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Multielement analysis of Xylem sap by total reflection X-ray fluorescence (TXRF) spectrometry (CAT#: STEM-ST-0211-WXH)

Introduction

Xylem sap is the plant exudate collected by cutting the stem in the region of the root collar and it corresponds to the stream transporting nutrient elements from the roots to the shoots. The exudation capability of plants differs, the usual sap volume hardly surpasses 1 mL; however, cucumber is amongst the few plants whose exudation rate is remarkably high. The adequate sap volume deposited on the quartz carriers can be investigated by TXRF after internal standardization (generally achieved with Ga) and drying procedure on a hot plate.




Principle

XRF describes the process where some high-energy radiation excites atoms by shooting out electrons from the innermost orbitals. When the atom relaxes, that is, when outer electrons fill inner shells, X-Ray fluorescence radiation is emitted.
Total-reflection X-ray fluorescence (TXRF) is a multi-element simultaneous analysis technology developed based on X-ray fluorescence (XRF). An aircooled X-ray tube generates an X-ray beam, which is reduced to a narrow energy range by a multi-layer monochromator. The fine beam impinges on a polished sample carrier at a very small angle and is totally reflected.

Applications

XRF is widely used as a fast characterization tool in many analytical labs across the world, for applications as diverse as metallurgy, forensics, polymers, electronics, archaeology, environmental analysis, geology and mining.

Procedure

1. Primary X-rays knock out an electron from one of the orbitals surrounding the nucleus within an atom of the material.
2. A hole is produced in the orbital, resulting in a high energy, unstable configuration for the atom.
3. To restore equilibrium, an electron from a higher energy, outer orbital falls into the hole. Since this is a lower energy position, the excess energy is emitted in the form of fluorescent X-rays.
The energy difference between the expelled and replacement electrons is characteristic of the element atom in which the fluorescence process is occurring – thus, the energy of the emitted fluorescent X-ray is directly linked to a specific element being analyzed.

Materials

XRF spectrometer (including X-ray source, sample chamber, analysing crystal, detector and signal processing computer)
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