Inverse gas chromatography as a sensitive tool to assess changes in the surface properties of polysaccharides occurring during functionalization reactions
José António Ferreira Gamelas, Portugal
In this presentation, the results of the physico-chemical characterization of several types of polysaccharides by inverse gas chromatography (IGC), including wood xylans and derivatized xylans, bleached cellulosic pulps, and superhydrophobized cellulose will be presented and critically discussed. IGC presents as a sensitive tool to assess changes in the surface chemical properties of material’s occurring during functionalization reactions, enabling to obtain information not possible to access by other techniques. This includes, for instance, the Lewis acid-base behavior and nanoroughness parameters of the material’s surface. For instance, it was found that cellulose after treatment with trichloromethylsilane shows a decrease of the dispersive component of the surface energy (sd) from ca. 42 to 14 mJ m-2, but the Lewis acid-base character, significantly increased with silanization (!). Another interesting studied case was the derivatization of a xylan. It was found that carboxymethylation and hydroxypropylation decreased significantly the sd value of xylan: from 47.6 mJ m-2 in the original xylan to 33.0 and 23.5 mJ m-2 in carboxymethylxylan (CMX) and hydroxypropylxylan (HPX), respectively. As for the Lewis acid-base properties, HPX showed a perfectly amphoteric behaviour while the surfaces of unmodified xylan and CMX showed a prevalence of Lewis acidic character over the Lewis basic character, being, however, the surface of CMX less acidic than that of the original xylan. These works evidenced the major influence of the incorporation of several functional groups (even in a low extent) on the surface properties of polysaccharides.
A new wettability parameter based on iGC to characterize the flotation process for the separation of fine mineral particles
Martin Rudolph1, Bent Babel1, Robert Hartmann2, Tom Leistner1, Klaus Graebe1
1Helmholtz-Zentrum Dresden-Rossendorf, Helmholtz Institute Freiberg for Resource Technology, Freiberg, Germany
2University of Oulu, Fibre and Particle Engineering Research Unit, Oulu, Finland
Flotation is a heterocoagulation based separation process for fine particles in aqueous dispersions (size range approx. 5 µm < x
References
Colloids and Surfaces A (2017) Vol. 513, p. 380-388
International Journal of Multiphase Flow (2015) Vol. 71, p. 83-93
Minerals Engineering (2014) Vol. 66-68, p. 181-190
Inverse liquid chromatography in the study of physicochemical properties of hydroxyapatite-polymer monolithic columns
Katarzyna Adamska, Monika Pietrzyńska, Adam Voelkel, Poland
Institute of Chemical Technology and Engineering, Poznan University of Technology
In this work inverse liquid chromatography was applied for physicochemical characterization of the monolithic material. The examined material – polymer-hydroxyapatite monolithic filling constitutes a new class of materials, currently used for determination of the binding capacity (adsorption) of a potential antiresorptive agents to hydroxyapatite. Hydroxyapatite is a calcium phosphate with a composition the same as bone. The most commonly used antiresorptive agents are bisphosphonates, used in the treatment of bone diseases, mainly osteoporosis. They exhibit a high affinity for hydroxyapatite, and their pharmacological effects is associated both with binding to the mineral part of bone and influence on the bone cells, primarily osteoclasts. Many studies have been carried on to clarify the molecular interactions between bisphosphonates and mineral component of bone, but the process of their action is not completely understood yet.
Retention data obtained from ILC measurements were used to determine the physicochemical characteristics and surface energy of the monolithic material. The effect of the hydroxyapatite content in the monolithic materials for ability to interaction was also analyzed.
Acknowledgement
This work was supported by Poznan University of Technology 03/32/DSPB/0700 what is gratefully acknowledged.
Characterizing mineral surfaces and their interactions by inverse chromatography techniques
Matthias Kellermeier, Germany
Classical minerals like calcium carbonate or calcium sulfate continue to be in the focus of research for many modern technologies and applications. In order to understand and control the formation of such inorganic compounds under reactive conditions (e.g. during their beneficial crystallization in construction materials or their unwanted precipitation from hard water), it is essential to characterize the surface properties of these minerals and thus to identify suitable binding patterns that eventually may allow for the design of more efficient crystallization additives. Along the same lines, already grown (i.e. “non-reactive“) mineral particles can maintain various types of interactions with different components in commercial formulations, where they are used for example as an “inert“ filler. Here, new methods need to be found and/or developed to unravel the complex interplay between the solid inorganic phase and the multiple, mostly organic, species existing in solution.
The present contribution reports on the use of different chromatographic techniques for the characterization of inorganic minerals both in dry state (inverse gas chromatography, iGC) and in contact with an aqueous environment (inverse liquid chromatography, iLC). While iGC provides information on surface energetics and polarities across the distinct faces of typical crystals, iLC allows for an on-line monitoring of adsorption/desorption processes occurring when these surfaces interact with polymers and/or surfactants in a surrounding solution. The results obtained by these two rather uncommon methods are complemented by data produced with more conventional approaches to the analysis of surface energetics and interactions.
Characterization of metal-organic frameworks by IGC for preconcentration
Max Rieger, Germany
Any detector or sensor systems performance is mainly defined by its limit of detection (LOD) and selectivity for a particular analyte. Aiming at lower detection limits (for substances bearing very low vapor pressures, e.g. explosives) in the gas phase, the plurality of interfering substances (being existent in this area of high dilution) is strongly increased. A common approach towards enrichment is atmospheric sampling combined with successive thermal desorption. A suitable sorbent material with strongly analyte depending sorption behavior (reflected in e.g. respective Henry constants) will not only provide for a strong but also for a selective enrichment of target analytes. Exhibiting high surface area, micropore volume, crystallinity and chemical diversity, metal-organic frameworks (MOFs), a novel class of mostly microporous coordination polymers, are promising candidates to be used for a selective enrichment of airborne trace analytes. In order to evaluate them as preconcentration- or sampling-material (for gas phase sensing), inverse gas chromatography proves to be a fast and suitable pre-screening method. Retention volumes of different nitro-alkanes (model substances for nitrate-esters like nitroglycerine) are determined at different temperatures to obtain respective sampling and desorption volumes for e.g. thermal desorption based enrichment. Comparisons towards breakthrough and thermal desorption investigations (being more time consuming) are made. Using linear, saturated hydrocarbons as probe molecules, dispersive components of the surface energy were determined, along with the specific contribution of the nitro group itself. Commercially available, archetype MOFs (such as HKUST-1 or MIL-53) were investigated and compared to Tenax ® TA, a macroporous state-of-the-art sorbent.
Exploring grafting effects of trialkoxysilanes on porous glass surface – IGC in comparison to other methods
Ralf Meyer, Dr. Frank Bauer, Prof. Dr. Enke, Germany
Inverse gas chromatography is a well-established method for the characterization of the non-planar surface of fibers, granulates and porous materials. Especially porous glass is suitable for surface functionalization by versatile organo-substituted trialkoxysilanes. It possesses a homogenous pore system and an adjustable pore diameter. Surface modification agents enable the linkage of these specific morphologic properties with required surface characteristics, which is a crucial issue for numerous industrial, biological, and environmental applications of these materials.
For investigating the effects of grafted trialkoxysilanes on surface properties, CHN analysis, thermogravimetry, nitrogen sorption, and 29Si CP MAS NMR measurements were performed. In addition, IGC experiments allowed the determination of adsorption enthalpies of polar and non-polar probe molecules. According to these measurements, an observation of the surfaces energy changes by trialkoxysilane grafting is possible. Furthermore, probe molecules with acidic/basic character (see Fig. 1) allow the determination of the surfaces acid/base functionality as well as the calculation of acid-base components of solid surface energies. For polar probe molecules, there is a larger difference in adsorption enthalpies due to surface modification than for non-polar alkanes.
The total surface energy received from IGC measurements was compared with contact angle measurements. Changes in the energetic heterogeneity of the surface caused by the grafting process were shown by Finite Concentration measurements.