ANALYTICAL CHARACTERISTICS OF SAMPLE EVAPORATION WITH THE MICRO-KUDERNA DANISH CONCENTRATOR

The analytical behaviour of dichloromethane, pentane, and hexane solut ions was studied through their evaporation in a micro-Kuderna-Danish c oncentrator. Initial sample concentration, final sample volume, matrix composition, system geometry and temperature gradients influence the process greatly. In general, solute loss increases exponentially when the final volume decreases. During the concentration process with very dilute solutions, the loss of solutes can be higher than 50% if the f inal volume reached is lower than 200 mu l. This means a decrease in t he quantification of the process, even though it is seemingly kept und er control (low R.S.D.). The solute losses are not just due to the dec rease in the number of plates during the reflux disappearance, but als o to the probability that droplets of the evaporating sample are proje cted against clean and dry walls of low retention capacity. This hypot hesis may explain the observed effects when concentrating more concent rated samples, or samples with a high content of some solutes. A more advantageous design for the micro-Kuderna-Danish receptor flask is als o proposed. The replacement of the cylindrical flask by a flask with a conical bottom permits a decrease in the volume of losses and an impr ovement in the quantification of the process.