Improvements for Digestion of Whole Grains and Plant Ground Matter for Phosphorus and Potassium B. Dolgin and I. Schechter Department of Chemistry, Technion — Israel Institute of Technology, Haifa, Israel S. Asido and D. J. Bonfil Department of Field Crops and Natural Resources, Agricultural Research Organization, Gilat Research Center, Negev, Israel Abstract: 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 (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ) 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 H 2 SO 4 (2 or 3.5 mL) or H 2 O 2 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 H 2 O 2 for 10 min, 2) careful addition of 2 mL of H 2 SO 4 followed by waiting for 5 min, and 3) performance of two digestion cycles with 2 mL H 2 O 2 per cycle; no postdigestion step was needed. The varied conditions ensured fastest digestion, without compro- mising 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, Received 23 December 2003, Accepted 30 August 2004 Address correspondence to D. J. Bonfil, Department of Field Crops and Natural Resources, Agricultural Research Organization, Gilat Research Center, MP Negev 85280, Negev, Israel. E-mail: bonfil@volcani.agri.gov.il Communications in Soil Science and Plant Analysis, 36: 1747–1761, 2005 Copyright # Taylor & Francis, Inc. ISSN 0010-3624 print/1532-2416 online DOI: 10.1081/CSS-200062437 1747