The retention of polar compounds, the separation of structural isomers and thermal stability make carbonaceous materials very attractive stationary phases for liquid chromatography (LC). Carbon clad zirconia (C/ZrO2), one of the most interesting, exhibits unparalleled chemical and thermal stability, but its characteristically low surface area (20-30m2/g) limits broader application as a second dimension separation in two-dimensional liquid chromatography (2DLC) where high retentivity and therefore high stationary phase surface area are required. In this work, we used a high surface area commercial HPLC alumina (153m2/g) as a support material to develop a carbon phase by chemical vapor deposition (CVD) at elevated temperature using hexane vapor as the carbon source. The loading of carbon was varied by changing the CVD time and temperature, and the carbon coated alumina (C/Al2O3) was characterized both physically and chromatographically. The resulting carbon phases behaved as a reversed phase similar to C/ZrO2. At all carbon loadings, C/Al2O3 closely matched the unique chromatographic selectivity of carbon phases, and as expected the retentivity was increased over C/ZrO2. Excess carbon - the amount equivalent to 5 monolayers - was required to fully cover the oxide support in C/Al2O3, but this was less excess than needed with C/ZrO2. Plate counts were 60,000-76,000/m for 5μm particles. Spectroscopic studies (XPS and FT-IR) were also conducted; they showed that the two materials were chemically very similar.
Bibliographical noteFunding Information:
The authors acknowledge the financial support from the National Institute of Health ( GM 054585 ) and the Institute of Technology Characterization Facility, University of Minnesota, part of the NSF-funded Materials Research Facilities Network ( www.mrfn.org ) for XPS data from Dr. Bing Luo. We also thank Prof. A. Stein at University of Minnesota for FT-IR use and Merck KGaA (Darmstadt, Germany) and ZirChrom Separations Inc. (Anoka, MN, USA) for the donation of porous alumina and carbon clad zirconia, respectively.
- Carbon clad zirconia
- Carbon coated alumina
- Chemical vapor deposition
- Stationary phase