DUAL-PHASE GAS-PERMEATION FLOW-INJECTION THERMOMETRIC ANALYSIS FOR THE DETERMINATION OF CARBON-DIOXIDE

A flow-injection configuration based on a dual-phase gas-permeation sy stem from a liquid donor to a gas acceptor stream with a thermistor fl ow-through detector is proposed for the direct analysis of the gas in the acceptor. This system was applied for the determination of carbon dioxide (in the form of carbonate) using the following chemical reacti on: CO2(g) + 2NH(3)(g) + H2O(g)= (NH4)(2)CO3(s), with a linear respons e from 1 x 10(-3) to 50 x 10(-3) mol l(-1) of CO32-. Carbon dioxide wa s produced in the liquid donor and permeated into the gaseous acceptor stream of air/water vapor. The detection limit is 1 x 10(-3) mol l(-1 ) of carbonate, and a sampling frequency of 60 h(-1) is achieved with a relative standard deviation of 4.1% for replicate injections. The du al-phase gas-permeation flow-injection manifold, along with the membra ne and phase separations, as well as the chemical reaction, provides e nhanced selectivity when compared with the system employing a liquid a cceptor stream, as serious interferents in this system, for instance, acetate and formate, among others, do not interfere in the proposed sy stem. (C) 1998 Elsevier Science B.V. All rights reserved.