New method for development of carbon clad silica phases for liquid chromatography: Part I. Preparation of carbon phases

Abstract

Owing to its combination of unique selectivity and mechanical strength, commercial carbon clad zirconia (C/ZrO2) has been widely used for many applications, including fast two-dimensional liquid chromatography (2DLC). However, the low surface area available (only 20 - 30 m2/g for commercial porous ZrO2) limits its retentivity. We have recently addressed this limitation by developing a carbon phase coated on the high surface area of HPLC grade alumina (C/Al2O3). This material provides higher retentivity and comparable selectivity, but its use is still limited by how few HPLC quality types of alumina particles (e.g., particle size, surface area, pore size) are available. In this work, we have developed useful carbon phases on silica particles, which are available in various particle sizes, pore sizes and forms of HPLC grade. To make the carbon phase on silica, we first treat the silica surface with a monolayer or less of metal cations that bind to deprotonated silanols to provide catalytic sites for carbon deposition. After Al (III) treatment, a carbon phase is formed on the silica surface by chemical vapor deposition at 700 °C using hexane as the carbon source. The amount of Al (III) on the surface was varied to assess its effect on carbon deposition, and the carbon loading was varied at different Al (III) levels to assess its effect on the chromatographic properties of the various carbon adsorbents. We observed that use of a concentration of Al (III) corresponding to a full monolayer leads to the most uniform carbon coating. A carbon coating sufficient to cover all the Al (III) sites, required about 4 – 5 monolayers in this work, provided the best chromatographic performance. The resulting carbon phases behave as reversed phases with reasonable efficiency (50,000 – 79,000 plates/meter) for non-aromatic test species.

Improved Synthesis of Carbon-Clad Silica Stationary Phases

“…1,2 The fines are removed by flotation. The slurry of 5 g of CCSi particles in 250 mL of THF are sonicated for 5 minutes, followed by gentle shaking and then left to settle slowly.…”

“…These phases have unique reversed phase selectivity, 3,4 high stability in acidic media, high mechanical strength, and high retentivity. 1–3 These properties make CCSi stationary phases good candidates for use in ultrafast liquid chromatography and two-dimensional liquid chromatography. 5,6 CCSi phases are prepared in two steps: First, an Al(III) CVD catalyst is homogenously precipitated on deprotonated silanol groups using the slow hydrolysis of urea in an acid solution of Al(III).…”

“…1,2 In that method, we showed that very close to exactly one uniform monolayer of Al (III) was deposited on the silica by a process analogous to precipitation from homogeneous solution in order to preclude pore blockage. The purpose of the Al(III) monolayer layer is to activate the surface for subsequent CVD of carbon.…”

Hybrid carbon nanoparticles modified core–shell silica: A high efficiency carbon-based phase for hydrophilic interaction liquid chromatography

“…Many hybrid stationary phases have been developed on inorganic oxides clad in monolayers of carbon such as carbon clad zirconia [24], carbon clad alumina [25] and carbon clad silica [26]. These hybrid phases were developed by a complex procedure of vapor deposition of carbon at high temperature.…”

Porous Silica Particles As Chromatographic Separation Media: A Review

“…54 The new carbon clad phase behaved as a reversed phase and had higher retentivity than carbon clad zirconia particles with reasonable separation efficiency (50,000-79,000 plates/m). Next, the same research group adopted the above method to develop a novel carbon phase on superficially porous silica (2.7 µm), and the new packing maintained the good mass transfer properties of core/shell particles as demonstrated by the effect of velocity on HETP, and exhibited efficiencies up to 5.6-fold higher than carbon clad zirconia particles especially for polar compounds.…”