Determination of water in ascorbic acid by the proton isoconcentration technique using the standard addition method

Water has been extracted from ascorbic acid into a dry mixture of equal volumes of methanol—organic solvents ( n-propanol, ethylene glycol or propylene carbonate) and was determined potentiometrically, using the calibration graph based on the large and systematic change in cell potential for addition of 0–1%, m/m water into a dry mixture of the above mentioned mixture containing 2 × 10 −3 M trifluoromethanesulphonic acid (TFMSA) using a combination pH glass electrode with silver—silver chloride reference electrode having tetraethylammonium chloride (TEACl) in methanol as a filling electrolyte. The method is fast, accurate, reproducible and simple for operation.