Waters has named its new-generation supercritical fluid chromatography (SFC) system UltraPerformance Convergence Chromatography, or UPC2 ®.
“It’s the combination, or convergence, of GC and LC,” says Ken Fountain, director of chemistry applied technology and global UPC2 applications.
Convergence chromatography exploits the advantage of carbon dioxide-based mobile phases in either supercritical or subcritical mode. UPC2 combines the unique properties of carbon dioxide mobile phases with the ability to run gradients with common organic solvents, like methanol or acetonitrile, on stationary phases that have both normal- and reverse-phase characteristics, to cover a wide selectivity range.
Like other LC systems built on Waters Acquity® platform, UPC2 employs sub-two-micron stationary phases, especially for nonchiral analysis. It is possible to use five-micron particle technology as well, as with UHPLC, but also like conventional LC, efficiency increases as particle size decreases. Efficiency improvements from smaller particles are in fact comparable to those obtained in HPLC/UHPLC. UPC2’s additional benefit is much higher linear velocity and throughput.
“Mass transfer kinetics are greatly improved. Diffusivity is closer to that of GC’s, between 10 and 100 times faster than that of LC,” Fountain says.
Waters’ original target market was chiral analysis, where SFC already enjoyed a healthy reputation. The company has demonstrated chiral SFC separations that require one-thirtieth the time compared with standard normal-phase HPLC. Solvent consumption and lower cost are additional benefits. In a typical example, the SFC method consumed 135 microliters of methanol, compared with 10 mL of hexane/ethanol for HPLC. Overall cost savings are dramatic, falling from about $6 for a conventional HPLC run to $0.05 for UPC2.
“When you consider this savings on the scale of hundreds to thousands of injections, the financial impact to an organization can be quite exceptional,” says Waters’ John van Antwerp.
Since its selectivity overlaps significantly with normal-phase chromatography, SFC is orthogonal to reverse-phase LC. The technique is applicable to a diverse range of compounds, including most organic-soluble compounds, most salts of organic acids and bases, strong organic acids and bases, small lipophilic peptides, and nonpolar solutes (e.g., waxes and oils). In addition to being the go-to method for chiral separations, SFC also separates positional isomers and diastereomers, and is compatible with most popular detection modes.