Plant elemental composition and portable X‐ray fluorescence (pXRF) spectroscopy: quantification under different analytical parameters

Abstract

Emergence of portable X-ray fluorescence (pXRF) systems presents new opportunities for rapid, low-cost plant analysis, both as a lab system and in situ system. Numerous studies have extolled the virtues of using pXRF for a wide range of plant applications, however, for many such applications, there is need for further assessment with regards to analytical parameters for plant analysis. While pXRF is a potential powerful research tool for elemental composition analysis, its successful use in plant analysis is made more likely by having an understanding of X-ray physics, calibration process, and ability to test a variety of homogenous and well-characterized materials for developing a matrix-specific calibration. Because potential pXRF users may often underestimate the complexity of proper analysis, this study aims at providing a technical background for plant analysis using pXRF. The focus is on elemental quantification under different analytical parameters and different methods of sample presentation: direct surface contact under vacuum, placement in a sample cup with prolene as a seal, and without the aid of a vacuum. Direct analysis on the surface of a pXRF provided highest sensitivity and accuracy (R 2 > 0.90) for light elements (Mg to P). Sulfur, K, and Ca can be reliably measured without the aid of a vacuum (R 2 > 0.99, 0.97, and 0.93 respectively), although lower detection limits may be compromised. pXRF instruments provide plant data of sufficient accuracy for many applications and will reduce the overall time and budget compared with the use of conventional techniques. Sensitivity and accuracy are dependent on the instrument's settings, make, and model. © 2015 The Authors. X-Ray Spectrometry published by John Wiley & Sons, Ltd.Additional supporting information may found in the online version of this article at publisher's web site. IntroductionKey plant nutrients, including potassium (K), phosphorus (P), and sulfur (S), play important roles in regulating processes such as photosynthesis, carbon respiration, and tissue building. Elemental analysis of plants is critical to plant studies and agriculture. However, despite the routine application of digestion-based analytical techniques in many laboratories, the slow and often hazardous sample digestion process can present a challenge in the analyses of plant nutrients, particularly where hundreds or even thousands of samples are to be analysed.[1] The conventional plant elemental analyses based on plant extracts are cumbersome and of variable accuracy and present major limitations to exploiting the full potential of plant nutrient analysis. An ideal system for analysis would include accuracy, replicability, portability, and minimal sample preparation. The technology that currently provides the best option to meet these needs is energy-dispersive X-ray fluorescence (ED-XRF), particularly in the form of a portable instrument portable X-ray fluorescence (pXRF). These instruments are commonly used for scrap metal sourcing, [2] geochemical provenience of obsidian,...

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

“…Particularly, the use of portable XRF (PXRF) systems in the determination of macro-and micronutrients in plant materials has received increased attention by the scientific community. 5,[27][28][29][30] The applicability of PXRF for total element determination, including macro-, micronutrients and the beneficial element (Si), was first demonstrated by McLaren et al 29 when analyzing corn, cotton, soybean and wheat materials. Test portions (2.0 g) composed of ground plant samples were weighed into cylindrical plastic containers and then sealed with a 76 by 40 mm rectangular sheet of 1.5 µm thick Mylar X-ray polyethylene film properly secured with a 20 mm rubber band.…”

“…Most recently, Towett et al 30 investigated several ways of sample presentation for analysis by PXRF of previously ground plant materials. The following analytical strategies were evaluated: (i) direct sample surface analysis under vacuum; (ii) use of an XRF sample cup sealed by a Prolene® thin-film window; (iii) analysis under atmospheric pressure.…”

Optimization of a primary X‐ray filter for X‐ray fluorescence analysis of uranium and plutonium

“…In this study, a Tracer III‐SD handheld XRF spectrometer (Bruker AXS Handheld, Inc., Kennewick, USA) capable of rapid onsite analysis was used. This device is light and convenient to carry, and therefore, it has been widely used for analyzing historical cultural assets, archeological bricks, plants, and architectural stones . Our Tracer III‐SD was equipped with a Ag anode X‐ray tube, a silicon drift detector with energy resolution of 142 eV, and the original primary X‐ray filter consisting of 304.8‐μm (12‐mil) Al, 25.4‐μm (1‐mil) Ti, and 152.4‐μm (6‐mil) Cu (1 mil = 1/1,000 inch [25.4 μm]).…”

“…This device is light and convenient to carry, and therefore, it has been widely used for analyzing historical cultural assets, archeological bricks, plants, and architectural stones . Our Tracer III‐SD was equipped with a Ag anode X‐ray tube, a silicon drift detector with energy resolution of 142 eV, and the original primary X‐ray filter consisting of 304.8‐μm (12‐mil) Al, 25.4‐μm (1‐mil) Ti, and 152.4‐μm (6‐mil) Cu (1 mil = 1/1,000 inch [25.4 μm]). Portable XRF devices such as XL3t‐950S (Thermo Fisher Scientific Inc.) used in our previous study are usually equipped with their primary X‐ray filters, and users cannot use their own filter.…”

Portable X-ray fluorescence (pXRF) applications in tropical Soil Science

“…Towet, Shephred and Drake (2015) evaluated the composition of leaves of several plants by using pXRF and found a high correlation (R 2 > 0.90) for Mg, P, S, K, Ca and Mn contents with those obtained by the traditional acid digestion followed by determination by ICP-OES.…”