OMB Meeting Book - Jan. 11, 2018

7. Repeatability

A gluten-free beverage sample was measured in 9-fold replicates to assess the variation of repeated measurements in a blank sample. The same sample was then spiked with gluten to obtain final theoretical contamination levels of 4, 50 and 200 mg/kg gluten to cover the whole quantitation range of the method. The samples were measured 9 times, only the spike at the lower limit of quantification was determined 20 times. The recovery was calculated for each gluten level and ranged from 95 to 111%. The repeatability RSD of the spiked samples ranged from 2 to 13%, depending on the gluten concentration. Data of all repeatability measurements are shown in tables 3 to 6.

Table 3: Repeated measurements of a gluten-free beverage sample

Sample

OD [450 nm]

1 2 3 4 5 6 7 8 9

0,08

0,082 0,074 0,051 0,054 0,063 0,045 0,044 0,043 0,060

Overall mean

Repeatability SD

0,02

Repeatability RSD, %

26

Table 4: Repeated measurements of a beverage sample spiked with 200 mg/kg gluten

Spike level [mg/kg]

OD [450 nm]

Gluten conc. [mg/kg]

Recovery, %=observed/nominal x 100

Replicate

1 2 3 4 5 6 7 8 9

1,797 1,795 1,812 1,821 1,799 1,771 1,815 1,795 1,800

189 189 193 195 190 183 193 189 190 190 3,57

95 94 97 97 95 91 97 95 95 95

200

Overall mean

Repeatability SD

Repeatability RSD, %

2

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