Microwave-assisted vapour-generation Fourier transform infrared spectrometric determination of carbonate in waters

A microwave-assisted vapour-generation Fourier transform infrared spectrometric procedure is proposed for the determination of total carbonate in waters. The method is based on the simultaneous injection of 100 μl of sample and 300 μl of 0.1 M nitric acid in a two-channel manifold with a merging zone; a coil located inside a microwave oven encourages the removal of CO2. The carbon dioxide is separated from the distilled 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 recording is registered as a function of time in the wavenumber range 2500–2150 cm−1. This provides direct quantification of total carbonate concentration in the range up to 1000 mg HCO−3 l−1 with a sampling frequency of 15 h−1. This procedure has a limit of detection of 15 mg HCO−3 l−1 and a variation coefficient of 1.3% for five independent analyses of 500 mg HCO−3 l−1. Results obtained for a series of real water samples compare well with those obtained using a titrimetric reference method.