Extraction of naphtholsulfonic acids from aqueous solutions with the use of a rotating concentrating unit and their photometric determination in the back extract

A new concentrating unit is proposed for the extraction of naphtholsulfonic acids; the unit is a ferromagnetic (steel) rod in a polyethylene or glass case coated with a mixture of cetyl alcohol with trioctylamine N-oxide. The rod is immersed in an analyzed solution and rotated in an alternating magnetic field (solid-phase extraction). The extraction-sorption characteristics of naphtholsulfonic acids were calculated, and a procedure was developed for their selective photometric determination in back extracts.