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 -> juice

Citations 8

"Simultaneous Flow Injection Determination Of 2- And 4-nitrophenol Using A Photodiode-array Detector"
Anal. Chim. Acta 1992 Volume 258, Issue 2 Pages 269-273
M. E. León-González*, L. V. Pérez-Arribas, M. J. Santos-Delgado and L. M. Polo-Díez

Abstract: The sample, e.g., fruit juice, was injected into a carrier stream of 0.5 M phosphate buffer of pH 7.4 (2 mL min-1) and mixed with 0.13% tetrabutylammonium nitrate solution (1.2 mL min-1). The ion pairs were extracted into 1,2-dichloroethane and the absorbances at 260 and 410 were measured for 2- and 4-nitrophenol, respectively. The calibration graphs were rectilinear from 0.1 to 12 mg l-1, with detection limits of 0.03 mg l-1. The coefficient of variation (n = 8) at 6 mg L-1 of either compound was 0.15%. Recoveries of 1 to 10 mg L-1 from fruit juice were between 90 and 105%. A batch method was also examined, but gave a coefficient of variation of 2.1%. A flow injection method for the simultaneous determination of o- and p-nitrophenol in apple and orange juices is based on formation and extraction of ion pairs by using Bu4N+ as counter ion at pH 7.4 and diode-array spectrophotometric detection at 260 and 410 nm for o- and p-nitrophenol, respectively. The calibration graphs were linear for 0.1-12 mg/L. The relative standard deviation at 6 mg/L was 0.15% for both o- and p-nitrophenol and the detection limits were 0.03 mg/L.
2-Nitrophenol 4-Nitrophenol Spectrophotometry Sample preparation Simultaneous analysis Method comparison Ion pair extraction Organic phase detection

"Application Of Square-wave Voltammetry For The Determination Of Ascorbic Acid In Soft Drinks And Fruit Juices Using A Flow Injection System"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 375-380
Ying-Sing Fung* and Song-Ying Mo

Abstract: A portion (100 µL) of test solution was injected into a stream of the supporting electrolyte (Britton - Robinson buffer) for transfer to a thin-layer electrochemical cell (volume 16 µL) equipped with vitreous-carbon working, stainless-steel counter and Ag - AgCl reference electrodes. The normal flow rate was 0.5 mL min-1, and the potential of the working electrode was scanned from +0.2 to +0.7 V in 1 s, with application of a computer-generated square waveform and measurement of the oxidation peak current at +0.46 V. The buffer pH was 2.87 to stabilize the ascorbic acid. The peak signal was rectilinearly related to ascorbic acid concentration. from 2 µM to 6 mM; food additives at normal concentration. levels did not interfere. Results obtained on blackcurrant juice, lemon tea, sugar-cane juice and apple juice were satisfactory. The application of square-wave voltammetry for detection in the flow injection determination of ascorbic acid in soft drinks and fruit juices was investigated. The pH of the solution was buffered at 2.87 to stabilize the ascorbic acid prior to anal. Parameters such as scan rate, square-wave amplitude, step height and flow-rate of electrolyte were found to have little effect on the potential, but a significant effect on the current. The anal. current is only slightly affected by the flow-rate of the electrolyte and a max. scan rate of 0.5 V/s can be used. As a compromise between sensitivity and selectivity, 40 mV was chosen as the amplitude of the square wave and 10 mV as the potential step height. Similarly, a flow-rate of 0.5 mL/min and an injection volume of 100 µL were chosen as a compromise between the sensitivity and resolution of the FIA method. With these procedures, the max. number of samples that could be analyzed was 120/h. The linear calibration range was from 2 x 10^-6 to 6 x 10^-3 M and the determination limit (10s) was 2 x 10^-7M. No significant interference was found from additives commonly found in juice and drink samples within their normal concentration. ranges. Four juice samples were analyzed using the developed method and the results were compared with those given by the established AOAC method. No significant difference was observed between the two methods used for the four samples studied.
Ascorbic acid Voltammetry Electrode Standard method Method comparison Interferences

"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

"Enzyme Assays For The Phenolic Content Of Natural Juices"
J. Agric. Food Chem. 1994 Volume 42, Issue 8 Pages 1824-1828
Stephen Cliffe, Matthias S. Fawer, Guenther Maier, Kyo Takata, and Guido Ritter

Abstract: The properties of a fungal laccase have been exploited to develop two enzyme assays for the phenolic content of natural beverages: first, by monitoring the fall in oxygen tension after addition of enzyme to a diluted juice sample in an end-point batch assay; second, by monitoring the current due to reduction of products after injection of sample into a flow injection analysis (FIA) system which incorporates the immobilized enzyme. Using apple juices, a linear (R gt 0.9) correlation was observable between these enzyme assays and the Folin-Ciocalteu wet chemical assay for total phenol content. Using purified substrates, a study has been made of those phenolic constituents measured in the two enzyme assays. Oxidative treatment of juices with laccase was shown by HPLC to specifically remove these phenolics. These enzyme assays may prove helpful to predict the stability of natural beverages.
Phenols Immobilized enzyme

"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

"Conductometric Measurement Of Sugar Content Of Food With Flow Injection Analysis System. Study On Electrochemical Measurement Of Sugar Content Of Food, Part VIII"
Nippon Shokuhin Kagaku Kogaku Kaishi 1985 Volume 32, Issue 12 Pages 916-919
Takakazu NOMURA, Hiroyuki UKEDA, Kiyoshi MATSUMOTO, Yutaka OSAJIMA

Abstract: The rapid and convenient methods based on conductometric flow injection analysis (FIA) were proposed for measuring sugar content of apple juice and juice of sugar beet root and for measuring total solids content of cow's milk. With the FIA system, all measurements were able to carry out under the same operational conditions of the system, by use of each calibration curve for each sample -apple juice, juice of sugar beet root and cow's milk, respectively. For apple juice and clarified juice of sugar beet root with tannic acid, sugar content estimated from the proposed mehtods agreed with that obtained from phenol-sulfuric acid method with an error of 0.24%. For cow's milk homogenate, the total solids content estimated from the proposed method agreed with that obtained from gravimetric method (method of A.O.A.C.) with an error of 0.19%.
Sucrose Total soilds Conductometry

"Automated Determination Of Total Polyphenols In Apple Juice"
Z. Lebensm. Unters. Forsch. 1993 Volume 197, Issue 5 Pages 424-426
Juan Mangas, Belén Suárez and Domingo Blanco

Abstract: Diluted apple juice was subjected to flow injection analysis on Tecator FlAstar 5010 Analyzer with a model 5017 sampler and a model 5023 spectrophotometric detector. The carrier was a solution of Folin-Cocalteu reagent containing 1% of Na2CO3, at 0.6-1 ml/min and 25-40°C; the channel length was 0.3-1 m. Chromogenic acid was used as a standard, for which a calibration graph was linear for up to 105 ng. Total content of 36 polyphenols in the samples ranged from 712-3390 mg/ml and RSD were 1%. An automated method of total polyphenols analysis in apple juice using the Folin-Ciocalteu reagent is presented. Chlorogenic acid was selected as the standard since a similar kinetic behaviour, standard-sample, was observed. A straightforward method with good reproducibility (CV < 1%), sampling frequency (48 h-1) and correlation with the traditional batch method (r = 0.9924) is proposed.
Polyphenol index Spectrophotometry Tecator Method comparison

"Spectrophotometric Determination Of Glucose In Foods By Flow Injection Analysis With An Immobilized Glucose Oxidase Reactor"
Z. Lebensm. Unters. Forsch. 1997 Volume 204, Issue 2 Pages 99-102
Renbing Shi, Kathrin Stein, G. Schwedt

Abstract: Samples, e.g., apple juice or banana jam were diluted up to 100-fold with 50 mM phosphate buffer of pH 5. Portions (0.1 ml) were injected into the carrier stream (1.3 ml/min) of 0.5% KI in the same buffer. The carrier stream passed through the immobilized glucose oxidase reactor (4.5 cm x 2 mm i.d., preparation described). The H2O2 formed and the KI were mixed with a catalyst solution (0.6 ml/min) of 0.06% starch and 0.006% ammonium heptamolybdate in 0.1 M H2SO4 and, after a stopped-flow delay of 20 s, the absorbance was measured at 620 nm. The calibration graph was linear for 0.1-2 mM glucose. The RSD (n = 5) was 1.6% at 1 mM. Because of the high dilution, there was no interference from ascorbic acid. If the reactor were stored in the buffer at 4°C between measurements it could be used for up to 200 determinations during one month. The results presented were in good agreement with those obtained by a standard enzymatic method.
Glucose Spectrophotometry Reactor Method comparison Interferences Stopped-flow Catalysis Immobilized enzyme