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 gaseou s samples. The volume of the bubbles is assessed indirectly by countin g the time elapsed by the passage (at constant flow rate) of the liqui d-gas and gas-liquid boundaries, defined for each bubble, through opti cal switches. Two optical switches are employed for bubble volume meas urement: one counts the bubble passage before analyte absorption and t he other is positioned after the inlet point of the reagent (added onl y into the liquid monosegment) and, therefore, can assess the bubble v olume after the analyte absorption. The ratio of the elapsed time inte rvals taken before and after the analyte absorption is used as analyti cal parameter and inversely related with the content of the gaseous an alyte. The instrument is controlled by a micro-computer. The principle has been applied to the determination of O-2 and CO2 (including when they are present in mixtures containing both specimens) in gaseous sam ples together with an inert gas. The results show a mean absolute erro r of 0.1% and 0.3% for determination of O-2 and CO2 present in the ran ge 5-50% and 5-15% (v/v), respectively, when calibration with standard gaseous mixtures is employed. An alternative procedure that employs t he volume ratio directly as the volumetric fraction of the gaseous spe cies in the sample was also evaluated. About 40 samples can be process ed per hour with the proposed system.