Chiang Mai Journal of Science

 This work describes a method based on vaporization techniques,for direct determination of calcium carbonate in fortified calcium tablets and for determination of total carbonate content in water.A discarded jam jar was adapted to be used as a closedreaction chamber.  A piece of cylindrical glass was fitted at the bottom to form a base for the sample vial.  In the experiment, a vial containing a carbonated sample was placed inside the jar, surrounding by a pH indicator solution (acceptor solution).The samples containing the carbonate were transformed from these solid or liquid states by acidification toa carbon dioxide gaseous phase inside the jar.The diffused carbon dioxide was then trapped into the indicator acceptor (Cresol red).  The change of the absorbance of cresol red, based on alteration of solution pH, was detected at wavelength 440 nm.  The system showed good linearity between absorbance and carbonate concentration allowing direct measurement of carbonate in both solid and liquid samples.  The results show that the developed system is both performs well and iscost-effective for quality control in industry and in environmental measurement.