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: Vegetable

Citations 30

"Flow Injection Determination Of Ammonia In Kjeldahl Digests By Gas Diffusion And Conductometry"
Anal. Chim. Acta 1987 Volume 193, Issue 1 Pages 19-27
Celio Pasquini and Lourival Cardoso de Faria

Abstract: The digest (100 µL) was injected into a stream of water (1.6 mL min-1) and mixed with a stream of 2 M or 3 M NaOH containing 1% of EDTA (1.6 mL min-1) at ambient temperature The resulting stream was passed (3.2 mL min-1) to a diffusion cell and the NH3 was allowed to diffuse through a PTFE membrane into a second water stream, which was passed into a flow cell for conductometric determination of NH3. The manifold was constructed from polyethylene tubing (0.8 mm i.d.). There was no interference from 1.25 M H2SO4, 7 to 30 g L-1 of K2SO4, 6 mM Ca(II), Fe(III), Al(III), Mg, Zn(II), Cu(II) or Se(IV) or 3 mM Hg(II) in the determination of 2 mM or 3 mM NH3. The method was applied to samples of vegetables, animal feeds and fertilizers, and results agreed with those by a distillation - titration method. In the determination of 1 to 4% of N the coefficient of variation (n = 5) was 1%. The sampling rate was ~100 h-1.
Ammonia Conductometry Gas diffusion Interferences Method comparison Teflon membrane Kjeldahl

"Determination Of Arsenic And Selenium In Environmental Samples By Flow Injection Hydride-generation Atomic Absorption Spectrometry"
Anal. Chim. Acta 1992 Volume 270, Issue 1 Pages 231-238
Chris C. Y. Chan* and Ram S. Sadana

Abstract: Environmental samples such as soil, vegetation, water, sediments and industrial wastes were digested (except for water) by heating at 200°C with HNO3 - H2SO4 - HClO4 (6:3:1). The cooled digest or water was treated with concentrated HCl to reduce Se6+ to Se4+; for As analysis the solution was treated with 10% KI - 1% ascorbic acid (10:1) to reduce As5+ to As3+. The analytes were converted to the hydrides with 1% NaBH4 in an automated hydride-generation system. A stream of Ar (3 mL min-1) carried the evolved hydride via a gas - liquid separator and an impinger to a heated quartz tube atomizer for analysis by AAS. The effects of the experimental variables are discussed. Interference by Cu and Ni on the determination of Se was masked with 1,10-phenanthroline. The detection limits for both As and Se were 0.3 ng mL-1. The coefficient of variation was 2.6% for As in a sediment (n = 10) and 2% in water (n = 5); similar precision was obtained for Se. The results for the standard reference materials agreed closely with their certified values. Flow injection analysis is applied to sample introduction in conjunction with automated hydride generation and AAS for the determination of As and Se in environmental samples such as soil, vegetation, waters, sediments, and industrial wastes. A large sample loop was used to provide high sensitivities with an absorbance of 0.4 for 10 ng mL-1 for both As and Se. The samples, except waters, are digested with a mixture of nitric, sulfuric, and perchloric acids. Se6+ in the digested solutions is pre-reduced to Se4+ by exothermic reaction in 6-8 M HCl solution, and As5+ to As3+ by reacting with KI. The analyte is then converted to hydride by NaBH4 in an automated hydride generation system. The evolved hydride is carried through to a heated quartz tube by a stream of argon, and the atomic absorption of the analyte is measured. 1,10-Phenanthroline is used as masking agent to control interferences from Cu and Ni on Se. The detection limits for both As and Se are 0.3 ng mL-1, equivalent to 75 ng g-1 in solid sample. Precision is 2.6% RSD Results for standard reference materials agree closely with the certified values.
Arsenic Selenium Spectrophotometry Reference material Interferences Volatile generation Volatile generation

"Comparison Of Plumbane And Tetraethyllead For The Determination Of Lead By Inductively Coupled Plasma Atomic-emission Spectrometry"
Anal. Chim. Acta 1995 Volume 309, Issue 1-3 Pages 369-378
M. C. Valdés-Hevia y Temprano, M. R. Fernández de la Campa and A. Sanz-Medel*

Abstract: Sediments and lichen (200 mg) were microwave digested in 1.5 mL concentrated HNO3, 0.5 mL 80% HClO4 and 0.5 mL concentrated HF (details given). After cooling, the excess HF was reacted with 3.5 mL 6% H3BO3, the mixture re-digested and the contents made to 100 mL with water. Citrus leaves and lyophilized vegetables (0.5 g) were digested in 5 mL 65% HNO3 and 2 mL H2O2 and the contents made to 25 mL with water. The solutions were mixed to contain 0.3% or 0.7% K2Cr2O7 for PbH4 (I) or tetraethyllead (II) analysis and merged at 1 ml/min with carrier streams (1 ml/min) of 360 mM or 600 mM lactic acid for I and II, respectively, and 5% NaBH4 in 0.1% NaOH for I or 1% sodium tetraethylboron in 1% NaOH for II. The mixed solutions were aspirated at 2.4-3 ml/min into a detuned grid-nebulizer for ICP-AES and Pb determined at 0.7 kW and 20.353 nm. Calibration graphs were linear up to 0.5 mg/ml of I and 1.5 mg/ml of Pb for II with detection limits of 2 ng/ml and 1 ng/ml of Pb, respectively. At 50 ng/ml of Pb the RSD (n = 10) were 1.3% for I and 1.2% for II. The selectivity of the two methods in the presence of chloride, nitrate and a range of cations was confirmed. The analysis of Pb via II was preferred as only Ni and Sb interfered.
Lead Sample preparation Spectrophotometry Interferences Volatile generation Optimization Volatile generation

"Turbidimetric Flow Injection Determination Of Total Nitrogen And Potassium In Vegetables"
Anal. Chim. Acta 1997 Volume 356, Issue 2-3 Pages 259-265
José L. F. C. Limaa, António O. S. S. Rangelb,*, M. Renata S. Soutob and Elias A. G. Zagattoc

Abstract: A turbidimetric flow injection system was developed for the determination of total nitrogen and potassium in vegetable samples using a single spectrophotometer as detector. As a precipitating agent, 3.0% (w/v) sodium tetraphenylboron solution prepared in 2.0% (w/v) poly(vinyl alcohol) was used. A gas diffusion process was included in the manifold to separate ammonium ions from the rest of the sample and to allow paired analysis. Total nitrogen and potassium determinations were carried out on the solutions remaining in the acceptor and donor streams, respectively. Results obtained were precise (relative standard deviations <2.1 and 1.6% for total N (<25 mg g-1) and K (<55 mg g-1) determinations, respectively) and in agreement with those of reference methods. Analysis can be carried out at a rate of up to 35 samples per hour (corresponding to 70 determinations per hour) within concentration range 87-430 mg N-NH4+ L-1 and 78-390 mg K+ L-1 for the total nitrogen and potassium determinations, respectively. 17 References
Nitrogen, total Potassium Turbidimetry Dual detection Gas diffusion Precipitation Method comparison

"Rapid Determination Of Zinc And Iron In Foods By Flow Injection Analysis With Flame Atomic Absorption Spectrophotometry And Slurry Nebulization"
Talanta 1990 Volume 37, Issue 7 Pages 711-718
Jo&atilde;o Carlos de Andrade*, Frederick C. Strong, III and Nadir J. Martin

Abstract: A rapid method of determining zinc and iron in food by flame atomic absorption spectrophotometry with slurry nebulization into an air-acetylene flame has been developed. A V-groove, clog-free Babington-type nebulizer, coupled to a single-line flow injection analysis (FIA) system, was employed to introduce the slurry into the spray chamber. Under the FIA conditions described, an injection frequency of 120/hr is possible, with negligible carry-over and memory effects. The calibration graphs were obtained by using various concentrations (up to 0.1 g/ml) of white bean homogenate as standards, rather than solutions. The method has been applied to various kinds of foods, including grains, vegetables, fruits and sausage. Homogenization of semi-prepared samples to form slurries took only 4 min. Relative deviations between results by the slurry and solution methods for both elements averaged 2-3%. Detection limits by the slurry method were 0.3 µg/ml Zn and 0.6 µg/ml Fe. A V-groove, Babington-type nebulizer, coupled to a single-line flow injection analysis system, was used to introduce sample slurry into the spray chamber for AAS determination. An injection frequency of 120 h-1 was possible, with negligible carry-over and memory effects. Calibration graphs were obtained by using 0.1 g mL-1 of white bean homogenate as standards. Homogenization of semi-prepared samples to form slurries took 4 min. Of air - acetylene and air - propane flames for the AAS, the former was preferred due to its rectilinear calibration graph. Relative deviations of results by slurry and solution methods for both Zn and Fe were 2 to 3%. Detection limits for the slurry method were 0.3 and 0.6 µg mL-1 of Zn and Fe, respectively. The method was applied to various foods, including grains, vegetables, fruits and sausage.
Iron Zinc Spectrophotometry Nebulizer Slurry

"Slurry-electrothermal Atomic Absorption-spectrometric Determination Of Aluminum And Chromium In Vegetables Using Hydrogen Peroxide As A Matrix Modifier"
Talanta 1995 Volume 42, Issue 4 Pages 527-533
P. Vi~nas, N. Campillo, I. Lopez Garcia and M. Hernandez Cordoba*,

Abstract: Fast heating programs for determining aluminium and chromium in vegetables using electrothermal atomic absorption spectrometry with slurry sampling are developed using wall atomization. The build-up of carbonaceous residues inside the atomizer is avoided by adding 4% hydrogen peroxide and 1% nitric acid to the slurries instead of using an air-ashing stage. In accordance with fast-program methodology, the conventional drying and charring steps are replaced by a modified drying stage, simplifying the heating programs. For suspensions containing 0.1% m/V of ground vegetables, the relative standard deviation (RSD) is about ±5% for aluminium. For chromium determination, the use of 0.5-1% m/V suspensions leads to RSDs close to ±4%. Calibration is carried out using aqueous standards. The aluminium and chromium contents of a number of vegetable samples obtained by using the slurry approach agree with those obtained by means of a conventional procedure based on the total dissolution of the samples. The reliability of the procedures is also confirmed by analyzing two certified reference materials.
Aluminum Chromium Spectrophotometry Slurry

"Lead Preconcentration Onto C-18 Minicolumn In Continuous-flow And Its Determination In Biological And Vegetable Samples By Flame Atomic Absorption Spectrometry"
Talanta 1996 Volume 43, Issue 6 Pages 977-983
Rosimar Lima, Katia Christina Leandro and Ricardo Erthal Santelli*

Abstract: Biological and vegetable materials were wet ashed with acid treatment. The sample stream (4 ml/min) in acetic acid buffer of pH 4.6 was merged with a reagent stream (0.27 ml/min) of diethylammonium NN-diethyldithiocarbamate and passed through a reaction coil (200 cm). The lead/diethyldithiocarbamate complex formed was retained on a C-18 minicolumn (3 cm x 2 mm i.d.). At the same time IBMK flowed to a loop (380 µL) and a carrier stream (3 ml/min) of water passed to the AAS instrument. The commutator switched and a small volume of water washed the minicolumn. The column was eluted with IBMK from the loop and the eluate was analyzed by AAS at 217 nm using an air/acetylene flame. Calibration graphs were linear for 20-100 µg/l of Pb with a detection limit of 3 µg/l. The RSD (n = 3) was 3.8% for 25 µg/l Pb. Sample throughput was 24 samples/h.
Lead Spectrophotometry Sample preparation Preconcentration MIBK

"Differential Conductometry In Flow Injection. Determination Of Ammonia In Kjeldahl Digests"
Analyst 1991 Volume 116, Issue 8 Pages 841-845
Jarbas Jos&eacute; Rodrigues Rohwedder and Celio Pasquini

Abstract: A differential conductivity meter is described (with circuit diagram) that consists of a Wien bridge, a measurement bridge with instrumentation amplifier and circuit for adjustment of sensitivity and balance and precision rectifier and output buffer. The meter was used to amplify the difference in conductance between two twin flow cells in the flow injection determination of NH3 in Kjeldahl digests of vegetables. The flow injection manifold is described (diagram given). The acceptor stream was 0.5 mM HCl and the reagent streams were 3 M NaOH containing 1% EDTA. Sample solution was injected into one reagent stream which was subsequently mixed with a second reagent stream before being passed to the gas diffusion cell. The acceptor stream passed through the reference flow cell before passing through the gas diffusion cell. This stream then passed through the indicator flow cell. Results correlated well (r = 0.999) with those obtained by an interlaboratory study. The sampling rate was 90 h-1 with negligible carryover and no matrix effects.
Ammonia Conductometry Gas diffusion Kjeldahl

"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

"Multipurpose Flow Injection System. 1. Programmable Dilutions And Standard Additions For Plant Digests Analysis By Inductively Coupled Plasma Atomic-emission Spectrometry"
J. Anal. At. Spectrom. 1992 Volume 7, Issue 6 Pages 865-868
Boaventura Freire dos Reis, Maria Fernanda Gin&eacute;, Francisco Jos&eacute; Krug and Henrique Bergamin Filho

Abstract: Combinations of the injector commutator and solenoid valves provided a simple way of achieving different flow injection configurations for standard additions and dilutions. Results for Ca, Mn and Zn in three vegetable samples agreed well with reported values. A flexible flow injection system to perform multipurpose functions related to sample handling is proposed. The flow network consists of a sliding injector commutator, solenoid valves, and other minor components. A dedicated microcomputer controls these devices, facilitating the definition of different flow configurations. Merging zones, zone sampling, intermittent flow, sequential injections, zone trapping, and stopped-flow are possible. Online programmed dilutions and standard additions for simultaneous determinations on plant digests by inductively coupled plasma atomic emission spectrometry were chosen to demonstrate some features of the system. Sample dilutions were accomplished by confluence at different points along the analysis path through a proper programming of the solenoid valves. Standard additions were performed by merging the sample zone with an aliquot delivered from a trapped standard zone in a modified version of the zone sampling process. To minimize matrix effects from the nitric-perchloric acid digests, a sequential dilution procedure is proposed for the major elements and standard additions for the minor constituents. No other standardization procedure was necessary and results were calculated by using the least squares regression method. Results obtained with the proposed procedure compared well with the reported values for plant reference materials.
Calcium Manganese Zinc Sample preparation Spectrophotometry Standard additions calibration Merging zones Reference material Commutation Stopped-flow Zone sampling Zone trapping

"Evaluation Of Various Sample-preparation Procedures For The Determination Of Chromium, Cobalt And Nickel In Vegetables"
J. Anal. At. Spectrom. 1997 Volume 12, Issue 4 Pages 479-486

Abstract: Continuous-flow microwave-assisted mineralization with 5% HNO3 is recommended for the sequential determination of the cited metals by GFAAS, for each of which the furnace conditions have been optimized. A diagram of the semionline flow system is presented. If only Co and Ni were to be determined, direct slurry sampling at 2% (w/v) in 1% HNO3/10% H2O2 solution with ultrasonication is adequate.
Chromium Cobalt Nickel Spectrophotometry Sample preparation Slurry

"Flow Injection System With Gas Diffusion For The Sequential Determination Of Total Nitrogen And Phosphorus In Vegetables"
Fresenius J. Anal. Chem. 1997 Volume 358, Issue 5 Pages 657-662
Jos&eacute; L. F. C. Lima, Antonio O. S. S. Rangel, M. Renata S. Souto

Abstract: Dried, ground vegetables were digested with Se and H2SO4/salicylic acid/H2O2 and then diluted in 0.8 M H2SO4. A portion (180 µL) of the solution was injected into a stream of 0.8 M H2SO4, which merged with a stream of 2.5 M NaOH and passed through a gas diffusion unit. The NH3 diffused into a secondary stream of 0.01 M Tris hydrochloride of pH 7.5 which converted it to ammonium prior to detection with an ISE. The primary stream, now purged of NH3, passed through a stream splitter to reduce the total flow and then merged with a stream containing ammonium molybdate, stannous chloride and hydrazine sulfate in H2SO4. The primary stream then passed through a flow cell for determination of phosphate at 710 nm. The calibration graphs were linear from 0.34-2.4 mM phosphate and up to 0.11 M ammonium, the detection limits were 43 µM phosphate and 1.4 mM ammonium, and the RSD (n = 10) were <3.5%. The sampling rate was 40-60/h. The ammonium and phosphate levels were indicative of the total N and P contents of the vegetables analyzed.
Nitrogen Phosphorus Electrode Sample preparation Spectrophotometry Dual detection Gas diffusion

"Bioluminescent Flow Sensor For L-glutamate"
Anal. Lett. 1992 Volume 25, Issue 4 Pages 637-652
Girotti, S.;Ghini, S.;Budini, R.;Pistillo, A.;Carrea, G.;Bovara, R.;Piazzi, S.;Merighi, R.;Roda, A.

Abstract: The method for the analysis of serum or meat, fish or vegetable extract is based on the reaction of the analyte with NAD+ and glutamate dehydrogenase (NAD(P)+). The NADH produced was monitored by the luminescence generated by its reaction with NAD(P)H dehydrogenase (FMN) and luciferase (both from Photobacterium fischeri). The reductant enzyme and the luminescent enzymes were immobilized on separate nylon coils in a continuous-flow system similar to that described previously [Analyst (London), 1990, 115, 889]. The calibration graph was rectilinear from 50 to 1000 µM with coefficient of variation (n = 7) of 7%. The recoveries were between 88 and 105%. The results agreed well with those obtained by a spectrophotometric method for stock cubes and by a chromatographic method for serum.
l-Glutamate Bioluminescence Sensor Immobilized enzyme Nylon Method comparison

"High Performance Liquid Chromatographic Determination Of Polyamines In Selected Vegetables With Post-column Fluorimetric Derivatization"
J. Chromatogr. A 1993 Volume 628, Issue 2 Pages 199-204
Hideaki Ohta, Yuko Takeda, Koh-Ichi Yoza and Yoichi Nogata

Abstract: A method is described for the HPLC analysis of the aliphatic polyamines agmatine, putrescine, cadaverine, spermidine and spermine in vegetables. Sample (1 g) was homogenised with 7 mL of 5% perchloric acid, cooled for 1 h at 0°C, and centrifuged. The supernatant was analyzed on a column (3.5 cm x 6 mm) of Polyaminepak (strong cation-exchange resin, 5 µm) with a mobile phase (0.65 mL min-1) of 1.0 M sodium citrate (pH 5.4) - acetonitrile (9:1). Post-column derivatization with phthalaldehyde (details given) and subsequent fluorescent detection was used.
Amines, poly Spermidine Spermine Cadaverine Putrescine HPLC Fluorescence Post-column derivatization

"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

"Simultaneous Determination Of Potassium And Sodium In Vegetables By Flame Emission Spectrometry Using A Flow Injection System With Two Dialysis Units"
Anal. Sci. 1996 Volume 12, Issue 1 Pages 81-85
J. L. F. C. LIMA, A. O. S. S. RANGEL and M. R. S. SOUTO

Abstract: Dried vegetable (2 g) was digested overnight with 30 mL 60% HClO4/70% HNO3 (1:4) and the digest was heated at 100°C for 2 h. The solution was evaporated at 180-200°C initially and the temperature was raised to 240°C until a dry residue was obtained. The residue was dissolved in 10 mL 2 M HCl with gentle heating and diluted to 50 mL with water. Portions (278 µL) of the solution were injected into a flow injection manifold (schematic shown), mixed with a carrier stream of water (5 ml/min) and driven to a dialysis unit (35 x 2 x 0.5 mm) previously described by Lima et al. (in: Automatic Control of Food and Biological Processes, 1994, 67). The ions diffused to the acceptor channel across the membrane and the dialysate was directed to a Corning 410 spectrometer for detection of K by AES. The undialysed solution was transferred by the carrier to a second dialyser (70 x 2 x 0.5 mm) and the new dialysate was transferred to a Buck Scientific PFP-7 spectrometer for the detection of Na by AES. Calibration graphs were linear from 24.6-230 and 60.6-14,700 mg/l, respectively, for Na and K. RSD (n = 10) were 1.7 and 1.6%, respectively, for 2.3-16 and 31-55 mg/g of Na and K, respectively. Sampling rates were 120-150 samples/h (corresponding to 240-300 determinations/h).
Potassium Sodium Spectrophotometry Dialysis Membrane

"Kinetic Determination Of Ascorbic Acid In Fruit Juices"
An. Quim. 1991 Volume 87, Issue 5 Pages 683-686
Erroz, C.L.;Hernandez Cordoba, M.;Sanchez Pedreno, C.

Abstract: Ascorbic acid was determined spectrophotometrically (600 nm) by measuring the initial rate of reaction at 25°C with 5-[N-(3,5-dichloroquinoniimine)]-8-hydroxyquinoline in a reaction mixture containing 20% EtOH and 0.08 M Britton-Robinson buffer (pH 5.5). This procedure was appropriate for the determination of 10^-5 - 4 x 10^-4 M ascorbic acid. The relative standard deviation was ≤4.2%. Good agreement with the AOAC procedure was obtained when the new method was applied to pineapple, pear, and peach nectars, and to apple juice. (SFS)
Ascorbic acid HPLC Kinetic

"Chemiluminescent And Spectrophotometric Determination Of Peroxidase And Lactoperoxidase In Foods Using Flow Injection"
Analusis 1994 Volume 22, Issue 2 Pages 76-81

Abstract: Fresh or frozen vegetables were homogenized with 10 mM Tris hydrochloride buffer of pH 7 containing 1 M KCl. The mixture was centrifuged and the extract was purified on a Sep-Pak C18 cartridge. The resulting solution was injected into a carrier stream of 3 mM H2O2 (1 ml/min). The carrier and the reagent stream, 1.5 mM luminol in 0.1 M Na2CO3 buffer of pH 8.5 (1 ml/min) were mixed in a coil (30 cm x 0.5 mm i.d.) and the chemiluminescence was measured with a photomultiplier. The calibration graph was linear for 25-500 nM-peroxidase; RSD was 1.95% (n = 15) for 250 nM. Yogurt or curd was treated as above, but with a filtration step before the Sep-Pak cartridge. Milk was treated with rennet to precipitate the proteins, the mixture was filtered and passed through the Sep-Pak cartridge. The solution was injected into the carrier, 2 mM H2O2 (1.4 ml/min) and, after mixing, the carrier was merged with 5 mM guaiacol solution in 0.1 M phosphate buffer of pH 7 (1.4 ml/min) and mixed in a coil (80 cm x 0.5 mm i.d.) with detection at 436 nm. The calibration graph was linear from 25-300 nM-lactoperoxidase; RSD (n = 15) were 1.09 and 0.76%, for 20 and 200 nM, respectively.
Enzyme, peroxidase Enzyme, lactoperoxidase Chemiluminescence Spectrophotometry

"Potentiometric Determination Of Chloride In Vegetables By Flow Injection Analysis"
Commun. Soil Sci. Plant Anal. 1996 Volume 27, Issue 1-2 Pages 37-46
Lima, J.L.F.C.;Rangel, A.O.S.S.;Souto, M.R.S.

Abstract: Dried powdered vegetables were mixed with 50 mL water and shaken for 5 min. The extract was filtered and analyzed using an FIA system. A Rheodyne 5020 valve introduced the filtrate (200 µL) in to the carrier stream flowing at 4 ml/min. A Crison 2002 voltammeter was used for potentiometric measurements. A homogenous crystalline membrane chloride ISE was the indicator electrode (Ferreira et al., Flow Injection Anal., 1993 10, 17) without an inner reference solution and with a tubular configuration. A Russel 90-0029 double-junction reference electrode was used with 0.1 M KNO3 in the outer compartment. A schematic of the FIA manifold is given. This system is a good alternative to the standard potentiometric titration procedure; comparable results are obtained at higher sampling rates (150-300 samples/h). Chloride concentrations in various vegetables are presented. RSD were 1.8, 0.39 and 0.78% (n = 3) for Cl concentrations of 9.53, 13.2 and 15.7 mg/l, respectively.
Chloride Potentiometry

"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

"Simultaneous Spectrophotometric Determination Of Nitrite And Nitrate In Environmental Water And Vegetable By Flow Injection Analysis"
Huanjing Kexue 1998 Volume 19, Issue 3 Pages 84-86
Gao Loujun, Zhang Zhiqi

Abstract: A flow injection spectrophotometry is proposed for simultaneous determination of NO2- and NO3- in environmental waters and vegetables based on the N-(1-naphthyl)ethylenediamine spectrophotometry. A technique of double zone injection and reduction column of Cd plated Zn power zone isolation was adopted. The range of determination was 0.01-2.0 µg/mL for NO2--N and 0.05-5.0 µg/mL for NO3--N, sampling rate 30 samples per h.
Nitrate Nitrite Spectrophotometry Simultaneous analysis Merging zones Reduction column

"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

"Determination Of Manganese In Vegetables And Medicinal Plants Using Flow Injection System"
Indian J. Technol. 1990 Volume 28, Issue 2 Pages 78-80
Devi, S.

Abstract: Sample solution (20 µL) was injected into a flowing stream (1 mL min-1) of methanolic 1 mM 2-acetylpyridine thiosemicarbazone (I) and buffer solution (pH 9.0), and the Mn(II) - I complex was extracted into CHCl3 by passage along a 50-cm coil. The phases were separated in a PTFE separator, and the absorbance of the organic phase was measured at 410 nm. The calibration graph was rectilinear for 50 to 150 µM-Mn, and the detection limit was 0.5 µM. The sampling rate was 60 h-1. The method was applied to plant material after dry ashing and acid dissolution. Results showed good agreement with those of AAS.
Manganese Sample preparation Spectrophotometry Sample preparation Buffer Calibration Extraction Method comparison Phase separator Organic phase detection

"Simultaneous Analysis Of Ascorbic And Dehydroascorbic Acid By High Performance Liquid Chromatography With Post-column Derivatization And UV Absorbance"
J. Agric. Food Chem. 1986 Volume 34, Issue 2 Pages 271-274
Bechir Kacem, Maurice R. Marshall, Richard F. Matthews, and Jesse F. Gregory

Abstract: Samples of fruit, vegetables or orange juice were mixed with 3% H3PO4 and filtered and the filtrate was purified on Sep-Pak C18. The resulting solution was analyzed by anion-exchange HPLC on a column of Alltech NH2 with a mobile phase of 75% acetonitrile in 0.05 M phosphate buffer (pH 5.9). Post-column derivatization of dehydroascorbic acid(I) was carried out with o-phenylenediamine to form a fluorescent quinoxaline derivative for fluorimetric detection. Ascorbic acid(II) was detected by absorbance measurement at 254 nm. Calibration graphs were rectilinear for up to 0.1 mg mL-1 and up to 40 µg mL-1 of II and I, respectively. Detection limits were 0.01 and 0.05 µg for I and II, respectively.
Ascorbic acid dehydroascorbic acid HPIC Fluorescence Spectrophotometry Post-column derivatization

"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

"Automated Nitrate Assay In Plant Material Following The Flow Injection Analysis Principle"
Landwirtsch. Forsch. 1985 Volume 38, Issue 1 Pages 99-104
Schwerdtfeger, E.

Abstract: Nitrate was determined in plant material by flow injection analysis with Cd reduction to nitrite and absorbance measurement at 540 nm. The relative standard deviation in the range 0.5-5.0 ppm was 1.6%, and the assay obeyed Beer's Law in the range 0.05-10 ppm. Matrix effects were minimized by the standard addition method. (SFS)
Nitrate Spectrophotometry Interferences Standard additions calibration

"Determination Of Selenium In Vegetables By Hydride Generation Atomic Fluorescence Spectrometry"
Anal. Chim. Acta 2004 Volume 512, Issue 1 Pages 11-17
P. Smrkolj and V. Stibilj

Abstract: A digestion mixture of H2SO4/HNO3/H2O2/HF/V2O5 was investigated for decomposition of plant samples and sensitive detection of selenium was achieved by hydride generation atomic fluorescence spectrometry (HG-AFS). The method was found to be accurate and reproducible, with a low detection limit (DL) (0.14 ng g-1 solution). The repeatability of the determination was mostly around 10%, the reproducibility over a period of 8 months for determination of selenium in the standard reference material Trace Elements in Spinach Leaves, NIST 1570a, was 9% and the relative measurement uncertainty was 7% using a coverage factor of 2.3 at 95% probability. The average recovery of the whole procedure was 90%. The characteristics of this method are simple and inexpensive equipment, low consumption of chemicals and the ability to analyze many samples in a short time. The whole procedure was carried out in the same PTFE tube, and in addition only a simple cleaning procedure is needed. As a consequence of all these advantages, the described method is suitable for environmental and nutritional studies. The selenium content was determined in 44 vegetable samples from different regions of Slovenia and the contents found were in the range 0.3-77 ng g-1 wet weight.
Selenium Fluorescence Reference material Volatile generation

"OnLine Coupling Of A Flow Injection System To TS‐FF‐AAS For Preconcentration And Determination Of Lead In Water And Vegetables"
Anal. Lett. 2005 Volume 38, Issue 9 Pages 1427-1443
C&eacute;sar Ricardo Teixeira Tarley and Marco Aur&eacute;lio Zezzi Arruda

Abstract: An online solid phase pre-concentration system coupled to thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) for Pb(II) ions determination is described. In the pre-concentration system, Pb(II) ions complexed with ammonium O,O-diethyl-dithiophosphate (DDTP) in an acidic medium are pre-concentrated as a neutral complex onto 20 mg of polyurethane foam (PUF) packed into a mini-column. The complex retained in the PUF is then released to TS-FF-AAS by using an 80% (v/v) ethanol solution. Chemical and flow variables associated with the pre-concentration, such as the pH dependence of the Pb-DDTP complex, the DDTP concentration, and pre-concentration and elution flow rates were optimized by the univariate method. The best sample pH value and DDTP concentration achieved are 2.0 and 0.5% (w/v), respectively, while the best pre-concentration and elution flow rates are 2.4 and 1.0 mL min-;1, respectively. Under the optimized conditions, the present method, which is operated in volume mode (only 2 mL), makes possible the determination of Pb(II) ions within a linear range from 5.2 to 300.0 µg L-;1 with a detection limit of 1.5 µg L-;1 and analytical frequency of 16 h-;1. The precision (n=10) assessed as relative standard deviation (RSD) is, respectively, 7.3 and 4.8% for 6 and 200 µg L-;1 solutions of Pb(II). The pre-concentration system provides an enrichment factor of 6.4 and consumption index of 310 µL. Hence, the coupling of the pre-concentration system to TS-FF-AAS is proven to be an efficient strategy to enhance TS-FF-AAS detectability. The applicability of the method was verified by analyzes of spiked water samples as well as with certified and reference vegetable materials.
Lead(2+) Spectrophotometry Preconcentration Column Polyurethane foam Optimization

"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.