University of North Florida
Browse the Citations
-OR-

Contact Info

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

View Stuart Chalk's profile on LinkedIn

Food

Classification: Food -> diet

Citations 6

"Flow Injection Spectrophotometric Determination Of Aspartame In Dietary Products"
Analyst 1994 Volume 119, Issue 9 Pages 2101-2104
Joaquim de Araújo Nóbrega, Orlando Fatibello-Filho and Iolanda da Cruz Vieira

Abstract: A flow injection spectrophotometric method has been developed for the determination of aspartame in dietary products using ninhydrin as a colorimetric reagent. The reaction was conducted in a 1 + 1 v/v methanol-isopropanol medium also containing potassium hydroxide. The absorbance measurements were made at 603 nm. The results obtained for the determination of aspartame in table sweetener, pudding, gelatin, and refreshment (i.e., a powder dissolved in water for drinking) are in good agreement with the results obtained using a conventional manual procedure (correlation coefficient, r = 0.9984). Thirty-six results were obtained per hour, and the relative standard deviation was less than 3.5% (n = 6) for all samples. The detection limit (three times the signal blank/slope) was 3.8 x 10^-5 mol L-1 of aspartame. Sample (0.2-0.6 g) was stirred with 10 mL of methanol/propan-2-ol (1:1; solvent A) for 2 min. The suspension was filtered and the filtrate was diluted to 25 mL with solvent A. A portion of the solution was injected into a carrier stream (2.5 ml/min) of solvent A and subsequently merged with streams (both 0.3 ml/min) of 0.293 M KOH and 0.037 M ninhydrin (both in solvent A). The mixture was transported to a helical reaction coil (2 m x 0.8 mm i.d.) immersed in a water-bath kept at 60°C. The solution then passed through a de-bubbler after which the absorbance was measured at 603 nm. A diagram of the manifold used is given. The calibration graph was linear from 0.34-2.4 mM aspartame, the detection limit was 38 µM and the RSD (n = 6) was 3.5%. Recoveries were quantitative and the throughput was 36 samples/h. The method was applied to several dietary products, viz., table sweetener, pudding, gelatin and refreshment powder.
Aspartame Spectrophotometry Heated reaction

"Atomic Absorption Spectrometric Analysis Of Solids With Online Microwave-assisted Digestion"
J. Anal. At. Spectrom. 1992 Volume 7, Issue 7 Pages 1085-1089
V. Carbonell, A. Morales-Rubio, A. Salvador, M. de la Guardia, J. L. Burguera and M. Burguera

Abstract: A description is given of a procedure for online microwave-assisted digestion of solid samples prior to analysis by flame AAS as described previously (Anal. Chim. Acta, 1990, 238, 417). A slurry of the sample is transported in HNO3 - H2O2 (1:1) to extract Cu and Mn quantitatively in a few min. Digestion times vary from 4 min for sewage sludges to 2 min for matrices like artichoke. Detection wavelengths were 324.7 nm for Cu and 279.5 nm for Mn. A closed flow injection system allows digestion to be conducted online. Sample flow rate was 2.8 mL min-1. Over 15 samples h-1 can be analyzed using the procedure which allows for sequential treatment of different samples. A procedure was developed for the online microwave-assisted digestion of solid samples and their anal. by flame atomic absorption spectrometry. The method involves the transport of a slurry of the sample in a 1+1 mixture of concentrated HNO3 and H2O2, which provides quant. extraction of Cu and Mn in a few minutes. Real samples of sewage sludges dispersed in 20 mL of HNO3 and H2O2 can be digested in 4 min and other matrixes, such as artichoke and diet samples dispersed in 10 mL of HNO3 and H2O2 are digested in only 2 min. A closed flow injection system permits the online digestion to be carried out; the use of two interconnected injection valves allows the measurement of standards during the digestion of samples. The method permits the anal. of more than 15 samples per h and provides accurate results, as demonstrated by the anal. of certified samples of sewage sludges and tomato leaves.
Copper Manganese Sample preparation Spectrophotometry Microwave Online digestion Slurry Reference material

"Selective Spectrofluorimetric Determination Of Zinc In Biological Samples By Flow Injection Analysis (FIA)"
Fresenius J. Anal. Chem. 1992 Volume 342, Issue 7 Pages 597-600
P. Fernández, C. Pérez Conde, A. Gutiérrez and C. Cámara

Abstract: Sample (0.25 g) was heated at 500°C for 2 h in a muffle furnace. The residue was dissolved in 0.5 mL of HNO3 and the solution was diluted to 25 mL with water. A 125 µL portion of the resulting solution was injected into a carrier stream (0.62 mL minmin1) of 0.5 M hexamethylenetetramine adjusted to pH 6 with HClO4 which merged with a stream (0.36 mL min-1) of 0.05% of 5,7-dibromo-8-quinolinol in ethyl ether. The two phases were separated and the organic phase was passed through a flow cell where its fluorescence was measured at 550 nm (excitation at 410 nm). The calibration graph was rectilinear up to 1 µg mL-1 of Zn(II); the detection limit was 3 ng mL-1. Sample throughput was 40 h-1. Among the 30 cations and anions studied, only Ni(II), Mn(II) and EDTA interfered seriously. The method was used to determine Zn in tap and well water, muscle, milk powder and whole diet. The automatization of a spectrofluorimetric method for the determination of zinc at trace level is described. It is based on the formation of the fluorescent complex Zn(II)-5,7-dibromo-8-quinolinol [Zn(II)-DBQ] followed by extraction into diethyl ether using flow injection analysis The optimum fluorescent emission is reached in hexamethylenetetramine (H2MTA+/HMTA) buffer pH 6.0. A membrane phase separator was used. The calibration graph is linear up to 1.5 µg/mL of Zn(II). The proposed method (detection limit 3 ng/mL) is very selective and has been successfully applied to determine Zn(II) in biological samples, tap waters, and various food items.
Zinc Fluorescence Organic phase detection Optimization Interferences Reference material Phase separator

"Sensitive Fluorescence Labelling For Analysis Of Organotin Compounds With Morin"
Fresenius J. Anal. Chem. 1992 Volume 342, Issue 10 Pages 839-845
M. Pfeffer, B. Gelbe, P. Hampe, B. Steinberg, E. Walenciak-Reddel, B. Woicke and B. Wykhoff

Abstract: An HPLC method has been developed for the determination of the toxicity of organotin compounds in peanut oil, water or diet mixtures as test compounds. According to the formulation, the tin compounds were diluted or extracted with propan-2-ol or methanol and portions were applied to reversed-phase columns (Spherisorb and Hypersil) with mobile phases of mixtures of acetonitrile, water, acetic acid and LiCl. Post-column derivatization was carried out with morin and the organotin complexes were determined fluorimetrically. No peak interferences were observed and the coefficient of variation were generally 5%. Results were in good agreement with those by AAS.
Tin, organic HPLC Fluorescence Post-column derivatization Interferences Method comparison

"Determination Of Aspartame In Dietary Food Products By A FIA Biosensor"
Biosens. Bioelectron. 1991 Volume 6, Issue 2 Pages 117-123
K. B. Male, J. H. T. Luong* and A. Mulchandani

Abstract: A flow injection analysis (FIA) biosensor system was developed for the determination of the artificial sweetener aspartame (N-L-α-aspartyl-L-phenylalanine methyl ester). The system consisted of two enzyme columns, containing purified peptidase and aspartate aminotransferase respectively, immobilized on activated aminopropyl glass beads and an enzyme electrode connected in series. The dipeptide bond of aspartame was cleaved by immobilized peptidase to release aspartic acid which was in turn transaminated by aspartate aminotransferase. The glutamate produced by transamination was monitored by the enzyme electrode which used L-glutamate oxidase immobilized on a nylon membrane in combination with a hydrogen peroxide electrode. The response of the FIA biosensor was linear up to 1 mM aspartame with a lower detection limit of 20 micromole and had good reproducibility (RSD2.2%). The FIA biosensor was stable for at least 30 h of continuous use at room temperature and the immobilized enzymes were stable for at least 1 month when stored in buffer at 4°C. Each assay takes ~7-8 min giving a sample through put of 8 h-1. When applied to aspartame measurements in dietary food products, the results obtained agreed well with those reported by the product manufacturer. The flow injection analysis system described contains two enzyme columns, containing purified peptidase and aspartate aminotransferase, respectively, immobilized on activated aminopropyl glass beads, and an enzyme electrode of L-glutamate oxidase immobilized on a nylon membrane in combination with a H2O2 electrode. The immobilization of the enzymes and the purification of the aspartame peptide-bond-cleaving enzyme are detailed. The effects of pH, flow rate, α-ketoglutarate and column length on the flow injection analysis response were measured. The calibration graph was rectilinear up to 1 mM aspartame, with a detection limit of 20 µM and a coefficient of variation (n=8) of 2.2%. The biosensor was stable for at least 30 h of continuous use at room temperature and the immobilized enzymes were stable for at least 1 month when stored in buffer at 4°C. Each assay takes 7-8 min. The method was applied to dietary food products.
Aspartame Electrode Sensor Buffer Column Glass beads Immobilized enzyme Nylon pH

"Actual Daily Dietary Intake Of Selenium In Belgium, Using Duplicate Portion Sampling"
Z. Lebensm. Unters. Forsch. 1994 Volume 199, Issue 4 Pages 251-254
Harry J. Robberecht, Peter Hendrix, Rudy Van Cauwenbergh and Hendrik A. Deelstra

Abstract: The dietary selenium (Se) intake in Belgium has been re-evaluated. Duplicate meal collection, wet acid destruction and flow injection hydride generation atomic absorption spectrometry were used as techniques. The daily intake ranged from 28.4 µg (Liège, Walloon part of the country) to 61.1 µg (Vilvoorde, central part of the country). Compared with intakes recently published for other countries, the actual Belgian value corresponds to intermediate ranges of Se intake.
Selenium Spectrophotometry Volatile generation Volatile generation