Before the DNA can be analyzed, it must be extracted from the cells and purified. The germanium was then chemically extracted and concentrated. It can be extracted from liquid air by fractional distillation. Essential oils are generally extracted by distillation, often by using steam. Nepetalactone can be extracted from catnip by steam distillation. The soluble pertechnetate can then be chemically extracted by elution using a saline solution. The sap is extracted and collected by a tapper. Blood plasma, containing the antibodies, is extracted by plasmapheresis. Minor amounts are probably also extracted from sulfidic copper ores. Iron ores are rocks and minerals from which metallic iron can be economically extracted. Groundwater can be extracted using a water well. Abietic acid can also be extracted from rosin by means of hot alcohol. These segments can then be extracted through gel electrophoresis. These salts could not easily be extracted from the ground due to the rain. Pigments may be extracted and used as dyes.