“In the presence of copper , the degradation rate of the vitamin in solutions containing lipoic acid at concentrations higher than its optimum concentration is lower than that in corresponding solutions in the absence of added copper.”
“The optimum concentration of lipoic acid at which its stabilizing efficiency is maximum is shifted on the addition of 20 ppm of copper , from 0.5 to 1.0 mmole/1, indicating that this optimum concentration is dependent on heavy metal ions concentration in the solution.”