Ekaterina P. Nesterenko

Zwitterionic ion-exchangers in ion chromatography: A review of recent developments.

Significant advances within the field of ion chromatography (IC) have often had their roots in research focussed on the development of new phase technologies, aimed to both simultaneously increase efficiency and vary selectivity. To increase selectivity it is necessary to develop new selective ion-exchangers, achieved by varying the nature of functional groups and the matrix of the stationary phase. In this comprehensive review, developments over the past decade in the production and application of zwitterionic and amphoteric ion-exchangers are presented and discussed. Zwitterionic and amphoteric ion-exchangers, where positive and negative charges are located in close proximity, exhibit alternative ion selectivity to standard anion and cation ion-exchangers, such as those traditionally used in IC, and have the potential for selectivity optimisation in IC due to control of the ratio of electrostatic attraction/repulsion forces between analyte ions and ion-exchange groups. This can result in the ability to utilise relatively dilute eluents, which increases detector sensitivity, with further advantages of zwitterionic ion-exchangers including their possible application to the simultaneous separation of cationic and anionic species.

Porous Graphitized Carbon Monolith as an Electrode Material for Probing Direct Bioelectrochemistry and Selective Detection of Hydrogen Peroxide

For the first time, graphitized carbon particles with a high surface area have been prepared and evaluated as a new material for probing direct electrochemistry of hemoglobin (Hb). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging revealed that the carbon monolithic skeleton was constructed by a series of mesopores with irregular shapes and an average pore diameter of ~5.6 nm. With a surface area of 239.6 m(2)/g, carbon particles exhibited three major Raman peaks as commonly observed for carbon nanotubes and other carbon materials, i.e., the sp(3) and sp(2) carbon phases coexisted in the sample. A glassy carbon electrode modified with carbon monoliths and didodecyldimethylammonium bromide exhibited direct electron transfer between Hb molecules and the underlying electrode with a transfer rate constant of 6.87 s(-1). The enzyme electrode displayed a pair of quasi-reversible reduction-oxidation peaks at -0.128 and -0.180 V, reflecting the well-known feature of the heme [Fe(3+)/Fe(2+)] redox couple: a surface-controlled electrochemical process with one electron transfer. This reagentless biosensing approach was capable of detecting H(2)O(2), a simple molecule but plays an important role in analytical and biological chemistry, as low as 0.1 μM with linearity of 0.1-60 μM and a response time of <0.8 s, comparing favorably with other carbon based electrodes (5 s).

Micro-bore titanium housed polymer monoliths for reversed-phase liquid chromatography of small molecules

A new method for the fixation of polymethacrylate monoliths within titanium tubing of up to 0.8 mm I.D. for use as a chromatographic column under elevated temperatures and pressures is described. The preparation of butyl methacrylate-ethylene dimethacrylate-based monolithic stationary phases with desired porous structures was achieved within titanium tubing with pre-oxidised internal walls. The oxidised titanium surface was subsequently silanised with 3-trimethoxysilylpropyl methacrylate resulting in tight bonding of butyl methacrylate porous monolith to the internal walls, providing stationary phase stability at column temperatures up to 110 degrees C and at operating column pressure drops of >28 MPa. The titanium housed monoliths exhibited a uniform and dense porous structure, which provided peak efficiencies of up to 59,000 theoretical plates per meter when evaluated for the separation of small molecules in reversed-phase mode, under optimal conditions (achieved at 15 microL/min and temperature of 110 degrees C for naphthalene with a retention factor, k=0.58). The developed column was applied to the reversed-phase isocratic separation of a text mixture of pesticides.

Monolithic porous layer open tubular (monoPLOT) columns for low pressure liquid chromatography of proteins

Glycidyl methacrylate-ethylene dimethacrylate (GMA-co-EDMA) based monolithic porous layer open tubular (monoPLOT) columns (0.05 mm I.D., monolithic layer thickness ≈ 5 µm) have been fabricated using an automated column scanning technique, providing UV polymerisation at 365 nm. Columns were chemically modified to obtain desired diol groups on the surface, and the longitudinal homogeneity of the stationary phase was profiled using scanning capacitively coupled contactless conductivity detector (sC4D), before and after such modification. Using the automated scanning polymerisation technique, column-to-column production reproducibility, including longitudinal phase thickness, was within ±5% RSD. The prepared columns were tested to evaluate their liquid chromatographic stationary phase selectivity, efficiency and reproducibility, with a series of test protein mixtures. Under optimised gradient conditions, the separation of up to 8 proteins was demonstrated on the open tubular column (510 × 0.05 mm I.D.), with a column pressure drop of <1.5 MPa.

Versatile Capillary Column Temperature Control Using a Thermoelectric Array Based Platform

A new direct contact platform for capillary column precise temperature control based upon the use of individually controlled sequentially aligned Peltier thermoelectric units is presented. The platform provides rapid temperature control for capillary and microbore liquid chromatography columns and allows simultaneous temporal and spatial temperature programming. The operating temperature range of the platform was between 15 and 200 °C for each of 10 aligned Peltier units, with a ramp rate of approximately 400 °C/min. The system was evaluated for a number of nonstandard capillary based applications, such as the direct application of temperature gradients with both linear and nonlinear profiles, including both static column temperature gradients and temporal temperature gradients, and the formation of in-capillary monolithic stationary phases with gradient polymerization through precise temperature control.

Holistic visualisation of the multimodal transport and fate of twelve pharmaceuticals in biosolid enriched topsoils

AbstractThe use of municipal biosolids as agricultural fertilisers has raised significant concerns in recent years. As part of this, the presence of complex mixtures of pharmaceutical residues and their effects on soil ecosystems remains particularly under-researched. This study focuses on the transfer of a selection of pharmaceutical residues from municipal sewage sludge to agricultural topsoils and their fate therein after an accelerated 6-month rainfall event. Twelve pharmaceuticals encompassing antibiotics, analgesics, anti-inflammatories, beta-blockers, hyperlipidaemics and stimulants were invesigated by employing a combination of extraction techniques and liquid chromatography-tandem mass spectrometry. Both liquid- and solid-phase pharmaceutical contents were analysed and pharmaceutical and personal care products quantified at defined timepoints to elucidate transport behaviour and transformation potential. Results show the distribution and separation of pharmaceuticals over a 100-mm soil depth following typical biosolid enrichment. Using experimentally determined solid–water partition coefficients (Kd) and hydrophobicity distribution ratios (Dow), mobility and modes of interaction under dynamic conditions are discussed. Finally, a brief study into the susceptibility of soil microbes is also presented. To our knowledge, this is the first investigation of pharmaceutical and personal care products release from amended biosolids to soils to include the factors and mechanisms governing their distribution and transformation even over relatively shallow depths. It applies multicompartmental and mass-balanced chemical analyses as well as microbiological approaches for a holistic view of these complex processes. FigureTransport behaviour and fate of pharmaceuticals in biosolid enriched topsoils

Preparation, characterisation and modification of carbon-based monolithic rods for chromatographic applications

A range of porous carbon-based monolithic (PCM) rods with flow-through pore sizes of 1, 2, 5 and 10 mum, were produced using a silica particle template method. The rods were characterised using SEM and energy-dispersive X-ray spectroscopy, BET surface area and porous structure analysis, dilatometry and thermal gravimetry. SEM evaluation of the carbon monolithic structures revealed an interconnected rigid bimodal porous structure and energy-dispersive X-ray spectroscopy analysis verified the quantitative removal of the embedded silica beads. The specific surface areas of the 1, 2, 5 and 10 mum rods were 178, 154, 84 and 125 m(2)/g after pyrolysis and silica removal, respectively. Shrinkage of the monolithic rods during pyrolysis is proportional to the particle size of the silica used and ranged from 9 to 12%. Mercury porosimetry showed a narrow distribution of pore sizes, with an average of approximately 700 nm for the 1 mum carbon monolith. The suitability of bare and surface oxidised PCM rods for the use as a stationary phase for reversed and normal phase LC was explored. The additional modification of PCM rods with gold micro-particles followed by 6-mercaptohexanoic acid was performed and ion-exchange properties were evaluated.

Separation of selected transition metals by capillary chelation ion chromatography using acetyl-iminodiacetic acid modified capillary polymer monoliths

Capillary housed laurylmethacrylate-co-ethylene dimethacrylate (LMA-co-EDMA) polymer monoliths were fabricated, functionalised with varying amounts of vinyl azlactone, followed by immobilisation of iminodiacetic acid (IDA), forming a range of acetyl-iminodiacetic acid (AIDA) functionalised monoliths, applied to the chelation ion chromatographic separation of selected transition and heavy metals. A number of monoliths of varying length and ligand density were prepared, resulting in increased cation retention and chromatographic resolution on those displaying the highest capacity. Ligand density and related column capacity were confirmed visually using scanning capacitively coupled contactless conductivity detection (sC(4)D) techniques. Column temperature studies to determine retention mechanism and the effect of temperature on the retention of Mn(II), Cd(II) and Cu(II) was investigated, showing an increase in retention with increased temperature for Cd(II) and Cu(II), whilst a decrease in retention was obtained for Mn(II). Isocratic capillary chelation ion chromatographic separations of Mn(II), Cd(II) and Cu(II) were obtained, with dual peak detection demonstrated using combined on-column C(4)D detection and UV-Visible detection following the post-capillary column reaction of the eluted metals with 4-(2-pyridylazo) resorcinol (PAR).

Microfluidic paper analytical device for the chromatographic separation of ascorbic acid and dopamine

Cellulose-based filter papers were used as base materials to construct microfluidic paper-based analytical devices (μPADs) coupling a separation channel with electrochemical detection. Channel widths were defined by hydrophobic wax, and gold-sputtering through a mask was used to pattern an electrochemical cell at the end of the channel. The physical properties and surface chemistries of various filter papers were studied with respect to the separation of ascorbic acid (AA) and dopamine (DA). Both porosity as well as the ion-exchange capacity of the filter papers were found to influence the separation. Under the conditions used, Whatman grade P81 strong cation exchange paper based on cellulose phosphate was found to fully retain DA. Detection of both AA and DA was achieved on the other filter papers, however, different behaviours were observed. Whatman 4 could not resolve AA from DA while VWR 413 could achieve baseline separation under the conditions used. Depending on the level of oxidative treatment that they undergo, cellulose papers can have carboxyl groups present on the fibres that can act as sources of ion-exchange sites, thus making these types of papers potentially useful for ion-exchange separations. The ion-exchange capacities of the filter papers were investigated and quantified. It was shown that the ion-exchange properties of the papers evaluated varied dramatically. Furthermore, eluent ionic strength and pH were optimised to achieve a baseline resolution of AA and DA. The limit of detection of DA was 3.41 μM when analysed in the presence of 1 mM AA showing the potential of this μPAD for the detection of catecholamines in biological samples containing high concentrations of AA.

Fabrication of Bonded Monolithic Porous Layer Open Tubular (monoPLOT) Columns in Wide Bore Capillary by Laminar Flow Thermal Initiation

A novel scalable procedure for the thermally initiated polymerisation of bonded monolithic porous layers of controlled thickness within open tubular fused silica capillaries (monoPLOT columns) is presented. Porous polymer layers of either polystyrene-divinylbenzene or butyl methacrylate-ethylene dimethacrylate, of variable thickness and morphology were polymerised inside fused silica capillaries utilising combined thermal initiation and laminar flow of the polymerisation mixture. The procedure enables the production through thermal initiation of monoPLOT columns of varying length, internal diameter, user defined morphology and layer thickness for potential use in both liquid and gas chromatography. The morphology and thickness of the bonded polymer layer on the capillary wall is strongly dependent on the laminar flow properties of the polymerisation mixture and the changing shear stress within the fluid across the inner diameter of the open capillary. Owing to the highly controlled rate of polymerisation and its dependence on fluid shear stress at the capillary wall, the procedure was demonstrably scalable, as illustrated by the polymerisation of identical layers within different capillary diameters.