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: Oil -> vegetable

Citations 16

"Direct Automatic Determination Of Free Acidity In Oils By Flow Injection Analysis"
Anal. Chim. Acta 1989 Volume 225, Issue 2 Pages 431-436
P. Linares, M. D. Luque de Castro and M. Valcárcel

Abstract: The sample is mixed with ethyl ether - ethanol (1:1) flowing at 1.5 mL min-1, and this is mixed with ethanolic 50 mM KOH - 0.01% phenolphthalein (0.9 mL min-1) and then with a second similar reagent stream. After passage through a 250-cm reaction coil, the decrease in absorbance of the mixture is measured at 562 nm. Peak heights are measured for low concentration. (0.15 to 0.81%) and peak widths or flow injection titration is used for higher concentration. (4.04%). The sampling rate is 60 h-1. Results agreed with those of the standard method.
Acidity Spectrophotometry Peak width Titrations Method comparison Standard method Organic phase detection

"Flow Injection Amperometric Detection Of Aniline With A Peroxidase Modified Carbon Paste Electrode"
Anal. Chim. Acta 1994 Volume 291, Issue 3 Pages 349-356
P. Dominguez-Sancheza, C. K. O'Sullivana, A. J. Miranda-Ordieresa, P. Tuñon-Blancoa and M. R. Smyth

Abstract: An enzymatic electrode for the detection of aniline, based on a horse-radish peroxidase modified C paste electrode, is described. The enzyme was dispersed in the C paste and immobilized on a nafion membrane. Cyclic voltammetry and differential pulse polarography were used to characterize the enzymatic electrochemical process. Cyclic voltammetry was conducted using a C paste working electrode, a Ag/AgCl/saturated KCl reference electrode and a Pt-wire auxiliary electrode. The electrode was used for the flow injection amperometric detection of aniline. The reference electrode was Ag/AgCl/saturated KCl. The electrode was applied to the detection of aniline in vegetable oil. Aniline was extracted with 2 M HCl. The supporting electrolyte was 0.1 M phosphate buffer of pH 8. For flow experiments the carrier solution and samples contained 10 mM H2O2. The flow injection amperometric detection of aniline at potentials down to +100 mV (Ag/AgCl) gave a fast response (30 s), RSD of 0.75% (n = 8), and a sampling frequency of 20 samples/h. The mean recovery was 99.4±3.2%.
Anilines Voltammetry Electrode Amperometry Nafion membrane

"Membrane Extraction-preconcentration Cell Coupled Online To Flow Injection And Liquid Chromatographic Systems. Determination Of Triazines In Oil"
Anal. Chim. Acta 1995 Volume 304, Issue 3 Pages 323-332
R. Carabias Martínez*, E. Rodríguez Gonzalo, E. Hernández Fernández and J. Hernández Méndez

Abstract: The membrane extraction-pre-concentration (MEP) cell consisted of two channels separated by a Celgard 2500 membrane (0.025 mm thick, 45% porosity, 0.04 µm effective pore size). Oil samples diluted with hexane (1:4) were propelled through one channel and the acceptor solution was propelled through the other channel. The acceptor solution was held stationary during the extraction-pre-concentration period while the diluted oil sample was circulated continuously. The MEP cell was coupled online to FIA or HPLC systems for the determination of triazines in vegetable oils. The FIA system used 0.1 M HClO4 as the acceptor solution. At the end of the 5-15 min MEP period, the acceptor solution was propelled to the diode-array spectrophotometer where the total triazines were determined at 220 nm. The calibration graphs were linear (range not given) with detection limits of 0.91 ppm. RSD (n = 10) were 6%. The HPLC system used 5 mM HClO4 in methanol/H2O (9:1) as the acceptor solution. After MEP, the acceptor solution was analyzed on a 5 µm Spheri-5-RP 18 column (25 cm x 4.6 mm i.d.) with 50% aqueous acetonitrile as mobile phase (1.25 ml/min) and detection at 220 nm. Calibration graphs for the determination of atrazine, ametryne, prometryne and terbutryne in corn, sunflower and olive oil were linear for 0.05-20 ppm and the detection limits were ~e;0.1 ppm. RSD (n = 10) were 10%.
Herbicides Atrazine Ametryne Prometryne Terbutryne Spectrophotometry HPLC Sample preparation Celgard Membrane Preconcentration Extraction

"Online Coupling Of A Liquid-liquid Extraction Flow-reversal System To A Spectrophotometric Flow-through Sensor For The Determination Of Polyphenols In Olive Oil"
Anal. Chim. Acta 1996 Volume 323, Issue 1-3 Pages 55-62
M. P. Cañizares, M. T. Tena and M. D. Luque De Castro*

Abstract: The sensor for the spectrophotometric determination of polyphenols at 750 nm consisted of a flow-through cell (18 µL volume, 1.5 mm optical pathlength) packed with DEAE-Sephadex anion exchanger (40-120 µm) impregnated with Folin-Ciocalteu reagent. The sensor was incorporated into a flow injection manifold for the liquid-liquid extraction of polyphenols from diluted olive oil. A 500 µL sample of diluted olive oil (1:5 with hexane) was injected into 0.1 M NaHCO3 and propelled (1.3 ml/min) through an extraction coil (100 cm x 0.7 mm i.d.) several times by flow reversal. Only the analyte-enriched aqueous phase reached the sensor, where the analyte was retained and detected. The calibration graph, prepared with use of caffeic acid and 10^-20 flow-reversal cycles, showed linear segments for 15-30 µg/ml and 35-90 µg/ml, and the detection limit was 10 µg/ml. The sensitivity of the method improved with the number of cycles (N), while the RSD decreased. The sampling frequency was 11 per h for N = 10 and 8 per h for N = 20. The method was applied to the analysis of eight different olive oils, and the results are compared with those obtained by a conventional method based on the same chemical reaction.
Polyphenols Ion exchange Spectrophotometry Sample preparation Sensor Method comparison Flow reversal Solvent extraction

"Spectrophotometric Determination Of Periodate With Salicylaldehyde Amidinohydrazone Using Flow Injection. Determination Of Glycerol In Vegetable Oils"
Analyst 1989 Volume 114, Issue 8 Pages 989-990
Juan José Berzas Nevado and Pablo Valiente González

Abstract: A 0.2 mL sample containing 50 ppm of IO4- was injected into a carrier stream of water (1 mL min-1) and then mixed with 0.06% salicylaldehyde amidinohydrazone solution followed by 0.25 M NH4Cl - NH3 buffer (pH 9.2) (both 1 mL min-1). The absorbance was measured at 490 nm; the calibration graph was rectilinear. Glycerol was determined by treatment with excess of IO4- and set aside for ~30 min before analysis as above. Oil was dissolved in CHCl3 before analysis. Recoveries from olive and sunflower oil were quantitative. The sampling rate was 20 h-1. Periodate has been determined using flow injection with spectrophotometric detection on the basis of the red color obtained when salicylaldehyde guanylhydrazone (SAG) and periodate were mixed in a basic medium. The carrier stream was de-mineralised water. The reagent stream was an aqueous SAG solution and another stream contained an ammonia buffer (pH 9.2) solution. The calibration graph was linear between 5 and 50 p.p.m. of periodate when the injection volume was 200 µL. The relative standard deviation (n= 10) was 1.0% and the detection limit, corresponding to a signal to noise ratio of 3, was 0.35 p.p.m. The proposed method was applied to the determination of glycerol in vegetable oils using the Malaprade reaction.
Periodate Glycerol Spectrophotometry Buffer

"Automated Determination Of Peroxides In Olive Oil By Flow Injection"
Analyst 1993 Volume 118, Issue 7 Pages 891-893
J. A. García-Mesa, M. D. Luque de Castro and M. Valcárcel

Abstract: A method for the determination of the peroxide value of olive oil based on flow injection principles is proposed. The method requires no pre-treatment of samples that have undergone natural or forced oxidation as the sensitivity can be accommodated over wide margins (determination range 3.4-537 meq. kg-1). The precision of the method, expressed as relative standard deviation, ranges from 0.7 to 2.4% and the sampling frequency is 15 h-1. A FIA system for the cited determination was developed (manifold illustrated). Sample (1.0-1.5 g) was injected directly into a hexane carrier stream (0.83 ml/min) and diluted by splitting the stream. After merging with a stream of acetic acid (0.54 ml/min), followed by a stream of 0.5% NaI in isopropyl alcohol (0.42 ml/min), the stream was passed through a flow cell connected to a diode-array spectrophotometer for measurement of the generated iodine at 360, 400 or 420 nm for the determination of peroxides in the ranges 3.4-62.0, 16.2-234 or 51.4-537 meq./kg, respectively. The RSD was 0.7-2.4% and the sampling frequency was 15/h.
Peroxide ion

"Determination Of Trace Amounts Of Nickel By Chelating Ion Exchange And Online Enrichment In Flow Injection Spectrophotometry"
Analyst 1995 Volume 120, Issue 2 Pages 555-559
Rajesh Purohit and Surekha Devi

Abstract: A flow injection spectrophotometric method for Ni determination is described. A portion (5 ml) of a Ni solution of pH 7.5-9 was passed (3 ml/min) through a column (4 cm x 2 mm i.d.) of 8-hydroxyquinoline chelating resin (several tested; details given). The column was washed with 0.2 M acetate buffer of pH 7.5-9. The chelated Ni was eluted from the column by injecting 20 µL of 2 M HCl into the FI system and was then mixed with 0.5% dimethylglyoxime and the absorbance was measured at 445 nm. A diagram of the manifold used is given. The calibration graph was linear from 10 (detection limit) to 70 µg/ml of Ni. The RSD (n = 5) were 0.4-2.8%. The method was applied to chocolate and vegetable oil. The results agreed with those obtained by AAS.
Nickel Spectrophotometry 8-Hydroxyquinoline Chelation Preconcentration Method comparison

"Flow Injection Fourier Transform Infrared Spectrometric Determination Of Oil And Greases: Preliminary Microwave-assisted Extraction Studies"
Analyst 1996 Volume 121, Issue 8 Pages 1031-1036
Yasmina Daghbouche, Salvador Garrigues and Miguel de la Guardia

Abstract: Mineral oil, edible oil, gasoline or petroleum samples were dissolved in CCl4. A portion (300 ml) of the resulting solution was injected into a carrier stream of CCl4 at a flow rate of 1.5 ml/min. The area under the FTIR absorbance spectrum from 3058-2780 cm-1, corrected for a baseline established between 3200 and 2700 cm-1, was used for quantification. The detection limit was 0.6-1.1 mg/ml oils and greases; RSD was 1.4-4.1% (n=10). The throughput was 60 samples/h. The method was also applied to aqueous solutions containing different types of oils, after microwave-assisted extraction of the oil into CCl4 by irradiation at 420 W for 6 min. Results are presented and discussed.
Sample preparation Spectrophotometry Organic phase detection Solvent extraction Microwave

"Coupled Robot-flow Injection Analysis System For Fully Automated Determination Of Total Polyphenols In Olive Oil"
Anal. Chem. 1993 Volume 65, Issue 23 Pages 3540-3542
Jose A. Garcia-Mesa, M. Dolores Luque de Castro, and Miguel Valcarcel

Abstract: Details are given of a robotic system, based on a Zymate II Plus robot and a System V controller, by which (i) standard solution of 2-(4-hydroxyphenyl)ethanol were prepared from a 500 µg/l stock solution and placed in a FIA system for calibration, (ii) the oil sample was weighed, diluted with hexane and twice extracted with aqueous 60% methanol, and (iii) the aqueous methanol extract was introduced into the FIA system for dispersion in Folin-Ciocalteu reagent and subsequent merging with aqueous Na2CO3 before photometric detection at 725 nm. The adaptation of the manual extraction-photometric method and its optimization are fully described. Analysis time for the robotic method was 30 min, compared with 120 min for the manual method and 3.3 min for a FIA method described earlier (Anal. Chim. Acta, 1990, 235, 441); the calibration graph was linear for 50-700 µg/g of polyphenols in each instance. The robotic method showed the best precision with a RSD (n = 11) of 1.6% at 463 µg/g. Correlation between the manual and the robotic method was good (r2 = 0.9959). The development of an online robotic/flow injection analysis (FIA) method for the fully automated determination of total polyphenols in virgin olive oil is discussed. This coupled system allows more efficient use of robotic stations, which can concentrate on tasks that are too difficult for other automatic alternatives to perform, while the FIA instrumentation deals with the simpler operations. .
Polyphenols Spectrophotometry Sample preparation Robot Extraction Optimization

"Determination Of Peroxide Value In Vegetable Oils By An Organic-phase Enzyme Electrode"
Anal. Lett. 1994 Volume 27, Issue 2 Pages 299-308
Mannino, S.;Cosio, M.S.;Wang, J.

Abstract: Vegetable oil (50 µL) was injected without pre-treatment into a carrier solution of CHCl3 (0.7 ml/min) saturated with aqueous 0.1 M phosphate buffer and containing 2 mM ferrocene as mediator and 0.1 M tetrabutylammonium bromide for FIA. Detection was at an enzymatic electrode operated at -0.1 V vs. an undefined reference electrode. The enzymatic electrode was prepared by coating a rough vitreous-carbon electrode with a horse-radish peroxidase/Eastman AQ-55D ester-sulfonic acid polymer mixture applied as solution and dried in situ. The calibration graph was linear from 5-200 ppm of lauroyl peroxide with test recoveries of 98-101%. The RSD (n = 7) were 2.8 and 3.1% for 10 and 52 ppm, respectively.
Peroxide ion Electrode

"Determination Of Tert-butylhydroxytoluene By Flow Injection Analysis At Polymer Modified Glassy Carbon Electrodes"
Electroanalysis 1998 Volume 10, Issue 12 Pages 832-835
C.D. Garcia, P.I Ortiz*

Abstract: A flow injection method for the determination of the antioxidant BHT using polymer modified electrodes in connection with amperometric detection is proposed. The procedure is based on the electrochemical oxidation at 0.700 V (vs. Ag/AgCl [3 M NaCl]) in phosphate buffer solution (pH 7.2). BHT is determined over the range 0.001-0.020 or 0.005-0.030 g/L. Other analysis parameters, such as electrode working potential, flow rate, electrodeposited charge, and solution pH were optimized. The proposed method was applied to the determination of BHT in electrical transformer and vegetable oils samples. The results were compared with the HPLC-UV detection standard technique.
tert-Butylhydroxytoluene Electrode Electrode Amperometry Optimization Method comparison

"High Performance Liquid Chromatography And Post-column Derivatization With Diphenyl-1-pyrenylphosphine For Fluorimetric Determination Of Triacylglycerol Hydroperoxides"
J. Chromatogr. A 1992 Volume 596, Issue 2 Pages 197-202
Kazuaki Akasaka, Setsu Ijichi, Kenji Watanabe, Hiroshi Ohrui and Hiroshi Meguro*

Abstract: Butter, margarine and mayonnaise were diluted with water and extracted (x 2) with CHCl3 - methanol (2:1). The combined extracts were diluted with CHCl3 and subjected to HPLC on (a) a column (15 cm x 4.6 mm) of TSK-gel ODS 80Tm (5 µm) with a mobile phase (0.6 mL min-1) of methanol - 1-butanol (9:1) or (b) a column (15 cm x 4.6 mm) of Develosil Ph-5 phenyl column (5 µm) with a mobile phase (0.6 mL min-1) of methanol - water (19:1). In both instances, the eluent was mixed with a solution of 3 mg of diphenyl-1-pyrenylphosphine in 400 mL of methanol - acetone (3:1) pumped at 0.3 mL min-1 and the mixture was passed through a coil (20 m x 0.5 mm) at 80°C before fluorimetric detection at 380 nm (excitation at 352 nm). Calibration graphs were rectilinear for 2 to 1000 pmol of monohydroperoxides; there was no interference from dialkyl peroxides, unoxidized fatty acids, hydroxy acids or their esters. Column (a) was useful for separation of individual monohydroperoxides and column (b) was useful for their total determination as a class. The method was also be applied to the analysis of vegetable oils which were diluted with CHCl3 and subjected to HPLC as above.
Triacylglycerol hydroperoxide HPLC Fluorescence Post-column derivatization Interferences

"Highly Sensitive Flow Injection Analysis Of Lipid Hydroperoxides In Foodstuffs"
Biosci. Biotechnol. Biochem. 1996 Volume 60, Issue 11 Pages 1772-1775

Abstract: Edible oil, butter, margarine and mayonnaise samples were extracted with methanolic 50% butan-l-ol (details given). Portions (1-50 µL) of the extracts were injected into a carrier stream (0.8 ml/min) of methanolic 50% butan-l-ol, which merged a stream (0.3 ml/min) of 7.5 µg/ml diphenyl-l-pyrenylphosphine (reagent) in carrier solution containing 0.5 µg/ml 2,6-di-t-butyl-p-cresol, passed through a stainless-steel reaction coil (30 m x 0.5 mm i.d.) at 80°C then through a similar cooling coil (50 cm x 0.5 mm i.d.) prior to fluorimetric detection for lipid hydroperoxides at 380 nm (excitation at 352 nm). A second FIA system was also used which had a carrier stream flowing at 0.7 ml/min, a 30 µg/ml reagent stream flowing at 0.6 ml/min and a 50 m reaction coil. All other details were the same. For the first system the calibration graph was linear from 2-201 pmol trilinolein hydroperoxides (I), the detection limit was 2 pmol I and the RSD (n = 8) were 1.7-3.2%. For the second system, the calibration graph was linear from 0.4-79 pmol I, the detection limit was 0.2 pmol I and the RSD (n = 8) were 1.9-3.8%. Samples could be analyzed every 2 minutes, and results from both systems correlated well with those obtained by a batch method. Recoveries were 91.8-102%.
Lipids Hydroperoxide, lipid Trilinolein hydroperoxide Sample preparation Fluorescence Heated reaction Method comparison

"The Lipoxygenase Sensor, A New Approach In Essential Fatty Acid Determination In Foods"
Biosens. Bioelectron. 1997 Volume 12, Issue 11 Pages 1089-1099
Michael Schoemaker, Rainer Feldbrügge, Bernd Gründig and Friedrich Spener

Abstract: Both an enzyme electrode and enzyme column with immobilized lipoxygenase, respectively, were used for the determination of essential fatty acids. The former was applied in a batch system, the latter was part of a fully automated flow injection analysis (FIA)- system. The oxygen consumption due to the lipoxygenase catalyzed oxygenation of essential fatty acids was monitored amperometrically. Both systems were compared with regard to linear ranges of the calibration plots, sensitivities, detection limits, apparent Michaelis- Menten constants and lifetimes. The enzyme electrode showed different sensitivities for linoleic and α-linolenic acids, the most common essential fatty acids. The reason for this was not a second oxygenation step by lipoxygenase in case of α-linolenic acid, but a different dialytic behavior of the two substrates. Hence, only the FIA-system was used for the determination of these fatty acids in real matrices such as vegetable oils and margarines. In the presence of detergent the triglycerides of the hydrophobic food samples were converted into water soluble glycerol and free fatty acids by a 15 min incubation with a ready to use lipase/esterase-mix, thus avoiding the use of organic solvents for analysis. Results obtained by the enzymatic FIA-system were in excellent agreement with those obtained by standard gas chromatography.
Fatty acids, free Amperometry Sensor Immobilized enzyme Method comparison

"Fluorimetric Flow Injection Determination Of Hydroperoxides In Foodstuffs"
Food Chem. 1993 Volume 46, Issue 3 Pages 301-305
Tomás Pérez-Ruiz*, Carmen Martínez-Lozano, Virginia Tomás and Otilia Val

Abstract: A reliable and sensitive stopped-flow injection method is described for the determination of hydrogen peroxide, cumene hydroperoxide and tert-butyl hydroperoxide. It is based on the oxidation of leuco-phloxin to the fluorescent phloxin by hydroperoxide and haematin. Linear calibration graphs were obtained between 4 times 10^-6 and 8 times 10^-5 M, with a sampling-rate of 25 samples h-1. The detection limit, defined as three standard deviations of the reagent blank, was 1.5 times 10^-7 M. The usefulness of the method was tested in the determination of lipohydroperoxides in six commercial oil samples and of hydrogen peroxide in six milk samples of different levels of skimming. The results agreed closely with those obtained by the iodometric method.
Hydrogen peroxide Cumylhydroperoxide t-Butylhydroperoxide Fluorescence Method comparison Stopped-flow

"Automated Method For Determination Of Free Fatty Acids"
J. Am. Oil Chem. Soc. 1981 Volume 58, Issue 10 Pages 935-938
Lars-Gösta Ekström

Abstract: An automated colorimetric method is described for determining free fatty acids (FFA) in vegetable oils using the flow injection analysis (FIA) technique. In this procedure, an almost linear relationship exists between the peak height and the FFA concentration. Liquid samples can be poured directly into the sample cups on the sampler for an automatic analysis of the FFA content. The dynamic range of this method is from 0.01 to almost 5%. Samples with higher FFA content must be diluted before analysis. The sample capacity is 12-20 injections/hr. No evidence of the existence of the earlier proposed cage-like complex (Cu(II)(FFA)2)2 in the organic phase was observed in this study.
Fatty acids, free Spectrophotometry Sample preparation Automation Extraction