New azo dyes as colored isoelectric point markers for isoelectric focusing in acidic pH region

Newly prepared azo compounds and several commercially available indicators were investigated for their applicability as colored isoelectric point (pI) markers for isoelectric focusing (IEF) in the acidic range below pH 5. The majority of compounds described here can serve as primary standards since their pI values were determined by UV–VIS spectrophotometry independently IEF and direct measurement with a pH electrode. Subjected to gel IEF they show narrow and well‐observable zones of different colors. Finally, our work resulted in suggestion of a color ladder composed of pI markers covering the pH range from 1.5 to 4.7.