title: Effect of helium in helium headspace carbon dioxide cylinders on packed-column supercritical fluid chromatography.
abstract: Supercritical fluid chromatography of PAHs was performed with pure carbon dioxide and helium headspace carbon dioxide at various cylinder fill levels. The retention times of the PAHs increased when helium headspace carbon dioxide was used as a carrier fluid relative to pure carbon dioxide. The increased retention times were affected by the level of the liquid phase present in the helium headspace carbon dioxide cylinder. As more liquid phase was removed from the cylinder, the effect of helium on the solvating power of CO(2) was reduced because the relative amount of helium dissolved in the liquid phase decreased. Furthermore, the effect of helium headspace carbon dioxide was investigated with methanol-modified carbon dioxide mobile phases for the analysis of steroids. We observed that the relative solubility of helium in carbon dioxide resulted in longer retention times when compared to pure carbon dioxide as the liquid level of carbon dioxide decreased.
authors: Chemistry Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, and Air Products and Chemicals, Inc., Hamilton Boulevard, Allentown, Pennsylvania 19158.
authors: E
authors: E
authors: Leichter
authors: J T
authors: JT
authors: Strode
authors: L T
authors: LT
authors: Taylor
authors: F K
authors: FK
authors: Schweighardt