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The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 8 Issue 4 (2003) pp 260-265

Identifying Variables Affecting the Oxidation of Ascorbic Acid in Orange Juice Using Derivative Ultraviolet Spectrophotometry

Richard J. Stolzberg

Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK 99775-6160, ffrjs@uaf.edu
Received April 25, 2003. Accepted June 28, 2003.

Published online: 19 July 2003

Abstract. A two-level factorial design experiment is used to determine the importance of four variables on the amount of oxidation of ascorbic acid in orange juice over one week. The concentration of ascorbic acid is measured using first-derivative ultraviolet spectrophotmetry. The instrument blank is ascorbic-acid-free orange juice. The presence of 5 ppm added Cu2+ (aq) is most frequently the major active variable. Brand of orange juice and temperature are often important. The relative standard deviation of the method is comparable to that for titrimetric and polarographic methods, but larger than that for a coulometric method. Synthetic unknown samples of ascorbic acid are analyzed to assess the ability of individual students to do accurate analyses. Twenty-one of the 47 reported analyses (45%) were unbiased.

Key Words:  Laboratories and Demonstrations; analytical chemistry; derivative spectrophotometry; experimental design; ascorbic acid; orange juice

(*) Corresponding author. (E-mail: ffrjs@uaf.edu)

Article in PDF format (450 KB) HTML format

Supporting Materials:

 

Supporting Materials:

A student laboratory handout in Microsoft Word format, Lab C Ascorbic Acid Oxidation and OJ 7July03.doc, can be downloaded as a Zip file. (44 KB)

Issue date: August 1, 2003

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