Fundamentals of chirality, resolution, and enantiopure molecule synthesis methods

The chirality of molecules is a concept that explains the interactions in nature. We may observe the same formula but different organizations revolving around the chiral center. Since Pasteur's meticulous observation of sodium ammonium tartrate crystals' structure, scientists have discovered many features of chiral molecules. The number of newly approved single enantiomeric drugs increases every year and takes place in the market. Thus, separation or resolution methods of racemic mixtures are of continued importance in the efficacy of drugs, installation of affordable production processes, and convenient synthetic chemistry practice. This article presents the asymmetric synthesis approaches and the classification of direct resolution methods of chiral molecules.

Hydrophobicity of polymer based anion-exchange columns for ion chromatography

The regularities of the retention of alkanoic and alkanesulfonic acids homologues were investigated for the set of 36 anion-exchange columns produced by various manufacturers. The role of hydrophobic and electrostatic interactions in the retention and separation of organic anions was studied. The methylene selectivity increments α(CH2) were measured for the studied columns with 10 mM sodium hydroxide eluent. The influence of matrix, surface area, polar group structure, ion-exchange capacity, the density of charged functional groups on the surface and other characteristics of anion-exchangers on resin hydrophobicity was considered. A unified approach for the measurements of hydrophobic properties of anion-exchange resins is proposed and the ratio of chloride retention factor (k Cl) to α(CH2) was introduced as mixed-mode factor. The synergetic effect of electrostatic and hydrophobic interactions was observed.

Enhancing Polyvalent Cation Rejection Using Perfluorophenylazide-Grafted-Copolymer Membrane Coatings

Surface modification offers a straightforward means to alter and enhance the properties and performance of materials, such as nanofiltration membranes for water softening. Herein, we demonstrate how a membrane's surface charge can be altered by grafting different electrostatically varying copolymers onto commercial membrane surfaces using perfluorophenylazide (PFPA) photochemistry for enhanced ion separation performance. The native membrane's performance-i.e., in terms of divalent cation separation-with copolymer coatings containing a positively charged quaternary ammonium (-N(Me)₃⁺), a negatively charged sulfonate (-SO₃^-), and an essentially neutral zwitterion (sulfobetaine, -N(Me)₂R₂⁺, and -SO₃^-), respectively, indicates that: (a) the sulfonated polymer induces robust Coulombic exclusion of divalent anions as compared to the negatively charged native membrane surface on account of its higher negative charge; (b) the positively charged ammonium coating induces exclusion of cations more effectively than the native membrane; and significantly, (c) the zwitterion polymer coating, which reduces the surface roughness and improves wettability, in spite of its near-neutral charge enhances exclusion of both divalent cations and anions on account of aperture sieving by the compact zwitterion polymer that arises from its ability to limit the size of ions that transport through the polymer along with dielectric exclusion. The outcomes thereby inform new pathways to achieve size- and charge-based exclusion of ionic, molecular, and other species contained in liquid streams.

Chiral Stationary Phases for Liquid Chromatography: Recent Developments

The planning and development of new chiral stationary phases (CSPs) for liquid chromatography (LC) are considered as continuous and evolutionary issues since the introduction of the first CSP in 1938. The main objectives of the development strategies were to attempt the improvement of the chromatographic enantioresolution performance of the CSPs as well as enlarge their versatility and range of applications. Additionally, the transition to ultra-high-performance LC were underscored. The most recent strategies have comprised the introduction of new chiral selectors, the use of new materials as chromatographic supports or the reduction of its particle size, and the application of different synthetic approaches for preparation of CSPs. This review gathered the most recent developments associated to the different types of CSPs providing an overview of the relevant advances that are arising on LC.

Adsorption and Selective Recovery of Citric Acid with Poly(4-vinylpyridine)

Citric acid (CA) is an important organic acid that is produced on a large scale by fermentation. Current methods to recover CA from the fermentation broth require large amounts of chemicals and produce considerable amounts of waste, while not all CA can be recovered. The use of adsorbents can increase the degree of product recovery and reduce chemical consumption and waste generation. In this work, poly(4-vinylpyridine) (PVP) is evaluated as an adsorbent for CA recovery. It has a high adsorption capacity (>30 wt %) at low pH and a high selectivity for CA at moderate pH in the presence of sulfate anions, two conditions that are frequently encountered during CA recovery. PVP could be efficiently regenerated after adsorption using simple alcohols like methanol and ethanol. Considering selectivity and regeneration, PVP distinctly outperforms more common adsorbents for organic acids, including commercial strongly and weakly basic anion exchangers. The desirable adsorptive features of PVP for CA can be attributed to the low basicity of the pyridine group.

Interactions of Anion-Exchange Resins with Polyacrylates in Atmosphere

The interactions of polyacrylates (PAs with mean molecular weight of 4.5, 25, and 250 kDa; Na⁺,pa^-) with anion exchange resins in the Br^- form (AXRs; -R⁺,Br^-) were studied under practical conditions by reaction stoichiometry and spectroscopy. The stoichiometric or an excess amount of PA(4.5 kDa) completely replaced Br- in the AXRs of the cross-linking degree of 2 or 8%, respectively, to give (-R⁺,pa^-), due to enhancement in selectivity of carboxylate group by multiple interactions. In contrast, PA(250 kDa) exchanged Br^- only on the surface of AXRs and did not penetrate into the resins; CO₂ was involved in the system to induce exchange with CO₃^2-. Using the slightly acidic condition caused substantially no exchange by CO₃^2- but induced coextraction of PA with proton as free Hpa. PA(4.5 kDa) once penetrating into the resin phase as (-R⁺,pa^-) or free Hpa was reversibly eluted under the appropriate conditions.

Anion Specificity of Polyzwitterionic Brushes with Different Carbon Spacer Lengths and Its Application for Controlling Protein Adsorption

Both ion-specific interaction and carbon spacer length have strong effects on the properties of polyzwitterions. In this work, we have investigated the anion specificity of poly(sulfobetaine methacrylamide) (PSBMAm) brushes with different carbon spacer lengths. The effectiveness of anions to enhance the hydration of the PSBMAm brushes increases from kosmotropic to chaotropic anions. The interactions between the anions and the PSBMAm brushes are strongly influenced by carbon spacer length because the strength of inter/intrachain association of the PSBMAm brushes decreases with increasing carbon spacer length. The inter/intrachain association of the PSBMAm brushes with a longer carbon spacer is easier to break by the external anions in the high salt concentration regime. On the other hand, a longer carbon spacer is more favorable for the zwitterionic groups to form cyclic intramolecular structures. As a result, the addition of anions can more effectively enhance the hydration of the PSBMAm brushes with a medium-length carbon spacer compared with that of the PSBMAm brushes with a either shorter or longer carbon spacer in the low salt concentration regime, determined by the balance between the inter/intrachain association and the formation of cyclic intramolecular structures. Our study also demonstrates that both anion identity and carbon spacer length can be used to control protein adsorption on the surface of the PSBMAm brushes.

Rheological behavior of hydrophobically modified polysulfobetaine methacrylate aqueous solution

Polysulfobetaine methacrylate (PSBMA) that was hydrophobically modified with methacrylic acid 2,3-epoxypropyl ester (GMA) was synthesized via micellar copolymerization method. Viscosity of the hydrophobically modified PSBMA solution was sensitive to added salt concentration.

Recent progress and applications of ion-exclusion/ion-exchange chromatography for simultaneous determination of inorganic anions and cations

One of the ultimate goals of ion chromatography is to determine both anions and cations found in samples with a single chromatographic run. In the present article, recent progress in ion-exclusion/ion-exchange chromatography for the simultaneous determinations of inorganic anions and cations are reviewed. Firstly, the principle and the control for the simultaneous separation and detection of analyte ions using ion-exclusion/cation-exchange chromatography with a weakly acidic cation-exchange column are outlined. Then, advanced chromatographic techniques in terms of analytical time, selectively and sensitivity are summarized. As a related method, ion-exclusion/anion-exchange chromatography with an anion-exchange column could be used for the simultaneous determination of inorganic nitrogen species, such as ammonium, nitrite and nitrate ions. Their usefulness and applications to water-quality monitoring and related techniques are also described.

Phase behavior of poly(sulfobetaine methacrylate)-grafted silica nanoparticles and their stability in protein solutions

Biocompatible and zwitterionic poly(sulfobetaine methacrylate) (PSBMA) was grafted onto the surface of initiator-modified silica nanoparticles via surface-initiated atom transfer radical polymerization. The resultant samples were characterized via nuclear magnetic resonance, Fourier transform infrared spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Their molecular weights and molecular weight distributions were determined via gel permeation chromatography after the removal of silica by etching. Moreover, the phase behavior of these polyzwitterionic-grafted silica nanoparticles in aqueous solutions and stability in protein/PBS solutions were systematically investigated. Dynamic light scattering and UV-visible spectroscopy results indicate that the silica-g-PSBMA nanoparticles exhibit an upper critical solution temperature (UCST) in aqueous solutions, which can be controlled by varying the PSBMA molecular weight, ionic strength, silica-g-PSBMA nanoparticle concentration, and solvent polarity. The UCSTs shift toward high temperatures with increasing PSBMA molecular weight and silica-g-PSBMA nanoparticle concentration. However, increasing the ionic strength and solvent polarity leads to a lowering of the UCSTs. The silica-g-PSBMA nanoparticles are stable for at least 72 h in both negative and positive protein/PBS solutions at 37 °C. The current study is crucial for the translation of polyzwitterionic solution behavior to surfaces to exploit their diverse properties in the development of new, smart, and responsive coatings.

Development and evaluation of new zwitterionic hydrophilic interaction liquid chromatography stationary phases based on 3-P,P-diphenylphosphonium-propylsulfonate

New zwitterionic stationary phases were synthesized by covalently bonding 3-P,P-diphenylphosphonium-propylsulfonate to silica gel. The resulting materials possess both a negatively charged sulfonate group and a positively charged quaternary phosphonium group, which means that there is no net charge over a wide pH range. The retention mechanism and chromatographic behavior of polar solutes under HILIC conditions were studied on these zwitterionic phases. Compared to the commercial ZIC-HILIC column and a bare silica gel stationary phase, the newly synthesized zwitterionic stationary phases provided greater retention, higher peak efficiency and better peak symmetry in the HILIC mode. The analytes examined included: β-blockers, nucleic acid bases and nucleosides, salicylic acid and its analogues, and water soluble vitamins. Factors, such as the type of organic modifiers, solvent composition, pH and the buffer concentration of the mobile phase, have been considered as potential variables for controlling the chromatographic retention of polar analytes.

Silica-based zwitterionic monolithic stationary phase for separation of neutral and ionized solutes using pressurized CEC

A porous zwitterionic monolith was prepared by in situ covalent attachment of lysine to a gamma-glycidoxypropyltrimethosysilane-modified silica monolith. The prepared column was used to perform neutral and ionized solutes separations by pressurized (pCEC). Due to the zwitterionic nature of the resulting stationary phase, the monolithic column provided both electrostatic attraction and repulsion sites for electrochromatographic retention for ionized solutes. Separation of several nucleotides was investigated on the monolithic column. It was shown that the nucleotides could be separated based on hydrophilic and electrostatic interactions between the stationary phase and analyte. Besides, the separation property of the zwitterionic silica monolith was compared with the use of diamine-bonded silica monolith as stationary phase. As expected, the lysine monolith exhibited a lower retention for the five nucleotides, which was due to the dissociation of the external carboxylic acid groups, leading to electrostatic repulsion with negatively charged solutes. Under the same experimental conditions, separation of the five nucleotides on the zwitterionic column was in less than 8 min, while that on the diamine column was in approximately 60 min.

High throughput methods for analyzing transition metals in proteins on a microgram scale

Transition metals are among the most common ligands that contribute to the biochemical and physiological properties of proteins. In the course of structural proteomic projects, the detection of transition metal cofactors prior to the determination of a high-resolution structure is extremely beneficial. This information can be used to select tractable targets from the proteomic pipeline because the presence of a metal often improves protein stability and can be used to help solve the phasing problem in x-ray crystallography. Recombinant proteins are often purified with substoichiometric amounts of metal loaded, so additional metal may be needed to obtain the homogeneous protein solution crucial for structural analysis. Furthermore, identifying a metal cofactor provides a clue about the nature of the biological role of an unclassified protein and can be applied with structural data in the assignation of a putative function. Many of the existing methods for transition metal analysis of purified proteins have limitations, which include a requirement for a large quantity of protein or a reliance on equipment with a prohibitive cost.The authors have developed two simple high throughput methods for identifying metalloproteins on a microgram scale. Each of the techniques has distinct advantages and can be applied to address divergent experimental goals. The first method, based on simple luminescence and colorimetric reactions, is fast, cheap, and semiquantitative. The second method, which employs HPLC separation, is accurate and affords unambiguous metal identification.

Preparation and evaluation of a silica-based 1-alkyl-3-(propyl-3-sulfonate) imidazolium zwitterionic stationary phase for high-performance liquid chromatography

A new zwitterionic stationary phase based on silica bonded with 1-alkyl-3-(propyl-3-sulfonate) imidazolium was synthesized and characterized in this paper. The materials have been confirmed and evaluated by elemental analysis, thermogravimetric analysis and X-ray photoelectron spectroscopy. Potassium and calcium were separated simultaneously with several common inorganic anions including an iodate, chloride, bromide, nitrate and iodide on the phase. The effects of the concentration, organic solvent and pH of the eluent on the separation of anions were studied. Operated in the anion-exchange mode, this new stationary phase shows considerable promise for the separation of anions. Bases, vitamins and three imidazolium ionic liquids with different alkyl chains are also separated successfully on this column. The stationary phase has multiple retention mechanisms, such as anion-exchange, electrostatic attraction and repulsion interactions, and hydrophobic interaction between the zwitterionic stationary phase and specimens.

Developments in ion chromatography using monolithic columns

The focus of this review is on current status and on-going developments in ion chromatography (IC) using monolithic phases. The use and potential of both silica and polymeric monoliths in IC is discussed, with silica monoliths achieving efficiencies upwards of 10(5) plates/m for inorganic ions in a few minutes or less. Ion exchange capacity can be introduced onto the monolithic columns through the addition of ion interaction reagents to the eluent, coating of the monolith with ionic surfactants or polyelectrolyte latexes, and covalent bonding. The majority of the studies to date have used surfactant-coated columns, but the stability of surfactant coatings limits this approach. Applications of monolithic IC columns to the separation of inorganic anions and cations are tabulated. Finally, a discussion on the recent commercialization of monolithic IC columns and the use of monolithic phases for IC peripherals such as preconcentrator columns, microextractors and suppressors is presented.

Reconciling Low- and High-Salt Solution Behavior of Sulfobetaine Polyzwitterions

We investigate the water-solubility upon salt additions, of homogeneous families of sulfobetaine-based polyzwitterions. These polymers bear both positive ammonium, and negative sulfonate charges on each monomer and as a result present an upper critical solution temperature (UCST) in the 0-100 degrees C temperature range. Two chemistries are investigated, with either a carboxylate-carrying function (SPE) or an amido-carrying one (SPP). In agreement with the literature published on pSPEs, we find that an addition of simple salts improves the water-solubility of pSPEs, as well as that of pSPPs, yet only once a threshold concentration of added salt has been reached in the solution. We verify using scaling arguments that the onset of solubility promotion, corresponds exactly to the complete screening of the attraction between positive and negative charges inside a polyzwitterionic coil. On the contrary, for salt concentrations smaller than the threshold concentration, we observe that an addition of salt can be adverse to the solubility of polyzwitterions, depending on the degree of polymerization, the type of salt, and the type of zwitterionic motive. Thanks to zeta-potential measurements and systematic variations of these three parameters, we demonstrate, in agreement with theoretical prediction, that this molecular weight-dependent enhanced solubility at small salt concentrations is due to charge asymmetry resulting from partial hydrolysis, combined with specific interactions between salts and zwitterion constituents, evidencing the complexity of the solution behavior of these macromolecules. We thereby reconcile the different behaviors in the domains of low- and high-salinity.

Separation of basic and acidic compounds by capillary electrochromatography using monolithic silica capillary columns with zwitterionic stationary phase

A novel monolithic silica column with zwitterionic stationary phase was prepared by in-situ covalent attachment of phenylalanine to a 3-glycidoxypropyltriethoxysilane-modified silica monolith. Due to the zwitterionic nature of the resulting stationary phase, the density and sign of the net surface charge, and accordingly the direction and magnitude of electroosmotic flow in this column during capillary electrochromatography could be manipulated by adjusting the pH values of the mobile phase. CEC separations of various acidic and basic compounds were performed on the prepared column in anodic and weakly cathodic EOF modes, respectively. The peak tailing of basic compounds in CEC on a silica column could be alleviated at optimized buffer compositions. Besides the electrophoretic mechanism and weak hydrophobic interaction, weak cation- and anion-exchange interactions are also involved in the separations of acids and bases, respectively, on the zwitterionic column.

Zwitterionic stationary phase with covalently bonded phosphorylcholine type polymer grafts and its applicability to separation of peptides in the hydrophilic interaction liquid chromatography mode

A novel phosphorylcholine type zwitterionic stationary phase was synthesized by graft polymerization of 2-methacryloyloxyethyl phosphorylcholine onto the surface of porous silica particles. The resulting material possesses both negatively charged phosphoric acid and positively charged quaternary ammonium groups, which renders it a low net charge over a wide pH range. The composition of the surface grafts were determined by elemental analysis and solid state NMR, and the surface charge (zeta-potential) in different buffer solutions were measured using photon correlation spectroscopy. Separation of several peptides was investigated on packed columns in the hydrophilic interaction liquid chromatography (HILIC) separation mode. It was shown that small peptides can be separated based on hydrophilic interaction and ionic interaction between the stationary phase and analyte. The organic solvent composition, the pH and the salt concentration of the eluent have strong effects on the retention time. Compared to native silica before grafting, the newly synthesized zwitterionic material gave more stable retention times for basic peptides over pH range 3-7 due to elimination of the dissociation of silanol groups.

Double gradient ion chromatography using short monolithic columns modified with a long chained zwitterionic carboxybetaine surfactant

The rapid separation of inorganic anions on short monolithic columns permanently coated with a long chained zwitterionic carboxybetaine-type surfactant is shown. The surfactant, N-dodecyl-N,N-(dimethylammonio)undecanoate (DDMAU), was used to coat 2.5, 5.0 and 10 cm long reversed-phase silica monoliths, resulting in a permanent zwitterionic exchange surface when used with aqueous based eluents. The unique structure of the surfactant results in a charge double layer structure on the surface of the stationary phase, with strong internal anionic and weak external cationic exchange groups. The dissociation of the weak external carboxylic acid group acts to shield the inner anionic exchange site, resulting in substantial effective capacity changes with eluent pH. Utilising this effect with the application of an eluent pH gradient, simultaneously combined with eluent flow-rate gradients, very rapid simultaneous separations of both weakly retained anions and strongly retained polarisable anions was possible, with up to 10-fold decreases in overall run times. Coating stability and retention times under isocratic and isofluentic eluent conditions were shown to be reproducible over >450 repeat injections, with peak efficiency values averaging 29,000 N/m for the 2.5 cm column and 42,000 N/m for the 10 cm monolithic column, again under isocratic elution conditions.

Separation of isomeric 2-aminopyridine derivatized N-glycans and N-glycopeptides of human serum immunoglobulin G by using a zwitterionic type of hydrophilic-interaction chromatography

Isomeric oligosaccharides and isomeric glycopeptides are sometimes difficult to separate on normal-phase (NP) and reversed-phase (RP) columns. A zwitterionic type of hydrophilic-interaction chromatography column with sulfobetaine groups (called ZIC-HILIC column) was first applied to the separation of 2-aminopyridine derivatized (PA) N-glycans and tryptic peptides of human serum immunoglobulin G (IgG). It is shown that the ZIC-HILIC column has high capability for structural recognition of isomeric N-glycans as well as high selectivity for glycopeptides. The former feature (i.e., structural recognition) was proven by sufficient separation of neutral PA N-glycan isomers, which are usually difficult to separate on NP and RP columns. In addition, it is noteworthy that IgG glycopeptides consisting of isomeric N-glycans and the same peptide sequences can be sufficiently separated on a ZIC-HILIC column. The latter feature (i.e., selectivity) was also demonstrated by easily separating two peptide groups with/without N-glycans. Thus, we note that the ZIC-HILIC column is highly promising for a simple analysis of N-glycans and N-glycopeptide samples.

Zwitterionic Metalates of Group 11 Elements and Their Use as Metalloligands for the Assembly of Multizwitterionic Clusters

Reaction of RNHC(S)PPh2NPPh2C(S)NR (HRSNS; R = Me, Et) with M(I) (M = Cu, Ag, Au) salts afforded zwitterionic complexes of the general formula [M(RSNS)] (M = Cu, Ag, Au). The ligand was found in the solid state in S,S-kappa2 and S,N,S-kappa3 coordination fashions. [Cu(RSNS)] and [Ag(RSNS)] can be used as metalloligand building blocks for the assembly of pentanuclear multizwitterionic Cu5, Cu3Ag2 and Ag5 core clusters of the general formula [M'2{M(RSNS)}3]2+ (M = Cu, M' = Cu, Ag; M = M' = Ag) upon reaction with suitable M' salts. The crystal structures of the most significant compounds are reported herein. Compound [Ag2{Ag(RSNS)}2(OTf)2] was also isolated and structurally characterized, representing a model for the intermediate species of the aforementioned assembly.

Fast ion chromatography of inorganic anions and cations on a lysine bonded porous silica monolith

A 0.46 cm x 10.0 cm silica monolith column was modified through the in situ covalent attachment of lysine (2,6-diaminohexanoic acid) groups. Due to the zwitterionic nature of the resultant stationary phase, the modified monolithic column contained both cation and anion exchange capacity. In the case of cation exchange, the capacity was found to be relatively low at between 5 and 6.5 micromoles Me2+ per column. However, as expected, the lysine monolith exhibited a higher anion exchange capacity at 12-13 micromoles A- per column (at pH 3.0), which was found to be dependent upon column pH, due to the dissociation of the weak acid carboxylic acid groups. High-performance separations of transition metal cations and inorganic anions were achieved using the modified monolith, with the effects of eluent concentration, pH and flow rate evaluated. Using elevated flow rates of up to 5 mL/min the separation of nitrite, bromate, bromide, nitrate, iodide and thiocyanate was possible in approximately 100 s with peak efficiencies of between 50 and 100,000 N/m and retention time %RSD of under 0.3%.

Zwitterionic ion chromatography with carboxybetaine surfactant-coated particle packed and monolithic type columns

Both particle packed (25 cm x 0.46 cm I.D. SUPELCOSIL 5 microm C18) and monolithic type (10 cm x 0.46 cm I.D. Merck Chromolith Performance C18) reversed-phase substrates were dynamically coated with a carboxybetaine type zwitterionic surfactant ((dodecyldimethyl-amino) acetic acid) and investigated as stationary phases for use in zwitterionic ion chromatography (ZIC). Investigations into eluent concentration and pH were carried out using KCl eluents containing 0.2 mM of the carboxybetaine surfactant to stabilise the column coatings. It was found that eluent concentration decreased anion retention whilst simultaneously increasing peak efficiencies, which may be due to the dissociation of intra- and inter-molecular salts of the carboxybetaine surfactant under higher ionic strength conditions. The Effect of eluent pH was an increase in anion retention with decreased eluent pH due to the increased protonation of the weak acid terminal group of the carboxybetaine, causing both a relative increase in the positive charge of the stationary phase and less repulsion of the anions by the dissociated weak acid group. The carboxybetaine-coated monolithic phase was applied to rapid anion separations using elevated flow rates and flow rate gradients.

A high-performance liquid chromatography method for determining transition metal content in proteins

Transition metals are common components of cellular proteins and the detailed study of metalloproteins necessitates the identification and quantification of bound metal ions. Screening for metals is also an informative step in the initial characterization of the numerous unknown and unclassified proteins now coming through the proteomic pipeline. We have developed a high-performance liquid chromatography method for the quantitative determination of the most prevalent biological transition metals: manganese, iron, cobalt, nickel, copper, and zinc. The method is accurate and simple and can be adapted for automated high-throughput studies. The metal analysis involves acid hydrolysis to release the metal ions into solution, followed by ion separation on a mixed-bead ion-exchange column and absorbance detection after postcolumn derivatization with the metallochromic indicator 4-(2-pyridylazo)resorcinol. The potential interferences by common components of protein solutions were investigated. The metal content of a variety of metalloproteins was analyzed and the data were compared to data obtained from inductively coupled plasma-atomic emission spectroscopy. The sensitivity of the assay allows for the detection of 0.1-0.8 nmol, depending on the metal. The amount of protein required is governed by the size of the protein and the fraction of protein with metal bound. For routine analysis 50 microg was used but for many proteins 10 microg would be sufficient. The advantages, disadvantages, and possible applications of this method are discussed.

Novel ion chromatographic stationary phases for the analysis of complex matrices

Ion chromatography (IC) has a proven track record in the determination of inorganic and organic anions and cations in complex matrices. Recently, application of IC to the separation and determination of bio-molecules such as amino acids, carbohydrates, nucleotides, proteins and peptides has also received much attention. The key to the determination of all of the above species in the most analytically challenging complex matrices is the ability to manipulate selectivity through control of stationary phase chemistry, mobile phase chemistry and the choice of detection method. This Tutorial Review summarises some of the most significant recent advances made in IC stationary phase technology. In particular, the review details stationary phases specifically designed for ion analysis in complex sample matrices, and considers in which direction future stationary phase development might proceed.

Control of electroosmotic flow and wall interactions in capillary electrophoresis capillaries by photografted zwitterionic polymer surface layers

A novel capillary with covalently bonded zwitterionic surface modification was prepared by photograft polymerization of the zwitterionic monomer N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl)ammonium betaine, onto the inner surface of a UV-transparent fused-silica capillary. Although the zwitterionic moieties in the resulting polymeric "tentacles" comprise both a positive quaternary ammonium group and a negative sulfonate group, the coating has a net zero charge. The electroosmotic flow (EOF) was therefore extensively suppressed on the grafted capillary compared to the native silica capillary and to the silica capillary that had been activated for graft polymerization by reaction with 3-(methacryloyl)oxypropyltrimethoxysilane. It was also found that the EOF can be varied by adding chaotropic anions or divalent cations such as perchlorate ion and magnesium ion to the running buffer, due to the interaction between these ions and zwitterionic functional group. This provides a new way of altering the EOF and the wall interaction without changing the pH or the overall ionic strength of the separation buffer. The influence of pH and ionic strength of separation buffer on the EOF were also investigated to optimize the separation conditions. Good separations of a mixture containing eight inorganic anions were achieved within 5 min under optimal conditions by capillary zone electrophoresis. The newly prepared capillary was also well suited for the separation of peptides or proteins.