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Thiex: Journal of AOAC International Vol. 99, N o. 2, 2016 359
Calculations.—Note: An example calculation can be found
in Appendix B of ref. 2 available on the J. AOAC Intl. Web site.
× ×



 ×
×

















× ( )
( )
( )
%AR =
AC ,
mg
L
1 g
1000 mg
0.255 L
0.250 L V, L
W, g A , g
100 g
100
ex1
ex1
t
× ×



 ×
×


















× ( )
( )
( )
%AR =
AC ,
mg
L
1 g
1000 mg
0.255 L
0.250 L
V, L
W, g A ,
g
100 g
100
ex2
ex2
t
−
























× ×



 ×
×






























× ( )
( )
( )
( )
%AR =
AC , mg
L
AC , mg
L
2
1 g
1000 mg
0.255 L
0.250 L
V, L
W, g A ,
g
100 g
100
ex3
ex3
ex2
t
−
























× ×



 ×
×






























×
( )
( )
( )
( )
%AR =
AC , mg
L
AC , mg
L
2
1 g
1000 mg
0.255 L
0.250 L
V, L
W, g A , g
100 g
100
ex4
ex4
ex3
t
= 

 + 

 + 

 + 

 ( ) ( ) ( ) ( ) %TAR %AR %AR %AR %AR
ex1 ex2 ex3 ex4
( ) ( )
= −















 ( ) ( )
( )
%WIN A % A %
%AR
100 t t
ex1
Graphing the release plot.—Plot the cumulative % of analyte
(nutrient) released on the y-axis versus the time in hours of
extraction on the x-axis. The release plot will be similar to
Figure 2015.15B, except for a change in the units on the
x-axis from cumulative days of extraction to cumulative hours
of extraction. An example graph can be found in Appendix B of
ref. 2 available on the J. AOAC Int. web site.
Discussion
Medina et al.’s validated methods, including alternatives
for a 180 day extraction and an accelerated extraction (1, 2),
were submitted by William Hall to the AOAC Fertilizer Expert
Review Panel (ERP), and adopted as First Action. Extensive
method development and validation data supporting both
alternatives as documented in Medina et al.’s studies (1, 2, 6)
was further reviewed by the ERP. The validation was deemed
thorough by the ERP, demonstrated that the method was
scientifically sound, and confirmed that such a method is needed
by the community.
Method reproducibility for both alternatives is proposed
to be determined via collaborative study. The ERP asked that
in addition to solid fertilizers, reproducibility data for liquid
fertilizers be generated. The ERP also asked that the 180
day ambient method be clarified for its application to coated
fertilizers (not including sulfur-coated) as reproducibility data
are generated. It was noted that it might be difficult to obtain
reproducibility data on the 180 day extraction within 2 years
due to the long analysis time.
The collaborative studies will provide reproducibility data
for N, P, K, and possibly other nutrients.
References
(1) Medina, L.C., Sartain, J.B., Obreza, T.A, Hall, W.L., &
Thiex, N.J.
org/10.5740/jaoacint.13-065
(2) Medina, L.C., Sartain, J.B., Obreza, T.A, Hall, W.L., &
Thiex, N.J.
org/10.5740/jaoacint.12-482
(3) Association of American Plant Food Control Officials, Inc.
(1995) AAPFCO Official Publication No. 48, D.L. Terry (Ed.),
West Lafayette, Indiana.
(4) Thiex, N
org/10.5740/jaoacint.SGEThiex_Intro
(5) Sartain, J.B., Hall, W.L., Littell, R.C., & Hopwood, E.W.
(2004) in Environmental Impact of Fertilizer on Soil and Water,
W.L. Hall & W.P. Robarge (Eds), Oxford University Press,
Washington, DC, pp 180–195
(6) Medina, L.C., Sartain, J.B, Obreza, T.A, Hall, W.L., &
Thiex, N.J.
org/10.5740/jaoacint.13-004