mike beauchaine txrf

Review of TXRF Applications for Trace Elemental Analysis

Mike BeauchaineTXRF 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

Each element shows a specific line pattern in a spectrum depending on the orbitals involved

LK transition = K line

MK transition = K line ML transition = L line

NL transition = L line

Principles of X-ray fluorescence (XRF) spectroscopy

Principles of ED X-ray fluorescence (ED-XRF) spectroscopy

Principles of WD X-ray fluorescence (WD-XRF) spectroscopy

Principles of total reflection X-ray fluorescence spectroscopy

absorption of primary beamand fluorescence radiation

secondary fluorescenceenhancement

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

Quantification in common X-ray fluorescence spectroscopy

Principles of total reflection X-ray fluorescence (TXRF) spectroscopy

X-ray tube

monochromator

detector

sample disc

Total reflection X-ray fluorescence spectroscopy

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: 0o / 90o

Principles of total reflection X-ray Quantification

iIS

ISiISi SN

SNCC

=

Ci: Element concentration

CIS: Internal standard concentration

Ni: Element net countrate

NIS: Internal standard net countrate

Si: Element sensitivity factor

SIS: Internal standard sensitivity factor


In TXRF the samples are prepared as thin films or layers

Matrix effects are negligible Quantification is possible


Element sensitivity

L-linesK-lines

Atomic number

In TXRF the samples are prepared as thin films or layers

Matrix effects are negligible 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


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 g respectively l range

Simple quantification

Matrix effects are negligible due to thin layer

Quantification is possible by internal standardization

Elements measured by the Mo PICOFOX

Elements measured by the W PICOFOX

TXRF SpectrumMulti-element standard

Typical TXRF ResultsMulti-element standard

Element Conc./(mg/l) LLD/(mg/l)Ca 0.991 0.003Ti 0.997 0.003V 0.986 0.002

Cr 0.994 0.002Mn 1.015 0.002Fe 0.996 0.001Co 1.006 0.001Ni 1.005 0.001Cu 1 0.001Zn 0.989 0.001As 1.019 0Se 1.1 0Sr 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 @ MnK 100 kcps

Automatic Version 25 sample cassette changer

Review of TXRF Applications

Current research areas

Environmental /Ecology

Clinical Research / Biology Forensics Semiconductor

Nanoparticles Food/Beverage Pharmaceutical/NutraceuticalUniversity Research

Sample preparationLiquid and digested samples

fill sample in micro tube

add internal standard

homogenize

Note: high matrix samples pipette on carrier

may require a dilution step

Youll need just a few steps for the preparation of liquid samples

Sample preparationFinal steps

dry by heat / vacuum

load the instrument

start data aquisition

Liquid SamplesTrace 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

fill powder in mortar

grind carefully

weigh about 20-50 mg

transfer to tube

Solid materials are ground to fine particle size and resuspended for direct analysis without digestion

Sample preparation of

plants, tissues, grains

Application studiesSample preparation for solids


suspend in detergent solution

add standard

homogenize

pipette on carrier


dry by heat / vacuum

load the instrument

start data aquisition

Application StudiesWheat Flour

SourceAnnouncement of the Federal Reserve Bank Of Minneapolis

Sales price for Se-poor wheat: < 3 US$/bushelSales price for Se-rich wheat: < 10 15 US$/bushel

Application studiesWheat 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

01

10

100

1000

10000

0 1 10 100 1000 10000

TXRF Values (mg/kg)

R

e

f

e

r

e

n

c

e

V

a

l

u

e

s

(

m

g

/

k

g

)


Results

element concentrations

Ni

Rb

BaCu Br

Mn

Zn Fe

Ca

Cl

S

P K

Se

01

10

100

1000

10000

0 1 10 100 1000 10000

TXRF Values (mg/kg)

R

e

f

e

r

e

n

c

e

V

a

l

u

e

s

(

m

g

/

k

g

)


Results

element concentrations

Ni

Rb

BaCu Br

Mn

Zn Fe

Ca

Cl

S

P K

Se

TXRF-value: 1.40 0.03 mg/kgReference: 1.23 0.90 mg/kg3 LLD: 60 g/kg

Application studiesPalladium 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


14.02.2012

Sample Prepared in

Organic Solvent /

Dilute Acid Diluent

5 10 mg

of Sample

Sample

Detector

Sample Solution

Spotted

and Dried

on Substrate

TXRF

Sample Spot

AnalysisInternal

Standard(s)

Diluent Choice

TXRF Solid Samples Preparation


Conclusion

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

Sample preparationMicroparticles

dab vacuum grease on carrier

pick-up some particles with a (glass) rod

drop particles on grease

Microparticles are measured semi-quantitatively and non-destructively

ParticlesCharacterization 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

Results

even smallest sample amounts allow the determination of element ratios in nanoparticles

S2 PICOFOXStandardless analysis applied

ParticlesCharacterization of nanoparticles

Element ratios of nanoparticles

Sample 2Sample 1

Sample 3

10

1

4

0

2

4

6

8

10

12

Zn/S Cd/Se Zn/Cd

R

a

t

i

o

(

w

t

.

-

%

)

Measured ratios of 3 samples versus target value ()

Application ExamplesConclusion

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

Accuracies and Sensitivities comparable to AAS or ICP without the need for complex and time-consuming sample preparation and instrument calibration

mike beauchaine txrf

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