An analytical method for precipitated particles using a co-precipitation reaction in includes feeding streams and a tracking metal into a reaction vessel; collecting a precipitated product containing the tracking metal from the reaction vessel in increments of time to obtain product samples; filtering each collected product sample to separate precipitated particles from filtrate; and performing elemental analysis for the tracking metal in the precipitated particles of each collected product sample and measuring a concentration of the tracking metal in the precipitated particles, to obtain a residence time distribution of the precipitated particles in the reaction vessel according to the concentration of the tracking metal in the precipitated particles. Therefore the preferred residence time of the precipitated particles in the reaction vessel can be ascertained, so that it is clear when the precipitated particles should be collected from the reaction vessel.