Browsing by Author "Wodajo, Negussie (PhD)"

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    Determination of Total Polyphenols in Ethiopian Red Wines by Reaction with 4-Aminoantipyrine and Photometric Flow Injection Analysis
    (Addis Ababa Universty, 2007-08) Geto, Alemnew; Wodajo, Negussie (PhD)
    A simple flow injection spectrophotometric method for the determination of total polyphenols in red wines is reported. The method is based on the oxidative coupling of polyphenols with 4-aminantipyrine in alkaline medium to yield a colored product with maximum absorption at 470 nm. After optimization by univariant approach, the linear range was established between 9.4 to 451.5 mgL-1. The proposed system was applied for the determination of total polyphenols in Ethiopian red wines using gallic acid as the standard and the results are given as gallic acid equivalent (GAE) in mgL-1 with RSD < 1%. The method enabled analysis of approximately 43 samples h-1. The selectivity of the method was evaluated using compounds that are normally present in wine such as sugars, tartaric acid, ascorbic acid, methanol, ethanol, ammonium sulfate, and potassium chloride and it was found to be fairly selective (relative error < 4.2%). The method was validated through recovery test and the result was in the acceptable region 90.5% - 107.3%.
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    Determination of Trace Iron in Aqueous Samples by Its Catalytic Effect in Trinder’s Reaction in a Flow Injection System
    (Addis Ababa Universty, 2007-08) Zewge, Balkew; Wodajo, Negussie (PhD)
    A kinetic catalytic flow injection spectrophotometric method for the determination of trace iron in aqueous samples has been proposed. It is based on the catalytic effect of iron on the oxidative coupling of 4-AP and DCPS in the presence of hydrogen peroxide and in slightly acidic medium to form quinine imine dye that has a maximum peak height at λmax of 510 nm. The peak height observed at the flow through detector was linearly proportional to iron (II, III) concentration over the range 1-20 μM. In the proposed method, iron acts as a catalyst by changing its oxidation state from Fe2+ to Fe3+ and recycle Fe3+ to Fe2+. This recycling action of iron can magnify its effect for the trace analysis in aqueous samples. Thus small amount of iron can be determined by measuring the rate of the formation of the product. After optimization of flow rate, pH of the carrier solution and concentration of each reagents attempt was made to utilize the developed method for the determination of iron content in commercially available bottled mineral waters (Aqua Addis, Aqua safe, Abyssinia springs, and Highland). However, the method was not sensitive enough for detection of traces of iron. Different activators were tested for their enhancement of sensitivity but no increment in signal was observed.