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Fonterra Co-operative Group

Page 10

Repeatability for the method in SPIFAN kit samples ranged between 1.5

5.2% which complies with the

11.0% limit set with the SMPR [2] The HorRat values were within acceptability criteria for repeatability of

0.3

1.3 [4]. Intermediate precision ranged between 3.1

7.9% with a mean value of 5.5%.

Limits of Detection and Quantitation

The limit of detection (LOD) is the lowest content that can be detected with reasonable statistical certainty.

This appropriate concentration for a spiked blank sample was determined by evaluating multiple samples

spiked at a range of concentrations and establishing which spike concentration gave equivalent signal to

~10X signal to noise. This was determined to be a spike concentration of 2 ng to a 2 g sample. The LOD

was determined from 10 independent analyses of a blank sample (unfortified whole milk powder) spiked with

vitamin D

2

and vitamin D

3

. The LOD and LOQ are calculated as described in equations 5 and 6.

LOD =

x

+ 3 x SD

equation 5

where:

x¯ = mean of replicates

SD = standard deviation of all replicates

LOQ =

x

+ 10 x SD

equation 6

where:

x¯ = mean of replicates

SD = standard deviation of all replicates

The LOD and LOQ for vitamin D

2

are determined to be 0.12 and 0.15 μg hg

-1

(0.013 and 0.016 μg hg

-1

) and

the LOD and LOQ for vitamin D

3

are determined to be 0.16 and 0.25 μg hg

-1

(0.018 and 0.028 μg hg

-1

)

(Tables 6

7). The LOD and LOQ for both vitamin D

2

and vitamin D

3

are lower than those defined in the

vitamin D SMPR [2].

Table 6: Limits of detection and quantitation for vitamin D

2

Vitamin D

3

Sample

Powder (μg hg

-1

)

RTF (μg hg

-1

)

Mean

0.102

0.011

Standard Deviation (SD)

0.005

0.001

3 x SD

0.014

0.002

10 X SD

0.045

0.005

Limit of Detection

0.12

0.013

Limit of Quantitation

0.15

0.016

VitD-18 (February 2016)

FOR ERP USE ONLY

DO NOT DISTRIBUTE