Humic acid-cetyltrimethylammonium bromide interaction: A fluorimetric study

Synchronous and excitation emission matrix fluorescence (EEMF) characteristics of humic acid-surfactant interaction have been studied. The variation of synchronous and EEMF spectral maxima and intensities with humic acid (HA)-cetyltrimethylammonium bromide (CTAB) composition sensitively reflects the extent of flocculation of HA. It was found that the concentration range for co-precipitation of HA-CTAB was similar for all concentrations (60 p.p.m., 80 p.p.m. and 100 p.p.m.) of humic acid studied. In the concentration range 60-150 p.p.m. of humic acid, the EEMF maximum is found at 460/540 nm, indicating the presence of ligneous materials. Fluorescence intensity measurement at this contour excitation/emission wavelength (460/540 nm) is suggested as a convenient and a sensitive method for studying the physical state of humic acid in the presence of cationic surfactants. No significant interaction of HA with sodium dodecylsulphate (SDS) and TX-100 was found. © 2008 John Wiley & Sons, Ltd.