 A staining method where at a fixed pH of about 5.5, different critical salt concentration (classically MgCl2, but NaCl, KCl, LiBr are potential alternatives) can be used where the smaller (faster diffusing) salt cation competes with alcian blue to bind to the anionic sites.Target material specific critical electrolyte concentration (CEC) is supposed to selectively identify sulphated, carboxylated and phosphated structures for example as the targets.According to John A. Kiernan—one of the editors of the 10th edition of "Conn's Biological Stains" 10th ed 2002" published on behalf of the Biological Stain Commission