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
Website: @unf

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Classification: Food -> chocolate

Citations 3

"Determination Of Trace Amounts Of Nickel By Chelating Ion Exchange And Online Enrichment In Flow Injection Spectrophotometry"
Analyst 1995 Volume 120, Issue 2 Pages 555-559
Rajesh Purohit and Surekha Devi

Abstract: A flow injection spectrophotometric method for Ni determination is described. A portion (5 ml) of a Ni solution of pH 7.5-9 was passed (3 ml/min) through a column (4 cm x 2 mm i.d.) of 8-hydroxyquinoline chelating resin (several tested; details given). The column was washed with 0.2 M acetate buffer of pH 7.5-9. The chelated Ni was eluted from the column by injecting 20 µL of 2 M HCl into the FI system and was then mixed with 0.5% dimethylglyoxime and the absorbance was measured at 445 nm. A diagram of the manifold used is given. The calibration graph was linear from 10 (detection limit) to 70 µg/ml of Ni. The RSD (n = 5) were 0.4-2.8%. The method was applied to chocolate and vegetable oil. The results agreed with those obtained by AAS.
Nickel Spectrophotometry 8-Hydroxyquinoline Chelation Preconcentration Method comparison

"Determination Of Biogenic Amines In Cheese And Some Other Food Products By High Performance Liquid Chromatography In Combination With Thermo-sensitized Reaction Detection"
J. Chromatogr. A 1986 Volume 356, Issue 2 Pages 311-319
H. M. L. J. Joosten and C. Olieman

Abstract: Biogenic amines were extracted from cheese, chocolate, fish, wine and sauerkraut by precipitation with trichloroacetic acid before HPLC on a radial-compression cartridge (10 cm x 8 mm) packed with Nucleosil C18 and equipped with a pre-column of Corasil C18. The mobile phase was aqueous 47% dimethyl sulfoxide containing 1 g L-1 of Na dodecyl sulfate and 2.8 M in Na acetate buffer (pH 5); ninhydrin (8 g l-1) and hydrindantin (0.6 g l-1) were dissolved in the mobile phase to effect post-column derivatization of the amines without need for an extra reagent pump. Detection was by using a PTFE knitted-tube reactor at 145°C and measuring the absorbance at 546 nm. Recovery of amines from cheese was 85 to 105%. The detection limit was 2 mg kg-1 in cheese and the response was rectilinear for 0.1 to 4 µg of amine injected. Detection limits for amines in sauerkraut and wine were 0.8 and 0.3 mg kg-1, respectively.
Amines, biogenic HPLC Spectrophotometry Heated reaction Open tubular reactor Post-column derivatization Knotted reactor

"Determination Of Copper In Powdered Chocolate Samples By Slurry-sampling Flame Atomic-absorption Spectrometry"
Anal. Bioanal. Chem. 2005 Volume 382, Issue 4 Pages 1099-1102
Walter N. L. dos Santos, Erik G. P. da Silva, Marcelo S. Fernandes, Rennan G. O. Araujo, Antônio C. S. Costa, M. G. R. Vale, S&eagrave;rgio L. C. Ferreira

Abstract: Chocolate is a complex sample with a high content of organic compounds and its analysis generally involves digestion procedures that might include the risk of losses and/or contamination. The determination of copper in chocolate is important because copper compounds are extensively used as fungicides in the farming of cocoa. In this paper, a slurry-sampling flame atomic-absorption spectrometric method is proposed for determination of copper in powdered chocolate samples. Optimization was carried out using univariate methodology involving the variables nature and concentration of the acid solution for slurry preparation, sonication time, and sample mass. The recommended conditions include a sample mass of 0.2 g, 2.0 mol L-1 hydrochloric acid solution, and a sonication time of 15 min. The calibration curve was prepared using aqueous copper standards in 2.0 mol L-1 hydrochloric acid. This method allowed determination of copper in chocolate with a detection limit of 0.4 µg g-1 and precision, expressed as relative standard deviation (RSD), of 2.5% (n=10) for a copper content of approximately 30 µg g-1, using a chocolate mass of 0.2 g. The accuracy was confirmed by analyzing the certified reference materials NIST SRM 1568a rice flour and NIES CRM 10-b rice flour. The proposed method was used for determination of copper in three powdered chocolate samples, the copper content of which varied between 26.6 and 31.5 µg g-1. The results showed no significant differences with those obtained after complete digestion, using a t-test for comparison.
Copper Spectrophotometry Optimization Slurry Calibration Detection limit Precision Statistics Accuracy