Abstract: A sensor for detecting ascorbic acid or a salt thereof is provided, the sensor having sensor means for detecting ascorbic acid or a salt thereof in a liquid sample and buffer means for buffering the sample before and/or at the time that the sample contacts the sensor means, said buffer means having two zones, a first zone for buffering the sample to a pH in the range of from 5.5 to 8, preferably from 6.5 to 7.5 and a second zone for receiving sample which has passed through the first zone and for buffering to a pH in the range from 1 to 5.