The feasibility of shock or shear sensitive colloidal separation by flow through thin channels is examined. Colloidal size particles have low diffusivities and may be fractionated by flow. In sepa- ration by flow a sample in a carrier is injected into a column with boundary layer velocity gradients developing, causing particles to emerge from the column according to size. This methods advantages is its ability to detect size distributions, low cost and ease of use with shock or shear sensitive materials.