Liquid Chromatography Studies of Acetonitrile Sorption on Silica-Based Octyl Phases

Abstract

A complex mechanism of the reverse-phase chromatography can be envisioned as a combination of partition and adsorption processes. In the partition-displacement (P-D) model, partition accounts for the distribution of solute between the mobile and stationary phases, while displacement mostly involves competitive adsorption of solvents in the stationary phase. Therefore, chromatographic properties of a given stationary phase are largely dependent on the intercalation of solvents in the surface layer. The current work is a continuation of the ongoing studies of the factors affecting the surface composition of the stationary phase. Specifically, the goal of this work was the investigation of chromatographic behavior of two octyl phases of a similar surface coverage, which were synthesized from different silica supports. Analysis of methylene selectivity data showed that sorption of acetonitrile on both octyl phases was similar. This outcome could be related to a significant similarity of their structural and surface properties as demonstrated by analysis of the corresponding nitrogen adsorption and solid-state NMR data.

Simulation Studies on the Effects of Mobile-Phase Modification on Partitioning in Liquid Chromatography

“…The retentive material most commonly utilized in LC contains octadecyl chains that are chemically bound to silica. , This system is commonly referred to as reversed-phase liquid chromatography (RPLC) 1,2,5,6 and is the center of interest in our inquiry into LC retention mechanisms. Although a great deal of work has been done by a variety of theoretical and experimental approaches, − no consensus view has emerged on what factor(s) control the retention mechanism in RPLC. A first question revolves around whether the analyte can penetrate the retentive phase and resemble something like a “liquid−liquid” partitioning process or whether the analyte is retained by an adsorptive mechanism at the interface between solvent and retentive phases .…”

Desenvolvimento e caracterização de fases estacionárias monolíticas à base de octadecilmetacrilato para uso em eletrocromatografia capilar

“…Ainda segundo esses autores, o método BJH usado para a obtenção da curva de distribuição de poros assume que estes são cilíndricos e que o adsorbato pode ser retido nos poros do material adsorvente por dois mecanismos: adsorção física nas paredes dos poros ou condensação capilar. no material monolítico, além de ser citado em diversos trabalhos publicados na literatura[169][170][171][172][173][174][175][176][177][178] por ser mais facilmente compreendido. A comparação entre essas curvas e os diferentes materiais relacionados se dá em termos de tamanho médio de poro, o que, segundo Vansant et al[166], é de relevância estatística, não refletindo o tamanho atual de poro.Muitos modelos também foram desenvolvidos para a análise dos microporos existentes em uma estrutura porosa.…”