Prediction of pollutant concentration in river has been studied for a long time. Quall II solves time-dependent mass diffusion and convection simultaneously. Quall II is using numerical solution where the errors of prediction are 30-70%. These errors arise from large step in space (Dx). In this study a new mathematical method has been used to solve the second order partial differential equation where the pollutants along with diffusion and convection respect to time can be adsorped and desorped in down stream. An exact measurement can be used to verify accuracy of any prediction or calculations. The Gas Chromatography is exactly ideal system for finding the accuracy of these calculations. Since governing equation and physical characters are same in both cases, theses similarities can be tested by chemical measurement. The new mathematical method applied to solve the governing equation, and results shows only 7% error in predicted concentration respect to measured concentration in Gas Chromatography.