FC-06   ANALYTICAL DETERMINATION OF MELANIN IN HUMAN HAIR

M. Zoccola, R. Innocenti, R. Mossotti. C.N.R-ISMAC, Biella, Italy.

The natural colour of hair is determined by two chemically distinct types of melanin pigments, the black to brown eumelanins and the yellow to reddish-brown pheomelanins. Methods used for the quantitative determination of melanin in tissues follow a degradation approach, which makes unnecessary the isolation of melanin from tissues. The classical method is based on the formation of pyrrole-2,3,5 tricarboxylic acid (PTCA) by permanganate oxidation (eumelanin) and of aminohydroxyphenylalanine isomers (AHP) by hydriodic acid hydrolysis (pheomelanin). The products are determined by high performance liquid chromatography (HPLC). More recent study, show that the most reliable degradation approach for eumelanic tissues is alkaline oxidation with hydrogen peroxide, that afford high yields of PTCA, the characteristic structural marker of eumelanic pigments. Our work consisted in the analytical determination of PTCA in some undyed hair samples ranging from red, to blond, light and dark brown and black. Hair samples were submitted to alkaline H2O2 oxidation for 24 h with stirring. After the H2O2 decomposition, the mixture acidification and the centrifugation, the supernatant was injected for HPLC analysis, and the amount of PTCA was determined. The quantity of PTCA produced varies over quite a wide range from about 200 ng/mg (black hair) to 30 ng/mg (red hair). The same hair samples were analysed by Near Infrared Spectroscopy in reflectance mode. For the measurements, hair were fixed to the 12 mm measurement round window in a stationary configuration. NIR spectrum of human hair is dominated by combination bands of the N-substituted amide groups of the peptide linkage. Main differences between hair samples of different colours are present in the spectral region between 7000 and 10.000 cm-1 (near the visible region of the spectrum). A correlation between NIR spectra and PTCA determined by HPLC analysis was investigated.