In situ Determination of K, Ca, S and Si in Fresh Sugar Cane Leaves by Handheld Energy Dispersive X-Ray Fluorescence Spectrometry

Abstract

A portable energy dispersive X-ray fluorescence spectrometer was evaluated in the in situ analysis of fresh sugar cane leaves for real time plant nutrition diagnosis. Fresh leaf fragments (n = 10 sugar cane varieties; 20 fragments per leaf; 2 measurement sites per fragment) were irradiated and the averaged data from X-ray characteristic emission lines intensities (for K, Ca, S and Si Kα lines) were in close agreement with mass fraction data obtained by a validated comparative method. The linear correlation coefficients (r) ranged from 0.9575 for Ca to 0.9851 for Si. The obtained limits of detection were at least two-fold lower than the critical nutrient levels. Manganese can also be properly determined, but validation still requires more robust calibration models. The proposed method is a straightforward approach towards the fast evaluation of the nutritional profile of plants avoiding time-consuming steps, which involve drying, grinding, weighing, and acid digestion.Keywords: in situ analysis, portable X-ray fluorescence spectrometry, plant mineral analysis, sugar cane, silicon IntroductionPlant nutrition diagnosis is a well-established and reliable way for guiding the proper fertilizer recommendation contributing to the healthy growing of crops of economic importance.1 The analytical protocol most frequently applied for the determination of macro-and micronutrients in plant materials often requires an a priori test sample decomposition, usually performed by microwave-assisted acid sample dissolution, followed by determination using inductively coupled plasma optical emission spectrometry (ICP OES). 2Some studies have focused on the use of the direct solid sampling analysis based on X-ray fluorescence spectrometry (XRF), [3][4][5] laser-induced breakdown spectroscopy (LIBS) [6][7][8] or laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) 9-11 for assessing the mineral nutrition profile of plants. The most common way of sample presentation by using the aforementioned direct analysis methods involves the interrogation of a previously ground plant material in a pellet form.6,9 A promising trend of research is the direct analysis of the dried plant leaf without the need for grinding or pelletizing steps.12 On this subject, both LIBS and energy dispersive XRF (EDXRF) have been used.The increasing advances in the field of portable instrumentation has expanded the application of this emerging technology. Such a fast development is due to improvements in digital electronics and in the development of miniaturized sensors and other crucial components. These novel mobile equipment offer a plethora of advantages to the analyst such as real time and onsite determinations of organic and inorganic analytes in a myriad of sample matrices. [13][14][15] In case of the use of portable LIBS and EDXRF systems, the most common Guerra et al. 1087 Vol. 29, No. 5, 2018 in situ applications involve the determination of potentially toxic metals in soil, [16][17][18][19] and analysis of samples as diverse as those o...

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Espectroscopia de Energia Dispersiva (EDS) associada à Análise de Componentes Principais (PCA) para análise de composição elementar e comparação de alfaces do tipo crespa (Lactuca Sativa L.) de cultivo orgânico e convencional

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