AOAC ERP Fertilizers - March 2019

3/14/2019

AOAC EXPERT REVIEW PANEL FOR FERTILIZERS

• Method “updates” ‐ Dual/Radial view: • Radial view – improves linear dynamic concentration range, benefits high P and K samples • We now currently measure everything in radial view due to high P & K concentrations (and speed), but could  test all P in axial view and/or low P & K concentrations in axial and high in radial? • For radial, need hotter zone of plasma for P,  i.e. lower viewing height slightly • Can reduce the number of calibration standards with radial view • e.g. for axial K, used 3 wavelengths (766, 769 and 404 nm) – can drop “weak” K404 line if have radial view

• Inverted P and K concentrations  (i.e. Low‐to‐high P and High‐to‐low K) ICP calibration standards from commercial custom blend stock standard solutions Standard Volume Citrate Add Stock Add Stock P Conc P 2 O 5 P 2 O 5 P 2 O 5 K Conc K 2 O K 2 O K 2 O ID mL mL Order e 2,000 P Order e 3,000 K ug/mL ug/mL Solution Fertilizer ug/mL ug/mL Solution Sample mL a mL b % % % % Blank 100 40 - 0 - 0 0 0 0.00000 0.00 0 0 0.00000 0.0 1 100 40 10 2of Std 7 d 7 20 8 18.3 0.00183 0.9 600 723 0.07227 36.1 2 100 40 11 5of Std 7 d 8 15 20 46 0.00458 2.3 450 542 0.05421 27.1 3 100 40 12 10 of Std 7 d 9 10 40 92 0.00917 4.6 300 361 0.03614 18.1 4 100 40 4 5 13 20of Std 8 d 100 229 0.02291 11.5 150 181 0.01807 9.0 5 100 40 3 10 14 10of Std 8 d 200 458 0.04583 22.9 75 90 0.00903 4.5 6 100 40 2 15 15 4 of Std 8 d 300 687 0.06874 34.4 30.0 36.1 0.00361 1.8 7 c 100 40 1 20 - 0 400 917 0.09165 45.8 na na na na 8 c 200 80 - 0 5 50 na na na na 750 903 0.09034 45.2 9 100 40 - 0 6 30 na na na na 900 1084 0.10841 54.2 a Stock1= 2000ug/mL P as PO 4 custom stockstandard b Stock2= 3000ug/mL K from KCl custom stockstandard c Standards7 & 8must be prepared before lower concentration standardssince theyserveasserial dilutions d Serial dilution from another standard; 2 of Std means take 2ml from Standard 8 . e Preparestandards in this order

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AOAC EXPERT REVIEW PANEL FOR FERTILIZERS

UPDATE ON ADDITIONAL VALIDATIONS AND NEXT STEPS FOR THE METHOD  • Method “updates” – Custom Stock Standards: • Exaxol Corporation • SP6170‐1 – 2,000 ug/ml P from  (NH 4 ) 2 HPO 4 • SP6202‐1 – 3,000 ug/ml K from KCl • Preserved in a biocide rather than acid, as acids will change pH of neutral ammonium citrate • Current price is $95 per L

• Get 20 sets of P standards from 1‐L • Get 8 sets of K standards from 1‐L • Shelf life of standards is up to 3 weeks

• Exaxol contact info:

14325 60th Street North Clearwater, FL 33760 Phone: 727‐524‐7732 Toll Free: 800‐739‐2965 www.exaxol.com

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