Hybrid monolithic columns present characteristics of both silica and organic monoliths, such as good mechanical properties, wide pH tolerance, high permeability and stability and little swelling or shrinkage. A common way to prepare this type of material is by using alkoxysilanes and organic monomers via the sol-gel process and click chemistry reactions. In this paper, a co-condensation organic-silica hybrid monolith was prepared based on tetramethoxysilane (TMOS) and vinyltrimethoxysilane (VTMS) as precursors for the sol-gel process. The hybrid monolithic matrix was modified with dodecanethiol through the thiol-ene click chemistry reaction and the resulting material was compared with a dodecanesilane bonded phase column, in order to evaluate the differences in the chromatographic performance of a stationary phase prepared by a classic reaction or by a thiol-ene click reaction. Additionally, the stability of the thiol-ene column over time was evaluated. The effects of different synthetic proportions were investigated in detail by scanning electron microscopy (SEM), scanning capacitively coupled contactless conductivity detection (sC4D), Fourier-transform infrared spectroscopy (FTIR) and retention behavior in capillary liquid chromatography (cLC). The hybrid monolithic column prepared with dodecanethiol was the best one for the separation of alkylbenzenes and polycyclic aromatic hydrocarbons by cLC-UV.

Colunas de alta eficiência cromatográfica de origem monolítica orgânica foram obtidas para uso em eletrocromatografia capilar (CEC) utilizando uma mistura de monômeros (concentrações constantes) com diferentes proporções de solventes porogênicos (1,4- butanodiol com álcool isoamílico, álcool amílico ou cicloexanol, na presença ou ausência de água). As fases estacionárias foram preparadas a partir do monômero precursor octadecilmetacrilato (ODMA), do agente de entrecruzamento etilenodimetacrilato (EDMA) e do monômero carregado ácido 2-acriloilamido-2-metilpropanosulfóxido (AMPS), sendo este necessário para tornar a fase estacionária carregada negativamente, garantindo o fluxo eletrosmótico durante a análise. As colunas monolíticas foram caracterizadas fisicamente através de porosimetria e microscopia eletrônica de varredura (SEM), e eletrocromatograficamente, através de cálculo dos parâmetros cromatográficos de separação. A coluna mais eficiente foi preparada a partir dos solventes porogênicos álcool amílico:1,4-butanodiol na proporção 65:35 (v/v) e apresentou 38 µm de altura de prato. Estas colunas foram aplicadas na separação de alquilparabenos e hidrocarbonetos policíclicos aromáticos (PAH).

Organic monolithic columns with high efficiency were obtained for use in capillary electrochromatography (CEC) from a mixture of monomers (constant concentrations) with different proportions of porogenic solvents (1,4-butanediol with isoamyl alcohol, amyl alcohol or cyclohexanol in the presence or absence of water). The stationary phases were prepared from the precursor monomer octadecyl methacrylate (ODMA), the cross-linking agent ethylene dimethacrylate (EDMA) and the ionizable monomer 2-acryloylamido-2-methylpropanesulfonic acid (AMPS), the latter being necessary to make the stationary phase negatively charged, assuring electrosmotic flow (EOF) during analysis. The monolithic columns synthesized were physically characterized by porosimetry and scanning electron microscopy (SEM), and electrochromatographically characterized by calculation of chromatographic parameters. The most efficient column was prepared using the porogenic solvent amyl alcohol:1,4-butanediol in a 65:35 (v/v) ratio and showed a plate height of 38 µm. These columns were applied for the separation of alkyl parabens and polycyclic aromatic hydrocarbons (PAH).

High-temperature liquid chromatography (HTLC) is a technique that presents a series of advantages in liquid phase separations, such as: reduced analysis time, reduced pressure drop, reduced asymmetry factors, modified retentions, controlled selectivities, better efficiencies and improved detectivities, as well as permitting green chromatography. The practical limitations that relate to instrumentation and to stationary phase instability are being resolved and this technique is now ready to be applied for routine determinations.

Monolithic stationary phases represent a new generation of chromatographic separation media. These phases consist of a continuous separation bed prepared by in situ polymerization or consolidation inside the column tubing. In recent years, their simple preparation procedure, unique properties and excellent performance have attracted quite remarkable attention in liquid chromatography and capillary electrochromatography. This review summarizes the preparation, characterization and applications of monolithic stationary phases. The analytical potential of these columns is demonstrated with separations involving various families of compounds in different separation modes.

Misturas de etanol:água foram reavaliadas para uso como fases móveis para Cromatografia Líquida de Alta Eficiência no modo fase reversa (CLAE-FR). A otimização das condições cromatográficas para as colunas C8 e C18 foram realizadas através de um planejamento fatorial o qual avaliou temperatura, concentração de etanol e vazão da fase móvel. Com a fase estacionária C8, as assimetrias dos picos não alteraram nos diferentes pontos do fatorial, enquanto os fatores de retenção e as resoluções diminuíram com o aumento da temperatura, na qual a viscosidade do etanol é mais baixa. Observações similares foram obtidas com a fase estacionária C18. A eficiência cromatográfica obtida com a fase móvel etanol:água na separação de misturas contendo compostos neutros e básicos foi comparada com aquelas obtidas usando fases móveis de metanol:água e acetonitrila:água. O etanol mostrou ser um bom modificador orgânico para CLAE-FR apresentando boas propriedades cromatográficas. Assim, considerando a menor toxicidade do etanol, a facilidade do seu descarte e seu custo favorável, etanol:água pode ser uma das escolhas de fase móvel para as diversas aplicações de CLAE-FR.

Ethanol:water mixtures have been reevaluated for use as reversed phase mobile phases. Optimization of the chromatographic conditions for both C8 and C18 columns was carried out through a factorial design which evaluates temperature, ethanol concentration and mobile phase flow rate. With the C8 stationary phase, peak asymmetries were not significantly altered at the different points in the factorial design while the retention factors and resolutions were somewhat lower at higher temperatures, where the viscosity of EtOH is lower. Similar observations were obtained with the C18 phase. The efficiency of the ethanol:water mobile phase for the separation of mixtures containing neutral and basic compounds was compared with those obtained using methanol:water and acetonitrile:water mobile phases. Ethanol was shown to be a good organic modifier for RP-HPLC, with good chromatographic properties. This, considering the much lower toxicity of ethanol, the facility of its disposal, and its favorable cost, should make ethanol:H2O the mobile phase of choice for many RP-HPLC applications.