Improved End Point Detection in the Redox Titration of Vitamin C in Green Peppers

Abstract

We have used E. R. Johnson's infamous pepper lab (titrimetric determination of vitamin C content in raw and cooked green peppers) in our introductory biochemistry course for years with varying success. In the original paper, Johnson states that after seeing the change from a bright green to a muddy green or gray a couple of times during the titration procedure that students can easily determine the endpoint. Because of the large variation in the colors of the solutions obtained from the cooking and extraction procedures, we did not find this to be the case. In fact, we found that the endpoint color was very different from sample to sample. Our solution to this problem is discussed in this article. It has proven to be remarkably simple, yet has produced dramatically improved results.