Bisegmented flow system for determination of low concentrations of gaseous constituents in gaseous samples

Abstract

The monosegmented flow approach has been modified to produce a bisegmented flow system aimed at the determination of gaseous analytes present in low concentrations in gaseous samples. The concentration ranges can vary from < 1% (v/v) to nl l −1. A flow pattern constituted of b#1-ls#1-b#2-ls#2-b#3, where b indicate a gas bubble and ls a liquid segment, is produced by a single movement of the injection device. The system is computer controlled and two procedures can be used for the determination of the gaseous analytes. In the first the b#2 segment constitutes the sample and a suitable reagent is added in ls#1 after the whole pattern is present inside the glass flow manifold. The gas sample is forced to flow over the liquid reagent layer left behind by ls#1 and a detectable specimen is formed. The ls#2 collects the product and carries it to the detection point. In the second procedure ls#1 contains a suitable absorbing reagent and forms an absorbing layer on the tube wall. The carrier flow is stopped when b#2 reaches an entrance arranged perpendicular to the glass reactor tube. Through this entrance a large volume of a gaseous sample is impelled. The gaseous analyte is absorbed and concentrated in the liquid layer. About 85% of the analyte can be retained by the absorbing layer. When this operation is finished the carrier flow is re-established and ls#2 removes the absorbed analyte from the liquid layer. This segment may or may not contain a suitable reagent. The system has been applied for the determination of O 2 (0–1% v/v) in the atmosphere of food packages by reacting the analyte with pyrogallate and of NO 2 in synthetic air by absorbing the analyte in triethanolamine and reacting it with Saltzman reagent in ls#2. The system is capable of determining NO 2 in air samples in the range 25–250 nl l −1.