A linear model is used to show that dynamic field gradient focusing (DFGF) can be scaled to preparative capacity, similar to O (10 rugs). This paper explains how the preparative-scale DFGF apparatus was designed and fabricated. Scaled-down experiments and mathematical modeling guided material selection and design changes during construction to increase the probability that the prototype preparative-scale DFGF apparatus would perform as intended. The finished prototype successfully focused bovine hemoglobin from an initial concentration of 6.82 to 15 mg/mL and allowed for 86% recovery of injected protein.