Synthesis and Evaluation of Silica Hydride-Based Fluorinated Stationary Phases

Silica-based fluorinated bonded stationary phases have shown enhanced selectivity with altered elution orders for molecules differing in hydrophobicity and hydrophilicity in comparison with C8 and C18 reversed phase columns. Hence, two novel silica hydride-based fluorinated bonded phases have been synthesized using a hydrosilation procedure to exploit fluorine-based unique selectivity for polar basic metabolites. Bonded moieties have been characterized by elemental and spectral analyses. Silica hydride-based aqueous normal phase (ANP) chromatography has retention behavior similar to normal phase chromatography, except for the use of water as a part of the binary solvent (\u3e60 % acetonitrile : water). In ANP, a higher percentile of nonpolar mobile phase shows increased retention for acids and bases, and nonpolar solutes can also be retained as in reversed phase chromatography (RPC). The synergistic effects of fluorinated phases\u27 altered selectivity and aqueous normal phase retentivity have been explored for small polar metabolites using high performance liquid chromatography (HPLC) coupled with several detectors. Hydride-based fluorinated stationary phases showed good stability and remarkable reproducibility in retention time with %RSD \u3c 1

The way to ultrafast, high-throughput enantioseparations of bioactive compounds in liquid and supercritical fluid chromatography

Until less than 10 years ago, chiral separations were carried out with columns packed with 5 or 3 μm fully porous particles (FPPs). Times to resolve enantiomeric mixtures were easily larger than 30 min, or so. Pushed especially by stringent requirements from medicinal and pharmaceutical industries, during the last years the field of chiral separations by liquid chromatography has undergone what can be defined a “true revolution”. With the purpose of developing ever faster and efficient method of separations, indeed, very efficient particle formats, such as superficially porous particles (SPPs) or sub-2 μm FPPs, have been functionalized with chiral selectors and employed in ultrafast applications. Thanks to the use of short column (1–2 cm long), packed with these extremely efficient chiral stationary phases (CSPs), operated at very high flow rates (5–8 mL/min), resolution of racemates could be accomplished in very short time, in many cases less than 1 s in normal-, reversed-phase and HILIC conditions. These CSPs have been found to be particularly promising also to carry out high-throughput separations under supercritical fluid chromatography (SFC) conditions. The most important results that have been recently achieved in terms of ultrafast, high-throughput enantioseparations both in liquid and supercritical fluid chromatography with particular attention to the very important field of bioactive chiral compounds will be reviewed in this manuscript. Attention will be focused not only on the latest introduced CSPs and their applications, but also on instrumental modifications which are required in some cases in order to fully exploit the intrinsic potential of new generation chiral columns

Synthesis, Structural Characterization And Chromatographic Evaluation Of Silica Hydride-Based Perfluorinated Stationary Phase

Silica hydride based stationary phases have demonstrated unique selectivity and specificity for small sized polar molecules. The weakly hydrophobic nature of silica hydride is thought to be the key reason for its remarkable retention capabilities. Traditional stationary phases bonded with fluorine moieties have also exhibited enhanced retention of small polar molecules. In this research, a perfluorinated silica hydride stationary phase was synthesized by hydrosilation and silanization procedures. Chromatographic characterization of the newly packed column was carried out by a large number of retention studies. The separation capabilities of the column were evaluated in both the aqueous normal-phase (ANP) and reversed-phase (RP) modes. The perfluorinated silica hydride based column showed remarkable retention ability for RP and ANP modes of separation. Hydrophilic molecules were strongly retained in the ANP mode and hydrophobic molecules were retained in the RP mode. Effect of varying pH of mobile phase on the retention time was summarized. Use of acetone as non-polar solvent was demonstrated. In the conclusion, silica hydride based perfluorinated stationary phase successfully exhibited dual retention capability for polar and non-polar analytes

Construction of abatement cost curves: The case of F-gases

Most of scientific research on Greenhouse Gases (GHG) focuses on CO2 emissions. But non-CO2 gases (mainly F-gases in the form of HFCs, PFCs, and SF6) are more potent at trapping heat within the atmosphere. Currently, F-gases constitute a small proportion of GHG emissions but they are extremely high Global Warming Potential gases. At the same time, they are expected to increase massively due to the expansion of some emitting industries, while the atmospheric lifetimes of PFCs and SF6 are very long. This study analyzes the economic and technical assumptions in abatement cost calculation in the case of the F-gases. The important factors for differences among countries in average mitigation costs are discussed and the least cost curve of F-gases control for the EU-27 and for the year 2020 is derived. It seems that it is more cost-effective to start abating SF6 first, and then moving to PFCs and then applying control methods to HFCs.F-gases; control methods; emissions; GWP

Uudsed eluendilisandid LC-MS baasil bioanalüütilistele metoodikatele

Väitekirja elektrooniline versioon ei sisalda publikatsiooneKäesoleva töö eesmärk oli laiendada teadmisi uudsete eluendilisandite kasutamiseks bioanalüütilises keemias kasutades vedelikkromatograafia-massispektromeetria (LC-MS) analüüsimeetodit. Nende kahe instrumendi: LC ja MS ühendamine laiendab määratavate analüütide hulka, kuigi seab ka piiranguid mobiilfaasi lenduvuse osas. Seejuures mitmed mittelenduvad eluendilisandid, mis aitavad suurendada LC analüüsi efektiivsust ja on küll laialdaselt kasutatud traditsiooniliste UV/Vis detektori puhul, kuid pole kasutatavad MS detektoritele. Uudsete fluoroalkoholide kasutamine eluendilisanditena võimaldab LC-MS analüüsile paljulubavat tulevikku. Fluoroalkoholid kui nõrgad happelised ühendid, millel on ioonpaaride moodustamise võimekus ja mis soodustavad analüütide ioniseerumist MS detekteerimisel, võimaldavad nii keerulistest segudest paremini komponente eraldada kui ka neid paremini detekteetida. Selleks, et uurida mõju ravimite retentsioonile pöördfaas-vedelikkromatograafias, testiti mitmeid paljulubavaid ühendeid aluselise pH juures. Lisandite uurimiseks kasutati erinevaid analüütilisi kolonne - C18, bifenüül ja pentafluorofenüül (PFP) ning uuriti mudel-analüütide ja üldlevinud ravimite ning narkootikumide käitumist. Töö raames leiti, et kasutatud fluoroalkoholid mõjutavad analüüsi vähendades happeliste analüütide retentsiooni ja suurendades aluseliste analüütide retentsiooni. Uudsed eluendilisandid rakendati ka kahes praktilises rakendusnäites. Esiteks kasutati neid uinutite morfiin, klonidiin ja midasolaam (ning nende metaboliitide) ülitundlikuks mõõtmiseks. Teiseks kasutati uudseid lisandeid südame- ja veresoonkonna ravimite milrinooni ja dobutamiini tundlikkuks mõõtmiseks. Neid kahte bioanalüütilist metoodikat kasutati ravimite ja metaboliitide mõõtmiseks laste vereplasmast farmakokineetiliste ja farmakodünaamiliste uuringute tarbeks. Uudsete eluendilisandite mõju analüütide ioniseerumisele võimaldas mõlema metoodikaga saavutada erakordselt madalaid määramispiire, vajades seejuures minimaalset proovikogust, mis oli sobilik just antud patsientide grupile.The aim of this thesis was to expand knowledge about novel eluent additives used in bioanalytical chemistry using liquid chromatography-mass spectrometry (LC-MS) analysis technique. The combination of the two instruments, an LC and MS expands the limits of analytes that can be detected and quantified. However, it also introduced considerable limitations in terms of mobile phase volatility. Thus, many eluent additives which helped to increase the efficiency of LC analysis and were widely used when UV/Vis was a detector did not pass the criteria anymore. However, a promising perspective in LC-MS analysis is offered by novel fluoroalcoholic eluent additives. They are weakly acidic compounds with ion-pairing capabilities and with a positive influence on analyte ionisation in the MS source. To research the influence on retention patterns of pharmaceuticals, several novel eluent additives were tested in the basic mobile phase pH range. Different analytical column stationary phases - C18, biphenyl and pentafluorphenyl (PFP) - were investigated, both with model analytes and a large set of common toxicology screening compounds. It was observed that the use of these fluoroalcohols influenced the analysis by decreasing retention of acidic analytes and increasing retention for analytes with basic properties. Two practical applications employing novel eluent additives were developed and validated for the pharmaceuticals morphine, clonidine, midazolam, and their metabolites, as well as, for milrinone and dobutamine. The two bioanalytical methods were used to obtain data for pharmacokinetic and pharmacodynamic studies in paediatric patients. Both methods reached exceptionally low limits of quantification, with minimal sample amount used due to the positive influence of novel eluent additives on analyte ionisatio

A new RP-HPLC method as an auxiliary tool for optimization of sample preparation procedures for tracing of PPCPs of different hydrophilicities

Recently, pharmaceutical and personal care products (PPCPs) have received considerable attention because of their increasing use. Analysis of PPCPs presents a significant analytical challenge, with high-performance liquid chromatography (HPLC) in reversed-phase mode, as the most widely used analytical technique. To facilitate the optimization of the procedures that are applied in the early stages of sample preparation, a simple and fast HPLC method is proposed in this work for the separation of some PPCPs with a wide range of hydrophilicity. Two columns were evaluated (Atlantis dC18 and Discovery HS F5); as for mobile phases: a formate buffer (40 mmol L-1, pH 4) and methanol were tested in a gradient mode. The fluorinated column allowed better separation in a shorter time and better resolution for all analytes (Rs >1). The proposed method delivered good performance for the tracing of PPCPs and is a suitable alternative to traditional C18-based HPLC methods