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
Email: schalk@unf.edu
Website: @unf

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John G. Dorsey

Abbrev:
Dorsey, J.G.
Other Names:
Address:
Department of Chemistry, Florida State University, Tallahassee, FL 32306-4390, USA
Phone:
+1-850-644-4496
Fax:
+1-850-645-5644

Citations 17

"Investigation Of Carbon Dioxide-modified Supercritical And Near-supercritical Carrier Streams For Flow Injection Systems"
Talanta 1993 Volume 40, Issue 12 Pages 1951-1959
Robert E. Malick and John G. Dorsey*, T. L. Chester and D. P. Innis,

Abstract: Mixtures of liquid CO2 and 10 mM methanolic p-dimethylaminobenzaldehyde were prepared and transferred to the cylinder of a syringe pump. The pump outlet was connected via a 60 nl injection loop to a manifold tube (3 m x 75 µm i.d.) of polyimide-coated fused silica with a detection window. The tube was mounted in a GC oven. The detector was of the type used for capillary electrophoresis and was set at 464 nm. It was followed by a flow restrictor to control pressure and density of the carrier stream. Measurements were made both with a non-reacting solute, C. I. Mordant Red 7, and with the reactant, barbituric acid. Peak height and peak variance were optimized for both solutes (the variance decreased continuously with increasing CO2 in the carrier). The best conditions were 27% CO2, 100°C and 100 atmospheres. Under these conditions, the calibration graphs were linear for 10.7-187 ng for the dye and 0.77-77 ng for the barbituric acid. These ranges were not very different from those without CO2 in the carrier, but, because of the decreased variance when CO2 was present, the detection limits were decreased by 25% to 257 and 29 pg, respectively.
Carbon dioxide Spectrophotometry Supercritical fluid

"Reduction Of Injection Variance In Flow Injection Analysis"
Talanta 1992 Volume 39, Issue 1 Pages 35-44
Beverly F. Johnson, Robert E. Malick and John G. Dorsey*,

Abstract: The use of packed sample loops to minimize band-broadening in flow injection analysis was studied. For test analytes detected directly or after reaction with a reagent, lower dispersion and improved detection limits were achieved with packed or distorted sample loops compared with those achieved with empty sample loops. Results are presented for ethyl methyl ketone and pyridoxal. In order to achieve max. sensitivity in flow injection anal., sample dispersion must be kept to a min. This dispersion process, however, is not well understood. Studies of the dispersion process have concentrated on dispersion within the flow manifold while dispersion due to the injection process has been largely ignored. Here sample injection loops packed with inert glass beads and a Serpentine II (distorted) empty loop were constructed and compared to traditional empty sample loops. Digitization of the response curves and subsequent calculation of the statistical moments were used to compare the contribution of each sample loop type to the total system dispersion. Both packed and Serpentine II sample loops were shown to decrease dispersion and increase throughput in flow injection systems. Plots of peak variance vs. injection volume show variance increasing 1.67 times faster with traditional open sample loops compared to packed loops. When combined with other peak width minimization techniques, this method should further lower concentration. limits of detection.
Pyridoxal Ethylmethylketone Injector Band broadening Dispersion Glass beads Mixing coil Peak width Theory

"Gradient Elution Techniques For Capillary Electrochromatography"
J. Chromatogr. A 2000 Volume 887, Issue 1-2 Pages 115-124
Catherine A. Rimmer, Stephanie M. Piraino and John G. Dorsey

Abstract: Capillary electrochromatography (CEC) is a rapidly maturing technique, but still in need of further instrumental development and in need of unique applications that are not possible by traditional pressure-driven LC. We review the development of gradient elution schemes for CEC, beginning with pH gradients initially developed for capillary electrophoresis. Step gradients are the most easily instrumentally implemented, but provide less flexibility in separation than continuous gradients. Pressure-assisted CEC is easily adapted to gradient elution schemes, but does not offer the advantages of very high column efficiency provided by totally electro-driven mobile phases. The development of flow injection interfaces allows a true solvent gradient to be generated by Ir-LC pumps, with the mobile phase drawn into the separation capillary by pure electroosmotic flow. While requiring both a CEC instrument and a traditional pump or pumps capable of generating the gradient, this method offers advantages of greatly reduced column handling, prolonging column lifetimes, and allows simple autosampling. We also discuss voltage gradients, which provide a mobile phase velocity gradient.
Interface pH

"Gradient Elution Electrochromatography With A Flow Injection Analysis Interface"
J. Chromatogr. A 1998 Volume 828, Issue 1-2 Pages 105-112
Ashley S. Lister, Catherine A. Rimmer and John G. Dorsey*

Abstract: A flow injection anal.-capillary electrochromatography interface was used for gradient elution capillary electrochromatography giving purely electroosmotic flow through the anal. column. Solvent gradients were generated with a micro-LC system connected to the interface. Injections were carried out online using an inert rotary LC valve controlled by an elec. actuator. Gradient shape was measured from acetonitrile (5% acetone)-water (50:50, v/v) to (100:0) in open tubular experiments When compared to conventional instrumentation, peak tailing and peak width increased slightly using the interface. A test mixture of nine solutes was evaluated in isocratic and gradient elution modes. Using the interface, a gradient of MeCN-water (60:40) to (90:10) provided baseline separation of all nine solutes in under 18 min with good band spacing. Reproducibility of retention times in eight replicate injections is better than 2% relative standard deviation for all solutes. This interface also allows use of autoinjectors and dramatically lessens movement of the packed column, improving column lifetime.
ECC Interface Electroosmotic flow

"Theoretical Study Of Critical Micelle Concentration Determination By Flow Injection Analysis"
J. Colloid Interface Sci. 1988 Volume 122, Issue 2 Pages 514-520
Alain Berthod, Stephen H. Brooks and John G. Dorsey

Abstract: Most critical micelle concentration (CMC) determinations are performed experimentally by monitoring the change of a physicochemical property of the solution with increasing surfactant concentration. A rapid and efficient method for determining surfactant CMC is to use flow injection analysis. A theoretical model which explains conductimetric results and which allows optimization of experimental parameters and extension of the method to nonionic surfactants is proposed. The spectrophotometric detection, monitoring the spectral changes of a micelle-solubilized dye, is envisaged. A simple model, taking into account the global kinetics of the processes, is exposed, and, to illustrate the equations proposed and to discuss the feasibility of the method, some theoretical curves are presented.
Critical micelle concentration Surfactants, non ionic Spectrophotometry Theory Micelle Optimization

"Enhanced Stability Of Electrochemical Detection With Surfactant Containing Mobile Phases In Liquid Chromatography And Flow Injection Analysis"
Anal. Lett. 1990 Volume 23, Issue 12 Pages 2327-2337
Clos, J.F.;Dorsey, J.G.

Abstract: The use of acetone containing mobile phases to prevent or reduce effects of adsorptive fouling of glassy carbon electrodes is reported. For the oxidative reaction studied, anionic surfactants have little effect on the fouling problem. Cationic surfactants however, have the desired effect. Two cationic surfactants, hexadecyltrimethylammonium chloride and n-decylamine were studied with solutes, p-nitrophenol, phenylenediamine and chlorpromazine. With the surfactants present in the mobile phase there was no loss of electrochemical response for up to 55 sequential injections. Adsorption of the electroactive species prior to the electron-transfer process is shown to be a significant cause of poor chromatographic efficiency for some solutes.
Surfactant

"Comparison Of Aqueous, Micellar And Microemulsion Carriers In Flow Injection Analysis. The Base Hydrolysis Of Acetylsalicylic Acid"
Anal. Lett. 1988 Volume 21, Issue 4 Pages 583-598
Stephen H. Brooks, Richard N. Williams and John G. Dorsey

Abstract: The potential applicability of surfactant solutions as carrier streams in flow injection analysis is examined. The reaction rates determined for the base catalyzed hydrolysis of acetylsalicylic acid in aqueous, micellar and microemulsion solutions show a rate enhancement of 40% for the static microemulsion system when compared to the aqueous solution. However, when the identical microemulsion solution is employed as a carrier stream in flow injection analysis with ultraviolet detection, this enhancement in rate is not observed. To our knowledge, all previous work employing microemulsions in FIA has been concerned only with detection enhancement, here we present direct comparisons between aqueous and microemulsion carriers concerning rates of reaction, peak dispersion and analytical figures of merit. The loss in relative sensitivity can be traced to the increased dispersion in the microemulsion system (D = 14.36) when compared to the aqueous carrier (D = 12.52). Additionally, an increased skewness was observed in the peaks obtained with a microemulsion carrier, yielding further information about the physical dispersion process occuring in the sample plug.
Acetylsalicylic acid Aspirin Spectrophotometry Emulsion Micelle

"Liquid Chromatography: Theory And Methodology"
Anal. Chem. 1994 Volume 66, Issue 12 Pages 500R-546R
John G. Dorsey, William T. Cooper, John F. Wheeler, Howard G. Barth, and Joe P. Foley

Abstract: A fundamental review is presented of developments in the chemistry of the separation process in LC, reported between December 1991 and December 1993. Topics discussed include: theory and optimization; data analysis; normal-phase and reversed-phase LC; biopolymer separations; affinity chromatography; ion chromatography; secondary equilibria; geometric and optical isomers; multi-dimensional chromatography and column switching; preparative LC; pre- and post-column derivatization; microcolumn and open tubular LC; trace analysis; and physiochemical measurements. (1107 references).
LC Review Post-column derivatization Optical isomers Optimization

"Liquid Chromatography: Theory And Methodology"
Anal. Chem. 1990 Volume 62, Issue 12 Pages 324R-356R
John G. Dorsey, Joe P. Foley, William T. Cooper, Robert A. Barford, and Howard G. Barth

Abstract: A review is presented, with 889 references, on developments in LC, e.g., size-exclusion, affinity and ion chromatography. Chemical equilibria, pre- and post-column derivatization and applications to separation of isomers and trace analysis are discussed.
LC Post-column derivatization Review Pre-column derivatization

"Solute Focusing In Flow Injection Analysis: Limits Of Detection And Linear Dynamic Range"
Anal. Chem. 1990 Volume 62, Issue 14 Pages 1392-1397
Beverly F. Johnson and John G. Dorsey

Abstract: On-line solute focusing traditionally utilizes a two-injection valve system In which the analyte is injected and concentrated on a suitable column and is subsequently eluted by the injection of a concentrated plug of a suitable elution solvent. Here a single injection valve solute focusing system was investigated. The solutes were injected In a chromatographically weaker solvent than the carrier stream in order to retain the solute at the head of the column until the carrier stream causes it to elute. This process causes a reduction in the solute bandwidth or "solute focusing". The use of a bonded- phase silica column as a solute focusing device for hydrophobic solutes improves the analysis over traditional flow injection analysis (FIA) in several ways. Solute focusing gives comparable or improved concentration limits of detection (LODs) relative to conventional FIA and gives absolute LODs independent of injection volume. A linear relationship is observed when one standard solution is injected in increasing volumes with the solute focusing method. This allows the use of only one standard solution for the construction of a calibration plot. Finally, when an on-line reaction is employed, no peak splitting at large injection volumes is observed with the solute focusing method.
Detection limit Linear dynamic range Solute focusing

"Dispersion Coefficient And Moment Analysis Of Flow Injection Analysis Peaks"
Anal. Chem. 1988 Volume 60, Issue 24 Pages 2737-2744
Stephen H. Brooks, Daniel V. Leff, Maria A. Hernandez Torres, and John G. Dorsey

Abstract: The dispersion coefficient (D) is the most popular peak descriptor in flow injection analysis (FIA). Yet this concept of dispersion yields no direct information describing peak shape and no information in the time domain. Using an exponentially modified Gaussian peak shape model and previously derived equations, we examine the second moment (variance) of single-line flow injection peaks and use this as a fundamental descriptor of the FIA response curves. Unlike the dispersion coefficient, the second moment is shown to obey a linear relationship with respect to flow rate and to yield valuable information in the presence of a chemical reaction. Reporting descriptors of an FIA response curve as a variance offers several advantages over the classical dispersion coefficient: peak width (in units of time or volume) is immediately obtainable from the variance, yielding a more direct measure of sample throughput; various FIA manifolds can be readily compared from their variance values, and the individual contributions to the total peak variance (including the contribution of the chemical reaction to the total variance) can be easily obtained through the additivity of variances.
Diffusion coefficients Peak analysis Theory

"Dispersion Phenomena In Flow Injection Systems"
Anal. Chim. Acta 1992 Volume 267, Issue 1 Pages 1-24
R. DeLon Hull, Robert E. Malick and John G. Dorsey*

Abstract: This review discusses the various models reported to describe sample dispersion in both non-reactive and reactive systems. Predictive models (which describe only the dispersion, e.g., in a flow injection manifold) and descriptive models (which may also describe dispersion in the injection, detection and connecting parts of the assembly) are reviewed. (112 references). A review 112 references. Reproducible dispersion is the basis for anal. by flow injection (FI) methods and is also used in several other sample handling and anal. systems (e.g., liquid chromatography connecting tubing, injectors, detectors, and post-column reactors). However, a uniformly acceptable understanding or description of dispersion is currently not available. Theoretical treatments (mathematical models) of dispersion were developed for both nonreactive (sample does not react with carrier) and kinetic (sample and carrier react) systems. Historically, chemical engineering hydraulic models were used as predictive estimators for FI response curves. These predictive models typically describe only the dispersion in the FI manifold and do not incorporate the influence of the injection, detection, or connecting components of the system. Recently, descriptive models which use deconvolution of the response curve to describe the dispersion produced by the anal. system were reported. This review details the various approaches that were used to describe dispersion in FI systems and includes both predictive and descriptive models.
Review Dispersion Modeling Deconvolution

"Solute Focusing In Flow Injection Systems: Effect Of Solute Capacity Factor And Position Of Solute-focusing Column"
Anal. Chim. Acta 1991 Volume 255, Issue 1 Pages 127-133
Beverly F. Johnson, James Bramlage and John G. Dorsey*

Abstract: Investigations of the use of reversed-phase chromatographic materials as a solute-focusing sorbent for non-ionic solutes are presented. By injecting the solute in a chromatographically weaker solvent than the carrier stream, real-time solute focusing occurs, and no change in carrier stream or second injection is required. The effect of the chromatographic capacity factor and the location of the focusing device in the flow manifold are both important considerations for attaining the maximum enhancement in sensitivity and detection limits.
Chromatography Capacity factor Solute focusing Sensitivity

"Moment Analysis For Evaluation Of Flow Injection Manifolds"
Anal. Chim. Acta 1990 Volume 229, Issue 1 Pages 35-46
Stephen H. Brooks, John G. Dorsey

Abstract: The application of the exponentially modified Gaussian peak-shape model was studied and statistical moment analysis was applied to obtain information, additional to that obtainable from peak height measurements, for evaluation of manifold performance in flow injection analysis. Special reference was made to single-bead string reactor and Serpentine II manifolds.
Manifold comparison

"Flow Injection System For Determination Of Critical Micelle Concentrations Of Ionic And Nonionic Surfactants"
Anal. Chim. Acta 1988 Volume 209, Issue 1 Pages 111-121
Stephen H. Brooks, Alain Berthod, Barbara A. Kirsch and John G. Dorsey

Abstract: A practical technique is presented for the rapid, accurate determination of the critical micelle concentrations (CMCs) of ionic and nonionic surfactants. The precision, speed and instrumental simplicity of a flow-injection system are combined with a gradient chamber and flow-through conductance and absorbance detection to produce a system capable of determining the CMC of surfactant solutions in less than 30 min. The exponential response gradients from the resulting system are monitored by a chart recorder and simple manual calculations yield the CMC. The validity of the technique is verified by determination of the CMC values for both ionic (cetyltrimethylammonium bromide and chloride and sodium dodecyl sulfate) and nonionic (Brij-35, Brij-56, Brij-99, Triton X-100) surfactants. The proposed technique does not require the extensive solution preparation, repetitive measurements, complex instrumentation and data manipulation typical of other methods for determining CMCs.
Critical micelle concentration Surfactants, anionic Surfactants, cationic Surfactants, non ionic Conductometry Gradient technique Micelle

"Micellar Catalyzed Reactions For Flow Injection Systems. Determination Of Pyridoxal"
Anal. Chim. Acta 1987 Volume 201, Issue 1 Pages 67-76
Maria A. Hernández Torres, Morteza G. Khaledi and John G. Dorsey

Abstract: Aqueous micelle carrier streams gave higher sensitivities and lower limits of detection than did aqueous streams alone in the determination of pyridoxal(I) by oxidation with CN-. With 0.09 M hexadecyltrimethylammonium bromide as surfactant, the optimum response was achieved at 49°C in 0.6 M phosphate buffer (pH 6.74) at a flow rate of 1.3 mL min-1. Detection was at 355 nm and by fluorescence at 435 nm (excitation at 355 nm), the rectilinear ranges being 77 to 2000 and 0.17 to 1100 ng of I, respectively, with corresponding coefficient of variation (n = 11) of 1.76 and 3.25% for 25.5 mg L-1 of I.
Pyridoxal Fluorescence Catalysis Heated reaction Micelle Surfactant

"Micellar Catalysis In Flow Injection Systems: The Nitrosation Reaction"
Analyst 1992 Volume 117, Issue 12 Pages 1833-1837
Beverly F. Johnson, Robert E. Malick, Ben Ghearing and John G. Dorsey

Abstract: An aqueous micellar carrier stream containing 20 mM hexadecyltrimethylammonium bromide (I) was used in the flow injection determination of NO2- by reaction with 5.7 mM NN-diethylaniline in 0.25 µ-phosphate buffer (pH 1.5) and monitoring the 4-nitroso-product at 470 nm. The reaction is accelerated by I, providing better sensitivity and lower detection limits: 0.257 mA ng-1 and 0.16 ng, respectively, compared with 0.117 mA ng-1 and 0.36 ng for an aqueous carrier. It also makes possible use of shorter flow manifolds with less dispersion and greater sample throughput. The use of aqueous micellar carrier streams in flow injection analysis is shown to catalyze online reactions and thereby improve the sensitivity relative to non-micellar systems. The effect of several different micellar systems on the nitrosation reaction of N,N-diethylaniline in acidic solution for the determination of nitrite was investigated. The mechanism of the micellar enhancement is discussed and the sensitivities of the method in both aqueous and micellar media are compared. The presence of the cationic surfactant, cetyltrimethylammonium bromide, is shown to improve the sensitivity of the anal. The effect of the micellar solution on the dispersion characteristics of the system was also studied. The greater viscosity of the micellar phase increases dispersion for non-reacting systems, but when monitoring a reaction product the increased reaction rate can counteract this and the micellar carrier can show less over-all dispersion than the aqueous carrier.
Nitrite Spectrophotometry Micelle Dispersion Catalysis Viscosity