Table 2 Evaluation of the pH effect on linearity

5.4

y = 1.8463x + 14.882

0.9806

8 hours

5.9

y = 2.3895x + 19.128

0.9898

8 hours

6.4

y = 1.5517x + 11.817

0.9977

8 hours

6.5

y = 2.134x + 7.4113

0.9975

8 hours

7

y = 1.7824 + 11.212

0.9794

9 hours

7.5

y = 1.875x + 11.009

0.9663

10 hours

8

y = 2.3651x + 9.3311

0.9763

11 hours