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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
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South African Journal of Chemistry

  • Publisher:
  • FAD Code: SAJC
  • CODEN: SAJCDG
  • ISSN: 0379-4350
  • Abbreviation: South Afr. J. Chem.
  • DOI Prefix: NA
  • Language: Afrikaans
  • Comments: Fulltext from 1918 V1

Citations 20

"Simple And Effective Procedure For Immobilization Of Oxidases Onto MnO 2-bulk-modified, Screen-printed Carbon Electrodes"
South Afr. J. Chem. 2004 Volume 57, Issue 1 Pages 1-7
Beyene, Negussie W.; Moderegger, Helmut; Kalcher, Kurt

Abstract: Nafion™ film entrapment of oxidases onto the surface of MnO 2-(5%, m:m) bulk-modified, screen-printed carbon electrodes was studied taking the inexpensive glucose oxidase as a model enzyme. The Nafion™-enzyme film was formed by drop-coating the suspension onto the surface of the electrode. Comparisons were made among biosensors developed by using as-received, neutralized, and diluted (to 1% in methanol, ethanol or phosphate buffer) Nafion™ in a flow injection (FI) mode. The amperometric response to injections of standard glucose solution was the highest for biosensors produced using neutralized Nafion™. The effect of enzyme load per electrode (10-1190 µg) was investigated and 50 µg enzyme in the film per electrode was found to produce very good sensitivity as well as to be economical. Good reproducibility was achieved for three different biosensors (RSD of the means = 5.7%). The operational parameters for the glucose biosensor produced with this immobilization procedure were assessed and figures of merit obtained at the selected parameters. It has been observed that the effect of Nafion™ to repel interfering ions like ascorbate and urate was lacking in this system. A preliminary investigation incorporating a hydrogen peroxide permselective membrane layer prior to enzyme immobilization gave promising result with polyurethane.

"A Stable Glutamate Biosensor Based On MnO2 Bulk-modified Screen-printed Carbon Electrode And NafionÆ Film-immobilized Glutamate Oxidase"
South Afr. J. Chem. 2003 Volume 56, Issue 1 Pages 54-59
Beyene, Negussie W.; Moderegger, Helmut; Kalcher, Kurt

Abstract: An amperometric glutamate biosensor was developed using screen-printed carbon electrodes bulk-modified with MnO2 (5%, m:m) onto which glutamate oxidase was immobilized via Nafion™ film entrapment. The analytical performance of the biosensor was assessed in a flow injection mode and peak heights of the current response were used to evaluate results. Best responses were recorded at an applied potential of 440 mV (vs Ag/AgCl) a flow rate of 0.2 mL min-1, and a pH of 7.75 of the carrier (0.1 mol L -1 phosphate buffer). The calibration curve exhibited linearity in the concentration range 10^-160 mg L-1, with a detection limit (as 33 value) of 1.7 mg L-1, and a relative standard deviation 3.3% (c = 20 mg L-1, n = 10). This biosensor was used for the determination of monosodium glutamate in food seasonings, and the values obtained were similar to those obtained with spectrophotometry. The biosensor exhibited extraordinary stability when left on the FI system at a flow rate of 0.1 mL min-1 at room temperature retaining 50% of the original response towards glutamate even after 65 days. Stored in the working buffer for more than 60 days, the same biosensor showed extended linear range, 20-710 mg L-1. This 'aged' (stored) biosensor was used to determine monosodium glutamate in food seasonings and gave similar result to those obtained with a freshly prepared biosensor.

"On-line Determination Of Hydrochloric Acid In Process Effluent Streams By Potentiometric Sequential Injection Acid-base Titration"
South Afr. J. Chem. 2002 Volume 55, Issue 1 Pages 43-55
Van Staden, J.F.; Mashamba, M.G.; Stefan, R.I.

Abstract: An on-line potentiometric sequential injection acid-base system for the titration of a hydrochloric acid solution with a standard sodium hydroxide solution in process effluent streams is proposed. A solution of 0.1 mol/l sodium chloride is used as carrier. The sample is sandwiched between two titrants in a holding coil, with the volume of the first base being twice to that of the second one and channeled by flow reversal through a reaction coil to the potentiometric sensor. A linear relationship between peak width and logarithm of the hydrochloric acid concentration was obtained in the range 0.025 mol/l - 0.05 mol/l of hydrochloric acid when a solution of 0.001 mol/l sodium hydroxide was used for the titration. Samples from process effluent streams were used to evaluate the feasibility of the method with that of an automated and manual titration. The results showed good agreement between the different methods. The percentage relative standard deviation (RSD %) was found to be less than 0.22. The sample frequency is 30 samples per hour.

"Determination Of Total Iron As Fe(II) In Multivitamins, Haematinics And Natural Waters Using A Sequential Injection (SIA) System"
South Afr. J. Chem. 2000 Volume 53, Issue 3 Pages 191-205
Van Staden, J.F.; Naidoo, E.B.

Abstract: The determination of total iron in pharmaceutical products and natural waters as Fe(II) using a sequential injection system was investigated. A cadmium reductor consisting of cadmium granules was used to reduce Fe (III) to Fe (II). The Fe (II) was then determined (by its reaction with 1,10 Phenanthroline) as a [Fe(phen)(3)(2+)] complex at 515 nm with a UV/Vis spectrophotometer. The linear range of the system is between 1 and 60 mg/l with a detection limit of 0.18 mg/l. The proposed system is suitable for the determination of total iron as Fe(II) in pharmaceutical products and natural waters at a rate of 24 samples/hour with a relative standard deviation of less than 2.5%. Statistical comparison between the proposed sequential injection (SIA) system, certified values and the standard methods (Inductively Coupled Plasma {ICP} and UV/Vis spectrophotometry) revealed that there is no significant difference at the 95% confidence level.
Preconcentration Tiron Speciation Reactor

"Spectrophotometric Determination Of Boron In Water Effluents And Fertilizers By Sequential Injection Analysis"
South Afr. J. Chem. 2000 Volume 53, Issue 2 Pages 77-85
Van Staden, J.F.; Van der Merwe, T.A.

Abstract: A sequential injection system for the on-line monitoring of boron in water effluents and fertilizer process streams is proposed. Azomethine-H, a condensation product of saljcylaldehyde and H acid (8-amino-1-naphtol-3,6-disulphonic acid) is used as the chromogenic reagent. In solution the chromogenic reagent exists as two constituents. When boron is added to the solution. Azomethine H is formed and measured at 420 nm. The proposed system is fully computerised and is able to monitor boron at a rate of 28 samples per hour with a relative standard deviation less than 1.6%. The calibration curve is linear up to 100 mg L-1. The system has a detection limit of 0.62 mg l-1.

"Improvement In The Flow Injection Spectrophotometric Determination Of Zinc With Zincon Through Elevated Temperatures"
South Afr. J. Chem. 2000 Volume 53, Issue 1 Pages 18-22
Van Staden, J.F.; Mulaudzi, L.V.

Abstract: The enhancement of the performance of the zincon method at elevated temperatures is described. The technique exploits the acquired kinetic energy brought about by raising the temperature rapidly and specifically de-masking the cyanide-metal complexes with cyclohexanone. The rate of determination is increased from 80 to 120 samples per hour due the reduction period of the rate-determining step. The reduction of the reaction time eliminates interferences. The method was evaluated for the determination of zinc from soft drinks, beer, energy drinks, fertilizer, and steel wool. The % relative standard deviation (RSD) was found to be less than 0.5 with a percentage recovery of 97%. The results of the proposed FIA system compare favourably with those obtained for a standard ICP procedure.
Dialysis Reactor

"On-site Monitoring Of Chloride In Milk With A Dialyser/UV/Vis Spectrophotometer/flow Injection System"
South Afr. J. Chem. 1999 Volume 52, Issue 4 Pages 145-149
Van Staden, J.F.; Mulaudzi, L.V.

Abstract: This paper describes an on-site flow injection system for the determination of chloride in milk at a rate of 80 samples per hour. Interferences like protein are removed with the incorporation of a dialyser into the manifold of the flow injection system. The system is based on the spectrophotometric measurement of the iron(III) thiocyanate complex at a wavelength of 480 nm. The system is suitable for the monitoring of chloride in milk in the range 500-2500 mg I-1 with an RSD better than 0.5%. The results obtained with the proposed system compare favourably with the standard Volhard titration method.

"Simultaneous Spectrophotometric Determination Of Nitrate And Nitrite In Foodstuffs And Water By Flow Injection Analysis"
South Afr. J. Chem. 1999 Volume 52, Issue 1 Pages 49-54
Van Staden, J.F.; Makhafola, M.

Abstract: A simple method is described for the simultaneous determination of nitrate and nitrite in foodstuffs and water. Cadmium is used to reduce nitrate to nitrite. Nitrite is diazotised in the FIA system with N-(l-naphthyl)ethylenediammonium dichloride to form the highly colored ate-dye, which is measured at 540 nm. The detection limit is 0.085 µL-1) for a sample injection of 400 µL. The sampling rate is about 50 samples per hour and the relative standard deviation is 1.56% and 0.77% for both nitrate and nitrites, respectively. The effect of pH, length of reductor column. and various types of cadmium reductor on the yield of nitrite is investigated. At pH above 8.05 a maximum yield of nitrite is obtained. Cadmium coarse powder and cadmium granules all give practically the same yield. The results of the variables mentioned are discussed thoroughly.

"Simultaneous Determination Of Cadmium(II) And Mercury(II) In Aqueous, Urine And Soil Samples Using Sequential Injection Extraction (SIE)"
South Afr. J. Chem. 1999 Volume 52, Issue 1 Pages 36-43
Taljaard, R.E.; Van Staden, J.F.

Abstract: This paper introduces a flow-based extraction system in which aqueous sample solutions and an organic extractant solution are injected sequentially into an extraction coil. and are mixed and separated due to the differential flow velocities of the aqueous and organic phases, An orange-yellow mercury dithizonate is formed during acidic extraction with dithizone (lambda(max) = 485 nm) and a reddish-orange cadmium dithizonate is formed during alkaline extraction (lambda(max) = 488 nm). In order to determine both analytes in the same sample without prior separation, a double extraction method was used. Two sample zones containing both mercury(ll) and cadmium(ll) ions were sandwiched around a CCl4 zone in which the color reagent dithizone was dissolved. The sequence of zones was as follows: an alkaline zone (2% NaOH solution), a 220 µl aqueous sample zone, an organic (dithizone dissolved in CCl4) zone, another aqueous sample zone (90 µl) followed by an acidic zone (1 mot L-1 H2SO4). Acidic extraction occurred first during the reverse movement of the pump. During this step the aqueous sample was mixed with H2SO4 to ensure that the correct pH was obtained and then extracted into the organic dithizone zone where flow was impeded due to the hydrophobic interactions with the walls of the Teflon coil. Once formed [Hg(HDZ)(2)] is stable in dilute alkaline solutions and therefore did not decompose when the flow was reversed to allow the alkaline extraction to take place in the same way as the acidic extraction. The organic phase containing both analytes was then measured spectrophotometrically at 486 nm. Detection limits of 60 µg L-1 Hg2+ and 50 µg L-1 Cd2+ were calculated with a %RSD of 2.43 and 1.07, respectively.
Dithizone

"Simultaneous Determination Of Certain Selected Trace Elements With An Online Preconcentrating Flow Injection ICP-OES System"
South Afr. J. Chem. 1999 Volume 52, Issue 1 Pages 27-35
Du Plessis, H.; Van Staden, J.F.

Abstract: The detection limits of an ICP instrument were improved by online pre-concentrating samples on a miniature ion exchange column incorporated into the conduits of a flow injection (FI) system. Several operating parameters for both the ICP and the ion exchange column were optimized to maximise the advantages of the pre-concentrating system. These include the pH and loading rate of the sample, the length and diameter of the column and the eluent concentration. The pre-concentrating FIA-ICP system gave simultaneous multi-element detection limits, which were between five and 30 times better than for conventional continuously aspirating systems for the elements barium, calcium, chromium, copper, manganese, iron and lead. Precision was better than 3.5% RSD at the 50 µg L-1 level for Ba, Ca, Cr, Cu, Fe and Mn, and the 250 µg L-1 level for Pb. Analysis of spiked rain water in the µg L-1 level gave nearly 100% recovery. The sampling rate was six samples per hour.

"Online Monitoring Of Calcium In Natural, Borehole And Boiler Feed Water With A Flow Injection System Using A Calcium-selective Membrane Electrode As A Sensor"
South Afr. J. Chem. 1999 Volume 52, Issue 1 Pages 24-26
Van Staden, J.F.; Stefan, R.I.

Abstract: An online automated system for the determination of calcium in natural, borehole and boiler feed water based on the concept of flow injection with a calcium-selective membrane electrode as sensor is described. The system is suitable for the on-site monitoring of calcium at a sampling rate of 60 samples per hour in the linear range 10^-4 - 10^-2 mol L-1 (approximately 4-400 mg l-1) with an RSD better than 0.7%. The detection limit of the system is 2.1 x 10^-6 mol L-1 (about 0.084 mg l-1).
pH

"Spectrophotometric Determination Of Nitrite In Cured Meat With Sequential Injection Analysis"
South Afr. J. Chem. 1998 Volume 51, Issue 2 Pages 109-113
Van Staden, J.F. & Van der Merwe, T.A

Abstract: A sequential injection system for the determination of nitrite in cured meat is proposed. The meat samples are partially dissolved in a 1 mol-1 ammonium chloride solution at pH 9. Nitrite is coupled and diazotized in the SIA system with sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride, respectively, to form a highly colored azo dye which is measured at 540 nm. The sample throughput is 49 samples per h with sample volumes of 250 µL and a relative standard deviation of <1.7%. The results obtained for nitrite in cured meat by the SI system compared well with data obtained by a standard method.
Nitrite Meat Spectrophotometry Sequential injection

"Evaluation Of The Operational Parameters Affecting Dispersion In Sequential Injection Analysis"
South Afr. J. Chem. 1998 Volume 51, Issue 2 Pages 100-108
Van Staden, J.F. & Botha, A.

Abstract: Sequential injection analysis (SIA) is known for its use as an analysis technique, having the advantage of reduced sample and reagent consumption compared with flow injection analysis (FIA). An important aspect that needs critical attention in the optimization of this system is the dispersion, which could have a direct effect on the zone penetration that takes place within the SIA flow conduit. The dispersion in the SIA manifold is influenced by certain operational parameters, and studies were carried out to study the effect these parameters have on dispersion. Because of a lack of information on the effect operational parameters have on the dispersion that takes place within an SIA flow conduit, it was decided to study these parameters in depth to contribute to this knowledge. A study was made on the effect mixing chamber have on dispersion within the SIA manifold. The optimized dimensions of the parameters that were studied are: pump tubing internal diameter (internal diameter), 1.85 mm; pump speed, 18.0 rpm (peristaltic pump); sample and reagent zone volumes, 600.0 and 1200.0 µL; holding coil length, (3.50 m) and internal diameter (1.60 mm); reaction coil length (1.10 m) and internal diameter (1.02 mm); and a 1.0 mL mixing chamber in the holding coil position of the SIA manifold.
Sulfate Industrial Dispersion Sequential injection Dilution Mixing chamber Optimization

"Aspects Of Signal-processing In Flow Injection Systems: Review"
South Afr. J. Chem. 1995 Volume 48, Issue 1-2 Pages 8-14
Van Staden, J.F.

Abstract: Much valuable information is contained in the output signal of a detection system in flow injection analysis. The form of the peak obtained and deviations therefrom are functions of the type of detector and manifold used. The shape and quality of the analytical signal obtained may have a major influence on the performance of a flow injection analyzer.. There are a number of factors to consider in the accumulation and processing of such signals. Among these are noise, signal-to-noise ratio and signal transport. A number of signal-processing techniques for the filtering of noise are described in this review. Multianalyte information from a single sample injection is addressed using a multivariate calibration technique. Response surface mapping has proved to be a useful way of visualizing the effect of multivariable optimization. (64 References)
Impulse response Kalman filter Multivariate calibration Optimization Response surface Review Signal to noise ratio

"Behavior Of Silver Orthophosphate As The Electroactive Sensor Of A Coated, Tubular Solid-state Phosphate-selective Electrode In Flow Injection Analysis"
South Afr. J. Chem. 1993 Volume 46, Issue 1-2 Pages 14-19
Van Staden, Jacobus F.

Abstract: A coated, tubular solid-state phosphate-selective electrode based on silver orthophosphate as electroactive material was prepared and constructed as a small, tubular sensor (volume 15.7 µL) from a silver tube and Tygon tubing. The silver-silver orthophosphate membrane was activated by anodic deposition and conditioned in an orthophosphate medium for at least 14 days. The incorporation of the coated, tubular electrode into the conduits of a continuous-flow system and a flow-injection system is described and its behavior and suitability evaluated. With 600 µL samples injected into the flow injection analysis system, the flow-through electrode responded well in the range 10^-5000 mg L-1 at a sampling rate of about 30 samples h-1 and with a frequency of 60 h-1 possible. Silver, chloride, bromide, iodide, and sulfide ions interfere at a concentration of 1 mg L-1 and high levels of ammonia eventually destroy the electrode response.
Phosphate Industrial Electrode Sensor Apparatus Detector

"Ion Chromatographic Separation Of Chromium(III) And Chromium(VI) And Spectrophotometric Detection Of Chromium(III)-EDTA And Chromium(VI)-DPC Species"
South Afr. J. Chem. 1991 Volume 44, Issue 4 Pages 105-109
De Beer, H.; Coetzee, P.P.

Abstract: A solution (5 ml) containing Cr(III) and Cr(VI) was treated with 7 mL of 0.1 M EDTA and 10 mL of 10 mM Na2CO3 and the resulting solution (pH 5.5) was heated for 3 min on a hotplate, allowed to cool and diluted to 50 mL. A portion (50 l) of the solution was injected into a stream of 10 mM Na2CO3 (2 mL min-1) for ion chromatography in a Dionex 2000i system equipped with AG5 guard and AS5 separator columns. Post-column derivatization was effected by reaction with 2.5 mM diphenylcarbazide (I) in methanol - concentrated H2SO4 - water (2:1:10). The absorbance of the Cr(III) - EDTA and the Cr(VI) - I complexes was measured at 545 nm. The working ranges and detection limits were 0.5 to 150 mg L-1 and 0.04 mg l-1, respectively, for Cr(III) and 0.05 to 10 mg L-1 and 0.04 mg L-1 for Cr(VI). Of the foreign ions investigated, only Ni interfered in the determination of Cr(III) and CrV (1000-fold excess) in that of Cr(VI). The method was applied to a industrial effluent and to samples from a chromate production plant.
Chromium(III) Chromium(VI) HPIC Spectrophotometry Speciation Heated reaction Interferences Post-column derivatization

"Determination Of Sulfate By Flow Injection Analysis Using A Coated-tubular Solid-state Lead Ion-selective Electrode"
South Afr. J. Chem. 1991 Volume 44, Issue 1 Pages 13-16
van Staden, J.F.

Abstract: A flow injection analysis system for the indirect determination of sulfate by direct measurement of Pb with a coated tubular Pb-selective electrode (Fresenius' Z. Anal. Chem., 1989, 333, 226) is described. Samples were injected into a carrier stream (3.9 mL min-1) of 1 M sodium perchlorate in 5% methanol - 1 mM formaldehyde and passed through a reaction coil (105 cm x 0.51 mm). The solution was merged with a reagent stream (1.4 mL min-1) of 4 mM lead perchlorate and 1 M sodium perchlorate in 50% methanol - 1 mM formaldehyde - 1 mM acetic acid - 10 µm-sodium acetate buffer (pH 4 to 5). After the solution was passed through a coil (160 cm x 0.51 mm) the lead was determined by the electrode. Sulfate can be determined from 50 to 10,000 mg L-1 with a coefficient of variation of 1.7%. Interference by other ions is discussed. The method was used for the analysis of natural water with recoveries of 95 to 99%.
Sulfate Environmental Electrode Electrode Buffer Interferences

"Automatic Precipitation In Flow Injection Analysis With Online Dialysis - Indirect Determination Of Sulfate By Measurement Of The Unprecipitated, Excess Barium In The Dialysate Stream Of The Flow System"
South Afr. J. Chem. 1990 Volume 43, Issue 3-4 Pages 78-82
van Staden, J.F.; van Rensburg, A

Abstract: The method is based on a combination of the formation of a continuous solid - liquid interface (precipitation) and a continuous liquid - liquid interface (dialysis). Sulfate from a 30 µL sample is precipitated turbidimetrically with an excess of BaCl2 to form a suspended ppt. of BaSO4. Excess Ba2+ is transported with the carrier stream to the donor channel of the dialyser where it dialyses to the detector channel. The dialysate of Ba reacts with methylthymol blue to form a complex which is measured spectrophotometrically at 608 nm. The pH was kept relatively high with NaOH. The proposed flow injection procedure is suitable for the indirect determination of SO42- at a sampling rate of 60 samples h-1 with a coefficient of variation of 1.4%. The calibration graph was rectilinear in the range 100 to 1000 mg L-1 and the recovery was 98.8 to 100.5%.
Sulfate Turbidimetry Automation Precipitation Dialysis Solid liquid interface pH Calibration Indirect

"Determination Of Cyanide By Flow Injection Analysis Using A Tubular Solid-state Ion-selective Electrode As Detector"
South Afr. J. Chem. 1989 Volume 42, Issue 1 Pages 25-28
Jones, E.A.; Barnes, D.

Abstract: Cyanide was determined by incorporation of a hollow tubular Ag - Ag2S-coated CN--selective electrode (cf., e.g., Van Staden, Anal. Chim. Acta, 1986, 179, 407) into a flow injection system. The system also included Tefzel tubing (0.5 mm i.d.), an Orion Model 90-01 reference electrode, and 0.2 M KNO3 - 20 mM Na2CO3 - ethylenediamine (30 ppm) - 5 mM NaH2BO3 - CN- (5 mg l-1) as carrier stream (1.5 mL min-1). Sixty samples can be analyzed in 1 h. The range of application is 10 to 200 mg L-1 of CN-, and the coefficient of variation was 1% for 100 mg l-1. The method was applied to metallurgical process solution, with negligible interference.
Cyanide Process liquor Electrode Electrode Detector Interferences

"Spectrophotometric Determination, By Flow Injection Analysis, Of Thiocyanate In Metallurgical Process Solutions Containing Free Cyanide And Metal Cyanide Complexes"
South Afr. J. Chem. 1989 Volume 42, Issue 1 Pages 6-8
Jones, E.A.; Hemmings, M.J.

Abstract: Sample (50 µL) was injected into carrier solution comprising 50 g L-1 of Fe(NO3)3 in 10% HNO3 flowing at 1.5 mL min-1. After passage of the stream through a 50-cm reaction coil, the absorbance of the solution was measured at 480 nm. The calibration graph covered the range 10 to 200 mg L-1 of SCN-, and the limit of determination was 1 mg l-1. For 12.5 mg l-1, the coefficient of variation was 0.7%. Sixty samples could be analyzed in 1 h.
Thiocyanate ion Process liquor Spectrophotometry Complexation