ИСТИНА

Determination of macro- and micronutrients in plants is an important problem, since it's well known that the deficit or excess of some elements (for example, magnesium) in living organisms lead to serious disturbance of metabolic processes. Cations and anions are involved in energy exchange, photosynthesis, water balance and in maintenance of salt balance. Therefore, the study of their distribution in plants presents scientific interest and brings new fundamental knowledge in the plant physiology. Moreover, some micronutrient content in agricultural species should be known for optimizing growing condition and environmental control. Following this, the rapid direct methods of local analysis of plants, including living plants, have undoubted advantages. Physiological study often requires knowledge of the elemental distribution in plant tissues. Since plants mainly consist of light elements LIBS seems to be the most appropriate technique. We evaluate LIBS possibilities for quantification of non-metals (boron and chlorine) and alkaline/alkaline-earth metals in plants. The special attention was focused on elemental mapping, sensitivity enhancement for non-metal determination (double-pulse LIBS) and the study of moisture content influence on analytical signal. We have considered fresh and dried leaves of birch (Bétula péndula) and mandarin (Cītrus reticulate) and a number of CRMs for quantification. Firstly, we found that the softly focused 3rd harmonic of Nd:YAG laser provides the best precision for all elements with the except of chlorine. In latter case the best result was achieved by double pulse LIBS. Quantitative measurements were made with dried and homogeneous samples and the obtained values were in good agreement with reference analysis by ICP-MS and INAA. It was also shown that the electron density and OH-band intensity correlate with the water content in leaves and can be used to correct the signal for direct measurements of living leaves. We assembled system for 2D-mapping of elemental distribution in living leaves and investigated distribution of boron. Since we used single shot measurement to avoid leaf destroying, we normalized B I 249.77 nm signal to background and C I 247.86 nm intensity. Thus, we conclude that LIBS sensitivity is enough for light elements quantification in plants including study of their spatial distribution.