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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
in radial ICP systems. These need to be addressed because they can have an adverse affect
based on system hardware used.
ER 2
Perhaps more emphasis could be placed on Section F (e) regarding interelement interference in
instruments that don't have software to correct for this issue.
ER 3
Favors metals that are extractable in acid rather than alkali
Does not provide extractant pH levels
Reports total metals which is not indicative of plant availability
Could tend to mislead consumers if construed as a micronutrient label guarantee
Not an appropriate method for fertilizer materials in determining plant availability
ER 4
N/A
ER 5
"cut" (page 112) could be replaced.
ER 6
may not be applicable foe all fertilizer products
ER 7
none
ER 8
The following weaknesses of the proposed method may be mentioned:
Calibration and linearity
Some deconvolution effects have to be considered (Fe, Co) when speaking of certain
wavelengths for arsenic, cadmium, lead and selenium (calibration range: 0-10 μg/mL).
Precision
Many results show many HorRat values below 0.3 for a single validation study. However, RSD
values for the proposed method are extremely reduced if compared with collaborative study
2006.03 results. In addition, RSD for Group B metals remain low enough, in general.
LOD and LOQ
It should be noted that lower limits for Group B elements can be achieved by altering the test
portion size or choosing more sensitive wavelengths.
Ruggedness trial
It has to be noted that:
1) Se values in the sample are at or below the method LOQ. For this reason, the proposed
method is not recommended for Se
2) Certain ‘Relative percent difference’ values show that the determination of iron has to be
carried out carefully. This element is reported to be the most variable element and ruggedness
test results seem to confirm the affirmation.
ER 9
All of the ruggedness work was done on the digestions portion of the study, but none was done
on ICP variables. How software varies from instrument to instrument may yield different lines
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