Biological processes preferentially take up the lower mass isotope through kinetic fractionation. These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis. Chromatography, electrophoresis and Field Flow Fractionation are representative of this field. This effect is known as isotopic fractionation. In equilibrium fractionation between phases, heavier phases prefer the heavier isotopes. Denitrification can lead to a condition called isotopic fractionation in the soil environment. During this time, there was an increase in molybdenum isotope fractionation. Organelles are identified by microscopy, and can also be purified by cell fractionation. These are obtained by various methods of fractionation or depolymerisation of polymeric heparin. It is a separation technique based on the theory of field flow fractionation (FFF). That is the origin of the name "fractional distillation" or "fractionation". Another variation involved a heat ethanol fractionation. This process is sometimes called cold alcohol fractionation or ethanol fractionation. Another possibility to overcome these issues is the separation by field-flow fractionation (FFF). Ultracentrifuges can also be used in the study of membrane fractionation.