Spectrophotometric Study of Relation and involving factors in Cong red-Xanthan Interaction

Xanthan, the extracellular polysaccharide of the phytopathogenic bacterium Xanthomonas campestris, has many applications in different industries, especially in petroleum, food and pharmaceutical industries. Development of the simple and inexpensive methods for accurate measurement of xanthan concentration in aqueous solutions would be greatly appreciated. In this work, quantitative effect of xanthan interaction with congo-red was spectrophotometrically evaluated. It was demonstrate that at low concentrations, xanthan, induces hypochromocity (decreasing of the maximum absorbance) in solutions of congo red dye. Also, an overnight conservation of xanthan solutions before performing the colorimetric test is recommended for its establishment; simple up/down agitation provides an appropriate and quick procedure to obtain a mixture of the colored liquid and the xanthan solution. The best results were obtained by using Congo red dye at 4080- μg/l concentrations, 492 nm wavelength at all of the tested xanthan concentrations. Heating of xanthan solutions at 121 °C affected the absorbance without remarkable change in pattern of absorbance. This research provides basic information for development of a colorimetric method for measurement of xanthan concentration in aqueous solutions.