Determination of Calcite and Dolomite in Calcareous Soils with the Carbonate-Meter and EDTA.

Inorganic carbon (IC) in calcareous soils has two components, calcitic-carbon  and dolomitic-carbon.  Even though there are several procedures for quantifying IC, available literature pertaining determination of calcite and dolomite in calcareous soils is very scarce. Our objective was to develop a method to directly quantify calcitic-carbon and dolomitic-carbon in calcareous soils. Total analysis of IC is done gravimetrically with the Carbonate-Meter, and determination of calcite and dolomite is done complexometrically in the acidic solution with EDTA.  The Carbonate-Meter can be prepared in the laboratory with one 50-ml Erlenmeyer flask, one 6-ml glass vial, and one number-1 rubber stopper with one hole.  Iceland spar calcite and NIST dolomitic limestone standards were analyzed gravimetrically for IC, and volumetrically with EDTA for calcite and dolomite. The Carbonate-Meter was used to determine IC in 0.200 ± 0.020 g of sample and 4.0 ml of 0.8 M HCl. The acidic solution containing the Ca and Mg in the Erlenmeyer flask is separated from the soil residue by filtration, spiked with 1 ml 2% MgCl₂, then brought to 100 ml volume, homogenized well, and analyzed for Ca and Mg  at pH = 10.00 with 0.02M EDTA, on a 20 ml aliquot in the presence of eriochrome-black.  Calcium was analyzed at pH > 12.5 after Mg precipitation with 2M NaOH, on a 20 ml aliquot using murexide as indicator.  Results showed for Iceland spar calcite and NIST dolomitic limestone, IC precisions of 0.364 % and 0.354 % and recoveries of 101.58 % and 101.63 %, respectively.  Calcite and dolomite precisions were 0.775 % and 0.332 %, respectively, while recoveries of 98.364 % and 98.509 % were found for Iceland spar calcite and NIST dolomitic limestone, respectively.  The procedure is easy to follow in the laboratory, it is economical, and has a good precision and accuracy.