Chromatographic methods for the isolation, separation and characterisation of dissolved organic matter

This review presents an overview of the separation techniques applied to the complex challenge of dissolved organic matter characterisation. The review discusses methods for isolation of dissolved organic matter from natural waters, and the range of separation techniques used to further fractionate this complex material. The review covers both liquid and gas chromatographic techniques, in their various modes, and electrophoretic based approaches. For each, the challenges that the separation and fractionation of such an immensely complex sample poses is critically reviewed

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 (kCl) to α(CH2) was introduced as mixed-mode factor. The synergetic effect of electrostatic and hydrophobic interactions was observed

Preparation and properties of porous graphitic carbon monoliths embedded with nanodiamonds and other temperature-induced nano carbons

Porous graphitised carbon monoliths embedded with nanodiamonds (CMND) are presented in this work. Nanodiamond (ND) (sp3 carbon) has a variety of favourable properties including an interesting and tuneable surface chemistry, mechanical and thermal stability and conductivity. CMND was prepared using a hard templating method. Bare 5 μm silica particles and nanodiamonds (5-15 nm diameter) were added to the co-polymerisation mixture containing a resorcinol/iron(III) complex. Polymerisation of this mixture was followed by carbonisation at either 900 or 1250 °C under N2. Removal of the silica template and catalyst was achieved by hydrofluoric acid etching. A blank carbon monolith (CM blank) was also prepared using bare silica templates for comparative purposes. BET surface area measurements showed CMND to have a higher specific surface area than CM blank (400 m2/g and 349 m2/g respectively, with carbonisation at 900 °C). HRTEM and FESEM characterisation of CMND revealed a variety of interesting carbon nanostructures to be present in the monolith following carbonisation at 1250 °C. Apparent onion-like carbon (OLC), carbon nano-rods up to several μm in length and graphene sheets were observed. OLC clusters can be produced by a temperature-induced transformation of ND. The temperature of carbonisation was critical in the formation of these carbon nano-structures, as were the localised heating effects resulting from the thermal conductivity of ND. Carbon nano-structures have high surface areas and a high sorption capacity making them suitable for a variety of prospective applications. Porous graphitic carbons are also receiving significant research interest due to their high surface areas and bimodal pore structure which make them ideal for use in a variety of applications including energy storage, as electrode materials or as adsorbents in solid phase extraction

Geometrical Alignment of Multiple Fabrication Steps for Rapid Prototyping of Microfluidic Paper-Based Analytical Devices

Three main fabrication steps for microfluidic paper-based analytical devices (μPADs) were fully integrated with accurate geometrical alignment between the individual steps in a simple and rapid manner. A wax printer for creating hydrophobic barriers was integrated with an inexpensive (ca. $300) electronic craft plotter/cutter for paper cutting, followed by colorimetric reagent deposition using technical pens. The principal shortcoming in the lack of accurate and precise alignment of the features created by these three individual fabrication steps was addressed in this work by developing appropriate alignment procedures during the multistep fabrication process. The wax printing step was geometrically aligned with the following cutting and plotting (deposition) steps in a highly accurate and precise manner using optical scanning function of the plotter/cutter based on registration marks printed on the paper using the wax printer and scanned by the plotter/cutter. The accuracy and precision of alignment in a two-dimensional plane were quantified by cutting and plotting cross-shaped features and measuring their center coordinates relative to wax printed reference lines. The average accuracy along the <i>X</i>- and <i>Y</i>-axis was 0.12 and 0.16 mm for cutting and 0.19 and 0.17 mm for plotting, respectively. The potential of this approach was demonstrated by fabricating μPADs for instrument-free determination of cobalt in waters using distance-based readout, with excellent precision (%RSD = 5.7) and detection limit (LOD) of 2.5 ng and 0.5 mg/L (mass and concentration LODs, respectively)

Investigating the Effect of Column Geometry on Separation Efficiency using 3D Printed Liquid Chromatographic Columns Containing Polymer Monolithic Phases

Effect of column geometry on the liquid chromatographic separations using 3D printed liquid chromatographic columns with in-column polymerized monoliths has been studied. Three different liquid chromatographic columns were designed and 3D printed in titanium as 2D serpentine, 3D spiral, and 3D serpentine columns, of equal length and i.d. Successful in-column thermal polymerization of mechanically stable poly­(BuMA-<i>co</i>-EDMA) monoliths was achieved within each design without any significant structural differences between phases. Van Deemter plots indicated higher efficiencies for the 3D serpentine chromatographic columns with higher aspect ratio turns at higher linear velocities and smaller analysis times as compared to their counterpart columns with lower aspect ratio turns. Computational fluid dynamic simulations of a basic monolithic structure indicated 44%, 90%, 100%, and 118% higher flow through narrow channels in the curved monolithic configuration as compared to the straight monolithic configuration at linear velocities of 1, 2.5, 5, and 10 mm s^–1, respectively. Isocratic RPLC separations with the 3D serpentine column resulted in an average 23% and 245% (8 solutes) increase in the number of theoretical plates as compared to the 3D spiral and 2D serpentine columns, respectively. Gradient RPLC separations with the 3D serpentine column resulted in an average 15% and 82% (8 solutes) increase in the peak capacity as compared to the 3D spiral and 2D serpentine columns, respectively. Use of the 3D serpentine column at a higher flow rate, as compared to the 3D spiral column, provided a 58% reduction in the analysis time and 74% increase in the peak capacity for the isocratic separations of the small molecules and the gradient separations of proteins, respectively