Hanks' salts are designed for atmospheric equilibration, therefore no carbon dioxide is required. Earle's salts are designed for the bicarbonate/carbonic acid system commonly used in media. Earle's salts rely on the equilibration of gaseous and liquid carbon dioxide to maintain pH in a carbon dioxide equilibrated incubator.

• The link for the formulation of MEM with Hanks' salt: http://www.invitrogen.com/content.cfm?pageID=95&fuseaction=MediaForm.dsp_mediaForm&productId=111
• The link for the formulation of a typical MEM with Earle's salt: http://www.invitrogen.com/content.cfm?pageID=95&fuseaction=MediaForm.dsp_mediaForm&productId=92