Zur Mikrobestimmung des Gesamtschwefels in Pflanzengewebe

Abstract

SO₂ is one of the most important air pollutants. Plants, particularly forest trees, are more sensitive to it than is man. SO₂, enters the plants via stomates of assimilatory tissue and is stored in the latter. Foliar analysis for S is therefore an important method to detect air pollution by SO₂ even at low concentrations. Plants thus may be utilized as bioindicators of SO₂−pollution. The present paper examines the suitability of colorimetric S-determination in plant tissue with barium chloranilate in connection with tissue ashing in the Schöniger flask. Due to controversial opinions expressed in literature particularly the influence of the following potential sources of analytical error is checked: — removal of interfering cations by exchange resin in the presence or after destruction of peroxide (added to the Schöniger flask); — pH-dependence of color intensity; — duration of reaction to form the colored acid chloranilate ion. Reproducible results are obtained only if excess peroxide is destroyed, if interfering cations are removed from the ash solution, if prescribed pH-value is maintained by efficient buffering, and if timing of formation of the chloranilate ion is standardized. If these precautions are considered, the method is suitable for determining S-contents in plant tissue accurately.