University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Website: @unf

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Classification: Vegetable -> juice

Citations 4

"Enzymatic Determinations With Rotating Bioreactors: Determination Of Glutamate In Food Products"
Anal. Chim. Acta 1998 Volume 369, Issue 1-2 Pages 147-155
Chitra Janarthanan and Horacio A. Mottola*

Abstract: The benefits of using rotating bioreactors for online or inline determination in food analyzes are illustrated with the determination of L-glutamate. Two enzymatic approaches have been implemented and samples used to illustrate the approaches included: beef and chicken bouillon cubes, soy sauce, chicken broth, seasoning salt, fruit and vegetable juices, and skim milk. One of the methods uses glutamate dehydrogenase (EC in the main enzymatic reaction and diaphorase (EC in the indicator reaction, which involves NADH and hexacyanoferrate(III). The monitored species, amperometrically detected at a platinum-ring electrode, is the hexacyanoferrate(II) produced by the indicator reaction. The second method utilizes a single enzyme, glutamate oxidase (EC, and amperometric monitoring of a product of the enzymatic reaction, H2O2, also at a platinum-ring electrode. Interference by ascorbate present in some samples is eliminated by inline use of a packed reactor containing ascorbate oxidase (EC The relative merits of both systems when using continuous-flow/stopped-flow/continuous-flow processing are discussed.
Glutamate Amperometry Electrode Interferences Immobilized enzyme Stopped-flow Manifold comparison

"Determination Of L-ascorbic Acid In Fruit And Vegetable Juices By Flow Injection With Immobilised Ascorbate Oxidase"
Analyst 1990 Volume 115, Issue 10 Pages 1297-1299
Gillian M. Greenway and Peter Ongomo

Abstract: Ascorbate oxidase was immobilized on cyanogen bromide activated-Sepharose 4B and incorporated in a flow injection system with amperometric detection at a glassy carbon electrode at +0.6 V. On passage through the immobilized ascorbate oxidase a fraction of the L-ascorbic acid was converted into dehydroascorbic acid and the decrease in signal was measured. This could be directly related to the amount of L-ascorbic acid present. The calibration graph was linear over the range 0-400 ng mL-1 with a correlation coefficient of 0.9994. The detection limit (2s) in phosphate buffer (0.08 M, pH 5.5) was 4.0 ng mL-1. The relative standard deviation for a 200 ng mL-1 standard was 1.0% (n = 10) and the sampling throughput was 30 samples h-1. The method was used for the simple and rapid determination of L-ascorbic acid in fruit and vegetable juice.
l-Ascorbic acid Amperometry Electrode Immobilized enzyme Sepharose beads Calibration Detection limit Buffer Column

"Evaluation Of An HPLC Method For The Determination Of Phylloquinone (vitamin K1) In Various Food Matrices"
J. Agric. Food Chem. 1994 Volume 42, Issue 2 Pages 295-300
Sarah L. Booth, Kenneth W. Davidson, and James A. Sadowski

Abstract: Phylloquinone was extracted from vegetable juice, cows milk, spinach, bread and beef with propan-2-ol/hexane (details given) with 2,3-dihydrophylloquinone or 2-methyl-3-(3,7,11,15,19-pentamethyl-2-eicosenyl)-1,4-naphthalenedione added (internal standards; details given). The extracts under went solid-phase extraction on silica columns (described) with elution effected by hexane/ethyl ether (93:3). Beef extracts were further purified by HPLC on a C18 column (described). The purified extracts were dissolved in methanol containing 10 mM ZnCl2, 5 mM acetic acid and 5 mM sodium acetate (milk extracts were dissolved in 10 mM ZnCl2, 5 mM acetic acid and acetonitrile) and analyzed on an Hypersil ODS (3 µm) column (15 cm x 4.6 mm i.d.) with a mobile phase (1 ml/min) of methanol/CH2Cl2 (9:1) containing 5 ml/l of 2 M ZnCl2, 1 M acetic acid and 1 M sodium acetate with fluorescence detection at 418 nm (excitation at 244 nm) after post-column derivatization in an online chemical reactor (50 mm x 2 mm) with Zn metal (200 mesh). Intra- and inter-day RSD were 6.6-13.6% with between sample RSD (n = 10) of 7.8% (milk), 32.6% (spinach) and 44.6% (vegetable juice).
Vitamin K1 HPLC

"Solid-phase Extraction Cleanup For Determining Ascorbic-acid And Dehydroascorbic Acid By Titration With 2,6-dichlorophenolindophenol"
J. AOAC Int. 1996 Volume 79, Issue 5 Pages 1236-1243
Krishna K. Verma, Archana Jain, Bhushan Sahasrabuddhey, Kalpana Gupta and Sanjeev Mishra

Abstract: Ascorbic acid is frequently determined by titration with 2,6-dichlorophenolindophenol. The determination is rapid, but the method is neither specific for ascorbic acid nor very sensitive. The coloring matter in the assay solution interferes with the visual endpoint, and iron(II), copper(I), sulfite, and sulfhydryl substances such as cysteine and glutathione interfere with the color reaction. Sample cleanup by solid-phase extraction with C-18 bonded silica was developed to remove the coloring matter. Extraction sorbent impregnated with 2,2'-bipyridyl, 2,9-dimethyl-1,10-phenanthroline (neocuproine) acid N-ethylmaleimide removes Fe(II), Cu(I), and sulfhydryl compounds, respectively. The procedure was applied to highly colored multivitamin pharmaceuticals, soft drinks, and fruit and vegetable juices. In contrast to the results from the original method, which is not applicable to such samples, the results obtained by the method incorporating cleanup were accurate and selective for ascorbic acid. The sample cleanup also permitted determination of dehydroascorbic acid by reducing it to ascorbic acid with cysteine and titrating the ascorbic acid formed with indophenol. As little as 3 µg ascorbic acid was determined by the method incorporating cleanup.
Ascorbic acid dehydroascorbic acid Sample preparation Spectrophotometry HPLC Titrations Interferences Solid phase extraction