effectively determine the residue of four model AAs in honey samples with recovery ranging from 90% to 110%. The limit of detection (and the limit of quantitation) of streptomycin, gentamicin, spectinomycin and dihydrostreptomycin was 4.5 (15.0), 2.4 (8.0), 6.0 (20.0) and 1.8 (6.0) µg/kg, respectively. Relative standard deviations of intraday and inter-day assay under three spiked levels were 4.4-12.0% and 6.8-14.6%, respectively.

Preparation and evaluation of C10-cationic latex particle coated open-tubular column for capillary electrochromatography.

A simple way was proposed to prepare reverse phase open tubular column (OTC) for capillary electrochromatography (CEC) by dynamically coating cationic latex particles with C(10) functional groups onto the fused silica capillary with surface sulphonation. The latex particles are bounded into the capillary wall via electrostatic attraction force and demonstrate good stability under test conditions. Relative bare silica capillary, reverse electroosmotic flow (EOF) is generated for the OTC due to the existence of cationic latex particles onto the capillary. Preliminary separation of aromatic compounds on an OTC with 50 i.d. has been demonstrated.