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Using indigo absorbance to calculate the indigo sensitivity coefficient
Author(s) -
Gordon Gilbert,
Gauw Renee D.,
Miyahara Yuko,
Walters Bryan,
Bubnis Bernard
Publication year - 2000
Publication title -
journal ‐ american water works association
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.466
H-Index - 74
eISSN - 1551-8833
pISSN - 0003-150X
DOI - 10.1002/j.1551-8833.2000.tb09074.x
Subject(s) - indigo , absorbance , molar absorptivity , analytical chemistry (journal) , calibration , calibration curve , coefficient of variation , sensitivity (control systems) , chemistry , indigo carmine , materials science , chromatography , mathematics , nuclear chemistry , optics , detection limit , statistics , physics , electronic engineering , engineering
The standard method for measuring residual ozone (O 3 ) is based on the decolorization of indigotrisulfonate at 600 nm using a sensitivity coefficient of 0.42 L mg –1 cm –1 (ε ~ 20,000 M –1 cm –1 ). The sensitivity coefficient for a source of indigo is calculated following a time‐consuming and labor‐intensive O 3 calibration. In contrast, the data presented in this article show that a simple initial absorbance measurement can be used to calculate the indigo sensitivity coefficient, thereby eliminating the need for O 3 calibration when routine measurements are made. The molar absorptivity for seven sources of indigo ranged from 15,800 to 20,355 M –1 cm –1 . These results indicate that indigo purity (and stability) is potentially a significant source of measurement error when unvalidated indigo stock solutions are used to measure O 3 . The authors describe indigo solution decomposition and offer a simple initial absorbance method for validating the O 3 sensitivity coefficient.