A new strategy for membraneless gas-liquid separation in flow analysis: Determination of dissolved inorganic carbon in natural waters

Abstract

Mechanization of separation and preconcentration processes by flow analysis is noteworthy due to improved precision, low consumption of reagents and samples, as well as lower risks to the analyst, of analyte losses, and contamination. The low efficiency of gas diffusion may however limit the sensitivity of flow-based procedures involving gas-liquid separation. This paper deals with the evaluation of potentialities and limitations of a flow analyzer exploiting a new strategy for gas-liquid separation. The manifold comprised a lab-made syringe pump connected to a separation chamber and solenoid valves for solution management. Gas diffusion without barriers for phase separation was implemented inside the chamber under an air flux, followed by the transference of headspace towards an acceptor/derivatization solution inside the syringe. The innovation was exploited for the determination of dissolved inorganic carbon in natural waters. Sample and an acidic solution were aspirated to the chamber and the generated CO2 was directed towards a bromothymol blue solution, whose color change was monitored by spectrophotometry. A linear response range was attained within 0.5 and 5.0 mg L−1, with limit of detection of 0.25 mg L−1, variation coefficient < 5% (n = 10), and sampling rate of 12 h−1. An 11.5-fold increase in sensitivity was attained with the proposed procedure in relation to the analogous membrane-based procedure. Results for the analysis of river waters agreed with those attained by the reference procedure at the 95% confidence level.