Table 1 Robustness investigation

Volume of 1, 2-naphthoquinone-4-sulfonate solution (mL)

0.8

98.45 ± 1.26

1.0

99.95 ± 0.45

1.2

98.69 ± 0.37

pH of buffer solution

9.0

100.10 ± 1.14

9.2

98.85 ± 1.56

9.4

98.87 ± 1.85

Water bath temperature (°C)

58

98.56 ± 1.32

60

100.05 ± 1.24

62

97.45 ± 1.65