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Fonterra Co-operative Group
Page 9
RSD
r
(%) =
x
S
r
x 100
equation 2
where:
S
r
= repeatability standard deviation
x¯ = mean of all replicates
The Horwitz ratio for repeatability (HorRat) is estimated in equation 3:
HorRat =
RSD
r
0.5 x pRSD
R
equation 3
where:
RSD
r
= repeatability standard deviation
pRSD
R
= predicted reproducibility from Horwitz curve (2C
-0.1505
)
C = concentration in mass/mass or mass/volume units
The intermediate precision relative standard deviation (RSD
iR
) between duplicates was calculated as in
equation 4.
RSD
iR
=
x
S
iR
x 100
equation 4
where:
S = standard deviation of all replicates
x¯ = mean of all replicates
Precision was assessed for all of the fortified samples in the SPIFAN kit by testing duplicate samples on six
separate days by two different analysts on a single instrument, with fresh calibration standards and reagents
made each day (Table 5).
Table 5: Repeatability and intermediate precision of method for vitamin D
3
Sample
Repeatability
RSD%
(HorRat)
Intermediate
Precision RSD%
In-House Reference Powder
5.2 (0.2)
5.4
NIST SRM1849a
2.8 (0.1)
5.4
Infant Formula Powder Partially Hydrolysed Milk-Based
4.4 (0.2)
7.4
Infant Formula Powder Partially Hydrolysed Soy-Based
1.8 (0.1)
5.0
Toddler Formula Powder Milk-Based
2.2 (0.1)
4.4
Infant Formula Powder Milk-Based
2.1 (0.1)
4.4
Adult Nutritional Powder Low Fat
3.7 (0.1)
6.3
Child Formula Powder
3.3 (0.1)
5.8
Infant Elemental Powder
3.5 (0.1)
3.1
Infant Formula Powder FOS/GOS-Based
1.5 (0.1)
4.7
Infant Formula Powder Milk-Based
3.3 (0.1)
6.4
Infant Formula Powder Soy-Based
2.6 (0.1)
3.6
Infant Formula RTF Milk-Based
2.3 (0.1)
7.8
Adult Nutritional RTF High Protein
1.6 (0.1)
5.2
Adult Nutritional RTF High Fat
4.9 (0.2)
7.9
VitD-18 (February 2016)
FOR ERP USE ONLY
DO NOT DISTRIBUTE