The investigation of ion-exchange properties of novel zwitterionic and amphoteric stationary phases and their application to the separation of inorganic and organic ions

Over recent years development of ion chromatography (IC) has focused on new phase technologies to s~multaneously increase efficlency and vary selectivity. To increase selectlvlty it IS necessary to develop new selective ]on-exchangers by varying the nature of functional groups and the matrix of the statlonary phase. Zwittenonic ioncxchangcrs, where positlve and negatlve charges are located in close proxlmlty, exhibit potentla1 for selectivity optlm~sationin IC due to vanation of the ratio of electrostatic attract~onlrepulsion forces between analyte ions and ion-exchange groups. The main advantage of zwitterionic ion-exchangers is the possibility of their use for the simultaneous separation of catlons and anlons and the use of diluted elucnts, which significantly increases the sensltlvlty of detection and can contribute to the increased efficlency. Here various reversed-phase sorbents dynamically coated wlth N-(dodecyl-N,Nd~methylammonio)alcanoates were produced and charactensed. The ion-exchange properties of these new phases were investigated and the retention mechanism of Ions on these stationary phases elucidated. From investigations into the effect of pH, concentration, nature and charge of the eluent catlon on the retention of anions, it was shown that separation of anions occurs due to chaotropic interactions with quaternary ammonium groups, shlelded by external weak carboxylic acld groups, which themselves interact with eluent catlons according to increasing charge. These effects were exploited to demonstrate a previously unreported cation charge gradlent approach to anlon separations, resulting in considerable reductions in retention times whilst maintaining resolution. In addition, the new phases were used wlth a novel combined triple eluent concentration, pH and flow gradient technique for the simultaneous separation of 18 nucleotides, nucleosides and nucleobases and the method developed as applied to the separation of nucleic acids precursors in yeastolate samples. An nvestigation into the retention of transltlon metal cations was also made and it was hown that cations could be simultaneously separated with inorganic anions, as anlonlc complexes with the eluent anion, on the new zwitterionlc phase. This simultaneous separation of inorganic anions and cations was shown and optimised conditions were applied to the separation of anions and cations in a natural water sample. Finally, the application of short monolithic zwittenonlc columns for anion separations was investigated, w~ t hth e separation of 6 anions obtalned under flow gradlent conditions on a 4 mm - long column coated with N-(dodccyl-N,N-dimethylarnmonio)undecanoate and an application to the analysis of a sallne sample is shown

Gold nano-particle modified silica monolithic micro-columns for selected chromatographic and biological applications.

Monolithic microcolumns and especially silica monoliths are showing several advantages compared to classical particle packed and organic polymeric monolithic columns: ease of production and functionalisation, excellent mechanical and thermal stability. Morphology of the monolithic columns can easily be tuned by simply changing the compositions of reaction mixtures. High porosity and interconnected flow-through pores ensure low back pressures at higher flow rates so increasing reaction speeds. High salt resistance allows use water based buffer solutions without any swelling of the stationary phase, large biomolecules can be utilised and conditions to prevent denaturation and comformation changes of these biomolecules can be maintained. Introduction of gold nano-particles on the surfaces of silica monoliths allows increase of the surface areas and alows creation of new, exotic surfaces. Gold shows strong affinity towards thiol groups, which can be found in different biomolecules so utilisation of this phenomena would allow production of micro-reactors and bioreactors in order to mimic biological reactions happening in living organisms and large biological systems. Silica monoliths were synthesised using classical sol-gel process. In order to immobilise gold nano-particles, surfaces of the silica monoliths were amminated using standard silanisation reaction with 3-aminopropyl-methyl-diethoxysilane. 20 nm citrate stabilised gold nano-particles were immobilised on the surfaces afterwards. Depending on the desired application, gold nano-oparticle modified silica monoliths were functionalised afterwards. Immobilisation of ionic species such as amino acids and small peptides would allow creation of stationary phase for ion chromatography, retention of enzymes and other biologically active molecules would allow to create micro-reactors. Leaving gold nano-particles unmodified would make ideal stationary phase for micro-extraction. These modified monoliths were characterised using microscopy techniques, such as scanning electron microscopy (SEM) and field emission SEM. They were used to characterise morphology of the monoliths as well as to evaluate the coverage of the surface with gold nano-particles. The fabricated stationary phases were used for selected biological and chromatographic applications (incorporanting classical chromatographic techniques in order to evaluate the performance of these new modified monolithic materials)

Focussed ion beam serial sectioning and imaging of monolithic materials for 3D reconstruction and morphological parameter evaluation

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)

Segmentation effect on inhomogeneity of [110]-single crystal deformation

This work presents a detailed analysis of segmentation process in FCC single crystals with compression axis [110] and side faces( ̅110) and (001) considering effect of octahedral shear crystal-geometry and basic stress concentrators. Sequence of meso-band systems formation on side faces is determined. Macro-segmentation patterns are specified, that are common to the FCC single crystals under investigation. It is proved that rectangular shape of highly compressed crystals, elongated in direction of operating planes, is conditioned by orientation symmetry of compression axis, single crystal side faces and shears directions, which are characteristic for the given orientation. The specified patterns are characteristic only for the samples with initial height-to-width ratio equal to 2. When varying sample height relative to the initial one, segmentation patterns will also vary due to crystal geometry variations

Fabrication and characterization of nanotemplated carbon monolithic material

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

Comparative metal distribution in scalp hair of Pakistani and Irish referents and hypertensive patients

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 < 0.001); whereas, the concentration of zinc was lower in the scalp hair samples of hypertensive patients of both genders. The deficiency of zinc and the high exposure of trace and toxic metals may be the risk factors associated with hypertension

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 0C for each of 10 aligned Peltier units, with a ramp rate of approximately 400 0C/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

Parallel analysis of glycoproteins using lectin-functionalised monoPLOT columns integrated in micro-fluidic chips

Glycoprotein isolation, purification and analysis is critical in the production of biologics. Therefore, there is a growing interest in new methods and techniques that allow ultra fast analytical characterisation and detection of glycoproteins and their glycoforms in the biological samples employed within the biopharmaceutical industry. In that context, micro-fluidic devices offer a great potential owing to the very fast analysis they allow, the low sample/reagent consumption, the disposability, and the ease of integration with other analytical systems, among others. In this work, a micro-fluidic device integrating porous layer open tubular columns based on dimethacrylate monoliths (monoPLOT) and functionalised with Erythrina cristagalli lectin (ECL) were used for extraction of selected glycoproteins. Polymer monoliths are very versatile materials as they can be prepared with different porosities, pore sizes, and a wide variety of functionalities using many different precursors and chemistries. The monoPLOT columns were fabricated and functionalised off-chip, and then bonded to the channel walls before final channel lamination. In order to increase the monolith surface area, immobilisation of gold nano-particles (AuNPs) was carried out prior to covalent attachment of the ECL to the AuNPs. Detection was carried out with capacitively coupled contactless conductivity detection (C4D)

Controlled ultraviolet (UV) photoinitiated fabrication of monolithic porous layer open tubular (monoPLOT) capillary columns for chromatographic applications

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)