Packed Capillary Column Solvating Gas Chromatography Using Mobile Phases That Transition from Liquid to Gas between the Column Inlet and Outlet

Abstract

In this study, organic solvents at temperatures higher than their normal boiling points were used as mobile phases for packed capillary column chromatography. No restrictor or back pressure was imposed on the column outlet. As a result, a large difference in mobile-phase properties existed, and a phase transformation from liquid to gas occurred, along the column. Solvating gas chromatography (SGC) was used to characterize this chromatographic process because, near the column outlet, a gaseous mobile phase existed. Chromatographic performance characteristics including mobile-phase flow, column efficiency, mobile-phase solvating power, and solute retention were investigated using fused-silica capillary columns packed with microparticles (5-and 10-µm diameters). It was found that when the temperature was increased to values that were higher than the normal mobile-phase boiling point, the mobile-phase linear velocity increased rapidly at constant column inlet pressure. Although large differences in mobile-phase properties existed between the column inlet and outlet, high column efficiencies (reduced plate heights of less than 2) were achieved. At elevated temperature, the optimum mobile-phase linear velocity increased, and the dependence of column efficiency on linear velocity decreased. Solute retention factors also decreased with increasing temperature, even for temperatures higher than the normal boiling point of the mobile phase. Large polycyclic aromatic hydrocarbons and enantiomers were rapidly separated under SGC conditions.

Temperature Programming for High-Speed GC

“…Equation 2 assumes that H is constant over the separation. In general, H shows considerable variation with retention, and more accurate expressions for isothermal peak capacity have been reported. , …”

Fluidos supercríticos em química analítica. II. Cromatografia com fluido supercrítico: instrumentação

“…(1) onde: ∆P = pressão (bar) u = velocidade linear (cm/s) ψ = constante (~1000 para partículas esféricas de empacotamento) η = viscosidade (poise) L = comprimento da coluna (cm) d p = diâmetro da partícula de empacotamento (mm) O maior problema da variação da pressão através da coluna é que a densidade do fluido de arraste no início e no final da coluna serão diferentes e, conseqüentemente, o poder de solvatação será diretamente proporcional à variação da densidade do fluido e, com isso, o poder de eluição varia dentro da coluna 11 . Um resumo das vantagens e desvantagens do uso das colunas capilares e empacotadas é apresentado na Tabela 3.…”

Peak capacity in packed capillary column solvating gas chromatography

“…Taking into account the dependence of column theoretical plate number on retention, our ,previous study showed that peak capacity could be expressed generally as follows for column chromatography [3]: When solvating mobile phases are used in packed column gas chromatography (solvating gas chromatography, SGC), high column efficiency and speed can be obtained. In SGC, the mobile phase can change from a supercritical fluid to a gas [4] or from a superheated liquid to a gas [5], or remain as a solvating gas [6] throughout the column length. Both adsorbents [6] and bonded phases [7] have been used in SGC to perform solvating gas-solid chromatography (SGSC) and solvating gasliquid chromatography (SGLC).…”