Micro determination of ascorbic acid using methyl viologen

A new simple and sensitive analytical spectrophotometric method is developed for the determination of ascorbic acid reduces methyl viologen to form a stable blue coloured free radical ion. This method has a sensitivity and lower limit detection of 0.1 μg ml−1 of ascorbic acid (0.1 ppm) which is comparable to the flow injection analysis reported earlier. Beer's law is obeyed over the concentration range of 1.0–10 μg ml−1 of ascorbic acid per 10 ml of the final solution (0.1–1.0 μg ml−1) at 600 nm. The molar absorptivity and Sandell's sensitivity were found to be 1.5 × 105 ± 100 l mol−1 cm−1 and 0.001 μg cm−2, respectively. The method has been applied to the determination of ascorbic acid in food, pharmaceuticals and biological samples.