Detection modes with high temperature liquid chromatography - A review

Recent developments of thermally resistant stationary phases based on porous graphitic carbon, zircon, titania, or organic polymers allow the use of high temperatures in liquid chromatography (HTLC). These temperatures can reach 200 degrees C without any degradation of the stationary phase. Temperature becomes an additional parameter to improve the performance of classical HPLC. Indeed, at high temperature, viscosity and mobile phase polarity decrease while solute diffusion coefficients increase. Thus, with the same hydro-organic mobile phase, separations 5 to 20 times faster can be obtained without loss of efficiency and the organic modifier content in the mobile phase can be largely reduced. In some cases, a 100% water mobile phase can be used. This allows the hyphenation of HTLC with some detection modes that could not be used in classical LC. These detection modes are more universal, sensitive, or selective than traditional UV detection. This paper reviews the general use of elevated temperatures (up to 200 degrees C) in liquid chromatography. It focuses on detection modes exposing the drawbacks and advantages of several detection modes used in HTLC: Ultraviolet (UV), Flame Ionization Detection (FID), Mass Spectrometry (MS), Evaporative Light-Scattering Detection (ELSD), Inductively Coupled Plasma (ICP), Nuclear Magnetic Resonance Spectrometry (NMR), and Refractive Index detection (RID).