Handbook of Solvents - George Wypych - ChemTech - Ventech!

21.1 Supercritical solvents 1427
Figure 21.1.11. Estimation of solubility and partial molar volume using supercritical fluid chromatography.
supercritical fluid that is ensured to exit with an equilibrium amount of the solid.
The chromatographic and calorimetric information can also be used to infer phase behavior
information. For example, solubility measurements can be performed on a Supercritical
Fluid Chromatograph (SFC) where a relatively short fused silica capillary tubing
system replaces the usual column. Sample is coated into this tubing using the same techniques
that are used to coat a stationary phase on an analytical capillary column. Raising the
solvent pressure stepwise from a selected starting point allows isothermal measurements of
solubility. At each step, the ion current in the mass spectrometer, which is used as the detector,
is monitored to determine the quantity of solute in solution. Also, solubility may be estimated
from the last equations in Approach A and Approach B summarized in Figure
21.1.11. 19 This is true provided that the adsorbent is a solid and partial molar volume of the
solute (e.g., naphthalene) in the stationary phase is equal to the solid molar volume of the
solute.
It is worth noting that Supercritical Fluid Chromatography is an important experimental
tool for measurement of a portfolio of physical-chemical properties as depicted in
Table 21.1.2.
However, indirect approaches and methods that involve sampling suffer from magnification
of propagated error due to the high sensitivity and non-linear nature of governing
fundamental relations in the critical region.