Good afternoon Muhammad ...

Good afternoon Muhammad Forhadul.

How are you today? My answer is Yes, It is. There are samples with TDS readings higher than the EC readings. I have to say that it is not very common and the reason may be because of the presence of organic compounds . Please allow me to explain myself. Basically, as you know, the conductivity is a measure of the ability of an aqueous solution to carry an electric current and it is depends on the ions (concentration, mobility and valence) and the temperature of the sample. It is important to note since this is a waste water sample the presence of organic compounds that do not dissociate in aqueous solution conduct a current very poorly.

Now, base on the method for checking correctness of analyses (SM 1030 E #5 (*)) the radio of calculated TDS to conductivity should be between 0.55 and 0.7. (TDS/CON = 0.55-0.7). If the ratio is above 0.7, the higher ion sum is suspect, it is recommend to re-analyze the sample, now if the ratio falls bellow 0.55 the lower ion sum is suspect, it is recommend to re-analyze the sample. We ran and re-ran for many years samples with a ratio up to 2. These are waste water samples with high concentration of molasses. On the other hand, I should mentioned, since I have very limited information about your data, analysis, sample collections, holding times, calculations, instruments, calibrations etc it is very difficult to determine if there is an issue with the data (either accuracy or precision). I will be more than happy to help you. If you have any questions please let me know. Thanks for sharing your experience with us.

*Standard Methods for the examination of Water and Wastewater 21st Edition, 2005 D. Eaton Andrew, S. Clesceri Lenore, W. Rice Eugene and E. Greenberg Arnold.