AOAC ERP Gluten Assays - Dec 2018

Annex B

4.1.7

Matrix Study

4.1.7.1

Estimation of Limit of Detection (LoD)

To estimate the matrix-specific LoD, blank samples for oat cereals, flaked oats, and oat flour were extracted 10 times and analyzed using 4-parameter logistic regression. Table 7 clearly shows that it was not possible to obtain true blank samples, as is often the case for oat-based samples. Mean concentrations varied between 1.9 mg/kg gluten and 4.1 mg/kg gluten. Therefore it was not reasonable to use the widespread formula LoD = mean concentration of blank samples + 3-fold standard deviation of these samples. For a true blank sample, the mean concentration is zero and the LoD is the threefold standard deviation.

Table 7. Estimation of LoD in cereals, flour, and flakes by extracting 10 replicates (arranged in two columns) and estimating concentrations by using a 4-parameter logistic regression curve fitting; for each matrix and test kit lot the mean concentration, standard deviation, mean + 3- fold SD, and 3-fold SD are given in mg/kg gluten.

Lot 1

Lot 2

mg/kg

Flour

mg/kg

mg/kg

mg/kg

1 2 3 4 5

3.21 3.12 2.39 2.49 2.94

3.16 3.09 3.18 4.76 3.03

2.38 2.42 2.00 1.91 2.24

2.53 2.20 2.06 4.09 2.26

mean

3.14 0.64 5.05 1.92

2.41 0.62 4.27 1.86

SD

mean + 3 x SD

3 x SD

Flakes 1

2.58 2.73 2.82 2.73 2.51

3.01 2.92 3.16 2.76 2.83

1.76 1.82 1.84 2.02 1.91

2.13 2.02 2.00 1.80 1.89

2 3 4 5

mean

2.67 0.13 3.05 0.38

1.87 0.10 2.17 0.30

SD

mean + 3 x SD

3 x SD

Cereals 1

3.67 4.70 3.69 4.38 4.02

4.08 4.40 4.34 3.87 3.52

3.07 4.46 4.40 4.48 3.64

3.77 4.07 4.36 4.60 3.07

2 3 4 5

mean

4.07 0.38 5.22 1.15

3.99 0.58 5.73 1.74

SD

mean + 3 x SD

3 x SD

Page 19 of 33

RIDASCREEN ® Total Gluten In-house validation report 2018-10-21