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Fonterra Co-operative Group

Page 8

Figure 5: Linearity and residuals plots for vitamin D

3

linearity experiment 2

Figure 6: Linearity and residuals plots for vitamin D

3

linearity experiment 3

Precision

Repeatability refers to the degree of agreement of results when conditions are maintained as constant as

possible. Precision was only evaluated for vitamin D

3

since none of the SPIFAN kit samples were fortified

with vitamin D

2

.

The repeatability standard deviation (S

r

) was calculated as in equation 1:

S

r

=

n

d

n

i

2

1

2

¦

equation 1

where:

d

i

= is the difference between duplicate results for the sample i

n = number of pairs of duplicates

The repeatability relative standard deviation (RSD

r

) for the method is calculated below in equation 2:

y = 1.537x - 0.1227

R² = 0.9989

0

5

10

15

20

25

30

35

40

45

50

0.0

10.0

20.0

30.0

Peak Area Ratio

Concentration Ratio

Linearity: Vitamin D

3

29

th

Dec 2015

-1.2

-0.6

1E-15

0.6

1.2

0.0

20.0

40.0

60.0

Residuals

XVariable

Residual Plot: Vitamin D

3

29

th

Dec

2015

y = 1.4096x - 0.1562

R² = 0.9999

0

5

10

15

20

25

30

35

40

45

0.0

10.0

20.0

30.0

Peak Area Ratio

Concentration Ratio

Linearity: Vitamin D

3

5

th

Jan 2016

-0.2

-0.1

0

0.1

0.2

0.0

20.0

40.0

60.0

Residuals

XVariable

Residual Plot: Vitamin D

3

5

th

Jan 2016

VitD-18 (February 2016)

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