Purification can be achieved by preparative chromatography. The compound was isolated by preparative gas chromatography. In preparative chromatography, GC can be used to prepare pure compounds from a mixture. The wide flow range makes it suitable both for analytical and preparative chromatography. The preparative SEC can be used for polymer fractionation on an analytical scale. F. Francuskiewicz gives an overview about preparative polymer fractionation. Because of practical limitations, protein electrophoresis is generally not suited as a preparative method. Many preparative procedures afford a mixture of equal amounts of both enantiomeric forms. Traditional affinity columns are used as a preparative step to flush out unwanted biomolecules. PAGE may also be used as a preparative technique for the purification of proteins. Protein purification is either "preparative" or "analytical". Singlet oxygen can also be in non-photochemical, preparative chemical procedures. Nitrilases can also be used as catalysts in preparative organic chemistry. Antibody responses generated by DNA are useful as a preparative tool. The division went on to design and manufacture a range of preparative and analytical ultracentrifuges.