Microwave-assisted digestion employing diluted nitric acid for mineral determination in rice by ICP OES

•Nine elements were determined in seventy-seven different rice samples using ICP OES.•Rice mass of 500 mg was digested with only 5 mL of 1 mol L−1 HNO3 and 2.5 mL of H2O2.•Digestion method was efficient, economical, greener and with acceptable LOD and LOQ.•Carbon was quantified in solutions and solids using a spectrophotometric method.•Spectrophotometric method indicated as possible alternative to elemental analysis. A microwave-assisted digestion method using diluted HNO3 was developed for further determination of Al, Ca, Cr, Cu, Fe, K, Mn, Mo and Ni in rice samples by ICP OES. The following optimized conditions were established after full factorial design: digestion time of 14 min, concentration of 1 mol L−1 HNO3 and 2.5 mL of H2O2. The efficiency in decomposing organic matter with diluted acid was higher than 89%. The methodology was validated using the SRM NIST 1568a Rice Flour and recovery tests, with agreement between the determined and certified/added concentration values, and RSD of up to 12%. The limits of detection of the method were in the range of 0.0087 mg kg−1 (Mn) to 1.6 mg kg−1 (Ca). In addition, a simple and inexpensive spectrophotometric method was proposed for the quantification of organic carbon in varied samples (carbohydrates, proteins, lipids) in the form of digested or solids.