Free silanols on the surface of silica are the "villains", which are responsible for detrimental interactions of those compounds and the stationary phase (i.e., bad peak shape, low efficiency) as well as low thermal and chemical stability. For these reasons, we began this review describing new silica and hybrid silica stationary phases, which have reduced and/or shielded silanols. At present, in liquid chromatography for the majority of analyses, reversed-phase liquid chromatography is the separation mode of choice. However, the needs for increased selectivity and increased retention of hydrophilic bases have substantially increased the interest in hydrophilic interaction chromatography (HILIC). Therefore, stationary phases and this mode of separation are discussed. Then, non-silica stationary phases (i.e., zirconium oxide, titanium oxide, alumina and porous graphitized carbon), which afford increased thermal and chemical stability and also selectivity different from those obtained with silica and hybrid silica, are discussed. In addition, the use of these materials in HILIC is also reviewed.

Silica, hybrid silica, hydride silica and non-silica stationary phases for liquid chromatography.

Reversed‐phase chromatographic media have recently become available that are based on porous hybrid organic‐inorganic particles. The present paper reviews hybrid particles that are made from organosilanes (organic moiety) and tetraalkoxysilanes (inorganic moiety). The hybrid particles are defined and classified within the context of a broader definition of hybrid materials. First syntheses and chromatographic evaluations are discussed for this class of hybrid packing materials. Publications are then described, which characterize two distinguishing chemical properties of hybrid particles vs. silica gel: 1) less acidic silanols, and 2) markedly longer lifetimes in alkaline mobile phases. These properties are achieved without sacrificing mechanical strength, as is found for fully organic particles, i.e., polymers, with the same chemical features. Literature reports are then reviewed that employ hybrid based reversed‐phase column packings for HPLC. Topics covered include fundamental retention mechani...

Porous Hybrid Organic‐Inorganic Particles in Reversed‐Phase Liquid Chromatography

Liquid chromatography has seen a dramatic increase in speed and efficiency over the past decade. The advances in separation speed have been mostly related to the development of column technology and instrumentation. The column technology includes small uniform particles, monolithic columns, and thermally stable phases with various bonding chemistries. Relatively short columns packed with sub‐2 µm particles provide high speed and efficient separations. The high porosity and small skeleton size of monolithic columns permit operation at high flow rates on relatively long columns, using a conventional LC system for high speed and high efficiency separation. The new instrumentation is associated with ultra‐high pressure pump systems and high temperature systems. Ultra‐high or very high pressure pump systems have been used to overcome the high pressure drop generated by small particles. High temperature liquid chromatography allows fast separation using high linear velocities and stable stationary phas...

Fast and efficient separations using reversed phase liquid chromatography

Extension of the carotenoid test to superficially porous C18 bonded phases, aromatic ligand types and new classical C18 bonded phases.

At the present time, more complex analyses of apolar compounds with similar chemical structures or of polar compounds, especially basic ones, having diverse properties require more selective stationary phases having better stabilities. This paper describes several new stationary phases with directed selectivities that were prepared by immobilizing two different phenyl group-containing siloxanes and a trifluoropropyl-containing siloxane onto chromatographic silica and, in the case of the fluorinated siloxane, onto zirconized silica, using thermal treatment or microware radiation. The chromatographic properties and stabilities of these new phases were determined and several applications were evaluated. The phenyl-containing phases showed excellent characteristics related to the separation of several different types of aromatic compounds while the fluorinated phases, which present a more polar character, revealed selectivity for the separation of positional isomers as well as for a mixture of basic pharmaceuticals. Stability tests indicate that immobilization of the polysiloxanes increases column lifetimes by making the stationary phases less susceptible to dissolution, while the phases immobilized with microwave radiation were somewhat more stable than those immobilized by thermal treatments.

Some new selective stationary phases for RP-HPLC.

Hybrid organic‐inorganic particles combine the best properties of silica — high efficiency and excellent mechanical strength — with the best properties of organic polymers — a wide pH stability range and reduced silanol effects. In this article, the authors describe reversed-phase HPLC packings based on hybrid particles and demonstrate the packing’s retention and selectivity characteristics. They also show that these media have long lifetimes at elevated temperatures under conditions at which conventional bonded silica fails rapidly. The benefits of operating at elevated temperatures are increased efficiency and reduced back pressure. When combined with short columns containing 2.5- mm hybrid particles, these conditions enable fast, high-resolution gradient separations, which are useful for high-throughput analyses.

Hybrid Organic-Inorganic Particle Technology: Breaking Through Traditional Barriers of HPLC Separations

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Hybrid Organic-Inorganic Particle Technology: Breaking Through Traditional Barriers of HPLC Separations