Impact of the Polymer Backbone Structure on the Separation Properties of New Stationary Phases Based on Tricyclononenes.

The main purpose of this paper is to compare the chromatographic properties of capillary columns prepared with polymers with different backbone structures and to demonstrate the possibility of polymer differentiation via inverse gas chromatography. With the use of addition and metathesis types of polymerization of tricyclononenes, two new stationary phases were prepared. The metathesis polymer contained double bonds in the polymeric backbone while the backbone of the addition polymer was fully saturated and relatively mobile. A comparison of the separation and adsorption properties of new phases with conventional gas chromatography (GC) stationary phases clearly indicated their non-polar characteristics. However, the difference in the polymer structure appeared to have very little effect on the stationary phase separation properties, so other parameters were used for polymer characterization. The thermodynamic parameters of the sorption of alkanes and aromatic compounds in both polymeric stationary phases were also very similar; however, the entropy of sorption for hydrocarbons with seven or more carbon atoms was different for the two polymers. An evaluation of the specific surface energy of the stationary phases also allowed us to discriminate the two stationary phases.

Preparation and properties of GC capillary column with hypercrosslinked stationary phase.

For the first time, highly porous hypercrosslinked polystyrene layer was synthesized within a gas chromatography capillary column and successfully deposited onto the capillary walls generating porous layer open-tubular capillary column. Elaborated three steps synthetic procedure provides tightly bonded porous polymeric layer and ensues complete elimination of particle shedding and the needs for particle traps. Due to highly developed surface area, porous layer open-tubular column provides strong solute retention that is useful for the separation of various volatile solvents and light gas compounds including ethane, ethylene, ethyne. Aqueous injections will not harm the column.

Chromatographic Method for Evaluation of Polymeric GC Stationary Phases Ageing Using the Novel Non-Cross-Linked Poly(3-(Tributoxysilyl)Tricyclononene-7) as the Model Stationary Phase.

The chromatographic properties and thermal stability are investigated for the polymeric stationary phase based on the norbornene polymer. It was shown that without additional cross-linking, poly(3-(tributoxysilyl)tricyclononene-7) demonstrates properties similar to liquid chromatographic stationary phases. It was also found to be more thermally stable than previously studied trimethylsilyl- and trimethoxysilyl- derivatives. The long-term heating at 170 °C resulted in an increase of mass transfer rate between stationary and mobile phases which could be observed as a decrease of parameter C of Van Deemter equation. This effect is rather unusual, as the polymeric stationary phases tend in decrease of the layer volume and porosity while ageing. Additionally, the values of thermodynamic parameters of sorption are calculated for the polymeric stationary phase: enthalpy of sorption varied -28 to -37 kJ/mol, entropy change was -41 to -51 J/mol K. The compensation curves were plotted for the alkanes, arenes, and alcohols, and the parameters of compensation plot were calculated, demonstrating the different sorption mechanisms both for hydrocarbons and oxygen-containing compounds, and different classes of organic compounds.

Separation of polystyrenes by means of open tubular capillary chromatography.

Simulating polymer separation in flow-through channels of monolithic columns, separation of a mixture of polystyrene standards was investigated using open tubular capillary column of 2 µm inner diameter. High column efficiency was observed for polymers of molar mass ranged from few tens to few hundred kDas. Column efficiency significantly decreased for polymers with molar mass larger than 500 kDa nevertheless preserving value of few tens of thousands theoretical plates. Calibration curve observed for open capillary column is rather steep and can be well described by simple equation without quadratic term. In spite of low selectivity, capillary columns were able in separating wide range of polystyrene standards due to column high efficiency and in such a way supported an idea of hydrodynamic mechanism of polymer separation in flow-through channel of monolithic packings.

Enthalpy-entropy compensation effect on adsorption of light hydrocarbons on monolithic stationary phases.

Enthalpy and entropy of adsorption of light hydrocarbons C1-C4 have been measured for three monoliths of different polarity and for five different carrier gases: helium, hydrogen, nitrogen, carbon dioxide and dinitrogen oxide. Using carrier gas helium the highest values of enthalpy and entropy were observed for monolith based on ethylenedimethacrylate and the lowest values were observed for monolith based on silica, while monolith based on divinylbenzene demonstrated intermediate values. Entropy-enthalpy correlations were observed with carrier gas helium for all thee monoliths and possess similar slope indicating similar adsorption mechanism on all monoliths studied. Comparing different carrier gases entropy-enthalpy correlations within a homological series of solutes were observed for light carrier gases (He, H2 and N2) and were not observed for heavy carrier gases (CO2 and N2O). Instead, entropy-enthalpy correlations for heavy carrier gases were observed with pressure as variable and the higher the carrier gas pressure the lower the values of enthalpy and entropy observed. The observed changes in entropy-enthalpy correlations were explained by competitive adsorption of heavy carrier gas on monoliths.

Comparison of nonporous silica-based ion exchangers and monolithic ion exchangers in separations of inorganic anions.

Low capacity anion exchangers for IC have been prepared by modification of nonporous uniformed silica MICRA microbeads and by modification of the organic polymeric monolithic matrixes prepared in situ in quarz capillary. Due to the small particle size (1.5 microm) high-performance adsorbents were prepared allowing to obtain up to 190,000 tp/m. However, the column possesses a very high back-pressure and can be used in a short length up to 50 mm only to meet the requirements of conventional chromatographic equipment. An analysis of a test mixture of seven anions was completed within 3 min with a back column pressure of about 350 bar (HETP of about 5.5 microm, where HETP is the height equivalent to the theoretical plate). Monolithic capillary columns provide lower efficiency per column unit length than MICRA columns; however, they can be used at a longer length because of their low flow resistance. Monolithic column of ca. 40 cm length has workable pressure below 10 bar and allows separation of a five anions test mixture within less than 10 min. A better efficiency of monolithic column (HETP approximately 75 microm) can be achieved at reduced flow rates when the analysis time is not a critical parameter.

Poly[1-(trimethylsilyl)-1-propine] as chromatographic adsorbent and prospects of its application in packed and capillary columns.

The application of film-forming organic polymers, which are in common use in membrane technology, as chromatographic adsorbents for packed and capillary columns has been suggested. The chromatographic characteristics of poly[1-(trimethylsilyl)-1-propine] (PTMSP) as an adsorbent were studied. The film-forming properties of PTMSP simplify manufacturing of capillary and packed gas-solid columns. It was shown that separation of C1-C4 hydrocarbon gases on the columns with PTMSP is of practical interest. In the authors' opinion, PTMSP is also promising for the separation of inorganic gases.