Phosphorus fractionation in plant materials exploiting procedures for sample preparation and monosegmented flow analysis / Fracionamento de fósforo em plantas empregando diferentes procedimentos de preparo de amostras e sistemas de análise em fluxo monossegmentado

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

In this work, different sample treatment procedures were evaluated for fractionation of phosphorous in plant material (determination of organic and inorganic, soluble and insoluble fractions). The evaluated procedures aimed the conversion of different fractions in ortophosphate, minimizing time, reagent amounts and waste generation. It was developed a monosegmented flow system using discrete commutators (solenoid valves) to control the insertion of air bubbles, samples and reagents. For the determination of phosphate, it was used the reaction of molibdenium blue formation, using ammonium molibdate and ascorbic acid as reagents. Linear response was observed within 0.50 and 25.0 mg L-1 P, described by the equation A = 0.0402 + 0.0377C (mg L-1 P), r = 0.999 for solutions prepared in water. The sensitivity decreased about 8 and 22 % for reference solutions in 0.35 mol L-1 and 0.70 mol L-1 HNO3, respectively. Detection limit of 0.024 mg L-1 P (99.7% confidence level), coefficient of variation of 3.5% (n = 10) and sampling rate of 38 measurements per hour were estimated. The reagent consumption was 5.0 mg ascorbic acid and 0.60 mg ammonium molibdate per determination. The flow system was less prone to matrix effects and perturbations by Schlieren effect, both caused by variations of acidity in the samples. The system was applied to fractionation of phosphorous in a plant used as green manure (Crotalaria juncea). Several procedures for phosphorous extraction were evaluated, such as mechanic agitation using water or diluted nitric acid as extractor (extraction of soluble phosphorous), photodegradation of organic soluble phosphorous in acid medium and acid digestion assisted by microwaves (determination of total phosphorous and organic phosphorous). For determination of total phosphorous, procedures using different mass of plant material, different concentrations of HNO3 concentrated and addiction of H2O2 as auxiliary oxidant were evaluated. Good results were obtained using 100 mg of plant material and 500 µL HNO3, not being necessary the addiction of H

ASSUNTO(S)

análises em fluxo multicomutação material vegetal phosphorus fósforo plant materials flow analysis multicommutation

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