Development of a carbon clad core-shell silica for high speed two-dimensional liquid chromatography

Abstract

We recently introduced a new method ([1]) to deposit carbon on fully porous silicas (5 μm) to address some of the shortcomings of carbon clad zirconia (C/ZrO2), which has rather low retention due to its low surface area (20–30 m2/g). The method enables the introduction of a thin, homogeneous layer of Al (III) on silica to serve as catalytic sites for carbon deposition without damaging the silica’s native pore structure. Subsequent carbon deposition by chemical vapor deposition resulted in chromatographically useful carbon phases as shown by good efficiencies and higher retentivity relative to C/ZrO2. Herein, we use the above method to develop a novel carbon phase on superficially porous silica (2.7 μm). This small, new form of silica offers better mass transfer properties and higher efficiency with lower column back pressures as compared to sub 2 μm silica packings, which should make it attractive for use as the second dimension in fast two-dimensional LC (LC x LC). After carbon deposition, several studies were conducted to compare the new packing with C/ZrO2. Consistent with work on 5 μm fully porous silica, the metal cladding did not cause pore blockage. Subsequent carbon deposition maintained the good mass transfer properties as shown by the effect of velocity on HETP. The new packing exhibits efficiencies up to ~ 5.6 fold higher than C/ZrO2 for polar compounds. We observed similar chromatographic selectivity for all carbon phases tested. Consequently, the use of the new packing as the second dimension in fast LC x LC improved the peak capacity of fast LC x LC. The new material gave loading capacities similar to C/ZrO2, which is rather expected based on the surface areas of the two phases.

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.…”

“…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

“…For instance, the hybrid HILIC phase achieved h of 1.9 (95,000 plates m −1 ) which is about eight times lower than the carboxylate-PGC column (h ∼ 15.5) for BTMA. This hybrid carbon-silica phase shows improved efficiency as compared to the recently developed carbon clad core-shell silica phase (h ∼ 2.5) [27].…”

“…The carbon load on typical RPLC and HILIC Halo core-shell silica particles ranges from 3.5 to 8.2% w/w [30]. Carbon clad core-shell silica phases, created by vapor deposition process, have up to 7% w/w [27]. From the XPS data (Supplementary Table S2), the surface concentration of carbon increased from 33.2 to 35.5 at% C. The surface % N decreased from 1.58% to 1.33%, indicating that the latex AS9-SC coated core-shell silica is covered by the carbon nanoparticles.…”

“…These hybrid phases were developed by a complex procedure of vapor deposition of carbon at high temperature. More recently, vapor deposition of carbon has been used to create a carbon clad core-shell silica (2.7 m) phase [27].…”