Evaluation of triacid and dry ashing procedures for determining potassium, calcium, magnesium, iron, zinc, manganese, and copper in plant materials

Dry ashing and wet ashing techniques are routinely used for preparing plant materials for elemental analysis. The two techniques generally give similar results for the analysis of plant materials but differences have been observed in results using the two methods for elements such as calcium (Ca), iron (Fe), and zinc (Zn). We made a study to compare the dry ashing and triacid digestion procedures for determining potassium (K), Ca, magnesium (Mg), Fe, manganese (Mn), copper (Cu), and Zn in sorghum and rice plant samples having a range in concentration of these elements. For sorghum, the two procedures gave similar results for the determination of K, Mg, Mn, and Zn, the dry ashing procedure gave higher values for Ca, Fe, and Cu than those obtained using the triacid digestion procedure. For rice, the two procedures gave similar results for all nutrient elements except Ca for which the values were higher by the dry ashing procedure than with the triacid digestion procedure. Our results suggest that dry ashing technique provides more reliable results for the analysis of sorghum and rice plant materials for Ca and may be preferred over the triacid digestion procedure. Also, for sorghum, plant samples dry ashing seemed more reliable for determination of Fe and Cu. Both dry ashing and triacid digestion methods appeared satisfactory for the determination of K, Mg, Mn, and Zn