Experimental Problems

Abstract

A great deal of the separations reported in Chap. 9 were performed with eluents containing THF, which in gradient elution were used as component B. The choice of THF was often empirical but can be understood as a consequence of its favourable properties:

• 1. THF is a powerful solvent for many polymers. This is the reason why it is also a very popular eluent in SEC.

• 2. THF is miscible with apolar solvents (e.g. iso-octane, hexane, or cyclohexane) as well as with highly polar liquids, including methanol and water. Miscibility is prerequisite to gradient elution.

• 3. THF is polar enough to be used as an eluent B in normal-phase gradients. On the other hand, in combination with highly polar liquids as, e.g. methanol, it can be used also as component B in reversed-phase gradients. Its elution strength matches with a high dissolving power.

• 4. Since pure THF is sufficiently transparent, UV detection causes no problems when performed at e.g. 254 nm. With “sudden-transition gradients” (see Sect. 5.6) solutes can be monitored at 230 nm and, with the help of a double-beam spectrophotometer [1] detection was possible even at 215 nm.

• 5. THF has only moderate toxicity. The threshold limit value is 200 ppm [2] which compares favourably with tetrachloromethane (2 ppm), trichloro-methane (25 ppm), dioxane or acetonitrile (40 ppm each), 1,2-dichloroethane or 1-butanol (50 ppm each), or n-hexane (100 ppm).