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

Citations 15

"Stopped-flow Injection Determination Of Copper(II) At The Ng/ml Level"
Anal. Chim. Acta 1984 Volume 165, Issue 1 Pages 177-185
F. Lázaro, M. D. Luque de Castro and M. Valcárcel

Abstract: The catalytic action of Cu(II) on the di-2-pyridyl ketone hydrazone - H2O2 system is quantitative. The oxidation product shows an intense blue fluorescence at 427 nm (excitation at 350 nm) in a strongly acidic medium. The sampling rate (72 h-1), coefficient of variation (1.4%) and freedom from interference from most foreign ions allow determination of 0.2 to 300 ng mL-1 of Cu in foods (e.g., fruits and rice) and blood serum.
Copper(II) Fluorescence Interferences Catalysis Stopped-flow PPB

"Amperometric Flow-through Biosensor For The Determination Of Pesticides"
Anal. Chim. Acta 1995 Volume 308, Issue 1-3 Pages 129-136
C. La Rosa, F. Pariente, L. Hernández and E. Lorenzo*

Abstract: The amperometric flow-through biosensor for organophosphorus and carbamate pesticides was based on the inhibition of the acetyl cholinesterase (AChE)-catalyzed hydrolysis of 4-aminophenylacetate (PAPA). AChE was immobilized on the nylon grid discs (100-150 µm thickness, 5-6 mm diameter) and the disks were mounted in an amperometric flow cell. A potential of +0.25 V (vs. Ag/AgCl) was applied to the working electrode. Pesticide solution (500 µL) and 150 µL 1.2 mM PAPA substrate solution into a 0.08 M phosphate buffer of pH 8 carrier stream (0.55 ml/min). The catalyzed hydrolysis of the PAPA occurred in the immobilized AChE layer and the released 4-aminophenol was detected amperometrically. Calibration graphs were linear for 0.5-10 µM-paroxon and 0.5-50 µM-carbaryl and the detection limits were 0.1 µM. The RSD for the determination of 40 and 8 µM of either carbaryl or paroxon were 3.7 and 4%, respectively. The method was used to determine pesticides in lagoon water and fruits.
Pesticides, carbamate Pesticides, organophosphorus Amperometry Sensor Immobilized enzyme

"Amperometric Determination Of L-malic Acid In A Flow Injection Analysis Manifold Using Packed-bed Enzyme Reactors"
Analyst 1996 Volume 121, Issue 4 Pages 435-439
Mamas I. Prodromidis, Stella M. Tzouwara-Karayanni, Miltiades I. Karayannis, Pankaj Vadgama and Andrew Maines

Abstract: The sample (130 µL) was injected into a carrier stream (0.19 ml/min) of 0.05 M glycylglycine buffer of pH 9.5 (buffer A) containing 1.75 mM hexacyanoferrate(III) and merged with a reagent stream (0.14 ml/min) of 9.5 mM NAD+ in buffer A. The mixture was passed through a packed-bed reactor (3 cm x 2 mm i.d.) containing malate dehydrogenase and diaphorase co-immobilized on isothiocyanate-modified controlled-pore glass (preparation described). The hexacyanoferrate(II) produced was monitored amperometrically at a graphite electrode held at +0.3 V vs. Ag/AgCl. The calibration graph was linear for 20-400 µM malate, the detection limit was 1 µM and the RSD (n = 5) at the 100 µM malate level was 1.2%. The throughput was 30 samples/h. The method was applied to fruits and vegetables. Recoveries of malate were 95-108%. The results obtained agreed with those obtained by an enzymatic test-kit method.
l-Malic acid Amperometry Controlled pore glass

"Bioelectrochemical Determination Of Citric Acid In Real Samples Using A Fully Automated Flow Injection Manifold"
Analyst 1997 Volume 122, Issue 10 Pages 1101-1106
Mamas I. Prodromidis, Stella M. Tzouwara-Karayanni, Miltiades I. Karayannis and Pankaj M. Vadgama

Abstract: An enzymatic method for the determination of citric acid in fruits, juices and sport drinks is proposed. The method is based on the action of the enzymes citrate lyase, oxaloacetate decarboxylase and pyruvate oxidase, which convert citric acid into H2O2 with the latter being monitored amperometrically with a H2O2 probe. The enzymes pyruvate oxidase and oxaloacetate decarboxylase were immobilized. A multi-membrane system, consisting of a cellulose acetate membrane for the elimination of interferants, an enzymatic membrane and a protective polycarbonate membrane were placed on a Pt electrode and used with a fully automated flow injection manifold. Several parameters were optimized, resulting in a readily constructed and reproducible biosensor. Interference from various compounds present in real samples was minimized. Calibration graphs were linear over the range 0.01-0.9 mM pyruvate, 0.015-0.6 mM oxaloacetate and 0.015-0.5 mM citrate. The throughput was 30 samples h-1 with an RSD of 1.0% (n = 8); the mean relative error was 2.4% compared with a standard method. The recovery was 96-104%. A 8-10% loss of the initial activity of the sensor was observed after 100-120 injections.
Citric acid Biochemical analysis Electrochemical analysis Amperometry Sensor Automation Interferences Immobilized enzyme Optimization Method comparison Standard method

"Amperometric Flow Injection Determination Of Fructose With An Immobilized Fructose 5-dehydrogenase Reactor"
Anal. Chem. 1986 Volume 58, Issue 13 Pages 2732-2734
Kiyoshi Matsumoto, Osamu Hamada, Hiroyuki Ukeda, and Yutaka Osajima

Abstract: The method was based on the fructose 5-dehydrogenase(I)-catalyzed oxidation by Fe(CN)63- of D-fructose to 5-oxo-D-fructose. Sample solution (240 µL) was injected into the carrier solution of McIlvaine buffer (pH 5.0) containing 6 mM K3Fe(CN)6 and 0.1% Triton X-100 solution, and passed through a column (6 cm x 2 mm) packed with a I-containing phase (partially purified I from the cell membrane of Gluconobacter industrius immobilized on Amino-Cellulofine). The reduced acceptor was detected amperometrically in a platinum flow-through cell, with a platinum working electrode potential of +0.385 V vs. the SCE. The response of the sensor was rectilinear between 0.02 and 2 mM D-fructose, and the precision was <1.8% (n = 10). The assay speed was 15 samples h-1 with no carry-over. Interference of ascorbic acid was removed by using a pre-column of ascorbate oxidase immobilized on CNBr-activated Sepharose. Results of determinations of D-fructose in fruit samples agreed relatively well with those of the F-kit method.
Fructose Amperometry Electrode Immobilized enzyme Interferences Method comparison Triton X Surfactant

"Simultaneous Determination Of Glucose, Fructose, And Sucrose In Mixtures By Amperometric Flow Injection Analysis With Immobilized Enzyme Reactors"
Anal. Chem. 1988 Volume 60, Issue 2 Pages 147-151
Kiyoshi Matsumoto, Hideaki Kamikado, Hiroaki Matsubara, and Yutaka Osajima

Abstract: The flow injection system (described) incorporated three immobilized-enzyme reactors (prep. described), one each for glucose(I), fructose(II) and sucrose(III), in parallel, a I-eliminating enzyme reactor (placed in series with the III reactor), and a multi-channel flow-through amperometric detector. Sample solution was injected into the system by an injection valve and into each of the three carrier streams by valve switching. For I determination, the carrier stream was 0.1 M phosphate buffer (pH 6.0), the reactor contained immobilized I oxidase, and the H2O2 produced was determined at +0.65 V vs. Ag - AgCl. For II determination, the carrier stream was McIlvaine buffer (pH 5.0) containing 6 mM K3Fe(CN)6 and 0.1% of Triton X-100, the reactor contained immobilized II 5-dehydrogenase, and the Fe(CN)64- formed was determined at +0.385 V vs. Ag - AgCl. For III determination, the carrier stream was 0.1 M phosphate buffer (pH 7.0), the reactor contained immobilized β-fructofuranosidase, aldose 1-epimerase and I oxidase, and the H2O2 formed was determined as before. The coefficient of variation (n = 10) for 1 mM I, -II and -III were 1.8, 1.8 and 1.6%, respectively. Calibration graphs (response vs. concentration.) were rectilinear from 0.02 to 1 mM for I, II and III. The method was applied to food samples.
Glucose Fructose Sucrose Amperometry Immobilized enzyme Multicomponent Triton X Valve Surfactant

"Amperometric Flow Injection Determination Of Citric Acid In Food Using Free Citrate Lyase And Co-immobilized Oxalacetate Decaboxylase And Pyruvate Oxidase"
Electroanalysis 1995 Volume 7, Issue 6 Pages 527-530
Kiyoshi Matsumoto, Tadayuki Tsukatani, Yuko Okajima

Abstract: Controlled-pore glass was refluxed with 6 M HCl for 6 h, dried and silanized with 10% (3-aminopropyl)triethoxysilane solution in toluene at 130°C for 10 h. Oxalacetate decarboxylase and pyruvate oxidase were co-immobilized (Matsumoto et al., Anal. Chem., 1988, 60, 147). This support was packed in to a glass tube (10 cm x 2 mm i.d.) and used in a FIA system with a carrier solution of 0.1 M phosphate buffer of pH 7 containing 10 mM MgCl2/80 µM-thiamine pyrophosphate/ 10 µM-flavine adenine dinucleotide. The sample (50 µL) and citrate lyase solution in phosphate buffer of pH 7 (80 µL) were injected in to the carrier stream (0.85 ml/min) and the mixture was pumped through a reactor containing ascorbate oxidase immobilized on controlled-pore glass to remove L-ascorbate, and then through the prepared reactor. H2O2 was determined amperometrically in a flow-through cell equipped with a Pt working electrode set at +0.6 V vs Ag/AgCl. Calibration graphs were linear from 0.1-1 mM citrate. The detection limit was 0.02 mM; RSD was 1.23% at the 0.5 mMlevel (n=10). An interference study was carried out (details given). The frequency was 15 tests/h. The system was applied to determination of citrate in several fruits; results correlated well with those from a kit enzymatic method.
Citric acid Amperometry Electrode Immobilized enzyme Interferences Controlled pore glass

"Flow Injection Analysis Of Oxalate In Foods Using Titanium(IV)-porphyrin Reagent"
Anal. Sci. 1995 Volume 11, Issue 2 Pages 245-249

Abstract: Homogenized fruit (or vegetable; 20 g) was dissolved in 60 mL water, the pH was adjusted to 2-3 with HCl and the solution was incubated at 50°C for 15 min. On cooling the solution was adjusted to pH 2 with KOH, diluted to 100 mL with water and filtered (0.45 µm). A 20 µL portion of the diluted solution was injected into a stream of 0.05 M succinate buffer of pH 3 (0.4 ml/min) and passed through an immobilized oxalate oxidase column (3 cm x 2 mm i.d.). The H2O2 produced was reacted with a stream of 30 µM-Ti(IV)-porphyrin reagent (details given) at 0.4 ml/min in a mixing coil (15 m x 0.5 mm i.d.) and the absorbance of the peroxo complex formed was measured at 450 nm. The calibration graph was linear from 0.5-250 µM-oxalate (100-5000 pmol/20 µL injection). The RSD (n = 10) was 0.48% at 25 µM-oxalate (500 pmol/20 µL injection). The method was also applied to the analysis of beer and millet jelly solutions.
Oxalate Spectrophotometry Immobilized enzyme

"Measurement Of L-malate Using Immobilized Enzyme Reactors Comparison Of Results Obtained With Four Different Enzymatic Systems"
Biosci. Biotechnol. Biochem. 1996 Volume 60, Issue 5 Pages 847-851

Abstract: For the measurement of malate by an enzyme sensor, we did a comparative study using malate dehydrogenase (MDH) alone, MDH and glutamate oxaloacetate transaminase (GOT) together, a malic enzyme (ME) that requires NADP as a cofactor, and MDH and NADH oxidase together, With respect to the response of each reactor to 0.5 mM L-malate, the systems using ME alone and MDH plus NADH oxidase gave high values, The ranges of measurements were 0.05-1.00 mM (MDH alone), 0.01-0.05 mM (MDH plus GOT), 0.01-0.50 mM (ME alone) and 0.02-1.00 mM (MDH plus NADH oxidase), In the system with MDH alone, however, reducing sugars in the sample interfered with measurements and it was impossible to use this system for practical analysis of fruit samples, By contrast, the systems using ME alone or MDH plus NADH oxidase were unaffected by the presence of reducing sugars and were suitable for analysis of samples, Thus, the MDH-NADH oxidase system is recommended for practical analyzes of samples.
l-Malate Amperometry Enzyme Interferences Immobilized enzyme

"Banana Tissue Electrode Sensitized For Oxalate"
Fenxi Huaxue 1992 Volume 20, Issue 2 Pages 186-189
Song, Y.;Shen, G.

Abstract: The cited electrode was prepared by coupling banana pulp tissue with an O electrode. The electrode response was rectilinear at steady-state and flow conditions from 88 µM to 0.63 mM and from 50 µM to 1.8 mM oxalate, respectively. The effects of buffer composition, pH, temp., flow speed, sample volume and immobilization are discussed. The selectivity and life-span of the electrode were also determined. Of the 19 foreign ions studied only catechol interfered. Average recoveries for 7 types of sample (such as tea leaves, vegetables and fruits) using the statical response and flow injection methods were 98.4 and 98.9%, respectively. Results agreed well with literature values.
Oxalate Electrode Electrode Optimization Interferences

"Optimization Of An Analysis Method For The N-methylcarbamate Pesticide-residues Determination"
Ind. Aliment. 1995 Volume 34, Issue 342 Pages 1160-1163

Abstract: This paper describes the determination of N-methylcarbamate pesticides in fruit and vegetable with multiresidue analysis method. The extracts are purified by gel permeation chromatography and their final detection is carried out by HPLC with post-column derivatization and fluorescence detection. The method has an high sensitivity and a very high selectivity for these molecules. (11 references)
N-Methylcarbamate HPLC GPC Fluorescence Post-column derivatization Optimization

"Simplified Multiresidue Method For Liquid Chromatographic Determination Of N-methylcarbamate Insecticides In Fruits And Vegetables"
J. AOAC Int. 1988 Volume 71, Issue 3 Pages 542-546
Chaput D.

Abstract: The chopped sample (100 g) was homogenized with methanol, and after filtration and the addition of aqueous 4% Na2SO4, the extract was partitioned with CH2Cl2. The separated CH2Cl2 phase was concentrated to 1 ml, made up to 10 mL with cyclohexane - CH2Cl2 (1:1), and subjected to gel-permeation chromatography on a column (60 cm x 2.5 cm) of Bio-Beads SX-3 resin (200 to 400 mesh). The fraction eluting after 24 min was collected at 5 mL min-1 for 12 min. Crops with high chlorophyll and carotene content were further cleaned up (online) on Nuchar-Celite. The N-methylcarbamates (aldicarb, carbaryl, carbofuran, methiocarb, methomyl, oxamyl and propoxur) and three related metabolites, in methanol, were separated on a column (25 cm x 4.6 mm) of ODS (5 µm), with gradient elution at 1.0 mL min-1 with methanol - water (program given) followed by post-column hydrolysis with NaOH at 95°C to yield methylamine, and derivatization with phthalaldehyde and 2-mercaptoethanol before fluorimetric detection at 455 nm (excitation at 340 nm). Recoveries from 5 different crops fortified at the 0.05- and 0.5 ppm levels averaged 93%. The coefficient of variation were 5% (n = 40) and the detection limits ranged from 5 to 10 ppb.
Insecticides Carbamates, N-methyl GPC Fluorescence Heated reaction Post-column derivatization

"Automated Analysis Of Total Vitamin C In Foods"
J. Micronutr. Anal. 1989 Volume 6, Issue 2 Pages 109-117
Vanderslice J.T.; Higgs D.J.

Abstract: To determine the sum of ascorbic and dehydroascorbic acids (I and II, respectively), the fruit or vegetable sample is extracted in a robotic system with metaphosphoric acid - acetic acid, the extract is filtered (0.45 µm), and the filtrate is passed through a preparative C18 column into autosampler phials. The resulting solution is subjected to flow injection analysis, with 0.1 M citrate buffer (pH 4.0) containing 5 mM EDTA as initial carrier; this stream is mixed with aqueous 2.5 mM HgCl2 as oxidant for I and then with aqueous 3.1 mM o-phenylenediamine as fluorigenic reagent for total II at 70°C before fluorescence measurement (cf. J. Chromatogr. Sci., 1984, 22, 485). The only manual operation is the transfer of the autosampler phials to the autosampler.
Ascorbic acid dehydroascorbic acid Fluorescence Buffer

"Simplified Flow Injection Slurry Method For Direct Flame Atomic Absorption Spectrometric Determination Of Calcium, Magnesium, Sodium And Potassium In Fruits"
Water Air Soil Pollut. 1991 Volume 57, Issue 1 Pages 489-493
J. L. Burguera, M. Burguera and Gladys Becerraa

Abstract: A rapid, direct flow injection slurry atomization flame atomic absorption spectrometric procedure for Ca, Mg, Na and K determination is shown to give reproducible and accurate results for a variety of tropical fruits. The optimized conditions obtained for instrumental, slurry formation and manner of calibration graphs preparation are detailed. Ground fruit is simply suspended by being shaken in a Triton X-100 solution. Statistical evaluation of results from certified and non-certified materials indicate that the flow injection slurry method is both accurate and comparable in precision to a traditional wet acidic sample digestion procedure.
Calcium Magnesium Potassium Sodium Spectrophotometry Slurry

"Optimization Of Selenium Determination In Vegetables, Fruits, And Dairy Products By Flow Injection Hydride Generation Atomic Absorption Spectrometry"
Chem. Pap. 2003 Volume 57, Issue 3 Pages 155-157
M. Kore&#328;ovsk&aacute;

Abstract: A flow injection hydride generation atomic absorption spectrometric (FI-HG-AAS) method was developed for determination of selenium in vegetables, fruits, and dairy products after microwave digestion of samples. The experimental conditions for FIAS 400 (concentration of reducing agent and carrier acid, time of reduction, flow rate of argon carrier gas) were optimized. The linearity range under optimized conditions was 0.20-25.0 ?g dm -3.The detection limit of the proposed method was 0.06 ?g kg -1 and limit of quantitation was 0.20 ?g kg-1. The procedure was validated by the method of standard additions (5.0 ?g dm -3 and 10.0 ?g L-1 in vegetables, fruits, and dairy products) and the recoveries were from 88% to 104%. The accuracy was evaluated using BCR 150 skin milk reference material (found: 0.128 mg kg-1, Sx = 0.004 mg kg-1, certified: 0.132 mg kg-1, Sx = 0.010 mg kg-1). The combined standard uncertainty of selenium was 8.4%. The method was developed and used for determination of selenium in vegetables, fruits, and dairy products consumed in Slovakia.