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

The analytical behaviour of dichloromethane, pentane, and hexane solutions was studied through their evaporation in a micro-Kuderna-Danish concentrator. 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 final volume reached is lower than 200 mu l. This means a decrease in the quantification of the process, even though it is seemingly kept under control (low R.S.D.). The solute losses are not just due to the decrease in the number of plates during the reflux disappearance, but also to the probability that droplets of the evaporating sample are projected against clean and dry walls of low retention capacity. This hypothesis may explain the observed effects when concentrating more concentrated samples, or samples with a high content of some solutes. A more advantageous design for the micro-Kuderna-Danish receptor flask is also proposed. The replacement of the cylindrical flask by a flask with a conical bottom permits a decrease in the volume of losses and an improvement in the quantification of the process.