PURPOSE: To transfer a product or impurities under optimal state between processes or machines by analyzing the composition of solution discharged from a process and then determining destination of the solution based on the results of analysis.

CONSTITUTION: Product solution 1 containing impurities is introduced to a process 2 for removing impurities from the product and discharged from the process 2 after the impurities are removed. In this regard, a part of the product solution 1 discharged to an analyzer 5 is sampled and the impurity concentration of sampled solution 6 is measured. Magnitude of measurement is then decided and a control signal 7 is delivered to a three-way valve 8. Consequently, the product solution 1 is transferred to process 3 or 4 depending on the impurity concentration of solution processed through the process 2. This method allows normal management of process (under optimal state) while transferring the solution to a process optimal for the composition thereof.