Determination of soil calcareous efficiency using flow system with pervaporative separation Original Research Article

A method is described for the conductimetric determination of CO2. The proposed system was constructed with a pervaporator chamber coupled to a flow system comprised of a six-way solenoid valve, a conductivity cell, a conductivimeter and a PC microcomputer for data acquisition and external controls. An amount of 2 g of dry soil samples were directly weighted in the donor compartment of the pervaporation chamber. The CO2 was determined from an analytical curve within 5.0×10−3–5.0×10−2 mol kg−1 CaCO3. This curve was constructed with the matrix matching approach and presented a linear regression of y=13.58+584.77r (r=0.9962). Soils with different lime amounts were analyzed by the proposed methodology and with the official method, that uses the calcium difference between the total, extracted with HCl 1 mol l−1 and exchangeable, extracted with the KCl 1 mol l−1. After paired t-test application, no significant difference between the methods was found at the 95% probability level. The proposed method presented sampling rate of 17 h−1, detection limit of 8.0×10−4 mol kg−1 CaCO3, and R.S.D.<3%. The use of the pervaporator allowed the in situ soil pretreatment for the residual lime determination.