Determination of phosphate species in nutrient solutions and phosphorus in plant material as phosphovanadomolybdic acid by flow injection analysis

A flow-injection spectrophotometric method for the determination of orthophosphate is described. The signal from the yellow phosphovanadomolybdic acid complex is recorded at 400 nm. The detection limit is 0.1 mg P 1^?1 (as orthophosphate), the calibration graph is linear up to 30 mg P 1^?1 and up to 240 samples can be analysed per hour. The method is used in the determination of phosphorus in digested plant material, and is also applicable for separating free orthophosphate from acid-labile aluminium phosphate colloids in nutrient solutions.