Metals and phosphorus determination in vegetable seeds used in the production of biodiesel by ICP OES and ICP-MS

Methods for the determination of 5 major (Ca, K, Mg, Na and P) and 14 minor elements (Al, Ba, Cd, Co, Cu, Fe, Ga, Mn, Mo, Ni, Pb, Rb, Sr and Zn) in vegetable seeds by ICP OES and by ICP-MS, respectively, are proposed. After a common sample preparation consisting of smashing and homogenization in an agata mortar, followed by acid digestion in a microwave oven, the diluted sample solutions were measured in the spectrometers using conventional pneumatic nebulizers. External calibration with aqueous standard solutions was used for both techniques. Internal standard was not required, due to the absence of non-spectral interference. For the major elements, the detection limits were in the range of 0.01 (Mg) to 0.3 µg g^− 1 (Na and K) and for the minor elements they were in the range of 0.001 (several) to 0.4 µg g^− 1 (Fe). The detection limits were adequate for the seed analysis. The accuracy was validated by analyzing a botanical certified reference material (Pine Needles). Agreement of the concentrations with the certified or informed values was obtained, according to the t-test for a confidence level of 95%. The relative standard deviations were below 10% indicating an adequate precision. Seeds from seven different plants were analyzed: cotton seed, sunflower, castor bean, fodder turnip, curcas bean, soybean and tung. The element concentrations varied considerably in the different samples. The results were also evaluated using the principal component analysis.