The hard work has been done and the purification is “complete”—the target compound has been separated from the other organic compounds in the mixture but is still in solution, and may possibly be “contaminated” by buffer salts or other inorganic compounds. The final, relatively easy, but necessary, step is to prepare the target compound in a usable form. This generally means producing a concentrated solution of pure compound or the pure dry solid, which may or may not be crystalline. The process of crystallization from solution can be used as a purification step in its own right or used to produce crystals for molecular structure determination by single-crystal X-ray diffraction—these two aspects are discussed in Subheading 5.