Hyphenation of high-temperature liquid chromatography with high-pressure electrospray ionization for subcritical water LC-ESI-MS.

High-pressure electrospray ionization (HP-ESI) performed under super-atmospheric pressure allows a stable and efficient electrospray of pure aqueous and/or superheated solutions even under a μL min-1 flow rate regime. In this paper, we report the direct coupling of the HP-ESI source to high-temperature liquid chromatography (HT-LC) operated at ≤30 μL min-1 flow rates. In addition to ESI, the ion source functions as a back-pressure regulator to keep the mobile phase in the liquid phase when the column is heated to >100 °C. Under an ion source pressure of 7 bar, the LC column can be operated up to 160 °C. LC is performed under isocratic elution, and besides the isothermal mode, the temperature of the column can also be programmed to increase the selectivity while keeping the ion source at a constant temperature. For a given solution flow rate, the analytical time can be shortened by increasing the column temperature. HT-LC-ESI-MS using pure water as the mobile phase with a capillary column is also demonstrated.