Influence of Sampling Filter on Determination of Anions in Airborne Particulates

Abstract

Concerning the analyses of SO₄^2- and NO₃^- on filters on which airborne particulates were collected, the measurement conditions of SO₄^2- and NO₃^- on filters and the influences of SO₂ and NO₂ at low concentration on the analytical value were investigated in order to find out the suitable filter for the airborne particulates sampling. The filters used were glass fiber filter (G. F), quartz fiber filter (Q. F), teflon binding glass fiber filter (T. B), and teflon coated glass fiber filter (T. C). To extract SO₄^2- and NO₃^- on filters completely, more than ten minutes' work on ultrasonics was needed. Amounts of the ions showed no serious errors by the portions cut from the filters. Anions on filters were stable for 30 days when stored in a freezer under -20°C.
The amount of SO₄^2- produced by exposuring SO₂ to filters was in the order of G. F >> Q. F > T. B ≈ T. C. As to NO₃-amount produced by exposure of NO₂, differences among the filters were not appreciably observed. Q. F showed slightly high value of SO₄^2- in airborne particulates but it fits to the monitoring because of its high collection efficiency and low pressure drop.
T. C showed the least influence of SO₂ and NO₂ on the amount of SO₄^2- and NO₃^- as well as high collection efficiency, but drastic pressure drop by clogging. It was suggested that T. C was suitable for accurate determination of anions in airborne particulates samples collected in a short time.