Determination of gaseous species by monosegmented flow systems. Volumetric determination of oxygen and carbon dioxide

A Monosegmented Flow System was developed to determine the content of gaseous analytes in gaseous samples. The proposed system, in contrast with previous monosegmented systems, employs the gas bubbles as gaseous samples. The volume of the bubbles is assessed indirectly by counting the time elapsed by the passage (at constant flow rate) of the liquid-gas and gas-liquid boundaries, defined for each bubble, through optical switches. Two optical switches are employed for bubble volume measurement: one counts the bubble passage before analyte absorption and the other is positioned after the inlet point of the reagent (added only into the liquid monosegment) and, therefore, can assess the bubble volume after the analyte absorption. The ratio of the elapsed time intervals taken before and after the analyte absorption is used as analytical parameter and inversely related with the content of the gaseous analyte. The instrument is controlled by a micro-computer. The principle has been applied to the determination of O2 and CO2 (including when they are present in mixtures containing both specimens) in gaseous samples together with an inert gas. The results show a mean absolute error of 0.1% and 0.3% for determination of O2 and CO2 present in the range 5–50% and 5–15% (v/v), respectively, when calibration with standard gaseous mixtures is employed. An alternative procedure that employs the volume ratio directly as the volumetric fraction of the gaseous species in the sample was also evaluated. About 40 samples can be processed per hour with the proposed system.