Comparison of microwave digestion with block digestion for selenium and boron analysis in plant tissues

Abstract

Abstract Microwave digestion and block digestion of selected plant tissues, including National Institute of Standards and Technology (NIST) Standard Reference Materials, were conducted and evaluated for their effectiveness in the determination of selenium (Se) and boron (B). With microwave digestion, two major parameters were manipulated for digesting botanical materials, microwave energy power profiles (power, time, and pressure) and volume of chemical reagents. Results show that microwave digestion is at least four hours faster than block digestion. However, the recovery rates for Se and B are 20–30% lower by microwave digestion if there is no predigestion and the inappropriate volume and combination of chemical reagents are used. The optimal combinations for microwave digestion of the tested parameters are as follows: for Se, the 0.25 g of sample material is predigested for fourhours with 2 mL nitric acid (HNO3), 2 mL 30% hydrogen peroxide (H2O2), and 1 mL H2O. The microwave is set at 95% power and pressure at 150 psig (10.5 kg/cm) for 30 min. For B, 0.25 g of sample material is predigested for 30 min with 0.5 mL HNO3and 2.5 mL 30% H2O2. The microwave is then set at the first stage at 50% power, pressure at 10.5 kg/cm for 15 min followed by the second stage at 90% power, and pressure at 10.5 kg/cm for 30 min. The concentrations of Se and B from block digestion are consistent with the concentrations of Se and B reported by NIST.