Abstract
Abstract A semi-automated method for the turbidimetric determination of extractable sulphate-S (SO4-S) in plant material by flow injection analysis (FIA) is described. Inorganic SO4-S is extracted with calcium orthophosphate and trichloroacetic acid (both 0.5%) buffer solution containing added activated charcoal. Extract subsamples are injected into a carrier stream, where BaSO4 is precipitated and determined turbidimetrically by FIA at 400 nm. A programmable timer and two solenoid valves regulate merging zones of sample and reagents in one stream, and alternate BaCl2 and alkaline EDTA entry into the other stream. In seven plant materials, SO4-S concentrations ranging from 50 to 13180 mg kg−1 were determined with a coefficient of variation of 2.5 %. Only NO3-N at levels exceeding 5 % by weight interfered with the method. Handling rates of 120 samples hr−1 are possible with the proposed FIA system in which intermittent flow reduces peak “tailing”.
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