On‐line solvent evaporator for coupled LC systems

Abstract

The mobile phase of a fraction eluted from a first LC column is removed by an on-line evaporator in order to reconcentrate the solute material or to exchange the eluent before performing a subsequent LC separation. Evaporation essentially occurs by concurrent evaporation, i.e. the solvent evaporates at a rate equal to the flow rate of the incoming eluent, and is driven by the overflow principle, i.e. vapors leave the tube as a result of the expansion resulting from evaporation. The liquid is introduced into a small tube (e.g., 4 cm x 1.3 mm i.d.)which is packed, e.g., with a coarse silica gel.The outlet of the evaporator is connected to vacuum in order to enable evaporation at reduced temperature and to increase retention of the volatile components. With normal phase eluents, evaporation rates may approach 1 ml/min; n-dodecane was the most volatile n-alkane fully retained by the evaporator.

Determination of p,p′‐DDE and PCBs in adipose tissues using high‐performance liquid chromatography coupled on‐line to capillary GC – the EURAMIC study

“…Organochlorines such as p,p'-DDT [2,2-bis(p-chlorophenyl)-1, 1,l -trichloroethane] and some polychlorinated biphenyls (PCBs) are known to be animal carcinogens [I, 21. The metabolite p,p'-DDE and several chlorobiphenyls are highly persistent in the environment, and are eliminated slowly from the body so long-term health effects, including cancer, may be of particular concern.…”

“…It is possible to introduce large volumes of liquid into the GC by using either on-column or loop-type interfaces. The introduction of small volumes, typically less than 300 pl, causes problems when applying the looptype interface because it is difficult to obtain stable fully concurrent solvent evaporation [21]. Besides this, the loop-type interface needs a storage loop to hold the entire transfer volume which increases dead volumes and cross-contamination risks in the GC interface.…”

Concurrent solvent recondensation large sample volume splitless injection

“…In 1992, Grob et al introduced large volume splitless injection with vapor overflow [11] performed with a conventional splitless injector containing a packed liner. The liquid sample is rapidly injected into the hot packing.…”

“…The sample liquid may be stopped and kept in place by a packing of low thermal mass, such as deactivated glass or fused silica wool [26]. The fibers are rapidly cooled to the solvent boiling point and no longer repel the liquid.…”

“…As described for the overflow technique, volatile solutes, such as n-dodecane, may co-evaporate with a solvent such as hexane, but higher boiling components stay at the site until solvent evaporation is complete. Only then does heat transfer return the temperature to the thermostatted value, enabling the high-boiling sample constituents to be vaporized [30].…”