A study of the critical criteria for analyte stability in high-temperature liquid chromatography

There are three major impediments to the use of high-temperature ultrafast liquid chromatography. First, the stationary phase must be thermally stable. Over the past decade, a series of thermally stable, highly efficient stationary phases have been developed that can withstand temperatures exceeding 200°C. Second, the temperature mismatch between the incoming eluent and the column must be minimized (<5°C), because such a mismatch is a very serious cause of peak broadening, especially in ultrafast separations. The thermal mismatch problem can be significantly ameliorated at high column linear velocities by using narrow-bore columns (2.1-mm i.d.). Third, analytes that are exposed to high temperatures must be thermally stable on the time scale of the chromatographic run. We report here a study of the ability of a number of pharmaceuticals to withstand superambient temperatures on the time scale of fast separations. We propose criteria by which a particular analyte may be rejected as a candidate for high-temperature analysis, and we demonstrate that complex molecules are amenable to quantitation, even at temperatures in excess of 100°C in the aqueous media. We also show that as the time an analyte spends on hot column decreases, the extent of on-column reaction decreases for those analytes that do react. Although the seminal work of Antia and Horvath addresses these issues from a theoretical perspective, we hope to further alleviate fear of the use of high temperatures in liquid chromatography through the empirical approach used here.