Determination of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in freshwaters by sequential injection spectrophotometry with on-line UV photo-oxidation

Abstract

An automated sequential injection (SI) method for the determination of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) in freshwaters is presented. For DIC measurement on-line sample acidification (sulphuric acid, pH < 2), converted DIC to CO2 which subsequently diffused through a PTFE membrane into a basic, cresol red acceptor stream. The CO2 increased the concentration of the acidic form of the cresol red indicator, with a resultant decrease in absorbance at 570 nm being directly proportional to DIC concentration. DIC + DOC was determined after on-line sample irradiation (15 W low power UV lamp) coupled with acid-peroxydisulfate digestion, with the subsequent detection ..