A rapid spectrophotometric method for the determination of transparent exopolymer particles (TEP) in freshwater

A simple and rapid spectrophotometric method is proposed for the determination of transparent exopolymer particles (TEP) in freshwater samples. In this method, TEP reacts with excess of alcian blue solution yielding a low solubility dye–TEP complex. After centrifugation, the concentration of the remaining dye in the supernatant was determined at 602 nm and its concentration was related to the concentration of TEP in freshwater. The effect of alcian blue concentration from 1.5×10−3 to 9.0×10−3% (m/v), solution pH from 2.5 to 6.9 and stirring time from 20 to 120 s on the analytical curve was investigated. Under the optimum conditions established, such as alcian blue concentration of 3.0×10−3% (m/v); pH of 4.0 (0.2 mol l−1 acetate buffer solution) and stirring time of 1 min, the analytical curve was linear from 0.50 to 10 μg ml−1 (A=0.34−0.037[GX]; r2=0.9999; where A is the absorbance and [GX] the gum xanthan concentration in μg ml−1) with a detection limit of 0.10 μg ml−1. The recovery of TEP (as gum xanthan) for two samples ranged from 95.3 to 108 and the relative standard deviations (R.S.D.s) were lower than 0.8% for gum xanthan solutions at concentrations of 1.0 and 1.5 μg ml−1 (n=8). The results obtained for TEP in freshwater samples using the proposed spectrophotometric method and those obtained using a literature method are in agreement at the 95% confidence level and within an acceptable range of error.