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 -> cocoa

Citations 1

"Flow Injection Systems For Directly Coupling Online Digestions With Analytical Atomic Spectrometry. 1. Dissolution Of Cocoa Under Stopped-flow High-pressure Conditions"
J. Anal. At. Spectrom. 1992 Volume 7, Issue 2 Pages 301-306
Thomas J. Gluodenis Jr. and Julian F. Tyson

Abstract: Cocoa powder was mixed with 10% HNO3 and the slurry was injected into a double flow injection manifold incorporating a resistively heated oven operated at 210°C. The digestion was also carried out under stopped-flow and high-pressure conditions. A two-stage dual-column assembly allowed controlled depressurization of the system and subsequent gas - liquid separation. The resulting solution was analyzed after injection into a stream of water by flame AAS. Copper and Fe were determined at 324.8 and 248.3 nm, respectively. Reproducibility was affected in the determination of Cu due to higher dilution involved when compared to other methods. The low results for Fe were attributed to incomplete digestion of the sample. A double flow injection manifold incorporating a resistively heated oven was developed for the direct coupling of the digestion of solid samples with an anal. spectrometric technique. The potential of the system was illustrated by the dissolution of cocoa powder and subsequent determination of the Cu and Fe content by flame atomic absorption spectrometry (FAAS). The cocoa powder was slurried in 10% HNO3, injected into the manifold, and digested under stopped-flow, high-pressure conditions. Gas-liq. separation was effected by a 2-stage depressurization system. Cu and Fe were determined by flow injection FAAS with acid-matched standards Values of 44 and 144 mg/kg were obtained for Cu and Fe, respectively. The cocoa powder was also digested by using an open-vessel hot-plate method and a closed-vessel microwave digestion method. The results for Cu were 52 and 50 mg/kg, respectively. Both of these methods gave a value of 180 mg/kg for Fe. The relatively large uncertainty in the Cu result for the online method was related to the higher dilution in this system, producing a concentration. in the digest nearer the detection limit of the flame procedure. The low results for Fe were considered to be caused by incomplete digestion. The proposed procedure produces a clear solution, and increased sample throughput while minimizing sample contamination and decreasing sample and reagent consumption.
Copper Iron Sample preparation Spectrophotometry Microwave Online digestion Method comparison Stopped-flow Reagent consumption Slurry