DETERMINATION OF CARBONATES IN WATERS BY ONLINE VAPOR GENERATION FTIR

An electrically heated gas-permeation unit (GPU) has been employed for the vapor-generation Fourier transform infrared (FTIR) determination of total carbonate in waters. The developed method is based on the sim ultaneous injection of 100 mu l sample and 100 mu l nitric acid in a t wo-channel manifold with a merging zone, which provides the generation of CO2 through the GPU, heated at 90 degrees C, from which CO2 is swe pt by a stream of N-2 to a long-path infrared gas cell. Absorbance mea surements were made in the range from 2500 to 210 cm(-1) and the corre sponding flow injection recordings were obtained as a function of time . The areas of these peaks are interpolated in a calibration equation obtained from aqueous standards of Na2CO3 treated in the same way as s amples. The method provides a limit of detection of 4.6 ppm (expressed as mg of HCO3- l(-1)) and a sampling frequency of 30 h(-1). Results o btained for a series of natural waters compare well with those obtaine d by a titrimetric reference method. (C) 1998 Elsevier Science B.V.