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 -> orange

Citations 3

"Determination Of L-asparagine Using Flow Injection Systems With Spectrophotometric And Potentiometric Detection"
Anal. Chim. Acta 1996 Volume 336, Issue 1-3 Pages 113-122
Kathrin Stein*, Renbing Shi and Georg Schwedt

Abstract: Two FIA methods were developed for determining asparagine in foods. The first method was based on the catalyzed hydrolysis of asparagine by immobilized asparaginase to yield NH3. The NH3 diffused through a PTFE membrane and was detected (i) spectrophotometrically using an acid-base indicator solution as the acceptor or (ii) potentiometrically using a pH electrode and water as the acceptor. The linear ranges and RSD (n = 5) were 0.2-2.3 mM and 1.7% (at 0.75 mM asparagine), respectively, for spectrophotometric detection and 0.1-4 mM and 2.5% (at 1 mM asparagine), respectively, for potentiometric detection. The sampling frequency was 35/h. The second method used a biosensor fabricated by attaching a membrane with immobilized asparaginase on to a pH electrode. The linear range and RSD (n = 5) of this method were 0.1-2 mM and 2.3% (at 1 mM asparagine), respectively. The sampling frequency was 30/h. The methods were applied to apple and orange juice, oranges and asparagus. The sample preparation procedure involved diluting the fruit juices or filtering the homogenates of the solid foods. Recoveries of 50 mg/l or 50 mg/100 g asparagine from spiked foods were >94.3%.
l-asparagine Potentiometry Electrode Spectrophotometry Sensor Immobilized enzyme Teflon membrane Gas diffusion

"Determination Of Carbosulfan In Oranges By High Performance Liquid Chromatography With Post-column Fluorescence"
Analyst 1995 Volume 120, Issue 10 Pages 2479-2481
M. W. Brooks and A. Barros

Abstract: High performance liquid chromatography equipped with post-column fluorescence derivatization provides an automated and specific analytical method for pesticide determination. Carbosulfan, a carbamate pesticide, can be analyzed utilizing an existing and proven carbamate system after the addition of one additional hydrolytic reactor inline. Extraction of this compound from citris crops requires careful handling owing to the volatility and unstable nature of the analyte in acid conditions. This paper describes the necessary instrument modifications and presents a method for carbosulfan extraction. Analyses of orange homogenates were performed rapidly with recoveries of between 66 and 98% for residue levels between 0.03 and 0.25 µg kg-1.
Carbosulfan HPLC Fluorescence Post-column derivatization

"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