Concentration (μg/mL)

Three freeze-thaw cycles

At ice-water bath for 12 h

At room temperature for 12 h

At 4˚C for 3 days

RE (%)

RSD (%)

RE (%)

RSD (%)

RE (%)

RSD (%)

RE (%)

RSD (%)

0.2

13.60

0.67

−5.00

5.35

−44.05

21.78

5.95

3.51

1

−2.76

2.13

7.63

5.69

−40.03

9.36

1.78

2.74

8

−0.21

2.85

1.53

3.80

−21.07

6.52

−0.19

3.05