University of North Florida
Browse the Citations

Contact Info

Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Website: @unf

View Stuart Chalk's profile on LinkedIn


Classification: Food -> vinegar

Citations 13

"An Automatic Titrator Based On A Multicommutated Unsegmented Flow System - Its Application To Acid-base Titrations"
Anal. Chim. Acta 2000 Volume 407, Issue 1-2 Pages 213-223
Cristina M. N. V. Almeida, Rui A. S. Lapa, José L. F. C. Lima, Elias A. G. Zagatto and M. C. U. Araújo

Abstract: A continuous flow methodology to perform acid-base titrations is described. The titrations are carried out on a multicommutated flow system which simulates batch titration procedures. The titration strategy is based on sequential insertion of increasing titrant and decreasing titrand volumes in a reactor, thus accomplishing complete titration curves. The assessment of the titration end point is similar to that of conventional batch procedures. The theoretical model for the determination of titrand concentration without requiring any calibration process is presented and discussed. The present system was evaluated in vinegar acidity determinations and provided an accuracy better than 3% with a good repeatability (relative standard deviation (RSD) = 2.5%; n = 10) and reproducibility (RSD < 5%). The titration accuracy is time-dependent and has been tested in the 2-10 min range.
Acids Bases Potentiometry Electrode Multicommutation Titrations Theory

"Online Coupling Of Gas Diffusion To Capillary Electrophoresis"
Talanta 1998 Volume 45, Issue 3 Pages 477-484
Petr Kuban and Bo Karlberg*

Abstract: Online gas diffusion has been coupled to a capillary electrophoresis system (CE) via a specially designed interface. The sample is merged with a modifying solution, e.g., a strong acid, in a flow system to transform the analytes of interest into their respective gaseous forms. These transformed, gaseous analytes permeate through a PTFE membrane into an acceptor stream comprising of a tris-buffer. The continuously flowing acceptor stream is led into an injector forming an integrated part of a flow injection analysis (FIA) system. The sample receiving carrier stream in the FIA system, a chromate buffer, brings the sample, 50 µl, to the FIA-CE interface into which one end of a separation capillary has been inserted. A small portion of the injected sample enters the capillary (electrokinetic injection) and separation takes place. A UV detector is placed at the other capillary end and a run potential of 25 kV is applied to two platinum electrodes positioned in the flow system. Multiple sample injections can be performed in one uninterrupted electrophoretic run. A typical sampling frequency is 15 h-1; each run may result in quantitation of at least five anions. The overall repeatability is in the range 1.8-3.6% (RSD). The technique has been applied to the analysis of real samples such as soft drinks, vinegar and wine. Selective discrimination of anions which are unable to form volatile species is accomplished. No off-line sample pre-treatment is needed.
Anions Electrophoresis Gas diffusion Interface Teflon membrane Volatile generation

"Determination Of Titratable Acidity Of Wines And Total Acidity Of Vinegars By Discontinuous Flow Analysis Using Photometric End-point Detection"
Analyst 1991 Volume 116, Issue 10 Pages 1051-1054
Terence J. Cardwell, Robert W. Cattrall, Graeme J. Cross, Gregory R. O'Connell, John D. Petty and Geoffrey R. Scollary

Abstract: The titratable acidity of white and red wines and the total acidity of vinegars were determined using the flow-based titration technique, discontinuous flow analysis with photometric end-point detection. A flow cell was used which had a low-volume mixing chamber fitted with a high-speed stirrer. Detection of the end-point was achieved using a light emitting diode and photodiode incorporated into the flow cell. A sample throughput of one every 4 s was possible with a precision of better than 1% relative standard deviation (n= 6) being observed for all standards and most samples. The results compared well with those from a standard manual titration.
Acidity Spectrophotometry Stopped-flow Titrations

"Flow Injection Analysis Based On A Membrane Separation Module And A Bulk Acoustic Wave Impedance Sensor. Determination Of The Volatile Acidity Of Fermentation Products"
Fresenius J. Anal. Chem. 1998 Volume 360, Issue 2 Pages 272-274
Xiaoli Su, Lihua Nie, S. Yao

Abstract: A novel flow injection analysis (FIA) system has been developed for the rapid determination of the volatile acidity of some fermentation products like vinegars and juices. The proposed method is based on the diffusion of volatile acids, mainly acetic acid, across a PTFE gas-permeable membrane from an acid stream into an alkaline stream, and the acids trapped in the acceptor solution are determined online by a bulk acoustic wave impedance sensor based on changes in the conductivity of the solution It exhibited a linear frequency response up to 10 nmol L-1 acetic acid with a detection limit of 50 µmol L-1, and the precision was better than 1% (RSD) at a through-put of 72 hr-1. The effects of operating voltage for the detector, cell constant of the electrode, composition of acceptor stream, flow rates, and temperature on the FIA performance were also investigated.
Acidity, volatile Acetic acid Conductometry Sensor Sensor Teflon membrane Gas diffusion Optimization

"Flow Injection Potentiometric Determination Of Coke Acidity And Acetic Acid Content In Vinegar Using An Antimony Electrode"
Anal. Lett. 1996 Volume 29, Issue 5 Pages 711-724
Capelato, M.D.;Marli Dos Santos, A.;Fatibello, O.;Gama, R.

Abstract: An Sb/Sb2O3 electrode was used to measure the acidity of coke and vinegar samples by FIA. Sample (50 µL) was injected into a carrier solution of 0.1 M NaNO3 of pH 6.5 (2 ml/min) via a flow manifold (schematic given). Phosphate buffer solutions were used as pH standards. Solutions passed through a 50 cm helicoidal tubular reactor and on to a potentiometric detector cell comprising a circular plane Sb indicator electrode and a Ag/AgCl/0.1 M NaCl, 3 M NaNO3 as reference electrode. A linear response to acidity was achieved for 3.16-100 mM acetic acid with a slope of 30.1 mV/decade and a sample throughput of 23 samples/h. The average standard deviation was ±0.5%. The method should be suitable for routine analyzes.
Acetic acid pH Potentiometry Electrode Reactor

"Computerized Potentiometric Stripping Analysis Using Asyst Software: Application To Lead Determination In Wines And Vinegars"
Electroanalysis 1989 Volume 1, Issue 2 Pages 177-180
Saverio Mannino*, Giuseppe Fregapane, Mariagrazia Bianco

Abstract: A computerized system for potentiometric stripping analysis made of commercially available components with corresponding software is described. Application to the determination of lead in wines and vinegars is also reported.
Lead Potentiometric stripping analysis Computer

"Potentiometric Detectors For The Determination Of Acidity By Discontinuous Flow Analysis"
Electroanalysis 1992 Volume 4, Issue 8 Pages 805-810
Terence J. Cardwell, Robert W. Cattrall, Gregory R. O'Connell, John D. Petty, Geoffrey R. Scollary

Abstract: Three potentiometric detectors, each incorporating a vibrating reed mixer, were investigated for use in the determination of acidity by discontinuous flow anal. (DFA). Two of these used PVC and glass membrane pH-sensors, and the third employed a novel differential titration technique based on two quinhydrone electrodes. These detectors were applied to the determination of the total acidity of vinegars and the titratable acidity of wines, the results agreeing well with standard procedures. The anal. of wine proved to be difficult because of the gradual change in pH at the end-point and so a method was developed which determined the titratable acidity at pH 8.3.
Acidity Electrode Electrode Potentiometry Mixing Method comparison

"Electrochemical Detection Of Pyrroloquinoline Quinone Coupled With Its Catalytic Function By Liquid Chromatography"
Anal. Sci. 1993 Volume 9, Issue 2 Pages 207-211

Abstract: Samples of milk and swine serum were deproteinized by addition of 30% trichloroacetic acid. After centrifuging, the supernatant solution was acidified with HCl to pH 0.5 and extracted with butanol. A portion (20 µL) was analyzed by HPLC on a Cosmosil 5C-18AR column (25 cm x 4.6 mm) with methanol - 6 mM H3PO4 (3:7) containing 5 µM-K3Fe(CN)6 as mobile phase (1 mL min-1). Post-column derivatization was carried out by mixing the column eluate with a stream (0.2 mL min-1) of 3 M glycine - 2.5 M ammonium buffer. The reaction coil consisted of a Teflon tube (17.5 m x 0.5 mm) maintained at 25°C. Electrochemical detection was used with a vitreous-carbon working electrode, a Ag - AgCl reference electrode and a stainless-steel tube counter electrode. Calibration graphs were rectilinear from 0.2 pM- (detection limit) to 6 µM-pyrroloquinoline quinone. The method was also applied to table vinegar.
Pyrroloquinoline-quinone HPLC Electrode Catalysis Post-column derivatization

"Overhead Projector Flow Injection Analysis"
Anal. Proc. 1993 Volume 30, Issue 1 Pages 10-12
Kate Grudpan and Thanboosak Thanasarn

Abstract: A device (details and diagram given) is described in which the components are mounted on an acrylic sheet (30 cm x 30 cm x 2 mm) and then placed on an overhead projector to demonstrate the principles of flow injection analysis. The mixing coil (2 m x 1.3 mm; polyethylene tubing) is wound on a transparent former and attached via the injector to a gravity-fed carrier solution; a simple mixing chamber and a visual detector cell are also included. The device could demonstrate the effect on dispersion of coil length, sample size and flow rate. The performance was exemplified by the injection of acid solution into NaOH containing indicator, and of Cl- solution into a carrier containing Hg(SCN)2 and Fe(NO3)3. Calibration graphs of residence time vs. log concentration. were used to analyze commercial vinegars for acetic acid.
pH Chloride Acetic acid Spectrophotometry Education

"Flow Injection Titration Of Chloride In Food Products With A Silver Tubular Electrode Based On An Homogeneous Crystalline Membrane"
Food Chem. 1994 Volume 50, Issue 4 Pages 423-428
Isabel M. P. L. V. O. Ferreira, Jos&eacute;L. F. C. Lima* and Ant&oacute;nio O. S. S. Rangel

Abstract: Wine, milk, beer and vinegar were tested for chloride by pseudo-titration using FIA and potentiometric detection. Sample was injected into a carrier stream composed of 20 µM-AgNO3/0.1 M KNO3 and directed to a well-stirred mixing chamber. The decrease in the Ag concentration was monitored by an Ag tubular electrode with a crystalline membrane of AgS prepared by mixing equal volumes of equimolar (0.1M) AgNO3 and Na2S solution, filtering and drying at 100°C for 24 h. After grinding, the membrane discs were prepared by pressing 0.25 g of sensor at high pressure to produce discs 10 mm in diameter and 0.4 mm thick. The membrane was set into a support (details given). The operating characteristics of the tubular electrode were compared with conventional electrodes and found to be similar. The optimum Ag concentration in the carrier stream was 0.1 mM and optimum carrier flow rate was 8.1 ml/min. Calibration graphs were linear from 10^-500 mg/l, 100-1800 mg/l and 40-500 mg/l for wine, milk and beer, and vinegar, respectively. Sampling rate varied from 120-136 samples/h. A comparison with reference procedures showed maximum RSD of 6, 0.3 and 1% for wine and milk, beer, and vinegar, respectively.
Chloride Electrode Potentiometry Titrations Well stirred mixing chamber Optimization Indirect

"Conductometric And Colorimetric Determination Of Volatile Acidity Of Vinegars By Flow Injection Analysis"
J. AOAC Int. 1991 Volume 74, Issue 2 Pages 346-350

Abstract: Vinegar (10 ml) was treated with 3.5 M H2O2 and the mixture was diluted to 100 mL with water. The solution was injected into an aqueous carrier stream in a flow injection system (diagram given) which subsequently mixed with 0.05 M H2SO4. After mixing, the acetic acid present diffused through the PTFE membrane for conductometric detection. Alternatively, acetic acid passed through the membrane to mix with a bromocresol purple solution of pH 7 for colorimetric detection at 540 nm. Volatile acidity was determined by graphical interpolation as calibration curves were not linear. Different loops were utilized for the two methods to avoid retention of acetic acid on the walls (details given). Results for both methods agreed well with those obtained by traditional procedures.
Acidity Conductometry Spectrophotometry Diffusion Teflon membrane Method comparison

"Online Determination Of Acetic Acid In A Continuous Production Of Acetobacter Aceticus"
J. Biotechnol. 1993 Volume 31, Issue 3 Pages 267-275
T. Becker*, R. Kittsteiner-Eberle, T. Luck and H. -L. Schmidt

Abstract: A flow injection system for the determination of acetic acid in the 10^-60 mM range was conceived and optimized on basis of the coupled reactions of acetate kinase/pyruvate kinase/lactate dehydrogenase. The enzymes were immobilized in series, a reagent mixture containing PEP, ATP and NADH was pulsed into the analyte stream, and the decrease of the NADH absorption was determined. One injection cycle was performed within 90 s. Two identical parallel enzyme lines were installed, one of them being in use while the other was calibrated. Automated calibration, control of sample dilution, compensation for enzyme activity loss, the switching between the two enzyme lines and the control of all instruments were performed by an appropriate computer system. The analysis of vinegar samples resulted correct and reliable results. The semi-automated control of continuous vinegar production of 60 h yielded very satisfactory results in the range of 0.5-1.5 M after 40-fold dilution and was more reliable than the reference HPLC method. The extension of the analysis system to higher concentrations ranges still demands an optimization of the dilution method. In total, the enzyme-based FIA for continuous acetic acid determination seems to be a very useful and reliable method.
Acetic acid Spectrophotometry Sensor Immobilized enzyme Indirect Optimization

"A Monosegmented Flow Titration For The Spectrophotometric Determination Of Total Acidity In Vinegar"
Anal. Sci. 1999 Volume 15, Issue 7 Pages 665-668
Ricardo S. Honorato, M&aacute;rio C. U. Ara&uacute;jo, Germano Veras, Elias A. G. Zagatto, Rui A. S. Lapa And Jos&eacute; L. F. C. Lima

Abstract: A monosegmented flow system involving sample and titrant sequential injections and the establishment of a tandem plug between two air bubbles is proposed for automated titrations. The end point is found after successive variations of the sample and titrant volumes, determined by an algorithm based on the one-dimensional optimization method of Fibonacci. The set up includes a multi-port solenoid valve with four inlets and one outlet. The feasibility of the system was demonstrated in the spectrophotometric determination of the total acidity in vinegar with NaOH and phenolphthalein used as the titrant and indicator, respectively. The sample throughput was ~30 h-1 and consumption of the sample and titrant was about 0.7 mL. The results were in agreement with the expected values, with relative errors lower than ±0.4%. After 12 successive analyzes of typical samples with a 47.1 - 53.4 total acidity, expressed as g L-1 acetic acid, the relative standard deviations of the results were estimated within the 1.2 - 2.1% range.
Acidity, total Spectrophotometry Optimization Titrations Air segmentation