1. . 
An analytical procedure to determine the concentration of carbonate species using the Garrett Gas Train (GGT) when performed to API specifications. A water mud filtrate sample is put into the GGT. N2 or N2O is the carrier gas. A CO2 Draeger tube is used to measure the total carbonates released as CO2 when sulfuric acid is added to the chamber containing the sample. Total carbonates are measured by the amount of CO2 evolved in the test.
Reference: Garrett RL: "A New Field Method for the Quantitative Determination of Carbonates in Water-Base Drilling Fluids," Journal of Petroleum Technology 30, no. 7 (July 1978): 860-868.