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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