AOAC ERP Fertilizers - March 2019

3/14/2019

AOAC EXPERT REVIEW PANEL FOR FERTILIZERS  OMA 2015.18: Phosphorus and Potassium in   Commercial Inorganic Fertilizers

THURSDAY, MARCH 14, 2019 1:00PM – 4:00PM GAITHERSBURG MARRIOTT WASHINGTONIAN CENTER GAITHERSBURG, MARYLAND 20878 USA

AOAC INTERNATIONAL 2275 Research Blvd, Suite 300 Rockville, Maryland 20850 USA

AOAC EXPERT REVIEW PANEL FOR FERTILIZERS

BACKGROUND AND SUMMARY OF METHOD INCLUDING METHOD SCOPE/APPLICABILITY • SLV – Bartos et al.: Journal of AOAC International Vol. 97, No. 3, 2014, pp. 687‐699  (OPEN ACCESS) • AOAC Method – OMA 2015.18 • Fertilizers extracted in pH neutral ammonium citrate ; EDTA added as a chelating agent for any “metals” present,  which is a “carry‐over” from the spectrophotometric method  [993.31 B.(c)]  to limit P complexation • Instrument results for Available Phosphate expressed as P 2 O 5 and  Soluble Potash expressed as K 2 O  • Scope – Simultaneous/concurrent determination of P & K in commercial inorganic fertilizer products • Available Phosphate = PO 4 x‐ ; however, ICP measures any P source; method could have high bias in some instances 1. Any soluble/suspended organic P sources  (also applies to K, but less common) 2. “ Phosphite PO 3 3‐ or Phosphor ous acid” (fungicide) would be detected, but it is NOT plant available 3. Need to watch or model potential spectral interferences, Cu for P213 and P214, Li for K769

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