Mobile phase reservoir:

It holds one litre of the mobile phase. That reservoir is made up of stainless steel which is inert to most mobile phases and is not subject to breakage. Many different forms of reservoirs have been used, and simple units may be constructed from glass flasks or bottles of an appropriate size. Some reservoirs are designed so that the mobile phase may be degassed in situ. Degassing is required to eliminate dissolved gases, particularly oxygen. To permit in situ degassing, reservoirs are sometimes equipped with a heater, a stirring mechanism and inlets for applying vacuum and a nitrogen purge.