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: Agricultural -> grain -> wheat

Citations 7

"Multimycotoxin Detection And Cleanup Method For Aflatoxins, Ochratoxin And Zearalenone In Animal Feed Ingredients Using High Performance Liquid Chromatography And Gel-permeation Chromatography"
J. Chromatogr. A 1993 Volume 629, Issue 2 Pages 229-235
Catherine Dunne, Mary Meancy and Malcolm Smyth, Louis G. M. Th. Tuinstra

Abstract: A finely ground sample (25 g) of animal feed was shaken for 30 min with Celite, 1 M HCl and CH2Cl2 and the mixture was filtered. The filtrate was evaporated to near dryness and the residue was reconstituted in CH2Cl2 - ethyl acetate containing formic acid. A portion of the filtered extract was then cleaned up by gel-permeation chromatography on a glass column (6 cm x 6 mm) packed with Bio-Beads SX-3 gel. Elution was effected at 0.3 mL min-1 with CH2Cl2 - ethyl acetate - formic acid (499:499:2), and the eluate fraction collected between 25 and 45 min was extracted by shaking with water. The lower organic layer was dried by passage through anhydrous Na2SO4 and evaporated to near dryness. The residue was sonicated with aqueous 15% acetone and analyzed by HPLC on a column of Chromsphere RP-C18, with gradient elution with water - methanol - acetonitrile (13:7:4) containing 1 mM HNO3 and 1 mM KBr, and 0.01 M H3PO4 - acetonitrile (1:1) (program given). Post-column derivatization was performed with Br produced electrochemically from KBr in the mobile phase, followed by fluorimetric detection. Aflatoxins B1, B2, G1 and G2, ochratoxin A and zearalenone (I) were determined in animal feed including maize, palm and wheat with recoveries of >81% and limits of detection of 0.6 ng for I and 0.05 ng for the other analytes.
Mycotoxins Aflatoxin B1 Aflatoxin B2 Aflatoxin G1 Aflatoxin G2 Ochratoxin A Zearalenone HPLC Fluorescence Post-column derivatization Electrochemical reagent generation

"Trace Analysis Of Organothiophosphate Agricultural Chemicals By High Performance Liquid Chromatography-photolysis-electrochemical Detection"
J. Agric. Food Chem. 1984 Volume 32, Issue 3 Pages 622-628
Xiang Dong Ding and Ira S. Krull

Abstract: Organic thiophosphate agricultural chemicals, malathion, parathion and others, can be analyzed by the newer method of high performance liquid chromatography (HPLC) with online photolysis (hv), followed by electrochemical detection (EC) using single- or dual-electrode approaches for the species generated. This approach, HPLC-hv-EC, was applied to ~20 thiophosphates, most of which were widely used agriculturally and for which trace residue levels were routinely monitored. Dual-electrode response ratios were determined for all analytes, along with minimum detection limits (MDL) in many cases. These approaches were also used for the quality control evaluation of commercial formulations by flow injection analysis (FIA) with hv-EC and no HPLC separations. Wheat middling extracts were analyzed by the commonly used gas chromatography (GC) flame photometric detection (FPD) method of residue analysis, and by HPLC-hv-EC. These comparative studies indicate that the newer method was reproducible, accurate, precise and reliable. Standard additions were applied to wheat middling extracts, and the quantitative results were compared with the external standard method.
Malathion Parathion Electrochemical analysis UV reactor Photochemistry Standard method Method comparison Standard additions calibration

"Pulsed-amperometric Detection Of Amino-acids Separated By Anion-exchange Chromatography"
J. Liq. Chromatogr. Relat. Technol. 1992 Volume 15, Issue 3 Pages 423-439
D. A. Martensa; W. T. Frankenberger Jr.

Abstract: Protein amino-acids separated by anion-exchange HPLC on a column (25 cm x 4 mm) of Dionex AminoPac PA1, with gradient elution (0.8 mL min-1), were determined by triple-pulsed amperometric detection (PAD) at a Au working electrode. The pulse system was 0.15 V for 300 ms, 0.85 V for 120 ms and -0.60 V for 60 ms with settings of 1-s response time and output range 1 µA. A complex gradient mobile phase system (details given) was employed which involved use of NaOH - sodium borate - Na acetate and H3BO3 in a 70-min cycle. Detection limits were 0.01 to 1.2 µM, lower than those obtained by post-column derivatization with ninhydrin and 570 nm detection. The method was applied in the determination of amino-acids in roots of and exudates from two wheat varieties; exudates were extracted with 20% ethanol and roots were hydrolyzed with 4 M methanesulfonic acid at 120°C.
Amino Acids HPIC Amperometry Sample preparation Spectrophotometry Post-column derivatization

"Flow Injection Catalytic Spectrophotometric Determination Of Trace Manganese By Use Of The Reaction System Nitrilotriacetic Acid-manganese(II)-fuchsine-potassium Periodate"
Lihua Jianyan, Huaxue Fence 1994 Volume 30, Issue 2 Pages 86-88
Zi, Y.Q.;Chen, L.G.;Zeng, Q.G.

Abstract: Mn(II) solution (0.1 ml) was injected into the flow injection analyzer. to mix with a stream of 0.12 mM basic fuschine before further mixing and reaction with streams of 0.2 M acetic acid/0.2 M sodium acetate buffer of pH 4.5, 3 mM nitrilotriacetic acid and 15 µM-KIO4 (all streams at 2.52 ml/min) in a 130 cm reaction tube in a constant-temp. bath of 75°C, cooling in a 40 cm tube with running water as coolant and measurement of the decreased absorbance at 540 nm. The response was linear for up to 0.35 µg/ml, and the detection limit was 0.3 ng/ml. There was no interference in the determination of 0.1 µg/ml of Mn. The sampling frequency was 24 per h. The method was applied to environmental water, soil and cereals, including wheat and beans, with RSD of 1.3%.
Manganese Spectrophotometry Catalysis Heated reaction Interferences

"FAAS Determination Of Calcium And Magnesium In Gelatin Using The FIA Online Automatic Dilution Technique"
Lihua Jianyan, Huaxue Fence 1996 Volume 32, Issue 2 Pages 82-91
Zhang Min, Chen Shuyu, Lin Shuqin and Cheng Lin

Abstract: Sample (1.2 g) was soaked in 15 mL water for 15 min and digested with 1 mL concentrated HCl, 1 mL concentrated HNO3 and 4 mL H2O2. The digest was diluted with to 25 mL with water for FIA with flame AAS detection of Ca and Mg. Test solution was injected and carried to two sampling loops with a stream of water for alternating feeding, primary and secondary injection volumes being 21 and 70 µL, respectively. The solution was allowed to mix with a stream of 0.3% La solution prior to splitting into two streams by passing through two dilution tubes of 50 and 150 cm in length, respectively, with dilution of 87 to 233-fold, and detection. The peak B of the sets of signals was employed for measurement of Ca whereas the trough E for Mg. Determination was at µg/g level. RSD were 1.3-2.1%. The method was applied to the analysis of wheat, shrimp, pig liver and shrub leaves. Interference from phosphate was overcome. Sampling frequency was 96 runs/h.
Calcium Magnesium Sample preparation Spectrophotometry Interferences Dual injector Sample splitting

"The Rapid Diagnosis Of Nutritional States Of Crops. 1. The Rapid Procedure For The Analysis Of Inorganic Nutrients Of Plants By Combining H2SO4 - H2O2 Digestion With Flow Analysis And Atomic Absorption"
Miyagiken Nogyo Senta Kenkyu Hokoku 1987 Volume 55, Issue 1 Pages 1-12
Saito, K.;Hasegawa, E.;Sasaki, J.

Abstract: A rapid and labor-saving method was established for determining N, P, K, Ca, and Mg in crop plants by H2SO4-H2O2 digestion, flow anal., and atomic absorption. Si in rice was determined also. For determination of N and P, the digested samples were diluted with water and were subjected to flow anal. SiO2 ppt. in digests was dissolved in diluted aqueous HF and analyzed with a flow-analyzer. For Ca, Mg, and K determination, the digested samples were diluted with water containing 1500 ppm La and were subjected to atomic absorption spectrophotometry in an air-acetylene flame under atomic absorption and flame emission mode, respectively. Contents of these elements in rice, wheat, and soybean plants were determined by this and conventional methods, and the data agreed excellently. (SFS)
Nitrogen Phosphorus Potassium Calcium Magnesium Silicon Sample preparation Spectrophotometry Method comparison

"A Flow Injection System For The Determination Of Starch In Starch From Different Origins With Immobilized α-amylase And Amyloglucosidase Reactors"
Starch 1993 Volume 45, Issue 8 Pages 264-270
Jenny Emnéus, Gunilla Nilsson, Lo Gorton

Abstract: Starch (1.2-4 g) was dissolved in 4 mL of 0.5 M NaOH and, if necessary, heated in a boiling water bath for 10 min for complete dissolution. The solution were diluted to 50 mL with 0.1 M acetic acid solution of pH 2.7, to give a final pH of 4.6. A 15 µL portion was injected into a stream of Ca(NO2)2 in 0.05 M acetate buffer of pH 6 (0.17 ml/min) in the FIA system before passing into the Termamyl reactor. After merging with a second flow of 0.1 M acetate buffer of pH 4.5 (0.33 ml/min) and passing through the amylerglycosidase reactor, the effluent was merged with 0.2 M phosphate buffer of pH 7.4 containing 4 mM NAD+ (1 ml/min). The effluent passed through the glucose dehydrogenase/aldose 1-epimerase reactor and a flow-through detector and was monitored at 340 nm. The peak height and integrated peak areas were evaluated by a computer program. Lipids, proteins and chemical modifications of starch interfered with the determination probably due to steric hindrance of the enzymes resulting in incomplete degradation to glucose; detection limits and RSD are not given. The FIA system can be fully automated. The cited method was applied to wheat, corn rice and potato starch.
Starch Spectrophotometry Immobilized enzyme Automation Interferences