Comparative Study Of Wet Digestion Methods Of Sample Preparation For Elemental Analysis.

Nine wet digestion methods were used on two guava samples and eighttomatoe samples for the purpose of elemental determination. These samples"belong to the group of fruity vegetables. Acid and acid mixtures wereused to digest the samples; these include HNO3., HNO3/H2SO4, , HNO3/HC104,HN03/HC104/H2S04 , HN03/NH4 N03, and HCl/HNO3. Selenium was used asa catalyst in one of the procedures. Eleven metals were determined.These are sodium, potassium, calcium, magnesium, iron, zinc, copper,manganese, lead, cobalt, and cadmium. Atomic Absorptionspectrophotometry and flame photometry were used to determine the metals.The reliability of each digestion method, for the determination ofeach, metal in each sample was assessed, by calculating the mean andstandard deviation, and by performing the multiple range tests on theresult of each method.It was found that, no one single method of digestion could releaseall the metals of interest quantitatively and reliably from each sample.A minimum of three digestion methods for each sample was found tt beneeded for the determination of these metals, each method being reliablefor a group of metals. Some methods such as these involving the use ofperchloric acid in the digestion mixture and those using nitric acidalone were found to lead to partial or total losses in certain traceelements like Co, Cd and Pb. The three most valuable digestion methodsthat are recommended for the types of biological samples studied aremethod A (H2SO4/HNO3), method B (modification of A), method F(HNO3/NH4N03).

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