Theoretical and Analytical Aspects of Carbonic Species Determination in Rain, Ground, Geothermal and Petroleum Waters

Abstract

We present the acid-base titration procedure for the determination of carbonic species in four types of waters: a. rainwater containing low concentration of dissolved species and low alkalinity, b. ground and surface water which contains mainly carbonic alkalinity, c. geothermal water which has carbonic and other alkalinities, and d. petroleum waters which have high concentration of salts and no contact with the present atmospheric CO2.
The calibration of standards is crucial. The NaOH solution mostly contains a small amount of CO2 dissolved. Therefore, the standardization of NaOH solution is performed with titrating up to the carbonic acid equivalence point (H2CO3EP) instead of pH = 7.0.
The Gran titration method for rainwater is performed with adding a small amount of NaOH (or HCl) and then titrating with HCl (or NaOH). The NaOH standard solution must be free from dissolved CO2.
The H2CO3EP alkalinity method requires the subtraction of other alkalinities (such as boric, silicic) from the total alkalinity in order to obtain a representative carbonic alkalinity for geothermal waters. This method is also applicable for ground waters. The preliminary results for the determination of carbonic species in petroleum waters show the existence of very little or no carbonic alkalinity in them. However, the proposed method requires a complete analysis of all parameters which contribute to the H2CO3EP alkalinity including dissolved gases like H2S.