COMPARISON BETWEEN 2 DRY MINERALIZATION METHODS (WITH AND WITHOUT HF)OF PALM LEAVES FOR DETERMINATION OF POTASSIUM - INFLUENCE OF SILICA

Many possibilities exist for the preparation of plant samples for elem ental analyses, each having its merits and disadvantages. Wet acid dig estion presents several drawbacks, such as potential risk of explosion when using perchloric acid, corrosion of apparatus, and contamination by elements from acids, therefore dry ashing is preferred for routine analyses. In this paper, dry ashing without hydrofluoric acid (HF) wh ich provides insolubilization of silica (SiO2) is compared to dry ashi ng with HF (CII-Method) which eliminates silicon by the evaporation of SiF4. For samples rich in silica, such as oil palm leaves, the minera lization without HF gives lower results for calcium (Ca), magnesium (M g) and above all potassium (K) as compared to results using the HF pro cess. Silica present in botanical materials may form insoluble silicat es, and therefore retain elements by adsorption. This study dealt with the relationship between the level of silica in palm leaves and the p recision of the determination of K by inductively coupled plasma (ICP) emission spectrometry. The correlations indicated that equivalent res ults are obtained by the two methods when the level of silica in the l eaves is lower than 3.5% (dry matter). Above that level, when using th e method without HF, the decrease in K content determined increases pr oportionally with the silica level in the sample and can reach as much as 17% for a K value at 0.6%.