Improvements for digestion of whole grains and plant ground matter for phosphorus and potassium

Sample digestion is the most time-consuming step in the elemental analysis of agricultural and food products. Moreover, a proper digestion procedure is crucial, because it affects the accuracy and precision of the analysis. In this study, a digestion procedure using sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) as digestion reagents was optimized for whole grains (chickpea, wheat, and safflower) and dry matter (wheat straw and pea). Several digestion parameters as quantity of digestion reagents either H2SO4 (2 or 3.5 mL) or H2O2 per cycle (0.5, 1, 2, or 4 mL) needed for reaction, predigestion time (5 min to overnight) and postdigestion necessarily were tested. The basic optimized procedure was 1) predigestion in 2 mL H2O2 for 10 min, 2) careful addition of 2 mL of H2SO4 followed by waiting for 5 min, and 3) performance of two digestion cycles with 2 mL H2O2 per cycle; no postdigestion step was needed. The varied conditions ensured fastest digestion, without compromising the final accuracy and precision. The digestion duration was reduced from 90-240 min to 30-45 min, and accurate results were obtained for a wide range (0.06-0.5%) of phosphorus (P) concentrations. The proposed method is suitable for determination of phosphorus and potassium (K) in complicated crop samples containing high percentages of fat, proteins, or starch, particularly in whole grains, seeds, and ground samples. The procedure is also applicable to ground samples of dry matter. Hence, there are many potential uses for the suggested improved method.