Method of purifying solution comprising polynucleotide

A method of purifying a solution which comprises polynucleotides and contaminants, the solution being contained in a well of a filter plate, the well being equipped with a filter, said method comprising:

• (i) a step of adding a chaotropic agent to the solution contained in the well to get a mixture,
• (ii) a step of incubating the mixture so that a precipitate and a supernatant are obtained in the well, the precipitate comprising the polynucleotide and the supernatant comprising at least a part of the contaminants,
• (iii) a step of applying a differential pressure to the well in order to eliminate the supernatant through the filter, the precipitate being retained by the filter, and
• (iv) a step of adding a low salt eluant to dissolve the polynucleotides in the precipitate and transfer the polynucleotides dissolved in the low salt eluant into a container,
• wherein the method is carried out in the well equipped with the filter and the method comprises a step of enzymatically synthesizing the polynucleotide before the step of adding a chaotropic agent, the step of enzymatically synthesizing the polynucleotide being performed in the well in which the step of adding a chaotropic agent is performed.