CHROMATOGRAPHIC SEPARATION AND SPECTRO-ANALYTICAL CHARACTERIZATION OF A NATURAL AFRICAN MINERAL DYE

Abstract

Chromatographic fractionation and spectroscopic characterization of a natural African mineral dye have been carried out. The chromatographic separation of the dyes made use of column and thin layer chromatographic techniques. Some physicochemical properties of the dye including solubility in polar and non-polar solvents, pH, ash and organic contents were determined. The spectro-analytical techniques used for characterization included energy dispersive X-ray fluorescence (EDXRF), X-ray diffractometry (XRD), Optical microscopy, infrared (IR) and UV-VIS spectroscopy. Four different fractions having colours yellow, grey, orange and purple were obtained from the chromatographic separation. All the fractions were found to contain aromatic nucleus based on IR and UV-VIS spectroscopic data. Other functional groups detected are
Ar-NH₂, -CONH₂, C=C, C-C and metal-carbon chelate rings. The presence of aromatic amine in the dye provides strong evidence for its use as hair dye. The dye was found to be soluble in both aqueous and non-aqueous solvents. The pH of the dye's aqueous solution was found to be 8.6, and the ash and organic content of the raw dye were 49 % and 51 % respectively. The XRF revealed that the dye contains twenty elements with concentrations ranging from major to ultra-trace levels. The XRD also showed that the sample contains about forty-six mineral phases which include both inorganic and organic components. The maximum absorption wavelength (λ_max) in UV-VIS of the aqueous solution was found to be 464 nm. The optical microscopic investigation gave indication that the dyes are likely to be of the marine origin.

KEY WORDS: Natural African mineral dye, Chromatographic separation, Composition, Inorganic, Organic, XRF, XRD, Optical microscopic, Marine, Aromatic amine


Bull. Chem. Soc. Ethiop. 2007, 21(2), 159-170.