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The comparative study of adsorption properties of several adsorbents with focus on selective isolation of water-soluble B vitamins (B2, B, B6 and B12) from food products and some pharmaceutical formulations by solid-phase extraction is performed. The adsorption of vitamins was investigated for eleven adsorbents including bare silica, silica modified with polyvinylpyrrolidone, octadecyl-, aminopropyl-, cyanobutyl-functional groups, poly(styrene–divinylbenzene) modified with lactam groups, hypercrosslinked polystyrene, activated carbon and porous microdispersed sintered detonation nanodiamond. Dynamic adsorption capacities of adsorbents for each of the tested vitamins were determined from the dynamic output curves. The highest adsorption capacity was found for HCPS-based sorbents, but complete desorption from these sorbents required harsh conditions. On this reason MSDN was suited better for the preconcentration of water soluble vitamins.

It is important to be able to control the physical and chemical integrity of carbon-based porous monolith structures while being tailored for targeted analytical, energy and catalytic based applications. A set up using a CO2 laser in continuous mode (CW CO2 laser) was implemented to cut fragile and porous carbon monolithic (CM) and nanotemplated carbon monolithic (NTCM) rods into discs with a prescribed thickness and dimensional integrity (denoted as LCM and LNTCM, or LCMs). Changes in structure, porosity and composition of LCMs were induced by the efficient thermal energy afforded by the CW CO2 laser irradiation under tightly controlled process conditions. The main effects observed before and after laser cutting were studied in comparison with traditional scalpel blade cutting of carbon monolithic (SCM). FE-SEM images confirmed that the resulting LCMs exhibited a more open, interconnected macroporous structure and smoothed mesopores to a depth of approximately 5 μm, while the structure of the bulk section remained intact. Minimal changes in chemical compositions were confirmed by XPS. Raman spectroscopy revealed a modest increase in the graphitic content on the cross sections of LCM discs. Phenol and Bisphenol A (BPA) was used as a model analyte for demonstration of resulting discs adsorption performance.

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 (kCl) to α(CH2) was introduced as mixed-mode factor. The synergetic effect of electrostatic and hydrophobic interactions was observed., Ion chromatography, Mixed-mode chromatography, Retention mechanism, Ion-exchange, Methylene selectivity, Hydrophobicity, Alkanoic acids, Alkanesulfonic acids.

New approaches for fabrication of centrifugal microfluidic platforms (μCDs) for sample micro-extraction and pre-concentration in bioanalytical and environmental applications are presented. The integration of both octadecylsilica (C18) micro-particulate and porous carbon monolithic stationary phases was demonstrated and on-disc extractions of analytes in samples of different nature were performed. A novel strategy based on the packing of micro-particulate stationary phases using porous organic polymer monoliths as column frits was demonstrated through the in situ photo-polymerisation of monolithic frits in a specific area of the micro-channel, thereby greatly facilitating stationary phase packing within μCD platforms. An enrichment factor of 3.7 was obtained for vitamin B12 following on-disc pre-concentration on the octadecylsilica columns. UV-Vis absorbance measurements were also performed in the outlet reservoir permitting quasi-on-line analysis of the small volume fractions collected after extraction, with limits of detection (LODs) found for vitamin B12 (LOD = 43 μM) being rather similar to those found with a commercially available spectrophotometer (LOD = 37 μM). Furthermore, the first integration of carbon monoliths within microfluidic channels is reported. Carbon monoliths were fabricated as rods and cut into discs for their integration within the microfluidic network, offering a highly porous bimodal structure with low flow-through back-pressures, excellent chemical stability as well as adequate mechanical stability. The carbon monolith-based μCD platform was evaluated as a rapid semi-automated pre-concentration approach suitable for in-field use prior to in-lab HPLC quantitation of pollutants at low concentration levels. Calculated mean recoveries for phenol from tap water spiked-samples by using this on-disc pre-concentration method were 68 ± 4% (n = 4, RSD = 5%).

A method using zinc powder in conjunction with the common Griess assay was developed for the detection of nitrate in water. This method is applicable to portable water test kits and allows for the accurate determination of nitrate in freshwater. The linear range for the method was shown to be 0.5–45 mg L−1 NO3− and the limit of detection (LOD) was 0.5 mg L−1 NO3−. The proposed method was validated over a five-day period and acceptable recovery and uncertainties were achieved when analysing freshwater matrices. The performance of the developed method was compared to an ISO-accredited ion chromatographic (IC) method by carrying out blind sample analysis. A good agreement between the two methods was achieved as comparable concentrations were determined using each method. In addition, the Zn method was compared to the performance of a novel solid-phase reagent method, previously developed within the group. The most accurate performance was demonstrated by the Zn powder method when analysing freshwater samples. The novel solid-phase reagent method demonstrated the greater accuracy when analysing seawater samples.

A non-toxic solid-phase test reagent for rapid determination of nitrite and nitrate was developed. Powdered reagent utilised azo- and diazo-components (p-nitroaniline and chromotropic acid, respectively), solid organic acid acidifier (malonic, maleic or oxalic acid), zinc dust (for nitrate determination), catalyst and masking agent. Effects of solid acidifier and the amount of Zn reducing agent were evaluated. The optimal reagent formulation was established in terms of dynamic range and response kinetics, and validated by parallel measurements in split samples using an accredited ion-chromatographic method. The optimal reagent contained malonic acid as acidifier and 1.0% of Zn reducing agent, and showed good sensitivity for the determination of nitrite (LOQ of 0.03 mg L−1) and nitrate (LOQ of 0.17 mg L−1), and fast analysis time of under 6 min. These reagents were shown to be stable for at least 3 months with RSD of

A novel, simple and highly sensitive electrochemical method is developed for the determination of ascorbic acid (AA) and uric acid (UA) based on a palladium nanoparticles deposited on porous graphitized carbon monolith modified carbon paste electrode (PdNPs/CM/CPE). The chemical modified electrode was characterized by scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The PdNPs/CM/CPE displayed excellent electrochemical catalytic activities toward AA and UA with bare CPE, PdNPs/CPE, CM/CPE and PdNPs/CM/CPE by cyclic voltammetry (CV). The oxidation potentials of AA and UA at the PdNPs/CM/CPE shifted negatively and the peak currents were much larger than other electrodes. The amperometric signal of PdNPs/CM/CPE showed a good linearity with correlation coefficient greater than 0.997. The low detection limits (S/N = 3) for AA and UA were 0.53 μmol L −1 and 0.66 μmol L −1 , respectively. The proposed method showed easy fabrication, high sensitivity and stability, and good reproducibility. In addition, the modified electrode was applied to determine the AA and UA in human serum sample.

Polymer monolithic open tubular columns are presented as a solid adsorbent for fast and efficient gas phase separations. A porous monolithic layer of polystyrene–divinylbenzene was formed inside a capillary through an in situ polymerisation method creating a long, open bore column with high flow through permeability. The mechanical stability and chromatographic performance of the column was tested, showing the phase to be extremely stable up to 270 °C and capable of fast separations with efficiencies of almost 4000 theoretical plates per meter.

Unique porous carbon monoliths containing thermally annealed carbon onions, were prepared from a resorcinol formaldehyde precursor rod, containing silica gel acting as a hard template, detonation nanodiamond, and Fe3+ as a graphitisation catalyst. Detonation nanodiamond was converted to carbon onions during controlled pyrolysis under N2, where the temperature cycle reached a maximum of 1250 °C. Thermal characterisation and high resolution electron microscopy have confirmed the graphitisation of nanodiamond, and revealed the resulting quasi-spherical carbon onions with an average particle size of 5.24 nm. The bimodal porous composite contains both macropores (5 μm) and mesopores (10 nm), with a BET surface area of 214 m2 g-1 for a nanodiamond prepared monolith (0.012 wt% nanodiamond in the precursor mixture), approximately twice that of blank monoliths, formed without the addition of nanodiamond, thus providing a new approach to increase surface area of such porous carbon rods. Raman spectroscopy and X-ray photoelectron spectroscopy also confirmed an enhanced graphitisation of the monolithic carbon skeleton resulting from the elevated thermal conductivity of the added nanodiamond. TEM imaging has confirmed the nanodiamond remains intact following pyrolysis at temperatures up to 900 °C.

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.

In this work, glassy carbon electrode (GCE) was modified with porous graphitized carbon monolith (CM) as a new nanomaterials and multi-walled carbon nanotubes (MWCNTs) for simultaneous determination of ascorbic acid (AA) and uric acid (UA). Scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were employed for the surface analysis of the modified electrodes. In this simultaneous detection, the electrochemical response of AA and UA on MWCNTs/GCE exhibited broad anodic peaks and were resolved into separated CV peaks at +45 mV and +254 mV, respectively. In comparison, two well resolved peaks of CM/GCE were obtained at -39 mV and +233 mV with flat base-lines for oxidation of AA and UA, respectively. Under the optimum conditions, the performance of porous graphitized carbon monolith were superior to MWCNTs modified glassy carbon electrode. For CM/GCE, the oxidation peak current was linearly dependent on AA and UA concentration in the range 0.195–4.04 mM and 0.094–1.90 mM, with the correlation coefficients ( R 2 ) greater than 0.997. Detection limits ( S / N = 3) were found 0.39 μM and 0.15 μM for AA and UA, respectively. The recoveries of the AA and UA from spiked human serum were 76.0–94.2%. In addition, the CM/GCE showed high sensitivity, good reproducibility and long-time stability at least 1 month without significant loss of electrochemical signal.

Coiled planar capillary chromatography columns (0.9 mm I.D. × 60 cm L) were 3D printed in stainless steel (316L), and titanium (Ti-6Al-4V) alloys (external dimensions of ~5 × 30 × 58 mm), and either slurry packed with various sized reversed-phase octadecylsilica particles, or filled with an in situ prepared methacrylate based monolith. Coiled printed columns were coupled directly with 30 × 30 mm Peltier thermoelectric direct contact heater/cooler modules. Preliminary results show the potential of using such 3D printed columns in future portable chromatographic devices.

This review covers the latest developments and applications of porous layer open tubular columns in capillary liquid chromatography. Here, the authors provide a concise background on the fundamentals of porous layer open tubular columns, their fabrication and application. Over the past two decades, growing interest in the areas of proteomics and hyphenated LC-MS techniques have played a large part in the development of porous layer structures within capillary formats due to their high permeability, excellent efficiency and exceptional peak capacity. This review gives a brief overview of open tubular columns in general, however, it focuses predominantly on the applications of covalently bonded porous layer open tubular columns in liquid chromatography. Open tubular columns containing non-bonded or electrostatically attached layers will not be discussed in detail.

Investigation into the development of a fabrication approach for capillary porous layer open tubular (PLOT) chromatographic columns via infrared (IR) photo-initiated polymerisation and the optimisation of the technique is presented in this work. Polyimide coatings on fused silica capillaries absorb strongly in the visible region of the light spectrum making commonly used ultra-violet and visible light photo-initiated polymerisation methods impossible inside this type of capillary. In addition, polystyrene-based materials, which are commonly used as reversed phases and hydrophobic substrates in both liquid (LC) and gas chromatography (GC) also absorb strongly in the ultra-violet (UV) region making them unsuitable for polymerisation via common photo-initiated methods. However, by using infrared light, photo-polymerisation in polyimide coated capillary was made possible herein. Crucially, selecting a suitable photo-initiator with a high extinction coefficient ensures that the penetration ability of the incident light is greatly reduced thus making the technique highly suited to PLOT column fabrication. The described procedure provides a straight forward method for the photoinitiated fabrication of monoPLOT columns in polyimide coated capillary.

Direct analysis of Ca 2+ and Mg 2+ is required for accurate determination of metastable carbonate mineral phase saturation states (ΩCaCO 3 ; ΩMgCO 3 ) in seawater, sediment porewaters, and other high ionic strength brines. To this end, we have implemented a method using High Performance Chelation Ion Chromatography ( HPCIC ) in which metal ion complexation at the stationary phase renders separation efficiency insensitive to high ionic strength matrix effects common to other ion chromatography (IC) methods. This method, using direct automated on-column injection, vastly increases sample throughput capacity in comparison to current titration methods. Calcium and magnesium ions in IAPSO standard seawater were selectively separated using a monolithic silica column (100 × 4.6 mm ID) activated with a covalently bonded iminodiacetic acid (IDA) chelator. The colored ion complexes resulting from post-column reaction (PCR) of the ions with a metallochromic indicator, in this case 4-(2-pyridylazo)-resorcinol (PAR), were detected spectrophotometricaly at 510 nm. Optimization of flow rate, eluent concentration, pH, and sample injection volume allowed baseline separation of Mg 2+ (0.05474 mol kg –1 ) and Ca 2+ (0.01065 mol kg –1 ) in less than 8 min using 2 μL seawater sample injections. At a flow rate of 1 mL min –1 , peak elutions occurred respectively at 4 and 5 min, using an eluent containing 0.1 M potassium chloride and 1 mM nitric acid adjusted to pH 2.5. Retention time variability below 0.5% for both metals following more than 200 injections indicates long-term stability of the derivatized monolithic silica column. Method application to marine sediment porewaters is discussed.

A new method for the fast direct chromatographic determination of strontium in seawater has been developed. Two coupled silica monolithic columns (total dimensions 200 × 4.6 mm I.D.) chemically modified with iminodiacetic acid (IDA) functional groups were used for baseline separation of all alkaline-earth metals in seawater in less than 4 min at flow rate of 4.0 mL min− 1, using an eluent containing 0.25 M sodium chloride and 2 mM glycolic acid, pH 5.11. Several colour-forming ligands, including o-cresolphthalein complexone (o-CPC), methylthymol blue (MTB), xylenol orange (XO), 4-(2-pyridylazo)resorcinol (PAR) and ZnEDTA–PAR were evaluated as reagents for post-column reaction (PCR) based spectrophotometric detection. Sensitivity of the developed method for strontium was at the low mg L− 1 level in undiluted seawater samples, in the presence of excessive amounts of calcium and magnesium, using post-column reaction detection with o-CPC at 570 nm. The method allowed quantitative determination of strontium in seawater samples (LOD 3.23 ± 0.15 mg L− 1, sr = 4.6%), with direct injection of just 4 μL of seawater onto the chromatographic column.

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.

Highly reproducible fabrication of porous layer open tubular (PLOT) structures in fused silica capillaries is often challenging; thus, methods to measure layer thickness growth in real time represent a powerful tool for the production of such columns. The work presented herein demonstrates the application of optical absorbance in the near-infrared (near IR) range for the in-process measurement of polymer layer growth inside fused silica capillaries during the fabrication of PLOT columns. The proposed technique can be used for both on- and off-line measurements of layer thickness for thermal- and photo- initiated polymerisation methods, performed in either polytetrafluoroethylene (PTFE)- or polyimide-coated capillaries. Measurements of layer thickness were carried out at λ 700 nm, using 100 μm and 8 μm optical fibres, yielding relative standard deviation (%RSD) values of 27% and 22%, respectively.

An automated column fabrication technique that is based on a ultraviolet (UV) light-emitting diode (LED) array oven, and provides precisely controlled "in-capillary" ultraviolet (UV) initiated polymerization at 365 nm, is presented for the production of open tubular monolithic porous polymer layer capillary (monoPLOT) columns of varying length, inner diameter (ID), and porous layer thickness. The developed approach allows the preparation of columns of varying length, because of an automated capillary delivery approach, with precisely controlled and uniform layer thickness and monolith morphology, from controlled UV power and exposure time. The relationships between direct exposure times, intensity, and layer thickness were determined, as were the effects of capillary delivery rate (indirect exposure rate), and multiple exposures on the layer thickness and axial distribution. Layer thickness measurements were taken by scanning electron microscopy (SEM), with the longitudinal homogeneity of the stationary phase confirmed using scanning capacitively coupled contactless conductivity detection (sC(4)D). The new automated UV polymerization technique presented in this work allows the fabrication of monoPLOT columns with a very high column-to-column production reproducibility, displaying a longitudinal phase thickness variation within ±0.8% RSD (relative standard deviation).

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.

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 of28 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.

A range of porous carbon-based monolithic (PCM) rods with flow-through pore sizes of 1, 2, 5 and 10 m, 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 m rods were 178, 154, 84 and 125 m2/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 700 nm for the 1 m 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.

The 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 (K (d)) and hydrophobicity distribution ratios (D (ow)), 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.

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.

The retention and separation selectivity of inorganic anions and on-column derivatised negatively charged citrate or oxalate metal complexes on reversed-phase stationary phases dynamically coated with N-(dodecyl-N,N-dimethylammonio)undecanoate (DDMAU) has been investigated. The retention mechanism for the metal-citrate complexes was predominantly anion exchange, although the amphoteric/zwitterionic nature of the stationary phase coating undoubtedly also contributed to the unusual separation selectivity shown. A mixture of 10 inorganic anions and metal cations was achieved using a 20 cm monolithic DDMAU modified column and a 1 mM citrate eluent, pH 4.0, flow rate equal to 0.8 mL/min. Selectivity was found to be strongly pH dependent, allowing additional scope for manipulation of solute retention, and thus application to complex samples. This is illustrated with the analysis of an acidic mine drainage sample with a range of inorganic anions and transition metal cations, varying significantly in their concentrations levels.

Short reversed-phase columns (50 mm x 4.6 mm Gemini C(18)) were dynamically coated with carboxybetaines of the general structure, C(12)H(25)N(+)(CH(3))(2)(CH(2))(n)COOH, namely (N-dodecyl-N,N-dimethylammonio)undecanoate, DDMAU (n=10) and (N-dodecyl-N,N-dimethylammonio)butyrate, DDMAB (n=3), and investigated for the separation of inorganic anions in ion chromatography. The role of the ionic strength of coating surfactant solutions on their adsorption and resultant column capacity was studied. The retention of inorganic anions was investigated with different eluents at various concentrations and pH. Interestingly, no retention for anions was found with pure water as the eluent, but the addition of small amounts of electrolytes, up to 0.1 mM, caused a sharp increase in the retention of analytes. The effect of increasing anion retention with an increase in eluent cation charge was also observed. Based on this effect a new cation charge gradient concept was proposed and applied to the separation of a standard mixture of anions.

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.

A significant effect of pore size on selec- tivity was observed for anion exchange on polyaspartic acid-coated silica (PolyCAT A). The retention order of halogenide anions, Cl �

A novel hierarchical nanotemplated carbon monolithic rod (NTCM) was prepared using a novel facile nanotemplating approach. The NTCM was obtained using C60-fullerene modified silica gels as hard templates, which were embedded in a phenolic resin containing a metal catalyst for localized graphitization, followed by bulk carbonization, and template and catalyst removal. TEM, SEM, and BET measurements revealed that NTCM possessed an integrated open hierarchical porous structure, with a trimodal pore distribution. This porous material also possessed a high mesopore volume and narrow mesopore size distribution. During the course of carbonization, the C60 conjugated to aminated silica was partly decomposed, leading to the formation of micropores. The Raman signature of NTCM was very similar to that of multiwalled carbon nanotubes as exemplified by three major peaks as commonly observed for other carbon materials, i.e., the sp3 and sp2 carbon phases coexisted in the sample. Surface area measurements were obtained using both nitrogen adsorption/desorption isotherms (BET) and with a methylene blue binding assay, with BET results showing the NTCM material possessed an average specific surface area of 435 m2 g(-1), compared to an area of 372 m2 g(-1) obtained using the methylene blue assay. Electrochemical studies using NTCM modified glassy carbon or boron doped diamond (BDD) electrodes displayed quasi-reversible oxidation/reduction with ferricyanide. In addition, the BDD electrode modified with NTCM was able to detect hydrogen peroxide with a detection limit of below 300 nM, whereas the pristine BDD electrode was not responsive to this target compound.

A new complexing adsorbent was prepared by chemical modification of mesoporous silica Kieselgel 60 (dp = 37–63 μm, average pore size 6 nm, specific surface area 425 m2 g−1) with 3-glycidoxypropyltrimethoxysilane and 2-[(phosphonomethyl)amino]acetic acid (PMA), commonly known as glyphosate. The prepared adsorbent was fully characterised using elemental analysis, thermal gravimetric analysis (TGA), acid–base potentiometric titration, Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption isotherms at 77 K (BET), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS). The concentration of bonded PMA groups calculated from the nitrogen content was 0.38 mmol per gram. The adsorption of transition metal ions on PMA functionalised silica (HEPMAS) was studied from aqueous solutions having different pH and the following selectivity was established, Zn(II) < Co(II) < Cd(II) < Mn(II) < Ni(II) < Cu(II). The calculated values of distribution coefficients D for the adsorption of ecotoxic metal ions on HEPMAS are 5.0 × 104, 4.9 × 105 and 2.6 × 104 for Zn(II), Pb(II) and Cd(II), respectively.

A new characterisation method, based on the utilisation of focussed ion beam-scanning electron microscopy (FIB-SEM), has been employed for the evaluation of morphological parameters in porous monolithic materials. Sample FIB serial sectioning, SEM imaging and image processing techniques were used to extract the pore boundaries and reconstruct the 3D porous structure of carbon and silica-based monoliths. Since silica is a non-conducting material, a commercial silica monolith modified with activated carbon was employed instead to minimise the charge build-up during FIB sectioning. This work therefore presents a novel methodology that can be successfully employed for 3D reconstruction of porous monolithic materials which are or can be made conductive through surface or bulk modification. Furthermore, the 3D reconstructions were used for calculation of the monolith macroporosity, which was in good agreement with the porosity values obtained by mercury intrusion porosimetry (MIP).

Bare core-shell silica (1.7μm) has been modified with iminodiacetic acid functional groups via standard silane chemistry, forming a new N-hydroxyethyliminodiacetic acid (HEIDA) functionalised core-shell stationary phase. The column was applied in high-performance chelation ion chromatography and evaluated for the retention of alkaline earth, transition and heavy metal cations. The influence of nitric acid eluent concentration, addition of complexing agent dipicolinic acid, eluent pH and column temperature on the column performance was investigated. The efficiencies obtained for transition and heavy metal cations (and resultant separations) were comparable or better than those previously obtained for alternative fully porous silica based chelation stationary phases, and a similarly modified monolithic silica column, ranging from ∼15 to 56μm HETP. Increasing the ionic strength of the eluent with the addition of KNO3 (0.75M) and increasing the column temperature (70°C) facilitated the isocratic separation of a mixture of 14 lanthanides and yttrium in under 12min, with HETP averaging 18μm (7μm for Ce(III)).

A new high performance chelation ion chromatography method was developed for the direct separation and detection of selected transition metals in shellfish (mussel) tissue digest samples. Using two different bonded silica monolithic chelating stationary phases, exhibiting differing selectivities for metals of interest, were applied within the method. The bonded chelating chemistries were N-hydroxyethyliminodiacetic (HEIDA) and N-(2-hydroxyethyl)-N-(2-[phosphonomethyl)amino]acetic (HEPMA) acids. Quantitative determination of Mn(II), Cd(II) and Zn(II) concentrations within shellfish tissue (Mytilus edulis), following microwave assisted acid digestion. Post-column detection was achieved using spectophotometric detection at 510 nm after reaction with 4-(2-pyridylazo) resorcinol. The eluents employed were 0.5 M KNO3, pH 2.4, for the HEIDA-bonded stationary phase, and 0.1 M KNO3, pH 2.6, for the HEPMA-bonded monolithic column. The HEPMA phase provided improved resolution between Mn(II) and interfering alkaline earth metal cations compared to the HEIDA-bonded phase. Concentrations of metals were determined using standard addition, and Cd(II), Mn(II), and Zn(II) cations were detected at

A commercially available porous silica monolithic column (Onyx Monolithic Si, 100 mm × 4.6 mm I.D.) was ‘in-column’ covalently functionalised with 2-hydroxyethyliminodiacetic acid (HEIDA) groups, and applied to the simultaneous and rapid separation of alkaline earth and transition metal ions, using high-performance chelation ion chromatography (HPCIC). With a 0.3 mM dipicolinic acid (DPA) containing eluent, the baseline separation of various common transition and heavy metal ions and the four alkaline earth metal ions could be achieved in under 14 min with a flow rate of just 0.8 mL/min. Detection was achieved using spectrophotometric detection at 540 nm after post-column reaction (PCR) with 4-(2-pyridylazo)-resorcinol (PAR). Significant effects from variation of eluent nature, concentration and temperature upon selectivity and retention were demonstrated with the new monolithic silica chelating phase. Under optimised conditions (0.165 M LiNO3 eluent, pH 2.5), peak efficiencies of 54,000, 60,000 and 64,000 N/m, for Zn2+, Mn2+ and Cd2+, respectively, were recorded, far exceeding that previously reported for IDA based chelation ion exchange columns.

Lauryl methacrylate-co-ethylene dimethacrylate monoliths were polymerised within fused silica capillaries and subsequently photo-grafted with varying amounts of glycidyl methacrylate (GMA). The grafted monoliths were then further modified with iminodiacetic acid (IDA), resulting in a range of chelating ion-exchange monoliths of increasing capacity. The IDA functional groups were attached via ring opening of the epoxy group on the poly(GMA) structure. Increasing the amount of attached poly(GMA), via photo-grafting with increasing concentrations of GMA, from 15 to 35 %, resulted in a proportional and controlled increase in the complexation capacity of the chelating monoliths. Scanning capacitively coupled contactless conductivity detection (sC4D) was used to characterise and verify homogenous distribution of the chelating ligand along the length of the capillaries non-invasively. Chelation ion chromatographic separations of selected transition and heavy metals were carried out, with retention factor data proportional to the concentration of grafted poly(GMA). Average peak efficiencies of close to 5,000 N/m were achieved, with the isocratic separation of Na, Mg(II), Mn(II), Co(II), Cd(II) and Zn(II) possible on a 250-mm-long monolith. Multiple monolithic columns produced to the same recipes gave RSD data for retention factors of

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).

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 of0.8 s, comparing favorably with other carbon based electrodes (5 s).

The abnormal metabolism of metal ions plays an important role in health and disease conditions, and studies about them have been attracting significant interest. The aim of our study was to assess the heavy metals (cadmium (Cd), nickel (Ni), lead (Pb), and zinc (Zn)) in scalp hair samples of 50 Irish and 78 Pakistani hypertensive patients of an urban population together with 50 Irish and 96 Pakistani non-hypertensive male subjects in the age group of 30–50 years. The concentrations of trace and toxic elements were measured by inductively coupled plasma–atomic emission spectrophotometer and atomic absorption spectrophotometer before microwave-assisted acid digestion. The validity and accuracy of the methodology were checked using certified reference materials, and by the conventional wet acid digestion method on the same certified reference materials and on real samples. The recovery of all the studied elements was found to be in the range of 97.5–99.7% in certified reference material. The results of this study showed that the mean values of cadmium, nickel, and lead were significantly higher in scalp hair samples of both Pakistani and Irish hypertensive patients than in referents (p

An RP monolithic column coated with an amphoteric carboxybetaine type surfactant has been used with a combined triple eluent concentration, pH and flow gradient ion chromatography technique for the simultaneous separation of up to 18 nucleotides, nucleosides and nucleobases. The separation of up to eight precursors on a 1 cm long monolithic microcolumn using the combined gradient approach is also shown. The method was applied to the separation of the above nucleic acid precursors in perchloric acid extracts of yeastolates samples.

A technique for the in-process measurement of polymer stationary phase growth inside fused silica capillaries during the fabrication of monolithic porous layer open tubular (monoPLOT) columns is presented. In this work, capacitively coupled contactless conductivity detection (C4D) was applied as an online measurement tool for porous polymer layer growth within fused silica capillaries. The relationship between effective capillary diameter and C4D response was investigated for two polymers, butyl methacrylate–ethylene dimethacrylate (BuMA–EDMA) and polystyrene–divinylbenzene (PS–DVB) over a range of capillary diameters and layer thicknesses. The described technique can be used with both thermal and photo-initiated approaches for monoPLOT fabrication and provides an accurate, real-time measurement of the porous layer growth within the capillary, which should vastly improve column-to-column reproducibility. The technique was shown to be very precise, with a measured %RSD < 10%.

This review covers the latest developments and applications of nano-materials in stationary phase development for various modes of high-performance liquid chromatography. Specific attention is placed upon the development of new composite phases, including the synthetic and immobilisation strategies used, to produce either encapsulated nano-particles, or surface attached nano-particles, layers, coatings and other structures. The resultant chromatographic applications, where applicable, are discussed with comment upon enhanced selectivity and/or efficiency of the nano-particle modified phases, where such effects have been identified. In the main this review covers developments over the past five years and is structured according to the nature of the nano-particles themselves, including carbonaceous, metallic, inorganic, and organopolymer based materials.

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