OBJECTIVETo understand the particle settling characteristics of alcohol precipitation mixture of Paeoniae Radix rubra extract and establish models of the sedimentation rate.

METHODSFocusing on the particle settling characteristics such as particle settling curve, particle settling velocity (PSV), particle volume index (PVI), the particle settling process of alcohol precipitation was investigated. The effect of three key process factors on the settling process was discussed and mathematical models for describing the particle settling velocity were developed.

RESULTSControlling of higher final alcohol concentration, higher density of Paeoniae Radix rubra extract, or lower initial alcohol concentration, was conducive to settlement of alcohol precipitation particles. In the constant speed phase, an empirical calculation formula of v(0) was established, with both the variables PSV and PVI (v(0)=-0.236PSV+0.022PVI+7.521). Another developed model was applied to predict the settling velocity in decelerated phase and the simulation was very good [v=k(1-n(1)X)(4)exp(-n(2)X)/X].

CONCLUSIONThe results of this work will contribute to a better control and optimization of alcohol precipitation process, and help to implementation of accuracy control in the manufacture of botanical medicines.