MICROWAVE-ASSISTED VAPOR-GENERATION FOURIER-TRANSFORM INFRARED SPECTROMETRIC DETERMINATION OF CARBONATE IN WATERS

A microwave-assisted vapour-generation Fourier transform infrared spec trometric procedure is proposed for the determination of total carbona te in waters. The method is based on the simultaneous injection of 100 mu l of sample and 300 mu l of 0.1 M nitric acid in a two-channel man ifold with a merging zone; a coil located inside a microwave oven enco urages the removal of CO2. The carbon dioxide is separated from the di stilled water employed as carrier by means of gas-liquid separator and is introduced by a nitrogen carrier flow inside a long-path infrared absorption gas cell, from which the corresponding flow analysis record ing is registered as a function of time in the wavenumber range 2500-2 150 cm(-1). This provides direct quantification of total carbonate con centration in the range up to 1000 mg HCO3- l(-1) with a sampling freq uency of 15 h(-1). This procedure has a limit of detection of 15 mg HC O3- l(-1) and a variation coefficient of 1.3% for five independent ana lyses of 500 mg HCO3- l(-1). Results obtained for a series of real wat er samples compare well with those obtained using a titrimetric refere nce method. (C) 1998 Elsevier Science B.V.