Análisis de los elementos minerales esenciales y tóxicos en tejidos vegetales

Resumo

Conventional and classic techniques to analyze the essential or toxic elements for plants and humans, either the ones requiring solubilization of the sample and others emerging ones that do not need it, have undergone an accelerated development in recent times. Researchers in genetics, agronomy, nutrition, physiology, and biology rarely used advanced conventional and non-destructive techniques to assess the nutrient composition and quality of food, quantify essential and toxic metallic elements, in order to diagnose the nutritional status of crops and to study functional foods. These analytical techniques are applied to soils, fertilizers and manures also. Atomic emission spectrometry with inductively coupled plasma (ICP) and that of mass ICP (ICP-MS, Mass spectrometry with inductively coupled plasma) are of greater interest than the classical techniques used in laboratories in developing countries, such as emission spectrometry (AES, Atomic emission spectrometry) and atomic absorption spectrometry (AAS), which require matrix solubilization. The ICP-MS and the ICP allow the simultaneous analysis of the total contents of most of the essential elements for plant growth. Among the non-destructive techniques of the matrix, most of those considered in this essay are based on the interaction of X-rays with matter; such as X-ray photoemission (XPS, X-ray photoelectron spectrometry), particle-induced X-ray emission (PIXE), X-ray fluorescence (XRF) and dispersion spectrometry of X-ray energy (EDS, Energy-dispersive X-ray spectrometry), similar in their principles. These techniques, unlike the previous ones, do not require the solubilization of the sample or its preparation is minimal. Other advantages are their speed, the performance of simultaneous multi-element analysis, small sample size, acquisition of the distribution of chemical elements in the sample, and mapping in two dimensions. The four techniques described above analyze total contents. PIXE and XRF have higher sensitivity than the other two to quantify trace elements in concentrations of parts per million, and these two, in addition to EDS, can be coupled to ad hoc microscopes to obtain the distribution of chemical elements and mapping. The XPS technique allows the analysis of ionic fractions in studies of oxidation states of the elements, but the concentrations in samples must be greater than 0.1% by weight. The applications of nondestructive techniques generate complementary information to classic ones and provide fundamental knowledge. Besides, sample preparation requires less time, except when mapping is required. Its ability to run multi-analysis allows for reducing costs. In Mexico and other countries, there are research groups specialized in these techniques. Still, it is necessary to develop and implement applications to perform analyzes of biological matrices such as vegetables (seeds, leaves, and others), food, fertilizers, and soil organic matrix. More in-depth knowledge of these techniques allows the interaction of research groups and generate information for basic science studies in agronomy and food.