Characterization of the polarity of subcritical water

- Betaine dye (33) used to examine the polarity of subcritical water as temperature and pressure were changed.
- Temperature had a greater effect on polarity of subcritical water than pressure.
- The polarity of subcritical water is comparable to 30%-50% methanol/water mixtures and 20%-30% acetonitrile/water mixtures.

The polarity of subcritical water was studied solvatochromically with betaine dye (33) across a temperature range of 30 °C-180 °C and a pressure range of 13.8 bar (200 psi) to 124 bar (1800 psi). It was observed that temperature has a greater effect than pressure on the polarity of subcritical water. In addition, subcritical water was compared with traditional hydro-organic mobile phases and the polarity of subcritical water was found to be comparable to a range of 30%-50% methanol/water and a range of 20%-30% acetonitrile/water mobile phases. It was concluded that subcritical water is more suited to separations involving slightly polar and polar compounds than more nonpolar analytes.