Table 2: Variables and levels for the experimental design.

VariableLevel 1Level 2Level 3

Flow rate HCl (mL min−1)1.32.85.9
Flow rate NaBH4 (mL min−1)1.73.74.5
HCl% (v/v)51530
NaBH4  (% (m/v))0.10.20.5