Novel manganese colorimetric chemosensing investigations of Indigofera macrophylla Schum (Thonn.) stem and leaf dye extracts

Abstract

Purpose: To determine the chemosensor ability of dye extracts obtained from the stem and leaves of Indigofera macrophylla Schum (Thonn.), a scandent or climbing shrub belonging to the family Fabaceae.
Method: The dye extracts were obtained from the stem and leaves of the plant after optimizing the method of extraction, the concentration of base for precipitation as well as the contact time between base and aqueous plant extracts. The dyes were investigated for their colorimetric chemosensor properties using procedures such as screening of metals and non-metals, selection of analytical wavelengths, optimization of solvents, reaction temperature and time. Validation was carried out for the determination of manganese from aqueous solution by preparation of calibration curve, accuracy and reproducibility. Interference liabilities of the new method for manganese were studied in the presence of common cation and anions.
Results: The dyes were obtained in good yield and gave pink colours. Spot tests revealed the selective detection of manganese from the two dye extracts. These two dyes; the stems (DS and leaves (DL) dyes of Indigofera macrophylla) proved to be excellent colorimetric chemosensors for manganese in an aqueous solution. Linearity in Beer’s law plot were obtained within the concentration range of 10-50 μg/mL (r2 = 0.996 and 0.999 for DS and DL respectively). Accuracy gave relative errors generally less than 2.0% while for the precision, the relative standard deviations were less than 0.8%. There was no interference with common cations such as Cr³⁺, Cu²⁺, Zn²⁺ and anions such as CN^-and NO₂-
Conclusion: The natural dyes obtained from Indigofera macrophylla could be excellent sources of chemical principles for the detection and determination of manganese in aqueous solutions.

Keywords: Indigofera macrophylla, Natural dyes, Manganese, Colorimetric chemosensor, Interference studies