This method quantitatively determines the amount of phosphorus (PO4-P) in botanical materials by extraction with a solution of 2% acetic acid. Phosphorus concentration in the extract is determined spectrophotometrically by reacting with ammonium molybdate and antimony potassium tartrate under acidic conditions to form a complex. This complex is reduced with ascorbic acid to form a blue complex which absorbs light at 880 nm. The absorbance is proportional to the concentration of phosphorus in the sample. The method has shown to be correlated to plant deficiency and response to phosphorus fertilization. Samples are analyzed using an automated Flow Injection Analyzer (Lachat). The method has a routine detection limit of 50 ppm but samples that fall below 200 ppm are reanalyzed yielding a detection limit of 20 ppm.
Sample amount requested: 3 g (allows for reporting on a 100% dry basis).
Questions concerning limited sample size can be answered by the UC Davis Analytical Laboratory.
Prokopy, W. R. 1995. Phosphorus in acetic acid extracts. QuikChem Method 12-115-01-1-C. Lachat Instruments, Milwaukee, WI.