xrf microscopy and micro-spectroscopy -...

XRF Microscopy and Micro-Spectroscopy

Campinas 22/08/2016DVTEC – Laboratório de Instrumentação Nuclear

Asst. Prof. Hudson W.P. [email protected] of Applied X-ray Spectroscopy

CENA-USP

DVTEC – Laboratório de Instrumentação Nuclear

Overview

Micro-speciation, what for?

Sample preparation strategies

PCA and LC

Hands on: Quantitative analysis of Zn accumulation spot the

body of Daphnia magna


USB Stick Lecture

Data for hands on tutorial

Literature


Micro-speciation, what for?



Speciation using hard X-rayWhich spectroscopic tools?

XANES

Pre-edge

EXAFS

XRF weak lines

1XRF Microscopy and Micro-Spectroscopy


Why Micro-Speciation ? A simple example from materials science

2

A catalytic reactor: A tube filled with SiO2+ few wt% of a transition metal

Gas inlet Gas outlet

Is the metal chemical species the same along the tube?

P 1 P 2 P 3 P 4 P 5 P 6



Cu and Zn species depend on the position

3

Long time ago, catalysis scientists realized that catalysts must be studied in operando.



What about plants? Plants are far more complex than a glass tube with SiO2 inside!

4

0.90 mm

Two approaches:Where is it? What is it?

Xylem

Phloem

Phaseolus vulgaris, stem cross sectionTatiane Nishida, Masters ThesisCENA-USP



What about plants? Plants are far more complex than a glass tube with SiO2 inside!

5

0.90 mm

Two approaches:Where is it? What is it?

Xylem Phloem

Would you expect Feand Ca to be homogenously distributed?

Phaseolus vulgaris, stem cross sectionTatiane Nishida, Masters ThesisCENA-USP


X-ray Absorption Spectroscopy for the Direct Analysis of Solids


Elemental distribution

Distribution is discrete!

6

Ca

Fe

And the speciation?

Phaseolus vulgaris, stem cross sectionTatiane Nishida, Masters ThesisCENA-USPData record at LIN-CENA with an Orbis PC EDAX


Phytopatology leaf of Syzygium spp. carrying rust disease. At the disease spot one can see higher P and S concentration, whereas Ca is lower and K completely absent. Fe is distributed along the leaf presenting hotspots



Chemical speciation Distribution is discrete!

8

Phaseolus vulgaris, splitted beanSusi Savassa, Doctoral ThesisCENA-USPData recorded at XRF-LNLS



Sample preparation strategies



9

Several possibilities

X- not recomended for speciation

or radiation dose is <106



10

Is this procedure correct?

Cut Oven dried

For micro distribution: maybe yes…

For speciation: probably not http://www.agencia.cnptia.embrapa.br/Repositorio/muda_000fkmu488h02wyiv80sq98yq5k5aq1s.jpg



11

Some examples from our group @CENA-USP

In vivo spectroscopy

μ-XRF

XAFS2-LNLS

HH-XRFXRF-LNLS


DVTEC – Laboratório de Instrumentação Nuclear XRF Microscopy and Micro-Spectroscopy

PCA and LC



Procedure/mechanics

Component 1Component 2Component 2

Energy (eV)Number of pure

components

Pure spectra

Energy (eV)

Tem

pe

ratu

re

Tim

e

pH

Spectrum 1Spectrum 2Spectrum 3Spectrum 4Spectrum 5Spectrum 6Spectrum 7Spectrum 8Spectrum 9

Set of XAS data

c1

Concentration profiles

c2 c3

Tem

pe

ratu

re (

oC

)

How many components in total? The same as the number of spectra

How many principal components? PCA tells us you

How do I know whether a reference is part of the mixture?Target transformation

Once you know how many PC and the references….Perform linear combination fitting



Example: Transformation of Mo under reaction conditions

How many principal components?

How is Mo converted from one state to another?

Are there any intermediates?



How many principal components?

Three PC seems to be suitable





Linear combination analysis

DVTEC – Laboratório de Instrumentação Nuclear XRF Microscopy and Micro-Spectroscopy

Hands on:Quantitative analysis of Zn accumulation spot

in the body of Daphnia magna



Daphnia magna is a bio indicator

Chemical image recorded in our lab at CENA-USP



Daphnia magna is a bio indicator

Our equipment, Orbis PC, already plots the intensities



Quantitative XRF

IF = C.S.A

Elemental sensitity ≈ geometry, absorption, fluorescence yield, detector efficiency....

Absorption factor:Thin samples = 1 Thick samples= 1 / μ ρ D ( infinity thickness)

Concentration

Is the sample is thin

C = IF / S How to calculate the sensitivity?



Use a standard reference material to determine the sensitivity

51.6 51.8 52.0 52.2

33.8

34.0

34.2

coordinate xC

oord

inate

y

180.0

186.1

192.3

198.4

204.5

210.6

216.8

222.9

229.0

Net intensity

1st open the ‘Padrão Zn micromatter’ excel file 2nd Since the reference is not homogenous, take the average signal 3rd Determine the equipment's sensitivity for Zn

Standard: ZnTe 47.70 μg cm-2

Zn 16.16 μg cm-2

All coordinates in mm

http://www.micromatter.com/xrf.php



Plot the D. magnas’ data

4th open the ‘D_magna_nano_ZnO_treated’ excel file 5th Convert the intensities to concentration using the formula C =If / S 6th Plot the data

48.2 48.0 47.8 47.6 47.4 47.2

36.8

36.6

36.4

36.2

36.0

coordinate x

coord

inate

y

20.00

415.0

810.0

1205

1600

1995

2390

2785

3180

Net intensity

48.2 48.0 47.8 47.6 47.4 47.2

36.9

36.8

36.7

36.6

36.5

36.4

36.3

36.2

36.1

36.0

coordinate x

coord

inate

y

2.000

33.25

64.50

95.75

127.0

158.3

189.5

220.8

252.0

ug cm^-2



Plot the D. magnas’ data

D. magnaJoyce Paula, Doctoral ThesisCENA-USPData recorded at our lab


Summary

X-ray Absorption Spectroscopy for the Direct Analysis of Solids 22

Micro analysis:Useful when samples are not homogenous in micro scale level Allows you to locate and explore the chemical environment

Sample preparation: Main rule: don’t change your sample into something else

PCA and LC:Helps you to solve mixtures


Recommended Literature


Regular courses @CENA-USP / 2nd Semester

CEN5792- Principles of Nuclear and Electronic Spectroscopy (Aug-Sep)

CEN5785- Introduction to XRF and XAFS Spectroscopy (Oct-Dec)

Thank You [email protected]

Young Researcher FAPESP 2015-2019/05942-0 Multi-User Equipment FAPESP 2015-2017/19121-8 SPRINT FAPESP 2016-2018/50014-6 FINEP 01.12.0535.00 USP-Santander Mobilidade Novos Docentes 2016/2017

Funding:

Group of Applied X-ray Spectroscopyhttp://hudson731.wix.com/xraysatcena

X-rays Enlightening the Fate of Nanomaterials in Agriculture and Environment


PPG CENA Nota 7 Capes Título: Ciências

[email protected]

X-rays Enlightening the Fate of Nanomaterials in Agriculture and Environment

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