X-ray fluorescence (XRF) spectrometry XRF is an analytical method - - PowerPoint PPT Presentation

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X-ray fluorescence (XRF) spectrometry XRF is an analytical method - - PowerPoint PPT Presentation

Nov 16, 2022 564 likes •1k views

X-ray fluorescence (XRF) spectrometry XRF is an analytical method to determine the chemical composition of the materials in solid, liquid, powder, filtered, or other form. The method is fast, accurate and non- destructive, and usually

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X-ray fluorescence (XRF) spectrometry

XRF is an analytical method to determine the chemical composition of the materials in solid, liquid, powder, filtered, or other form. The method is fast, accurate and non- destructive, and usually requires only a minimum of sample preparation.

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Spectrometer systems

  • Energy dispersive system (EDXRF)

(C-U)

  • Wavelength dispersive system (WDXRF)

(Be-U) The concentration range: ppm-100%.

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Basics of XRF

X-rays

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Interaction of X-rays with matter

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Production of characteristic fluorescent radiation

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The Siegbahn and IUPAC notation (e.g. Fe Kα, Cr KL3)

Siegbahn IUPAC Siegbahn IUPAC Kα1 K-L3 Lα1 L3-M5 Kα2 K-L2 Lα2 L3-M4 Kβ1 K-M3 Lβ1 L2-M4 Kβ3 K-M2 Lβ2 L3-N5

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[ ]

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1 σ λ − ⋅ = Z K

Moseley law

λ, wavelength; K, constant; Z, atomic number; σ, constant.

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The fluorescence yield is the ratio of the emitted fluorescent photons and the number

  • f incoming photons.
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Absorption and enhancement effects

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Absorption and analysis depth

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Rayleigh and Compton scatter

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Polarization

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The XRF spectrometer

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The EDXRF spectrometer

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The WDXRF spectrometer

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The WDXRF spectrometer

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FeKα FeKβ NiKα MnKα MnKβ

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Comparison of EDXRF és WDXRF spectrometers

EDXRF WDXRF Elemental range C, Na…U Be…U Detection limit Less optimal for light elements. Good for heavy elements. Good for Be an all heavier elements. Sensitivity Reasonable for light elements. Good for heavy elements. Resolution Good for light elements. Less optimal for heavy elements. Costs Relatively inexpensive. Relatively expensive. Power consumption 5-1000 W 200-4000 W Measurement Simultaneous Sequential Critical moving parts No Crystal, Goniometer

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X-ray tubes

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Secondary targets

Fluorescent targets (heavy elements). Barkla targets (e.g. Al2O3). Bragg targets (crystal). The target acts as a source, and the radiation coming from the target is used to irradiate the sample.

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Detectors

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Multi channel analyzer (MCA)

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Escape peaks and pile-up peaks

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Filters

Filters are placed between the source and the sample. Filter used to filter tube lines:

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Filter used to filter background:

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Analysing crystal and collimator

A collimator is a set of parallel plates. It is used to obtain parallel X-ray beams.

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  • Masks

( A mask is placed between the sample and the detection system.)

  • Spinner

(A spinner rotate the sample to even out the effects of non-homogeneity and scratches.)

  • Vacuum and Helium system

(Vacuum chamber. Air can significantly absorb the low-energy radiation.)

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XRF analysis

  • Sample preparation
  • XRF measurement
  • Qualitative analysis
  • Quantitative analysis

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Sample preparation

  • Representative and homogeneous sample
  • Sample holder, cup (10-100 mm Ø)
  • Sample types:

– Solids; – Powders (loose or pressed powder); – Beads (1000-1200° C, e.g. Li 2B4O7 flux); – Liquids; – Materials on filters.

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XRF measurements

  • Optimum measurement conditions:

kV mA time filter air, helium spinner etc.

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Qualitative analysis in EDXRF

  • Background fitting
  • Peak search
  • Deconvolution
  • Peak match

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Qualitative analysis in WDXRF

  • Background

subtraction

  • Peak search
  • Measuring peak

height

  • Line overlap

correction

  • Peak match

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Counting statistics and detection limits

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Elements are said to be detectable if:

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Quantitative analysis in EDXRF and WDXRF

  • Matrix effects
  • Matrix correction models
  • Calibration
  • Standardless analysis

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Fundamental parameter (FP) matrix correction models

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EDXRF spectrum (Sárisáp kaolin)

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