UV–Vis Spectrometry for Quantitative Study of Tannin and Flavonoid Rich Dyes from Plant Sources

Abstract

The UV–Vis absorbance method is modified as a faster and cheaper means for the study of extraction of natural dyes from plant sources. The method was validated using standard methods of analysis viz: egg albumin precipitation and aluminium colorimetric methods for quantification of tannins and flavonoids respectively. The solvents selected for extraction of dye from plant samples included; distilled water, methanol (5% v/v), ethanol (5% v/v), acidified water pH 3.5 (acidified with acetic acid), and sodium bicarbonate solution (0.1% w/w). Qualitative UV scans were conducted on dye extract of each plant obtained from previously dyed cotton fabrics and wavelengths at maxima for extract of each plant was recorded. In the validation step, data obtained from the modified UV absorbance method were compared to that obtained from standard methods. The modified and validated method was used for the study of extraction output of dye from selected dye-yielding plants using the selected solvents. Extracts from the selected plants registered absorbance maxima at wavelengths unique to each viz: A. coriaria (291 nm), V. paradoxa (294 nm), M.lucida (300 nm) and H. madagascariensis (428 nm) these were employed in setting the analytical instrument. Data obtained from the modified method closely correlated to that from egg albumin and aluminium colorimetric methods with R² = 0.989 and 0.9258 respectively. The modified method registered minimal errors in the range of (0.3–8.7%) for the A. coriaria extracts and errors of (2.3–6.7%) for M. lucida extracts. The errors recorded from the standard methods were in the range of (2.1–7.9%) and (2.29–6.8%) for egg albumin precipitation and aluminium colorimetric methods respectively. Both the standard and the modified methods exhibited similar accuracy of analysis. Through the application of the modified method, sodium bicarbonate solution (0.1% w/w) was identified to give the best dye extraction output. This modified method gives a faster and cheaper means for quantitative analysis where data is required rapidly for decision making.