Highly selective visual distinction of pyrophosphate from other phosphate anions with 4-[(5-chloro-2-pyridyl)azo]-1,3-diaminobenzene in the presence of copper(II) ions

► This method needs no complicated modification and organic synthesis. ► This recognition process for PPi has a dramatic color change from red to cyan. ► We can visually detect PPi with naked eyes. ► This method has good selectivity for PPi against other anions such as nucleotides.