CONCENTRATION OF SMALL VOLUMES OF NONPOLAR SOLUTIONS CONTAINING TRACEVOLATILE COMPOUNDS

The analytical behaviour of the concentration of extracts under a stre am of nitrogen of small volumes of hexane solutions containing volatil e analytes has been studied. The proportion of analyte blown off the s olution is a function of its bailing point, of its polarity, and of th e final volume reached. For similar boiling points, the more polar the compound, the higher the level of losses. If the evaporation progress es to a final volume of 0.01 mi, all the compounds with boiling points below 150 degrees C are lost in proportions higher than 50%. Compound s with boiling points between 150 and 250 degrees C are lost in propor tions ranging from 70 to 25%, and only eicosane (b.p. 340 degrees C) i s almost fully retained in the solution. The addition of small amounts (5 mg) of dehydrated silica to the evaporating solution allows the ev aporation to proceed without noticeable losses of solutes more polar t han hydrocarbons. After concentration, the solutes can be easily recov ered by adding a small amount of ethanol or a mixture water-ether. (C) 1998 Elsevier Science B.V. All rights reserved.