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 -> potato

Citations 9

"Multi-enzymatic Electrochemical Sensor: Field Measurements And Their Optimisation"
Anal. Chim. Acta 1999 Volume 385, Issue 1-3 Pages 461-466
N. F. Starodub, N. I. Kanjuk, A. L. Kukla and Yu. M. Shirshov

Abstract: Using such enzymes as cholinesterases, urease and glucose oxidase, and electrolyte-insulator-semiconductor (EIS)-structures with silicon nitride ion-sensitive layers as transducers investigations have been performed on the determination of heavy metal ions and phosphororganic pesticides in solutions. The content of toxic elements indicated above was determined by estimation of the residual activity of enzymatic membranes after the injection of analyzed samples, The optimal conditions were chosen for analysis of heavy metal ions and phosphororganic pesticides in potato and cabbage saps. It was shown that multienzyme analysis followed by mathematical processing is one of the effective approaches to develop computer-controlled sensor arrays for toxic substrates,
Metals, heavy Pesticides, organophosphorus Sensor Apparatus Detector Computer

"Determination Of Paraquat By Flow Injection Spectrophotometry"
Anal. Chim. Acta 1987 Volume 199, Issue 1 Pages 203-208
E. Chico Guijarro, P. Yáñez-Sedeño and L. M. Polo Diéz

Abstract: Paraquat was reduced with freshly prepared 1% Na2S2O4 solution in 0.1 M NaOH and determined by flow injection absorption spectrophotometry at 605 nm. Rectilinear calibration graphs were obtained for 0.1 to 1.0, 1.0 to 10 and 5.0 to 30.0 mg L-1 of paraquat under optimized conditions, the lowest limit being forty times less than that of the established spectrophotometric method. The flow injection method provided sample and reagent economy and higher sample throughput (80 h-1). The method was used to determine paraquat added to potable water and potatoes. After pre-concentration. by cation exchange on a Dowex 50W-X8 column, reproducible recoveries were obtained of 65 to 69 and 54 to 57%, respectively. Diquat interfered but could be removed previously by precipitation with NaOH. Interference by Ca(II) and Mg(II) was avoided by treating the sample with EDTA at pH 9 before introduction into the column. The determination of paraquat in different herbicide samples gave results in good agreement with those obtained by polarographic and manual spectrophotometric methods.
Paraquat Spectrophotometry Interferences Preconcentration

"Spectrofluorimetric Determination Of Diquat By Manual And Flow Injection Methods"
Anal. Chim. Acta 1991 Volume 244, Issue 1 Pages 99-104
T. Pérez-Ruiz, C. Martínez-Lozano and V. Tomás

Abstract: In the manual method, sample solution, containing 0.03 to 9 µg of diquat (I), was mixed with 2 mL of 0.5 M borax buffer (pH 8), 1 mL of 0.5% sodium dithionite and water to 10 mL and, after 5 min, the resulting stable radical of I was detected fluorimetrically at 497 nm (excitation at 428 nm). The method was also adapted for use in a flow injection procedure (diagram of apparatus and details given. The calibration graph was rectilinear from 3 to 900 and 18 to 4000 µg L-1 of I by the manual and flow injection methods, respectively; the detection limit by the manual method was 0.4 µg L-1 and coefficient of variation were 2%. The method was applied in the determination of I in commercial herbicide formulations, water, potatoes, flowers and soil (sample prep. described) and in serum and urine directly with use of a standard additions method.
Diquat Fluorescence Buffer Standard additions calibration

"Determination Of Carbamate Residues In Crop Samples By Cholinesterase-based Biosensors And Chromatographic Techniques"
Anal. Chim. Acta 1998 Volume 362, Issue 1 Pages 59-68
Gilvanda Silva Nunes*, Petr Skládal, Hideko Yamanakacand Damiá Barceló

Abstract: An amperometric biosensor based on cholinesterase (ChE) has been used for the determination of selected carbamate insecticides in vegetable samples. The linear range of the biosensor for the N-methylcarbamates (aldicarb, carbaryl, carbofuran, methomyl and propoxur) varied from 5 x 10^-5 to 50 mg kg-1. Limits of detection were calculated on the basis that the ChE enzymes were 10% inhibited and varied, depending of the combination ChE (as acetyl- or butyrylcholinesterase) vs. inhibitor (pesticide), from 1 x 10^-4 to 3.5 mg kg-1. The biosensor-based carbamate determination was compared to liquid chromatography/UV methods. Three vegetable samples were spiked with carbofuran and propoxur at 125 µg kg-1 followed by conventional procedures. Good correlations were observed for carbofuran in the vegetable extracts (79, 96 and 91% recoveries for potato, carrot and sweet pepper, respectively), whereas for propoxur unsatisfactory results were obtained. Potato and carrot samples were spiked with 10, 50 and 125 µg kg-1 carbofuran, followed by direct determination by the amperometric biosensor. The fortified sampler; resulted in very high inhibition values, and recoveries were: 28, 34 and 99% for potato, and 140, 90 and 101% for carrot, respectively, at these three fortification levels.
Ammonium carbamate hydrate Amperometry Sensor Method comparison

"Spectrofluorometric Determination Of Paraquat By Manual And Flow Injection Methods"
Analyst 1998 Volume 123, Issue 7 Pages 1577-1581
Tomás Pérez-Ruíz, Carmen Martínez-Lozano, Virginia Tomás and José Fenoll

Abstract: The reaction involving the formation of a fluorescent charge-transfer complex between paraquat and benzaldehyde was studied in ethanol-water medium. In the presence of a large excess of benzaldehyde, the fluorescence intensity is linearly related to paraquat concentration. from 0.13 to 7.4 µg mL-1. The method can be easily adapted to a flow system using a two-channel manifold, the peak height being proportional to the paraquat concentration. over the range 1.6-22.3 µg mL-1. Manual and flow injection procedures were satisfactorily applied to the determination of paraquat in commercial herbicides, waters, soils and potatoes.
Paraquat Fluorescence Complexation

"Flow Injection Spectrofluorimetric Determination Of Ethylenethiourea"
Fresenius J. Anal. Chem. 1998 Volume 362, Issue 4 Pages 399-403
Tomás Pérez-Ruiz, Carmen Martínez-Lozano, Virginia Tomás, Antonio Sanz, Jesús Martín

Abstract: A flow injection configuration is proposed for the fluorimetric determination of ethylenethiourea. The procedure is based on the inhibitory effect of ethyl-enethiourea on the oxidation of thiamine to thiochrome by Hg(II). A linear calibration graph was obtained between 0.1-2.0 µg mL-1, with a sampling rate of 40 samples/h and a relative standard deviation of 1.11%. The usefulness of the method was tested for the determination of ethylenethiourea residues in water, milk, potatoes, pear, grape, and apple.
Ethylenethiourea Fluorescence Indirect

"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

"Determination Of Total Sulfite In Shrimp, Potatoes, Dried Pineapple, And White Wine By Flow Injection Analysis: Collaborative Study"
J. AOAC Int. 1990 Volume 73, Issue 1 Pages 35-42
Sullivan JJ, Hollingworth TA, Wekell MM, Meo VA, Saba HH, Etemad-Moghadam A, Eklund C, Phillips JG, Gump BH

Abstract: A method for the determination of total sulfite in shrimp, potatoes, dried pineapple, and white wine by flow injection analysis (FIA) was collaboratively studied by 8 laboratories. In the method, the sample solution is reacted with sodium hydroxide to liberate aldehyde-bound sulfite. The sample stream is acidified to produce SO2 gas, which diffuses across a Teflon membrane in the gas diffusion cell into a flowing stream of malachite green. The degree of discoloration of the malachite green is proportional to the amount of sulfite in the sample solution. Red wine was included in the study but interlaboratory precision for these samples was not satisfactory and correlation with Monier-Williams results was poor. The present method is not recommended for use with these samples. For shrimp, potatoes, dried pineapple, and white wine, average reproducibility (RSDR) of results was 25% for samples at 10 ppm SO2 and 10% for samples at greater than 50 ppm. Overall average reproducibility was 14%. Recoveries of sulfite added to samples averaged 80%. Comparison of FIA with the Monier-Williams method indicated comparable results by the 2 methods. The FIA method has been adopted official first action for determination of greater than or equal to 5 ppm total sulfite in shrimp, potatoes, dried pineapple, and white wine.
Sulfite Spectrophotometry Diffusion Teflon membrane Method comparison Gas diffusion

"A Flow Injection System For The Determination Of Starch In Starch From Different Origins With Immobilized α-amylase And Amyloglucosidase Reactors"
Starch 1993 Volume 45, Issue 8 Pages 264-270
Jenny Emnéus, Gunilla Nilsson, Lo Gorton

Abstract: Starch (1.2-4 g) was dissolved in 4 mL of 0.5 M NaOH and, if necessary, heated in a boiling water bath for 10 min for complete dissolution. The solution were diluted to 50 mL with 0.1 M acetic acid solution of pH 2.7, to give a final pH of 4.6. A 15 µL portion was injected into a stream of Ca(NO2)2 in 0.05 M acetate buffer of pH 6 (0.17 ml/min) in the FIA system before passing into the Termamyl reactor. After merging with a second flow of 0.1 M acetate buffer of pH 4.5 (0.33 ml/min) and passing through the amylerglycosidase reactor, the effluent was merged with 0.2 M phosphate buffer of pH 7.4 containing 4 mM NAD+ (1 ml/min). The effluent passed through the glucose dehydrogenase/aldose 1-epimerase reactor and a flow-through detector and was monitored at 340 nm. The peak height and integrated peak areas were evaluated by a computer program. Lipids, proteins and chemical modifications of starch interfered with the determination probably due to steric hindrance of the enzymes resulting in incomplete degradation to glucose; detection limits and RSD are not given. The FIA system can be fully automated. The cited method was applied to wheat, corn rice and potato starch.
Starch Spectrophotometry Immobilized enzyme Automation Interferences