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AOAC RESEARCH INSTITUTE
AOAC
OFFICIAL METHODS OF ANALYSIS
(OMA)
OMAMAN-28/AOAC 2006.03
Study Director: Sharon Webb, University of Kentucky, Division of Regulatory Services,
103 Regulatory Services Bldg, Lexington , Kentucky 40546-0275
being construed as a nutrient guarantee.
If we are going to advance a method it should therefore have some value or indication of its
solubility from the fertilizer material and potential plant availability. This is not what this
method is meant to determine.
ER 4
Looks good.
ER 5
I think this method is taking advantage of the technology that is available. The simultaneous
determination of the metals on ICP will be very beneficial to laboratories.
ER 6
more studies have to be done in order to improve the recovery of some elements
ER 7
Scope and applicability for ferilizers is appropriate for the specified metals.
ER 8
Webb, S., Bartos, J., Boles, R., Hasty, E., Thuotte, E., & Thiex, N. J. (2014). Simultaneous
Determination of Arsenic, Cadmium, Calcium, Chromium, Cobalt, Copper, Iron, Lead,
Magnesium, Manganese, Molybdenum, Nickel, Selenium, and Zinc in Fertilizers by Microwave
Acid Digestion and Inductively Coupled Plasma-Optical Emission Spectrometry Detection: Single-
Laboratory Validation of a Modification and Extension of AOAC 2006.03. Journal of AOAC
International, 97(3), 700-711.
The paper describes a single-laboratory validation study for the simultaneous determination of
arsenic, cadmium, calcium, cobalt, copper, chromium, iron, lead, magnesium, manganese,
molybdenum, nickel, selenium, and zinc in all major types of commercial fertilizer products by
microwave digestion and inductively coupled plasma-optical emission spectroscopy (ICP-OES)
analysis. The importance of the proposed method is correlated to the possible extension and
modification of the current AOAC 2006.03 (determination of arsenic, cadmium, cobalt,
chromium, lead, molybdenum, nickel and selenium, also named “Group A”, in fertilizers) with
the inclusion of calcium, copper, iron, magnesium, manganese, and zinc (also named “Group
B”). The use of a dual acid digestion system - hydrochloric and nitric acids – instead of simple
nitric acid is proposed as modification.
On the basis of obtained results, the proposed method is reported to:
a) Assure a significant increase in laboratory efficiency when compared to the use of both AOAC
Methods 965.09 – Nutrients (Minor) in Fertilizers, Atomic Absorption, Spectrophotometric
Method - and 2006.03. AOAC 695.09 is considered because of the necessity of validating results
for calcium, copper, iron, magnesium, manganese, and zinc
b) Assure a more efficient recovery of several metals in comparison with AOAC 2006.03
c) Meet the criteria recommended by the Association of American Plant Food Control Officials
(AAPFCO) Laboratory Services Committee.
The applicability of the proposed method has been declared. It has to be noted that AOAC
2006.03 mentions the use of nitric acid, while the proposed technique uses also hydrochloridric
acid (in both situations, fertilizers can produced exothermic reactions) in a closed vessel
microwave digestion system at 200 °C. The use of microwave digestion units has to be carefully
considered.
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