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 -> spinach

Citations 10

"Flow Injection Catalytic Spectrophotometric Determination Of Oxalic Acid Using The Redox Reaction Between Victoria Blue B And Dichromate"
Anal. Chim. Acta 2000 Volume 406, Issue 2 Pages 303-308
Zhi-Qi Zhang and Xiao-Qin Xu

Abstract: A flow injection catalytic method is developed for the determination of oxalic acid based on its catalytic effect on the redox reaction between Victoria blue B and potassium dichromate in dilute sulfuric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of Victoria blue B at the maximum absorption wavelength of 618 nm. A calibration graph from 1.0 to 80.0 µg mL-1 of oxalic acid and a detection limit of 0.8 µg mL-1 was obtained. The sampling rate was about 22 samples per hour. The proposed method is simple and inexpensive. The applicability of the method was demonstrated by the determination of oxalic acid in vegetable food, such as spinach and mushroom.
Oxalic acid Spectrophotometry Catalysis Indirect

"Differential Flow Injection Potentiometry With Double Sensitivity Using One Ion-selective Membrane"
Anal. Chim. Acta 1995 Volume 313, Issue 1-2 Pages 83-87
Frank Zuther*, Bernd Ross and Karl Cammann

Abstract: Nitrate was determined by differential flow injection potentiometry using a symmetrical flow-through cell equipped with one ion-selective membrane and two Ag/AgCl reference electrodes, one positioned on each side of the membrane. The two sides of the detection cell were connected by a PTFE tube (0.8 mm i.d.) which allowed the sample to come into contact with both sides of the membrane. Separate or overlapping peaks could be obtained by varying the length of the connecting tube. The ion-selective membrane (10 x 5 mm) consisted of tetradodecylammonium bromide, potassium tetrakis(4-chlorophenyl)borate and 2-nitrophenyloctyl ether in a PVC matrix. The carrier solution (3 ml/min) was 1 mM Li2SO4. The calibration graph for up to 10 mM nitrate showed a sensitivity of 115.2±1.2 mV/decade when using a connecting tube volume of 2 mL and an injection volume of 1 mL. A sensitivity of 110.5±0.8 mV/decade was obtained for the same calibration range with a connecting tube volume of 0.25 mL and an injection volume of 0.5 mL. A detection limit of 0.6 µM-nitrate was achieved with a connecting tube volume of 0.5 mL and an injection volume of 0.5 mL. The method was applied to the determination of nitrate in tap water and spinach and the results were confirmed by ion chromatography.
Nitrate Potentiometry Electrode Membrane

"Flow Injection Spectrofluorimetric Determination Of Oxalate Based On Its Enhancing Effect On The Oxidation Of Rhodamine B By Dichromate"
Analyst 1995 Volume 120, Issue 8 Pages 2111-2114
Tomás Pérez-Ruiz, Carmen Martínez-Lozano, Virginia Tomás and Rocio Casajús

Abstract: The sample was mixed with a 10 µM-Rhodamine B solution and a portion (100 µL) of the mixed solution was injected into a pre-mixed stream (1.2 ml/min) of 0.4 M H2SO4 and 2 mM potassium dichromate. The sample zone was then passed through a 60 cm reaction coil. A stop time of 60 s was applied while the sample zone was in the reaction coil, after which the flow was re-started and the decrease in the fluorescence intensity of the sample zone was measured at 577 nm (excitation at 561 nm). A diagram of the manifold used is given. The calibration graph was linear from 1.76-88 µg/ml of oxalate (I). RSD (n = 10) were 0.84 and 0.26%, respectively for 17 and 68 µg/ml of I. The throughput was ~e;35 samples/h. The method was applied to the analysis of I in urine and spinach after appropriate sample pre-treatment (details given). Recoveries of oxalate from both urine and spinach were >93%.
Oxalate Fluorescence Stopped-flow

"Flow Injection Spectrophotometric Determination Of Oxalate, Citrate And Tartrate Based On Photochemical Reactions"
Anal. Lett. 1998 Volume 31, Issue 8 Pages 1413-1427
Tomás Pérez-Ruiz; Carmen Martínez Lozano; Virginia Tomás; Antonio Sanz

Abstract: A flow injection configuration for the spectrophotometric determination of oxalate, citrate and tartrate is proposed. The procedure is based on the photochem. decomposition of the complexes formed between iron(III) and these anions. The iron(II) produced in the photochem. reactions was detected by measuring the absorbance after complexation with ferrozine (λmax=562 nm). Linear calibration graphs were obtained over the concentration. ranges 5.0 x 10^-6 - 1.0 x 10^-4 M, 8 x 10^-6 - 1.8 x 10^-4 M and 1.0 x 10^-6 - 2 x 10^-5 M for oxalate, citrate and tartrate, respectively. The relative standard deviations at the 1 x 10^-5 M concentration. level were within the range 1.29 - 1.47%. The sampling frequency was about 40 samples/h. The usefulness of the method was tested in the determination of oxalate in urine and spinach, of citrate in pharmaceuticals and soft drinks and of tartrate in pharmaceuticals. For the determination of oxalate in urine samples a prior separation of the analyte by precipitation with calcium chloride is recommended.
Oxalate Citrate Tartrate ion Spectrophotometry Photochemistry Complexation

"Flow Injection Extraction-spectrophotometric Determination Of Copper With Dithiocarbamates"
Anal. Sci. 1990 Volume 6, Issue 3 Pages 415-420

Abstract: Several dithiocarbamates were investigated as reagents for the determination of Cu, and a flow injection method was developed. Sample solution (300 µL) in aqueous NH3 buffer (pH 8.5) as carrier solution was mixed with 0.05% Pb diethyldithiocarbamate in CHCl3, and passed through a coil (400 cm x 0.5 mm). The phases were separated in a membrane separator, and the absorbance of the organic phase was measured at 436 nm. The detection limit is 0.04 ppm of Cu, and the calibration graph is rectilinear up to 2 ppm. The method was applied to water and plants; results were precise and accurate.
Copper Spectrophotometry Sample preparation Extraction Buffer pH Mixing Membrane Organic phase detection Detection limit Calibration

"Determination Of Oxalate Ion By Flow Injection Analysis Utilizing The Retardation Effect Of Oxalate Ion On The Hydrolysis Of A Fluorescent Aluminum - Schiff Base Complex"
Bunseki Kagaku 1992 Volume 41, Issue 10 Pages 503-509
Watanabe, K.;Tsuyuki, M.

Abstract: A 90 µL sample is injected into a carrier stream (0.5 mL min-1) of water before merging with reagent streams (both 0.5 mL min-1) of 0.1 mM Al(III) in 18 mM H2SO4 and 2 mM NN'-disalicylidene-ethylenediamine - 0.02 M ethylenediamine in aqueous 80% 1,4-dioxan. After passage through a 17-cm reaction coil the fluorescence is measured at 460 nm (excitation at 360 nm). Oxalate can be determined from 0.15 to 20 ppm, and the sampling rate is 40 h-1. The method has been applied to the analysis of spinach. Oxalate ion suppresses the rate of hydrolysis of an Al-Schiff base complex. An FIA system based on the hydrolysis-retarding reaction was developed to determine oxalate ion at the ppm level. By measuring the fluorescence intensities, oxalate ion could be selectively determined over the range 0.15 to ~20 ppm; 40 samples/h could be analyzed. The recommended conditions for the determination of oxalate ion are as follows. A three-channel FIA apparatus was used: one channel for the carrier stream (distilled water) and two reagent streams, 1 for Al (1.0 x 10^-4 M) in 0.018 M sulfuric acid and the other for DSED (2.0 x 10^-3 M N,N'-disalicylideneethylenediamine) containing 2.0 x 10^-2 M ethylenediamine and 80% 1,4-dioxane. The flow rate of each stream was maintained at 0.5 mL/min. The amount of free oxalic acid in spinach was determined by the proposed method.
Oxalate Fluorescence Indirect

"Flow Injection Spectrophotometric Determination Of Molybdenum In Plants"
Fenxi Huaxue 1992 Volume 20, Issue 3 Pages 319-321
Xu, Q.;Yuan, X.

Abstract: The method is based on the formation of Mo - SCN- - Rhodamine B (I) complex. Onion, spinach or tea is dried at 60°C for 24 h under reduced pressure, weighed, heated at 520°C for 2 h and the ash is dissolved with 5 mL of 5 M HCl. The solution is diluted with 5 mL of de-ionized water and boiled for 5 min. After filtration, the solution is diluted to 25 mL with water and analyzed by the cited method (flow diagram given). Beer's law is obeyed for up to 1.6 µg mL-1 of Mo. The detection limit is 0.02 µg mL-1 of Mo. The coefficient of variation (n = 5) for 1 µg mL-1 of Mo is 0.7%. Alkaline metals and alkaline-earth metals do not interfere.
Molybdenum Spectrophotometry Interferences Complexation

"Evaluation Of An HPLC Method For The Determination Of Phylloquinone (vitamin K1) In Various Food Matrices"
J. Agric. Food Chem. 1994 Volume 42, Issue 2 Pages 295-300
Sarah L. Booth, Kenneth W. Davidson, and James A. Sadowski

Abstract: Phylloquinone was extracted from vegetable juice, cows milk, spinach, bread and beef with propan-2-ol/hexane (details given) with 2,3-dihydrophylloquinone or 2-methyl-3-(3,7,11,15,19-pentamethyl-2-eicosenyl)-1,4-naphthalenedione added (internal standards; details given). The extracts under went solid-phase extraction on silica columns (described) with elution effected by hexane/ethyl ether (93:3). Beef extracts were further purified by HPLC on a C18 column (described). The purified extracts were dissolved in methanol containing 10 mM ZnCl2, 5 mM acetic acid and 5 mM sodium acetate (milk extracts were dissolved in 10 mM ZnCl2, 5 mM acetic acid and acetonitrile) and analyzed on an Hypersil ODS (3 µm) column (15 cm x 4.6 mm i.d.) with a mobile phase (1 ml/min) of methanol/CH2Cl2 (9:1) containing 5 ml/l of 2 M ZnCl2, 1 M acetic acid and 1 M sodium acetate with fluorescence detection at 418 nm (excitation at 244 nm) after post-column derivatization in an online chemical reactor (50 mm x 2 mm) with Zn metal (200 mesh). Intra- and inter-day RSD were 6.6-13.6% with between sample RSD (n = 10) of 7.8% (milk), 32.6% (spinach) and 44.6% (vegetable juice).
Vitamin K1 HPLC

"Flow Injection Determination Of Nitrate In Vegetables Using A Tubular Potentiometric Detector"
J. Agric. Food Chem. 1995 Volume 43, Issue 3 Pages 704-707
Jose L. F. C. Lima, Antonio O. S. S. Rangel, and M. Renata S. Souto

Abstract: Dried powdered vegetable was extracted by the method of Mitrakas and Alexiades (Mikrochim. Acta, 1990, 1, 7) and the extract was injected into a carrier stream (6 ml/min) of 1 µM-KNO3 in extractant solution (10 nM-lead acetate, 5 mM lead oxide and 10 mM sodium acetate) in a low dispersion FIA system. The flow passed through a tubular nitrate ISE with (4,7-diphenylphenanthroline) nickel(II) dissolved in o-nitrophenyl octyl ether immobilized in a PVC membrane and without an inner reference solution (preparation details given). The calibration graph was linear for 0.4-40 mM nitrate with a detection limit of 28 µM. Recoveries were 93.8-104% for nitrate in parsley, lettuce and spinach with RSD of 3%. A flow injection system with potentiometric detection for the determination of nitrate in vegetables was developed. For this purpose a tubular nitrate ion-selective electrode with the ion-exchanger system [(4,7- diphenylphenanthroline)nickel(II) dissolved in o-nitrophenyl octyl ether] immobilized in a PVC membrane and without inner reference solution was prepared. The flow injection manifold incorporating the tubular electrode was used for the determination of nitrate in vegetables (lettuce, parsley, and spinach), using a mixture of lead acetate, lead oxide, and sodium acetate as nitrate extractant, ionic strength adjustor, and interference suppressor solution. The quality of the results obtained by the proposed methodology was assessed by comparing them with those provided by a conventional potentiometric methodology and also through recovery tests (recoveries from 94 to 104% were found). A sampling rate of 120 samples per hour was achieved with a relative standards deviation lower than 2%.
Nitrate Electrode Electrode Potentiometry Electrode Method comparison Interferences

"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