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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Signal enhancement

Classification: Feature -> Signal enhancement

Citations 13

"Flow Injection Hydride Generation Atomic Absorption Spectrometric Study Of The Automated On-line Pre-reduction Of Arsenate, Methylarsonate And Dimethylarsinate And High-performance Liquid Chromatographic Separation Of Their L-cysteine Complexes"
Talanta 2000 Volume 51, Issue 6 Pages 1059-1068
Dimiter L. Tsalev, Michael Sperling and Bernhard Welz

Abstract: An automated on-line pre-reduction of arsenate, monomethylarsonate (MMA) and dimethylarsinate (DMA) using flow injection hydride generation atomic absorption spectrometry (FI-HGAAS) is feasible. The kinetics of pre-reduction and complexation depend strongly on the concentration of L-cysteine and on the temperature in the following increasing order: inorganic As(V) < DMA < MMA. Arsenate is pre-reduced/complexed within less than 50 s at 70-100°C compared to 1 h at room temperature, while MMA and DMA require 1.5-2 min at 70-100°C and up to 1-2 h at room temperature. The characteristic masses and concentrations for 100 µl injections are 0.01 ng and 0.1 µg L-1 in integrated absorbance and 0.2 ng and 2 µg L-1 in peak height measurements, and the limits of detection are ~0.5 ng and 5 µg L-1, respectively. In a high-performance liquid chromatography (HPLC)-HGAAS system, the L-cysteine complexes of inorganic As(III), MMA and DMA are best separated within 7 min by HPLC on a strongly acidic cation exchange column such as Spherisorb S SCX 120 x 4 mm (5 µm) with a mobile phase containing 12 mmol L-1 phosphate buffer (KH2PO4/H3PO4)-2,5 mmol L-1 L-cysteine, pH 3.3-3.5. Upon dilution to L-cysteine levels below 10 mmol L-1, which are compatible with HPLC separations, the DMA-cysteine complex is unstable on storage. No baseline separations are possible with anion exchange and reverse phase C-18 HPLC columns. The limits of detection with 50 µl injections in peak area mode are ~0.5 ng and 10 µg L-1, respectively.

"Reduction Of Interferences In The Determination Of Germanium By Hydride Generation And Atomic-emission Spectrometry"
Anal. Chim. Acta 1990 Volume 229, Issue 2 Pages 239-247
Ian D. Brindle and Xiao-Chun Le

Abstract: The effects of L-cysteine (I), S-free amino-acids and other reagents on interference were compared. A continuous-flow batch-type hydride-generation system was used, with Ar as carrier gas. The interference-reducing reagent (0.1 to 0.4 g), the test solution in 0.04 M HNO3 (9.0 ml) and solution of Co(II), Cu(II), and Ni(II) as interfering species (0.5 to 1.0 ml) were placed in the reaction vessel before introduction of 6% NaBH4 solution (1.5 ml). Simultaneous signal enhancement and interference reduction were achieved with I, L-cystine, penicillamine or 3-mercaptopropane-1,2-diol. Glycine, alanine, Na citrate, Na oxalate, thiourea and thiosemicarbazide also reduced interference to some extent. Histidine was superior to I in reducing interference from high levels of Ni, but did not enhance the Ge signal. Mechanisms for interference reduction are proposed.
Germanium Spectrophotometry

"Determination Of L-glutamate By Amperometric Flow Injection Analysis Using Immobilized Glutamate Oxidase: Manifold For Simultaneous Detection Of Component Signal And Blank Signal"
Anal. Chim. Acta 1992 Volume 261, Issue 1-2 Pages 155-159
Kiyoshi Matsumoto*, Koji Sakoda and Yutaka Osajima

Abstract: The system described (with diagrams) allows simultaneous detection of the L-glutamate (I) signal and the blank value. A microtube pump propels the carrier solution (0.1 M phosphate buffer of pH 7) and the sample solution to a 16-position switching valve; the carrier line includes an air damper, and two 180 µL sample loops are linked to the valve for injection. The stream of solution then passes through a glass tube (10 cm x 2 mm i.d.) containing glutamate oxidase immobilized on Amino-Cellulofine by means of glutaraldehyde (method described) or (for blank measurement) an enzyme-free Amino-Cellulofine column to a potentiostat (Anal. Chem., 1988, 60, 147) maintained at +0.65 V vs. Ag - AgCl for amperometry of the H2O2 produced. The blank signal is obtained from a sample that has passed through the blank reactor; the carrier solution is used to set the baseline. Response to L-aspartate and L-glutamine was only 0.48 and 0.25%, respectively, relative to that for I; complete selectivity for I over L-aspartate is attainable at pH 6.0. Sensor response is maintained for 15 days. Peak current is rectilinearly related to I concentration. from 0.01 to 0.3 mM; the coefficient of variation at 0.3 mM was 1.7% (n = 10). The method was applied to a range of foods. L-Glutamate oxidase was immobilized on Amino-Cellulofine and used as an enzyme reactor in a flow injection system. The hydrogen peroxide produced was monitored amperometrically. A new configuration is described for the determination of L-glutamate in food samples for which the matrix provides varying blank values. The peak current was linearly related to L-glutamate concentration. in the range 0.01-.03 mM, and the relative standard deviation was 1.7% in ten successive assays at the 0.3 mM level. The proposed method was used for seasoning anal. and compared well with results obtained with an L-glutamate kit (enzymatic, spectrophotometric) method.
l-Glutamate Food Amperometry

"Signal Enhancement Of Dansyl Amino Acids By Fluorimetric Detection With A Packed Flow Cell In Microcolumn Liquid Chromatography"
Anal. Chim. Acta 1995 Volume 311, Issue 2 Pages 231-236
Toyohide Takeuchi* and Tomoo Miwa

Abstract: Signal enhancement of dansyl amino acids has been achieved by fluorimetric detection with a packed flow cell in microcolumn liquid chromatography. The same materials as in the separation column were packed in a 0.32 mm i.d. cylindrical flow cell, where the analytes were detected in the presence of the stationary phase. The present detection system greatly improved the sensitivity of the late-eluting analytes, compared with common fluorimetric detection with an empty flow cell. Both peak height and peak area of analytes increased with increasing retention time owing to the focusing and environmental effects of the stationary phase. The detection limit of the analyte eluting in ~70 min was improved by a factor of 73 in comparison with that achieved by common fluorimetric detection with an empty flow cell.
Amino acids, dansylated Fluorescence HPLC

"Effect Of High Salt Concentrations On The Determination Of Arsenic And Selenium By Flow Injection Hydride Generation Electrothermal Atomic Absorption Spectrometry"
Analyst 1998 Volume 123, Issue 8 Pages 1697-1701
Robert I. Ellis, Nils G. Sundin, Julian F. Tyson, Susan A. McIntosh, Christopher P. Hanna and Glen Carnrick

Abstract: In the determination of As and Se by flow injection hydride generation ETAAS, the presence of up to 20% NaCl enhanced the signals for 20 µg L-1 As and Se by up to 28%. The enhancement was obtained with a variety of gas-liq. separators. A systematic study of the possible causes of the signal enhancement in the determination of Se was undertaken, from which the effect originated in the processes responsible for the distribution of the H selenide between the solution and gas phases. Processes related to the transport of the analyte from the gas-liq. separator and the trapping of the analyte on the interior of the atomizer were not affected by the presence of dissolved salts. As Na is transported to the atomizer, aqueous aerosol was deposited in the atomizer, although the quantities were irreproducible. The enhancement could be eliminated by increasing the borohydride concentration. However, with the small volume gas-liq. separator, this latter approach was limited because of carry-over of liquid to the atomizer. The effect could be compensated for by adding up to 40% (m/v) of salt to the borohydride reagent.
Arsenic Selenium Spectrophotometry

"Performance Of A Modular Thermospray Interface For Signal Enhancement In Flame Atomic Absorption Spectrometry Coupled Online To Flow Injection [analysis] Or Liquid Chromatography"
J. Anal. At. Spectrom. 1993 Volume 8, Issue 4 Pages 659-664
Erik H. Larsen and Jean-Simon Blais

Abstract: A simple and inexpensive thermospray interface is described that was connected to a flame AAS system without modification of the nebulizer and burner assembly. Details are provided of its construction and performance characteristics. The interface provided improved signal-noise and signal enhancement in a flow injection - AAS system with rectilinear calibration and detection limits of 1.9 ng of Cd, 8.5 ng of Cu and 27 ng of Pb. The use of the interface to couple HPLC to AAS was demonstrated for the determination of metallothioneins in biological samples.
Cadmium Copper Lead Biological Spectrophotometry

"Sensitive Determination Of Selenium By Inductively Coupled Plasma Mass Spectrometry With Flow Injection And Hydride Generation In The Presence Of Organic Solvents"
J. Anal. At. Spectrom. 1995 Volume 10, Issue 10 Pages 865-870
Riansares Mu&ntilde;oz Olivas, C. R. Qu&eacute;tel and O. F. X. Donard

Abstract: Two sample introduction methods, viz., pneumatic nebulization and hydride generation via a flow injection system were used to study the optimum conditions for Se determination. The effect of organic solvents in polyatomic interferences (40Ar, 37Cl, 40Ar, 38Ar and 40Ar2H2) suppression and signal enhancement were investigated. The organic solvents studied were: methanol, ethanol, propanol, acetone and acetonitrile. A SCIEX Perkin Elmer 5000 spectrometer was used. The pneumatic nebulization flow rate ranged from 0.95-1.05 L/min and the Ar flow rate for hydride generation was similar (1.05-1.1 L/min); other operating conditions are tabulated. Under optimum conditions (NaBH4 = 0.2%, pH = 1, methanol load = 6%) for flow injection hydride-generation ICP-MS a detection limit of 1 pg of Se was obtained using a 200 µL sample. The average RSD was 2%. The method was applied to estuarine water and Se levels ranged from 5 to 70-80 ng/L. Validation was via an EC certification campaign.
Selenium Estuarine Mass spectrometry

"Nonaqueous Solvents As Carrier Or Sample Solvent In Flow Injection Analysis/atomic Absorption Spectrometry"
Anal. Chem. 1984 Volume 56, Issue 3 Pages 439-442
Abdulrahman S. Attiyat and Gary D. Christian

Abstract: The use of methanol, ethanol, acetone and isobutyl methyl ketone(I) as carriers in flow injection analysis with AAS detection was studied with Cu as test analyte, and with water, aqueous acetone or aqueous ethanol as sample solvent. An eightfold enhancement of the signal (compared with that for aqueous systems) was achieved for the optimum sample - carrier solvent combination; acetone was the best sample solvent and I the best carrier. The effects of the length of the dispersion coil and of sample volume on the AAS signal for each of the carriers are considered.
Copper Spectrophotometry

"Behavior Of Liposomes In Flow Injection Systems"
Anal. Chem. 1988 Volume 60, Issue 8 Pages 792-797
Laurie Locascio-Brown, Anne L. Plant, and Richard A. Durst

Abstract: Liposomes, containing entrapped water-soluble molecules, were tested in continuous-flow systems as a means of signal enhancement of the entrapped analyte. Liposomes containing carboxyfluorescein were detected fluorimetrically at 515 nm (excitation at 450 nm). Peak profiles were obtained for the system with use of a 187 µL sample loop, a packed bead column, a knitted delay tube and a straight open-bore tube; the flow rate was 0.5 mL min-1. The effect of these parameters on the peak profiles was discussed.
6-Carboxyfluorescein Fluorescence

"An ISFET-FIA System For High-precision PH Recording"
Sens. Actuat. B 1993 Volume 15, Issue 1-3 Pages 68-74
P. Woias, S. Koch and E. M&uuml;ller, D. Barrow and J. Cefai, G. Curtis and H. Hughes

Abstract: A description is given of a differential ISFET/REFET (reference FET) pH measurement system for use in continuous-flow analysis or FIA. The system involves differential sensing between two ISFET with identical gate insulator compositions; this permits effective suppression of common mode disturbances, including drift, without requiring the use of a glass reference electrode. The sensor was tested in an isolated rat liver perfusion system (Powell et al., Drug Metab. Drug Interact., 1989, 7, 53). Continuous inline measurements were also made of the pH of bile from anaesthetized rats. Resolution in both instances was typically 0.01 pH and detection of rapid changes in pH was possible. A stable and accurate readout could be obtained at the low flow rates involved.
pH Electrode Field effect transistor

"Enhanced Luminescent Response Of A Fibre-optic Sensor For H2O2 By A High-salt-concentration Medium"
Sens. Actuat. B 1997 Volume 39, Issue 1-3 Pages 189-194
L. J. Bluma,* and A. B. Collaudina

Abstract: A H2O2 biosensor, based on the luminol-peroxidase system, exhibited an enhanced luminescent response in the presence of high concentrations of KCl or NaCl. The biosensor was fabricated by immobilizing horseradish peroxidase onto a polyamide membrane attached to an optical fiber. The biosensor was mounted in a black PVC detection cell (130 µL) and incorporated into a single channel FIA system. The FIA system was operated with a carrier stream (0.95 ml/min) of 0.1 M Tris-HCl buffer at pH 8.5 containing 55 µM-luminol and NaCl or KCl. The enhancement of the response was dependent on the H2O2 concentration and was 1-8 fold in the presence of 3 M KCl and 3-8 fold in the presence of 3 M NaCl for 6.25-25 nmol injected H2O2. The RSD (n = 40) for 250 pmol H2O2 were 3.2 or 2.7% in the presence of 3 M KCl or NaCl, respectively. The biosensor retained its full activity after 2 days of intensive use and 83% of its initial activity after 4 days of use. (21 References)
Hydrogen peroxide Sensor Chemiluminescence

"Flow Injection Analysis Determination Of Potassium Using Flame Photometric Method Of Detection"
Can. J. Anal. Sci. Spectrosc. 1991 Volume 36, Issue 2 Pages 70-74
Esmadi, F.T.;Kharoaf, M.A.

Abstract: Water and nine organic solvents were studied both as sample solvents and as liquid carrier streams. The optimum solvent - carrier combination was found to be methanol - pentan-1-ol, respectively, which gave a sixfold signal enhancement relative to aqueous solution and a detection limit of 2 ppb of K.
Potassium Spectrophotometry

"Study Of Sample Solvent/carrier Combination For Flow Injection Analysis Atomic Absorption Spectrometry"
J. Flow Injection Anal. 1987 Volume 4, Issue 1 Pages 26-35
Abdulrahman S. Attiyat

Abstract: Enhancement factors of absorption signals for Cu at 324.7 nm with respect to the use of H20 as both sample solvent and carrier are tabulated for 169 solvent - carrier combinations. The use of pentan-3-one as solvent and methanol as carrier gave nearly a tenfold signal enhancement, but it was necessary to optimize the flow rate for each combination.
Copper Spectrophotometry