DEVELOPMENT OF A METHOD TO PREPARE SAMPLES OF PLANT MATERIAL FOR THE DETERMINATION OF Ca, Cu, Mg, Mn, Fe and Zn BY FAAS, AND P USING COMPLEXOMETRY

The quantification of elements such as Ca, Cu, Fe, Mg, Mn, P and Zn, which are essential nutrients for plant growth, is of great relevance for the evaluation of plant nutritional health since it enables an early diagnosis of deficiencies, and the correction of this and other problems that could cause environmental and agricultural problems. Plant tissue samples such as seeds, leaves, bark or other plant parts need to be prepared by acid oxidation to convert the originally solid sample into a solution containing the elements in a suitable ionic form to be introduced as an aerosol, by nebulization in the spectrometers of Flame Atomic Absorption Spectrometer (FAAS) or Inductively Coupled Plasma/Optical Emission Spectrometer (ICP OES). The preparation used traditionally requires large volumes of concentrated inorganic acids such as nitric and perchloric acids, and high temperatures, generating vapors and residues that pose risks to the health and safety of the analyst as well as possible environmental problems. Therefore, this study developed a milder plant tissue preparation method, known as “green” or “clean” that uses only 5M nitric acid, 12% hydrogen peroxide with microwave heating in a closed system, eliminating the generation of acid fumes and the use of perchloric acid. The method achieved reduction of the time necessary for the dissolution of plant samples that are difficult to oxidize, such as soybean leaves, oat and wheat flour, maize and beans. That method allows the quantification of Ca, Cu, Fe, Mg, Mn and Zn by FAAS, P by complexometry with similar results to those obtained with the traditional method for inter-laboratory proficiency reference samples and more complex samples.