ISO 14235 pdf download

ISO 14235 pdf download.Soil quality — Determination of organic carbon in soil by sulfochromic oxidation 1 Scope This International Standard specifies a method for the spectrometric determination of organic carbon content in soil by oxidation in a sulfochromic medium. This International Standard is applicable to all types of air-dry soil samples. This International Standard is not applicable to soils containing mineral-reducing compounds, e.g. Cl 2 or Fe 2+ . By convention the chloride content in the test portion shall not exceed 2 mg. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revisions, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent additions of the standard indicated below. Members of ICE and ISO maintain registers of currently valid International Standards. ISO 3696:1 987, Water for analytical use — Specification and test methods . ISO 1 0694:1 995, Soil quality — Determination of organic and total carbon after dry combustion (elemental analysis). ISO 1 1 464:1 994, Soil quality — Pretreatment of samples for physico-chemical analysis. ISO 1 1 465:1 993, Soil quality — Determination of dry matter and water content on a mass basis — Gravimetric method. 3 Principle The organic carbon present in the soil is oxidized in a mixture of potassium dichromate solution (in excess) and sulfuric acid at a temperature of 1 35 °C. The dichromate ions, which colour the solution orange-red, are reduced to Cr 3+ ions which colour the solution green. The intensity of this green colour is measured spectrophotometrically. As it is assumed that the oxidation of one carbon atom of the organic matter produces four electrons, there is a direct relationship between the Cr 3+ formed and the amount of organic carbon. The method is calibrated using glucose as a source of readily oxidizable carbon.NOTE An amount of 2 mg of chloride present in the test sample corresponds to an apparent carbon content of about 0,7 mg. 5 Apparatus and glassware 5.1 Standard laboratory glassware. 5.2 Analytical balance, capable of weighing accurately to 0,1 mg. 5.3 Volumetric glass tubes of 75,0 ml ± 0,2 ml, adapted to fit the heating block (5.4). 5.4 Heating block, capable of maintaining a uniform temperature of 1 35 °C ±...