Fluorescent Dye and Media Properties Affecting Sorption and Tracer Selection

Abstract

Abstract This paper discusses the importance of fluorescent dye sorption when selecting dyes for tracer studies. The effect of dye and media properties on dye sorption was evaluated using four fluorescent dyes (fluorescein, rhodamine B, rhodamine WT, and sul‐forhodamine B), two oppositely charged mineral surfaces (alumina and silica), and n‐octanol (as a neutral organic phase). Fluorescein, which has only negative functional groups, sorbed least onto negatively charged silica but most onto positively charged alumina. The rhodamine dyes, with a permanent positive charge and negatively charged functional groups, sorbed onto both alumina and silica. Sulforhodamine B, with two strongly electronegative sulfonic groups, sorbed less onto negatively charged silica than did rhodamine WT, which has two carboxyl groups. Dye partitioning into n‐octanol was strongly pH dependent with fluorescein being the most hydrophobic, followed by rhodamine WT and sulforhodamine B. Since fluorescent dyes are subject to sorption, dye selection should be based on their chemical properties, media characteristics, and laboratory batch and column studies.