DNA sequencing protocols which utilize multiple cycles of DNA synthesis by Taq DNA polymerase require recovery of small sample volumes from beneath a layer of mineral oil. However, the small volume of aqueous phase and the high surface tension between the two phases makes complete recovery of the aqueous phase without contaminating mineral oil difficult. These difficulties can be largely eliminated by substituting low density silicone oil for the mineral oil. The surface tension of silicone oil is lower than that of mineral oil, allowing easier recovery of the aqueous phase without contaminating oil. Also, the silicone oil is somewhat soluble in isopropanol, allowing easy removal of any trace amounts of silicone oil which may be carried over.