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

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 O2 (0–1% v/v) in the atmosphere of food packages by reacting the analyte with pyrogallate and of NO2 in synthetic air by absorbing the analyte in triethanolamine and reacting it with Saltzman reagent in ls#2. The system is capable of determining NO2 in air samples in the range 25–250 nl l−1.