An arrangement for determining the concentration of nucleic acids in a sample in a microfluidic device. In at least one embodiment, the arrangement having a) a first chamber into which a the sample is introduced, b) an element in the first chamber for carrying out a number of cycles of an amplification reaction to be carried out in cycles for amplifying nucleic acids, c) a second chamber, connectable to the first chamber by way of fluidic communication, equipped with an element to determine concentrations of amplified nucleic acids, d) a control unit to introduce a defined volume of a solution containing reagents for the amplification reaction into the first chamber and to transfer a defined volume from said first chamber to the second chamber.