Determination of phase diagrams of polymer solutions with conventional techniques, like differential scanning calorimetry (DSC), is limited to sufficiently high concentrations due to a low signal/noise ratio. Controlling the nanoscale morphology formation upon solution processing of dilute conjugated polymer solutions however requires this information. In this work, we introduce an experimental methodology able to detect phase transitions in solutions over a wide concentration regime, by means of dielectric spectroscopy. We tested the validity of our method for solutions of poly(3-hexylthiophene) in toluene. Apart from providing crystallization and melting temperatures consistent with DSC data for the over-lapping sample concentrations, our method turned out to be able to detect phase transition down to trace level mass fractions as low as 10 ppm. (C) 2010 Elsevier Ltd. All rights reserved.