We quite wanna know what the working concentration of sodium metabisulphite (Sigma) should be appropriate.

sodium metabisulphite (Sigma) is antioxidant for protecting L-levodopa and dopamine

perchloric acid for lysing cells.

800 μl of cell culture supernatant in a well of 24-well plate was harvested and placed into tubes containing 80 μl of 2 M perchloric acid (Sigma) and and 80 μl of sodium metabisulphite (Sigma). The samples were thoroughly mixed, and once a precipitate had formed the samples were centrifuged at 10, 000 x g for 10 mins too remove to separate tubes and frozen in a -80℃ until the HPLC analysis.