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
Email: schalk@unf.edu
Website: @unf

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Vegetable

Classification: Vegetable -> lettuce

Citations 2

"Flow Injection Determination Of Nitrate In Vegetables Using A Tubular Potentiometric Detector"
J. Agric. Food Chem. 1995 Volume 43, Issue 3 Pages 704-707
Jose L. F. C. Lima, Antonio O. S. S. Rangel, and M. Renata S. Souto

Abstract: Dried powdered vegetable was extracted by the method of Mitrakas and Alexiades (Mikrochim. Acta, 1990, 1, 7) and the extract was injected into a carrier stream (6 ml/min) of 1 µM-KNO3 in extractant solution (10 nM-lead acetate, 5 mM lead oxide and 10 mM sodium acetate) in a low dispersion FIA system. The flow passed through a tubular nitrate ISE with (4,7-diphenylphenanthroline) nickel(II) dissolved in o-nitrophenyl octyl ether immobilized in a PVC membrane and without an inner reference solution (preparation details given). The calibration graph was linear for 0.4-40 mM nitrate with a detection limit of 28 µM. Recoveries were 93.8-104% for nitrate in parsley, lettuce and spinach with RSD of 3%. A flow injection system with potentiometric detection for the determination of nitrate in vegetables was developed. For this purpose a tubular nitrate ion-selective electrode with the ion-exchanger system [(4,7- diphenylphenanthroline)nickel(II) dissolved in o-nitrophenyl octyl ether] immobilized in a PVC membrane and without inner reference solution was prepared. The flow injection manifold incorporating the tubular electrode was used for the determination of nitrate in vegetables (lettuce, parsley, and spinach), using a mixture of lead acetate, lead oxide, and sodium acetate as nitrate extractant, ionic strength adjustor, and interference suppressor solution. The quality of the results obtained by the proposed methodology was assessed by comparing them with those provided by a conventional potentiometric methodology and also through recovery tests (recoveries from 94 to 104% were found). A sampling rate of 120 samples per hour was achieved with a relative standards deviation lower than 2%.
Nitrate Electrode Electrode Potentiometry Electrode Method comparison Interferences

"Determination Of Sulfite In Food By Flow Injection Analysis"
J. AOAC Int. 1986 Volume 69, Issue 3 Pages 542-546
Sullivan JJ, Hollingworth TA, Wekell MM, Newton RT, Larose JE

Abstract: A method is described for the determination of sulfite levels in food products by flow injection analysis (FIA). The method is based on the decolorization of malachite green by SO2, which is isolated from the flowing sample stream by means of a gas diffusion cell. The FIA method has a detection limit in food sample extracts of 0.1 ppm SO2 (3 times peak height of blank), which corresponds to 1-10 ppm SO2 in a food product, depending on the extraction procedure used. At the 5 ppm SO2 level in a food extract, the precision of replicate injections is±1-2%. The method was tested on a variety of both sulfite-treated and untreated food products and the results compared favorably with those obtained by the Monier-Williams, colorimetric (pararosaniline), and enzymatic (sulfite oxidase) methods. The average differences from the FIA results were 19, 11, and 12%, respectively, for those samples (n = 12) above 50 ppm SO2. At lower levels the results were somewhat more erratic due to inaccuracies of the various methods at low concentrations. The method is based on the decolorization of malachite green (C. I. Basic Green 4) by SO2, which is isolated from the flowing sample stream by a gas diffusion cell; the decrease in absorbance is measured at 615 nm. The detection limit is 0.1 ppm, which corresponds to 1 to 10 ppm in a food product, depending on the extraction procedure used, which itself depends on the type of food being analyzed. For 5 ppm of SO2 in a food extract, the precision of replicate injections is ~1 to 2%. The proposed method was tested on sulfite-treated and untreated wine, apple juice, dried apricots, potatoes, pickled onions, shrimps, lettuce, dried apples and cabbage to give results in good agreement with those obtained by the Monier-Williams, pararosaniline colorimetric and sulfite oxidase methods. The mean differences from the proposed method were 19, 11 and 12%, respectively for the 12 samples with SO2 contents >50 ppm. At lower levels the results were somewhat more erratic. The construction of the flow injection apparatus is described in detail.
Sulfite Spectrophotometry Sample preparation Gas diffusion Extraction Method comparison