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© Romer Labs, 2016
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
0,08
2
0,082
3
0,074
4
0,051
5
0,054
6
0,063
7
0,045
8
0,044
9
0,043
Overall mean
0,060
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]
Replicate
OD
[450 nm]
Gluten conc.
[mg/kg]
Recovery,
%=observed/nominal x 100
200
1
1,797
189
95
2
1,795
189
94
3
1,812
193
97
4
1,821
195
97
5
1,799
190
95
6
1,771
183
91
7
1,815
193
97
8
1,795
189
95
9
1,800
190
95
Overall mean
190
95
Repeatability SD
3,57
Repeatability RSD, %
2