Analytical problems arising from the use of bromide and rhodamine WT as co-tracers in streams

Abstract Bromide and the fluorescent red dye rhodamine WT were used as co-tracers to determine the hydrodynamic characteristics of an experimental stream. However, the presence of the dye caused a negative interference during the subsequent colorimetric analysis of bromide. Approximately two bromide atoms reacted with each molecule of rhodamine. The fixed stoichiometry of this reaction permitted the true concentration (in μM units) of bromide to be determined from the simple relationship: true [ Br]=apparent [Br] + 1.61 [ rhodamine ] . Thus, bromide and the dye can be used together as co-tracers without having to carry out a time consuming pre-treatment step to remove the rhodamine WT prior to the determination of the bromide. Bromide proved to be a more reliable tracer than Li+ or rhodamine WT in the stream that was studied.