An improved procedure for phosphorous fractionation in plant materials exploiting sample preparation and monosegmented flow analysis

Abstract

Sample treatment procedures were evaluated for fractionation of phosphorous in plant materials (determination of organic and inorganic, soluble and insoluble fractions). The procedures aimed the conversion of different species into orthophosphate, minimizing time, reagent amounts and waste generation. A monosegmented flow system with multicommutation was developed for the spectrophotometric determination of orthophosphate by the molybdenum blue method. Linear response within 0.5 and 25.0 mg L − 1 P, detection limit of 24 μg 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. Each determination consumes 5.0 mg ascorbic acid and 0.60 mg of ammonium molybdate. Total phosphorous determination can be carried out after microwave-assisted acid digestion by employing 100 mg of plant material and 500 μL of concentrated HNO 3. Extraction of soluble phosphorous can be carried out with water by stirring for 10 min and organic soluble phosphorous can be determined either after microwave-assisted acid digestion or photodegradation in the presence of ammonium persulfate in acid medium. The results for the different fractions agreed with those obtained by ICP OES at the 95% confidence level.