Abstract: A flow injection apparatus was constructed (illustrated schematically), which permits such analyzes. Determination of H2O2 involved amperometric oxidation with Pt working and auxiliary electrodes at 250 mV (Ag - AgCl reference electrode). The detection limit was 5 µg L-1 and the response was rectilinear up to 5 mg l-1. Selective and sensitive spectrophotometric detection of SO32-, formaldehyde and hydroxymethanesulfonic acid is described. For SO32- the reaction involved di-4-pyridyl disulfide; indirect procedures for the organic analytes are described. The limit of detection was 50 µg L-1 and response was rectilinear up to 5 mg l-1.