Standard addition methods:

Squeeze an orange, grape fruit or lemon until about 10 cm³ of juice is acquired.  Filter the juice by a porous funnel (pore size about 1 mm).

Prepare four 25 cm³ volumetric flasks. Add to each 0.5 cm3 of 0.5M acetate buffer, 2.0 cm³ of the juice and standard addition of 0, 200, 400, and 600 µdm³ of 0.2% ascorbic acid. Dilute to mark along with distilled water. Record polarograms under the similar conditions as in the calibration step.  Draw the standard additions plot and determine the concentration of ascorbic acid.  Report the concentration of ascorbic acid (Vitamin C) in the general sample (juice) in mol/l and also ppm.