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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
availability of metals can be affected by their concentration and other ions present, among
other things.
ER 4
Yes
ER 5
Yes
ER 6
Yes
ER 7
Yes
ER 8
Yes
ER 9
Yes
ER 10
Yes
Are there sufficient data points per product evaluated in accordance with AOAC requirements?
ER 1
Yes
ER 2
Yes
ER 3
Yes
ER 4
Yes
ER 5
Yes
ER 6
Yes
ER 7
Yes
ER 8
Yes
ER 9
Yes
ER 10
Yes
General Comments about the Method Scope/Applicability:
ER 1
Sound methodology but it does not address the hardware (actual ICP differences) sufficiently.
Without addressing this there will be biases based on plasma configuration used. Especially for
the heavy metals.
ER 2
Authors are to be commended for undertaking this important correction and addition of
additional elements to make this a more universal method for fertilizer analysis.
ER 3
The method states it is intended for fertilizers but; 1). Targets some metals and ignores others
(e.g. Al, Hg) that can be toxic to plants 2). Has a bias toward metals extractable by acid whereas
alkali extraction is ignored. It is known that some metals are more available in alkali
environments. 3). If a method is to be used for determining metals in fertilizers it should
consider the pH range of soils and crops, and, although an environmental test for metals may
include highly acidic soils, this is not the case for agricultural soils where pH ranges are normally
maintained within a specific range and may likely include alkali soils above pH 8.0. 4). If the
purpose is to limit plant availability then a leachable metals test would be more appropriate
than a total metals test considering the metals must be released from the fertilizer into soil
solution in order for plant uptake to occur 5). To include plant nutrients such as Ca, Mg, Fe, etc.
in this method for total metals could result in label guarantees for these fertilizer nutrients and
an acid extraction for total metals would not be indicative of plant availability and would do a
disservice to the end user. This has already happened in some states where a label warning is
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