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: Fruit -> apple -> dried

Citations 3

"Direct Determination Of Free Sulfur Dioxide In Wine And Dried Apple Samples By Using A Gas Generating And Purging Device Coupled To A Continuous-flow (injection) System"
Analyst 1995 Volume 120, Issue 7 Pages 2013-2018
Zheng-liang Zhi, Angel Ríos and Miguel Valcárcel

Abstract: Two flow injection (FI) methods for the cited determination are described. In both methods a gas generating and purging device was incorporated in the FI manifolds, whereby the sample (2.5 mL of wine or 0.2-2 g of dried apple) was mixed with 0.8 mL of 1 M HCl in a reaction vessel kept at 65°C (method A) or 70°C (method B) to generate SO2. In method A, the SO2 was purged by a N2 stream (5 ml/min) and passed through a cuvette containing 1 mL of color-developing reagent (0.002% pararosaniline/1.5% formaldehyde/0.2 M HCl). The absorbance was measured continuously at 568 nm and the kinetic features of the absorbance-time (A-t) profiles were used for quantification of SO2. In method B, the SO2 was purged by an air stream (3 ml/min) and a portion (500 µL) of the gaseous sample was injected into a stream (0.7 ml/min) of the color-developing reagent downstream of the detector. By operating the FI manifold in flow-reversal mode, the sample was cycled such that A-t multipeak recordings were obtained at 568 nm on which quantification of SO2 was based. Calibration graphs were linear from 0.03 (detection limit) to 3 and from 0.75 (detection limit) to 75 µg/ml of SO2 for methods A and B, respectively. The RSD (n = 11) were 5-7% and the throughput was 10^-15 samples/h.
Sulfur dioxide Spectrophotometry Flow reversal Gas stream

"Determination Of Oxamyl And Methomyl By High Performance Liquid Chromatography Using A Single-stage Post-column Derivatization Reaction And Fluorescence Detection"
J. Agric. Food Chem. 1992 Volume 40, Issue 6 Pages 1026-1029
Steven C. Stafford and Willy Lin

Abstract: Dried, powdered apple, orange, soybean leaf and insect samples (0.5 g), fortified with oxamyl (I) and methomyl (II) were ground with pre-washed C18. The mixtures were packed into a column and, after washing with hexane, I and II were eluted with CH2Cl2, the eluates were evaporated to dryness, and the residues were reconstituted with water (pH 3) and sonicated. The solution, and also river water samples (1 ml), were filtered, then analyzed on a column (25 cm x 4.6 mm) of Zorbax ODS at 40°C with linear gradient elution at 1 mL min-1 with water (pH 3.0) - acetonitrile, programmed from (4:1) to (1:4) during 16 min. Single-stage post-column hydrolysis of the analytes, and derivatization of the methylamine produced, was performed in an online flow reactor at 140°C, with a mixture of o-phthalaldehyde in methanol, aqueous 0.01 M KOH and 2-mercaptoethanol as reagent. Fluorimetric detection was carried out at 455 nm (excitation at 340 nm). A schematic diagram of the post-column reactor is given. The recoveries of both I and II ranged from 72 to 129%, and detection limits were 20 ng g-1 (raw agricultural commodities) and 5 mg mL-1 (water).
Oxamyl Methomyl Fluorescence HPLC Post-column derivatization Heated reaction

"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