Review of TXRF Applications for Trace Elemental Analysis

Review of TXRF Applications for Trace Elemental Analysis 

Mike Beauchaine 

TXRF Product Manager, Bruker AXS Inc. 

Madison, Wisconsin

Principles X-ray fluorescence (XRF) 

spectroscopy 

1 

2 

3 1. An X-ray quantum hits an inner 

shell electron in a (sample) 

atom. The electron is removed 

leaving the atom in an excited 

state 

2. The missing inner shell electron 

is replaced by an electron from 

an outer shell 

3. The energy difference between 

the inner and outer shell is 

balanced by the emission of a 

photon (X-ray fluorescence 

radiation)

Principles X-ray fluorescence (XRF) 

spectroscopy 

• The energy, and therefore the wavelength, of the X-ray 

fluorescence radiation is characteristic for the different 

chemical elements. 

QUALITATIVE ANALYSIS 

• The intensity of the X-ray fluorescence radiation is, in first 

approximation, proportional to the element concentration. 

QUANTITATIVE ANALYSIS 

Low Z High Z

Principles of X-ray fluorescence (XRF) 

spectroscopy 

Each element shows a specific line 

pattern in a spectrum depending on 

the orbitals involved 

LK transition = Kα line 

MK transition = Kβ line 

ML transition = Lα line 

NL transition = Lβ line

Principles of ED X-ray fluorescence (ED- 

XRF) spectroscopy

Principles of ED X-ray fluorescence (ED- 

XRF) spectroscopy

Principles of WD X-ray fluorescence (WD- 

XRF) spectroscopy

Principles of WD X-ray fluorescence (WD- 

XRF) spectroscopy

Principles of total reflection X-ray 

fluorescence spectroscopy 

Quantification in common X-ray fluorescence spectroscopy 

absorption of primary beam 

and fluorescence radiation 

secondary fluorescence 

enhancement 

Ii = f (ci, cj) and ci = f (Ii, cj)


fluorescence (TXRF) spectroscopy 

Total reflection X-ray fluorescence spectroscopy 

monochromator 

X-ray tube 

detector 

sample disc 

• Samples must be prepared on a reflective media 

• Polished quartz glass or polyacrylic glass disc 

• Dried to a thin layer, or as a thin film or microparticle 

Beam angle: 0 o / 90 o


Quantification 

C 

i 

= 

C 

IS 

⋅ 

N 

N 

IS 

C i: Element concentration 

i 

⋅ 

⋅ 

S 

S 

i 

IS 

C IS: Internal standard concentration 

N i: Element net countrate 

N IS: Internal standard net countrate 

S i: Element sensitivity factor 

S IS: Internal standard sensitivity factor



In TXRF the samples are prepared 

as thin films or layers 

Matrix effects are negligible 

Quantification is possible



In TXRF the samples are prepared 

as thin films or layers 


Quantification is possible 

• TXRF detects elements from Na(11) 

to U(92) 

• The element sensitivities depend on 

the atomic number 

• The sensitivity factors are calibrated 

ex works 

• Quantification requires the addition 

of one standard element 

K-lines 

Element sensitivity 

L-lines 

Atomic number



Samples for TXRF 

• Powders: Direct preparation 

or as suspension 

• Liquids: Direct preparation 

• Always as a thin film, micro fragment or 

suspension of a powder 

• Necessary sample amount: 

Low µg respectively µl range 

Simple quantification 


due to thin layer 

Quantification is possible by internal 

standardization

Elements measured by the Mo PICOFOX

Elements measured by the W PICOFOX

TXRF Spectrum 

Multi-element standard

Typical TXRF Results 

Multi-element standard 

Element Conc./(mg/l) LLD/(mg/l) 

Ca 0.991 0.003 

Ti 0.997 0.003 

V 0.986 0.002 

Cr 0.994 0.002 

Mn 1.015 0.002 

Fe 0.996 0.001 

Co 1.006 0.001 

Ni 1.005 0.001 

Cu 1 0.001 

Zn 0.989 0.001 

As 1.019 0 

Se 1.1 0 

Sr 0.987 0

The instrument - S2 PICOFOX 

Benchtop TXRF Spectrometer 

S2 Picofox 

Metal ceramic X-ray tube 

Mo or W anode 

Air cooled 

Multilayer Monochromator 

Xflash ® silicon drift detector 

Electro-thermally cooled 

≤149 eV @ MnKα 100 kcps 

Automatic Version 

25 sample cassette changer

Review of TXRF Applications

Current research areas 

Environmental / 

Ecology 

Clinical Research / 

Biology 

Nanoparticles Food/Beverage 

Forensics Semiconductor 

Pharmaceutical/ 

Nutraceutical 

University 

Research

Sample preparation 

Liquid and digested samples 

You‘ll need just a few steps for the preparation of liquid samples 

fill sample in micro tube 

add internal standard 

homogenize 

Note: high matrix samples pipette on carrier 

may require a dilution step


Final steps 

dry by heat / vacuum 

load the instrument 

start data aquisition

Liquid Samples 

Trace Element Analysis in Serum & Blood 

Measurements and sample preparation 

Blood Serum 

Dilution, Ultrapure water 

Int. Standard, Ga 

TXRF 

Whole Blood 

Digestion, 10% 

tetramethylammonium 

hydroxide @ 1 hr 

Dilute in 2% HCl 

solution



• Comparison of TXRF to ICP-MS reference values for trace elements in 

whole blood 

• Good concordance of TXRF with reference values for essential elements 

• Other elements (P, S, Cl, K, Ca, Br, Rb, Sr) could also be determined 

during One measurement 

• Samples analyzed at 600s



• Comparison of TXRF and AAS reference values in blood serum 

• TXRF has better standard deviations compared to AAS 

• No Digestion procedure was applied 

• Samples analyzed at 600s

Application studies 

Sample preparation for solids 

Sample preparation of 

plants, tissues, grains 

Solid materials are ground to fine particle size 

and resuspended for direct analysis without 

digestion 

fill powder in mortar 

grind carefully 

weigh about 20-50 mg 

transfer to tube



suspend in detergent solution 

add standard 

homogenize 

pipette on carrier



dry by heat / vacuum 

load the instrument 

start data aquisition

Application Studies 

Wheat Flour 

Source 

Announcement of the 

Federal Reserve Bank Of 

Minneapolis 

Sales price for Se-poor wheat: < 3 US$/bushel 

Sales price for Se-rich wheat: < 10 – 15 US$/bushel


Wheat Flour 

Demand for on-site analysis 

of Se in wheat 

Requirements 

Fast and easy sample 

preparation 

Rugged equipment with 

no need for external 

media 

High sensitivity/accuracy


Wheat Flour 

Results 

element 

concentrations 

Reference Values (mg/kg) 

10000 

1000 

100 

10 

1 

0 

Se 

Ni 

Zn 

Cu Br 

Ba 

Rb 

Mn 

0 1 10 100 1000 10000 

Fe 

Ca 

TXRF Values (mg/kg) 

Cl 

P 

S 

K


Wheat Flour 

Results 

element 

concentrations 

Reference Values (mg/kg) 

10000 

1000 

100 

TXRF-value: 1.40 ± 0.03 mg/kg 

Reference: 1.23 ± 0.90 mg/kg 

3σ LLD: 60 µg/kg 

10 

1 

0 

Se 

Ni 

Zn 

Cu Br 

Ba 

Rb 

Mn 

0 1 10 100 1000 10000 

Fe 

Ca 

TXRF Values (mg/kg) 

Cl 

P 

S 

K


Palladium Analysis 

Introduction: 

• Palladium is extensively used in pharmaceutical small molecule drug 

processes as a catalyst 

• It must be removed prior to release of the API 

• Looking for an easy to use technique with fast sample prep and little to no 

consumables that can be implemented on the manufacturing floor 

Study: 

• 6 separate pharmaceutical drugs 

• Standards 

• Determine linearity, sensitivity, accuracy, and precision for Pd plus Cr, Fe, 

Cu, Rh, and Pt 

• Compare TXRF vs. ICP-MS instrumentation 

14.02.2012



• TXRF Solid Samples Preparation 

5 – 10 mg 

of Sample 

14.02.2012 

Diluent Choice 

Internal 

Standard(s) 

Sample Prepared in 

Organic Solvent / 

Dilute Acid Diluent 

Sample Solution 

Spotted 

and Dried 

on Substrate 

Detector 

Sample 

TXRF 

Sample Spot 

Analysis



Conclusion 

o The choice of the X-ray target is very important for Pd 

analysis because of the Pd-L line interferes with Ar-K line 

o TXRF can accept organic solvent-based diluents 

o Instrument is easy enough for a technician to be able to run 

samples at or near the plant floor 

o Also allows for fast analysis of impurities with small sample 

size requirements 

Acknowledgments: Bradley Shaw, David Semin, et.al Analytical and Research Development, Amgen Inc. 

Thousand Oaks, CA “Comparison of Total Reflection X-Ray Fluorescence (TXRF) to Inductively-Coupled 

Plasma Spectrometry (ICP-MS): Applicability of TXRF for Open-access 

14.02.2012


Microparticles 

Microparticles are measured semi-quantitatively and 

non-destructively 

dab vacuum grease on carrier 

pick-up some particles with a (glass) rod 

drop particles on grease

Particles 

Characterization of nanoparticles 

Analytical question 

element ratios in CdSe nanoparticles 

coated with ZnS 

Analytical issues 

extremely small sample amount (R&D) 

non-destructive method preferred 

TXRF measurement 

transfer of nanoparticles to quartz carrier 

by cotton bud 

standardless quantification 

Results 

even smallest sample amounts allow the 

determination of element ratios in 

nanoparticles

Particles 

Characterization of nanoparticles 

Results 

even smallest sample 

amounts allow the 

determination of 

element ratios in 

nanoparticles 

S2 PICOFOX 

“Standardless” 

analysis applied 

Ratio (wt.-%) 

12 

10 

8 

6 

4 

2 

0 

10 

Element ratios of nanoparticles 

1 

Zn/S Cd/Se Zn/Cd 

Measured ratios of 3 samples 

versus target value () 

4 

Sample 1 

Sample 2 

Sample 3

Application Examples 

Conclusion 

Accuracies and Sensitivities comparable to AAS or ICP without the need for 

complex and time-consuming sample preparation and instrument calibration 

• Ability to analyze minute 

samples 

• Allows for analysis of toxic 

and nutritious elements at 

very low levels 

• Virtually any sample is 

possible with limited 

sample prep (powders, 

nanoparticles, liquids, thin 

films, etc.) 

• Elements Na to U within one 

measurement 

• Detection limits of 1 to 100 ppb 

for most elements

© Copyright Bruker Corporation. All rights reserved. 

www.bruker.com

Review of TXRF Applications for Trace Elemental Analysis

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