COMPARATIVE STUDY OF TITIMETRIC METHODS FOR DETERMINATION OF ORGANIC CARBON IN SOILS, COMPOST AND SLUDGE
Published: 1 Jun 2014
Abstract: The aim of this study was to evaluate different titrimetric methods of organic carbon determination (OC), using reference soils, compost and sludge as standards, as well as to clarify the effects of the phosphoric acid and the efficiency of the indicators used in the titration. SOC content was determined by 10 wet oxidation methods (7 which are commonly used in soil testing laboratories and 3 methods modified by us). The agreement between certified and measured results suggested that SOC could be completely recovered by using wet digestion under tested method described (except Walkley Black midified method). Organic carbon contents from the Walkley Black modified method were higher in all investigated samples than those obtained by the other titrimetric methods. The most significant increase is observed in the standards 3, 6 and 7, i.e. the standards with the highest content of organic matter. The Tube digestion method and Tjurin method (1500C with phosphoric acid added before titration) are very effective for soil samples up to 2 % of organic carbon. The Tube digestion method for organic carbon determination seem to be the most suitable methods, for soil samples, compost and sludge with high organic matter content. The indicators do not significantly affect the quantification of organic carbon in most studied samples. The determined values for all standard samples with indicator diphenylamine are little bit than those determined using the N-phenylanlhranilic acid and o-phenanthroline. N-phenylanthranilic acid can be used with H3PO4 addition before titration. Ferroin can be as effective as barium diphenylamine sulfonate if soil is filtered or centrifuged to get clear solution after the addition of water in the procedure, but this process involves a lot of time, hence barium diphenylamine sulfonate and N-phenylanthranilic acid, as indicators, are recommended.
Keywords: titrimetric methods, organic carbon determination, certified samples
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