A new determination method of anionic detergent in the seawater based on metachromasy and correlation between Azur A and methylene blue assays

Serap Akıncı, Kasım Cemal Güven

University of Istanbul, Institute of Marine Sciences and Management, Müşküle Sok., 1, Vefa, 34470 Istanbul, TURKEY

Abstract

Anionic detergents in seawater have usually been determined by methylene blue method. In addition, Azur A assay was proposed in this work correlation was sought between the two methods. The assays were made at α-band and metachromatic band (β-band) of both dyes. The calibration curves were plotted at 625 nm and 600 nm for methylene blue and at 637 nm and 600 nm for Azur A. Anionic detergent amounts in seawater found were 16.82 µg/L at 652 nm and 18.66 µg/L at 600 nm for methylene blue and 16.14 µg/L at 637 nm and 15.52 µg/L at 590 nm for Azur A. The results of the seawater plus 25 µg/L LAS were: 39.30 µg/L. µg/L for methylene blue and 41.14 µg/L 39.46 µg/L for Azur A respectively. The results of detergent amount in seawater and LAS added seawater are similar for α-bands of both dyes and slightly lower in metachronic bands (β-band). The interfering compounds in seawater influence the assay ehn using methylene blue and Azur A. It was difficult to eliminate totally this problem. The measurement can be made separately on the α and β bands of Azur A and also methylene blue. It is difficult to say either method as exact.

Keywords: Anionic detergent, methylene blue, Azur A, metachromatic assay, seawater