AOACSPIFANMethods-2017Awards

66

12 B runt et al .: J ournal of aoaC I nternatIonal V ol . 100, n o . 3, 2017

14 may be expected to be more variable because this sample contains the lowest fructan content, about 0.03 g/100 g, which is close to the LOQ. The intermediate reproducibility (RSD iR ) achieved in both laboratories is, in general, below 8%, again with the exception of sample No. 14 analyzed at CCC. Sample No. 14 was analyzed with an RSD iR of 14%, which is almost certainly linked to the low concentration of analyte in that sample. No limits were defined for RSD iR in SMPR 2014.002 (5), but the data suggest that achieving an RSD R of below 12% (as defined in SMPR 2014.002) for a multilaboratory trial could be possible, although it may be expected that samples containing fructan levels close to the LOQ may have higher variability. The analytical results and the established precision data of NRC and CCC agree very well with each other. There is no significant difference in the mean fructan content of the samples [paired t -test (α = 0.05)], but the RSD iR values of CCC are slightly higher than those of NRC (Table 2). This could be explained by the fact that CCC was able to introduce more variability in the execution of the intermediate reproducibility experiments than NRC: data at CCC were collected over the course of 4 months, whereas at NRC, the data were mostly collected over the course of 1 month; and data at CCC were acquired by two different people using three different instruments, whereas at NRC, most of the precision data were generated by a single person using two different instruments. Primary indications of the accuracy of the method were obtained at CCC during the determination of LOD and LOQ, because this was performed by spiking low levels of fructans into a blank matrix (Table 1). The fructan addition rate was 0.046 g/100 g on both days; thus, the average recoveries were 95.6% on day 1 and 104% on day 2, which are well within the defined target range of 90–110%. Accuracy/Trueness

Table 1. Determination of LOD and LOQ at CCC

Day 1 a

Day 2 a

Fructan content, g/100 g

Fructan content, g/100 g

Meets the SMPRs

Meets the SMPRs

Parameter Average b

NA c NA Yes Yes

0.044 0.002 0.005 0.016

0.048 0.003 0.009 0.030

NA NA Yes Yes

SD b

LOD d LOQ e

a Days 1 and 2 were separated by 3 months. b Average and SD values were calculated on 10 replicates measured on a single day. c NA = Not Applicable.

d LOQ calculated as 10SD. e LOD calculated as 3SD.

( 3 ) Sample No. 10, Infant Formula Powder, Milk-Based, Lot No. 4044755861. ( 4 ) Sample No. 12, Child Formula Powder, Lot No. 00866RF00. ( 5 ) Sample No. 14, Infant Formula Powder, FOS/GOS- Based, Lot No. 50350017W1. ( 6 ) Sample No. 19, Adult Nutritional RTF, High-Fat, Lot No. 0729RF00. These six samples were used in the precision study in both laboratories, with an additional two samples (Nestlé Ref 1 and 2) included at NRC. The repeatability and intermediate reproducibility were assessed by analyzing all samples in duplicate on 6 different days, with the exception of Nestlé Ref 2, which was analyzed in duplicate on 24 different days (Table 2). The repeatability (RSD r ) achieved in both laboratories (Table 2) is well below the upper level of 6% defined in SMPR 2014.002 (5), with only one exception, sample No. 14, which had an RSD r of 8.9% at CCC. The results for sample No.

Table 2. Summary of results from the precision study

Meets SMPR 2014.002 target

Mean fructan content, g/100 g

n a

RSD r , % NRC CCC NRC CCC NRC CCC NRC CCC NRC CCC , % RSD iR

Sample No.

Sample description

0.29 b

1.4 b

Yes b

7.8 b

0.8 2.0

Yes Yes

1.1 2.4

1 9

Child Formula Powder Toddler Formula Powder, Milk-Based Infant Formula Powder, Milk-Based Child Formula Powder Infant Formula Powder, FOS/GOS-Based Adult Nutritional RTF, High-Fat

6 × 2 6 × 2

6 × 2 6 × 2

0.27 0. 21

0.22

1.6

Yes

6.1

10

6 × 2

6 × 2

0.28

0.26

2.4

1.2

Yes

Yes

2.8

6.9

12 14

6 × 2 6 × 2

6 × 2 6 × 2

0.28 0.03

0.28 0.04

1.2 0.9

1.1

Yes Yes

Yes No c

1.1 2.5

6.1

8.9 c

14.2 c

19

6 × 2

6 × 2

0.48

0.51

1.8

2.6

Yes

Yes

1.6

4.2

NA d

2.9

NA

1.1

NA

Yes

NA 1.8

NA

Nestlé Ref 1 Nestlé Ref 2

Infant formula

6 × 2

Infant formula

24 × 2

NA

0.39

NA

3.3

NA

Yes

NA 4.3

NA

a n = Number of determinations, represented as days × replicates. b There was one (Grubbs) outlier in one of the duplicates; therefore, the results are based on a set of five duplicates instead of six. c The fructan content was close to the LOQ, resulting in somewhat increased RSD r and RSD iR values. d NA = Not Applicable.