Abstract
Indigo is one of the most important dyes in the textile industry. The control of the indigo concentration in dyeing liquors and effluents is an important tool to ensure the reproducibility of the dyed fabrics and also to establish the efficiency of the wastewater treatment. In this work, three analytical methods were studied and validated with the aim to select a reliable, fast and automated method for the indigo dye determination. The first method is based on the extraction of the dye, with chloroform, in its oxidized form. The organic solution is measured by Ultraviolet (UV)-visible spectrophotometry at 604 nm. The second method determines the concentration of indigo in its leuco form in aqueous medium by UV-visible spectrophotometry at 407 nm. Finally, in the last method, the concentration of indigo is determined by redox titration with potassium hexacyanoferrate (K3(Fe(CN)6)). The results indicated that the three methods that we studied met the established acceptance criteria regarding accuracy and precision. However, the third method was considered the most adequate for application on an industrial scale due to its wider work range, which provides a significant advantage over the others.
Highlights
The denim industry constitutes an important part of the textile sector, with an estimated world production of 109 blue jeans annually [1,2]
The characteristic blue color of denim clothes is due to the indigo dye, which is used in the dyeing of cellulose fibers [3,4]
Prior to the dyeing process, it has to be reduced into its leuco form
Summary
The denim industry constitutes an important part of the textile sector, with an estimated world production of 109 blue jeans annually [1,2]. The main disadvantage of indigo is the fast oxidation of its leuco form in contact with air. For this reason, some of the industrial dyeings are performed in nitrogen atmosphere. In order to ensure the reproducibility and regularity of dyed yarns, it is important to evaluate the indigo concentration in the dye baths during the dyeing process. Interest in recycling waste products has been extended to indigo-containing effluents. The aim of the present work was to establish a reliable analytical method for the determination of indigo dye concentration in both the dyeing baths and the residual effluents. None of them were focused on dyeing baths and effluents control and studies about reliability, reproducibility and accuracy were not included
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