On-Line Collection/Concentration and Detection of Sulfur Dioxide in Air by Flow-Injection Spectrophotometry Coupled with a Chromatomembrane Cell

Abstract

A simple and rapid procedure for SO₂ determination in air was developed by using a flow injection analysis (FIA) system coupled with a 3-hole chromatomembrane cell (CMC). The CMC was applied for the on-line collection/concentration of SO₂ from air into a solution of 2 g l^-1 triethanolamine (TEA) solution as an absorbing solution: SO₂ was converted to SO₃^2- in the alkaline absorbing solution. The solution containing absorbed SO₂ was introduced into the carrier stream of the FIA system. The amount of SO₃^2- in the absorbing solution was measured by spectrophotometry with a mixed reagent of pararosaniline and formaldehyde, and was converted to the concentration of SO₂ in the air sample. A calibration graph prepared by using standard sodium sulfite aqueous solutions was adopted for the determination of SO₃^-2 in the absorbing solution. The SO₂ concentration in indoor air examined was found to be 22.7 ± 0.2 ppbv using 20 ml of air sample with the air flow rate of 5 ml min^-1, where the relative standard deviation was 1.7%. The detection limit for aqueous solutions and air samples were 6.9 × 10^-8 M and 0.48 ppbv, respectively. The measuring time for one sample was about 10 min when a 20 ml air sample was used. The interferences from common anionic species, formaldehyde and acetaldehyde, were also examined.