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Sample Preparation and
Calibrations: Getting the best
results using XRF
Chris Shaffer
Thermo Fisher Scientific
CH-1024 Ecublens
Sources of Error in XRF Sample Related
 Sample preparation method
 Grain size effects (ideally should be less than 50 m)
 Mineralogical effects
 Line interference due to overlap of one X-ray line on another
 Absorption (100%): matrix effect
 Enhancement (10%): matrix effect
 Sample selection
 Sample deterioration (e.g filters, polymers, sedimentation in
liquids)
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Sources of Error in XRF Sample Related
 Sample preparation method
 Grain size effects (ideally should be less than 50 m)
 Mineralogical effects
3
Sample Homogenization
4
Petroleum
Rocks, Soils and
Minerals
Glass, Ceramic and
Refractories
Polymers
Rocks, Soils and Minerals
How do we get a representative
sample?
5
Rocks, Soils and Minerals
How do we get a representative
sample?
Random Sampling
6
Rocks, Soils and Minerals
How do we get a representative
sample?
Random Sampling
Crusher
7
Rocks, Soils and Minerals
How do we get a representative
sample?
Random Sampling
Crusher
Riffler
Grinding
8
Sample Grinding: Rocks, Soils, Mineral,
Refractories, Ceramics, etc
Can Be
• As simple as Mortar and pestle
9
Sample Grinding: Rocks, Soils, Mineral,
Refractories, Ceramics, etc
Can Be
• As simple as Mortar and pestle
• Miller Mill
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Sample Grinding: Rocks, Soils, Mineral,
Refractories, Ceramics, etc
Can Be
• As simple as Mortar and pestle
• Miller Mill
• Planetary Mill
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Sample Grinding: Rocks, Soils, Mineral,
Refractories, Ceramics, etc
Can Be
• As simple as Mortar and pestle
• Miller Mill
• Planetary Mill
• Puck Mill
12
Liquids (Oils, Fuel, Diesel, etc)
• Most common and easiest
is using Magnetic Stirrer
13
Liquids (Oils, Fuel, Diesel, etc)
• Most common and easiest
is using Magnetic Stirrer
• Conical Mixer
14
Liquids (Oils, Fuel, Diesel, etc)
• Most common and easiest
is using Magnetic Stirrer
• Conical Mixer
• Wrist Action Shaker
15
Liquids (Oils, Fuel, Diesel, etc)
• Most common and easiest
is using Magnetic Stirrer
• Conical Mixer
• Wrist Action Shaker
• Tabletop Shaker
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Polymers
• Cryogenic Mill
•
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Polymers
• Cryogenic Mill
• Shear Mill
• Extruder
• Sample Prep:
• Hot Press
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Polymers
• Cryogenic Mill
• Shear Mill
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Polymers
• Cryogenic Mill
• Shear Mill
• Extruder
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Polymers
• Cryogenic Mill
• Shear Mill
• Extruder
• Sample Prep:
• Hot Press
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Sample Preparation Conventional Solid Samples
Polymer or
Fused Glass Bead
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Bulk Sample
(Metal, Glass or
Pressed Powder)
Preparation of Powders as Pressed Pellets
To prevent analytical problems due to grain size effects, it is recommended
to grind to less than 50 microns
Briquet method
Apply pressure
Crush, grind
and mix
To grain
size <90um
5
To standard holder
Press
Weigh out
Die
Mortar or crusher
Protective ring
Specimen
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Pressed Pellets Methods
• Hydraulic Press
• Manual
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Pressed Pellets Methods
• Hydraulic Press
• Manual
• Semi-Automatic
25
Pressed Pellets Methods
• Hydraulic Press
• Manual
• Semi-Automatic
• Fully Automatic
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Pressed Pellets Methods
• Hydraulic Press
• Manual
• Semi-Automatic
• Fully Automatic
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Preparation of Powders as Fused Beads
The fusion of mineral, ceramic or raw materials samples into an
amorphous glass disk (also called bead) allows to prevent analytical
problems due to grain size effects and mineralogical effects
Melting method
Weigh out
and mix
Flux + Specimen
Heat for
Melting
Cast & Cool
1000° -1100° C
To standard holder
Glass disk
specimen
Platinum crucible
Remove bubbles
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Fusion Procedure
Step 1) Ignite:
LOI
(950⁰C for 1hr)
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Fusion Procedure
Step 1) Ignite:
Step 2) Weigh out:
Sample
Flux
(Wetting Agent)
(Oxidizer)
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Fusion Procedure
Step 1) Ignite
Step 2) Weigh out:
Step 3) Mix:
Stir Components
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Fusion Procedure
Step 1) Ignite:
Step 2) Weigh out:
Step 3) Mix:
Step 4) Fusion:
Gas or Electric
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Fusion Procedure
Step 1) Ignite:
Step 2) Weigh out:
Step 3) Mix:
Step 4) Fusion:
Step 5) Alternative
LOI:
Reweigh Sample
+ Crucible
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Fusion Procedure
Step 1) Ignite:
Step 2) Weigh out:
Step 3) Mix:
Step 4) Fusion:
Step 5) Alternative
Step 6) Clean:
Ultrasonic Bath
10% HNO3 or HCl
Never Both
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Fusion Procedure
Step 1) Ignite:
Step 2) Weigh out:
Step 3) Mix:
Step 4) Fusion:
Step 5) Alternative
LOI:
Step 6) Clean:
Step 6) Polish or
Resurface :
Element migration
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Alternative to Fusion Instruments
• Add Sample into
Graphite Crucibles
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Alternative to Fusion Instruments
• Add Sample into
Graphite Crucibles
• Place Crucibles into
Muffle Furnace
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Alternative to Fusion Instruments
• Add Sample into
Graphite Crucibles
• Place Crucibles into
Muffle Furnace
• Grind Samples
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Alternative to Fusion Instruments
• Add Sample into
Graphite Crucibles
• Place Crucibles into
Muffle Furnace
• Grind Samples
• Fuse Again in Muffle
Furnace
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Alternative to Fusion Instruments
• Add Sample into
Graphite Crucibles
• Place Crucibles into
Muffle Furnace
• Grind Samples
• Fuse Again in Muffle
Furnace
• Polish on Wet Diamond
Wheel
40
Solids and Powder sample issues
• Pressed pellets
• Must grind to a uniform partial size
• Press samples under exactly the same conditions each time
• Binders can be used to solidify pellets (Cellulose, Boric acid, etc) but must
same and cannot analyze elements in contained in binder
• Backers can be implemented for analysis of small amounts of sample
• Fused beads
•
•
•
•
Dilutes samples and time consuming
Evolve off volatile elements
Attach Pt ware
Overlap issues with wetting agents
• Solids
• Surface the same for each sample
• Be aware of infinite thickness issues
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Loose Powders and Liquids
Loose Pellets or
Granules
42
Liquids
Preparation of Liquids Standard method
Take up
specimen
Seal up liquid holder
Standard
cassette
Specimen
Polymer
container
Use liquid sample holder
and measure under
Helium atmosphere
Mylar film
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Liquid Procedure
• Liquid/ Loose Powers cups
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Liquid Procedure
• Liquid/ Loose Powers cups
• Mounting the cell
• Choosing the film
• Fill Cell:
• Pipette or
• Balance
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Liquid Procedure
• Liquid/ Loose Powers cups
• Mounting the cell
• Choosing the film
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Liquid Procedure
• Liquid/ Loose Powers cups
• Mounting the cell
• Choosing the film
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Liquid Procedure
• Liquid/ Loose Powers cups
• Mounting the cell
• Choosing the film
• Fill Cell:
• Pipette or
• Balance
48
Loose Powders and Liquids Sample Issues
• Liquids
• Definite issues regarding infinite thickness
• Escape depth through film for light elements and He absorption
• Very matrix dependent
• Loose powder
• Packing, particle size and mineralogical issues
• Escape depth through film for light elements
• Possible infinite thickness issues
49
Loose Powders and Liquids Sample Issues
• Liquids
• Definite issues regarding infinite thickness
• Escape depth through film for light elements and He absorption
• Very matrix dependent
50
Loose Powders and Liquids Sample Issues
• Liquids
• Definite issues regarding infinite thickness
• Escape depth through film for light elements and He absorption
• Very matrix dependent
Analyte Line Graphite Glass
51
Iron
Lead
Analyte Line Graphite Glass
U
La1
28000
1735
154
Pb
Hg
Lb1
La1
22200
10750
1398
709
125
65.6
22.4 Mn
63.9 Cr
34.9 Ti
W
Ce
La1
Lb1
6289
1484
429
113
40.9
96.1
22.4 Ca
6.72
Ba
Sn
La1
La1
893
399
71.3
44.8
61.3
30.2
4.4
Cl
3.34
Cd
Mo
Zr
Ka
Ka
Ka
144600
60580
44130
8197
3600
2668
701
314
235
77.3
Si
36.7
Al
28.9
Sr
Br
Ka
Ka
31620
18580
1947
1183
173
106
24.6 Mg
55.1 Na
As
Zn
Kb
Ka
17773
6861
1132
466
102
44.1
53 F
24 O
Cu
Ni
Fe
Ka
Ka
Ka
5512
4394
2720
380
307
196
36.4
29.8
164
20 N
16.6 C
11.1 B
K
S
Iron
Lead
Ka
Ka
2110
1619
155
122
131
104
9.01
7.23
Ka
Ka
920
495
73.3
54.3
63
36.5
4.52
3.41
Ka
Ka
Ka
Ka
355
172
116
48.9
40.2
20.9
14.8
16.1
27.2
14.3
10.1
4.69
3.04
2.19
4.83
2.47
Ka
Ka
31.8
20
10.5
7.08
3.05
1.92
1.7
1.13
Ka
Ka
12
3.7
5.56
1.71
1.15
0.356
0.728
0.262
Ka
Ka
Ka
Ka
1.85
2.5 0.178 0.143
0.831 1.11 0.0802 0.0713
13.6 0.424 0.0311 0.0312
4.19 0.134
0.01 0.0117
Layer Thickness (in µm), from where 90% of the Fluorescence
Radiation originates (L lines and K Lines)
Loose Powders and Liquids Sample Issues
• Liquids
• Definite issues regarding infinite thickness
• Escape depth through film for light elements and He absorption
• Very matrix dependent
52
Loose Powders and Liquids Sample Issues
• Liquids
• Definite issues regarding infinite thickness
• Escape depth through film for light elements and He absorption
• Very matrix dependent
53
Trace and Light Element Analysis in Liquids
• Filter Pad Analysis
• Eliminate films
• Concentrate Sample
54
Trace and Light Element Analysis in Liquids
• Filter Pad Analysis
• Eliminate films
• Concentrate Sample
• Add by weight or
volume
55
Trace and Light Element Analysis in Liquids
• Filter Pad Analysis
• Eliminate films
• Concentrate Sample
• Add by weight or
volume
• Place droplets
uniformly over surface
56
Trace and Light Element Analysis in Liquids
• Filter Pad Analysis
• Eliminate films
• Concentrate Sample
• Add by weight or
volume
• Place droplets
uniformly over surface
• Allow to dry
57
Mg LoD = 0.2 ppm
Trace and Light Element Analysis in Liquids
• Filter Pad Analysis
• Eliminate films
• Concentrate Sample
• Add by weight or
volume
• Place droplets
uniformly over surface
• Allow to dry
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Na LoD = 0.2 ppm
Calibrations
Analysis Types
• Standard Linear Regression Analysis
• Factory calibrations
• Onsite calibrations
• Create your own
• Semi-Quantitative or Standard-less Analysis
• QuantAS
• UniQuant
• Qualitative Analysis
• Scans
60
Linear Regression Analysis
• Standard Concentration vs. Intensity
• Must have standards
• Calibration is matrix matched
• Empirical corrections are more accurate than Fundamental
Parameters
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QuantAS™ – scan-based standard-less software
• The user friendly QuantAS optional package determines quickly
concentration levels in unknown liquid or solids samples.
• Full scan covering 70 elements from Fluorine to Uranium can be done
in only 3 minutes.
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UniQuant® - industry leading standard-less analyses
• Most advanced and powerful Fundamental Parameters algorithms
• Ideal for analysis of up to 79 elements in solid and liquids
•
•
•
•
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when standard samples are not available
when samples can only be obtained in small quantities
Or as irregular shapes
or coatings and layers on a substrate
Scan Analysis
• Qualitative peak overlays
• Quick comparisons of intensities
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Linear Regression - Defining Standards
• Types of standards
• Certified Reference Materials
• NIST, ConoStan, SCP
• In-house Reference Materials
• Certified by external labs
• Alternative instrumentation
• Criteria for Standards
•
•
•
•
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Similar Matrix
Wide enough Dynamic Calibration Range of Unknowns
Homogenous
Constant grain size (<50 µm)
Sources of Error in XRF Sample Related
 Sample preparation method
 Grain size effects (ideally should be less than 50 m)
 Mineralogical effects
 Line interference due to overlap of one X-ray line on another
 Absorption (100%): matrix effect
 Enhancement (10%): matrix effect
 Sample selection
 Sample deterioration (e.g filters, polymers, sedimentation in
liquids)
66
Sources of error in XRF Equipment related
 Systematic errors
•
•
•
•
•
•
•
67
Sample repositioning
Goniometer repositioning
X-ray tube deterioration
Short term drift
Long term drift
Dead time correction
Operating parameters selection
Step for Calibration
• 1st – Select Elements for Analysis
• Not only elements of interest but also any interfering ones present
• 2nd – Select Measurement Parameters and Conditions
• Crystal, Collimator, Detector, kV, mA, etc
• 3rd – Run Scans and Energy Profiles
• Overlap, Backgrounds, Constraints, etc
• 4th – Define and Measure Drift Corrections
• Setting Up Samples for instrument drift
• 5th - Measure Standards and Create Calibrations
• Overlap and inter-elemental correction
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Step 1: Element Selection
69
Step 2: Selecting Parameter and Conditions
• Crystals
• Detectors
• Collimators
70
• Lines
• kV
• mA
• Counting times
• PBF
Light Elements
•
•
•
•
71
Low kV and High mA is best
Always use K lines
No PBF
FPC Detector
• Crystals:
•
•
•
•
•
Be, B, C, N – all specific crystals
O, F, Na, Mg – same crystal
Al – PET
P, S, Cl – Ge111
K , Ca – LiF200
Transition Metals
• K lines
• Medium kV - medium mA
(50kV/50 mA)
• Crystals
• Either LiF200 or LiF220
• Detector
• Either FPC of SC
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• Al200: improves analysis of K lines of Ni, Cu
and Zn in all matrices
• Al750: K lines of Zn, Ga, Ge, As, Se in oils
• CuZn250: For analysis of Ru, Rh, Pd, Ag and
Cd
Heavy Metals and La and Ac Series
• Mostly 60 kV 40 mA
• Crystals
• Mostly Either LiF200 or LiF220
• Detector – SC
• Mostly 60 kV 40 mA
• Mostly L lines
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• Al500: improves analysis of L lines of Hg, Ta,
Pb, Bi
• Al20: improves analysis of L lines of Sn, Sb,
Te, I, Cs, Ba, La, Hf, Ta, W in light matrices
• Al750: improves analysis of L lines of Hg, Ta,
Pb, Bi
Analysis Considerations
Common peak overlaps
Element
V Ka
Cr Ka
Mn Ka
Fe Ka
Co Ka
Pb Ma
Pb La
Si Ka
Ti Ka
Al Ka
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Overlaps
Ti Kb
V Kb
Cr Kb
Mn Kb
Fe Kb
S Ka, Mo La
As Ka
W, Ta Ma
Ba La
Br La
Step 3: Scans and Energy Profiles
Comparison between LiF200
and LiF220
75
Resolution versus Sensitivity using Crystals
Zoomed spectral areas
76
Resolution versus Sensitivity Using Crystals
Details on Nb and Zr
77
Collimator Choice
78
Most suitable Spectral Lines
Example Zr: Heavy overlap on ZrKa by SrKb
79
Most suitable Spectral Lines
Example Zr: No overlap on ZrKb line
80
Background Situation
Comparison of 3 different samples with LiF220
81
Background Situation
Comparison of 3 different samples with LiF220
82
Background Situation
Comparison of 3 different samples with LiF220
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Background Correction
Traditional BG correction: Example Nb
84
Background Correction
Traditional BG correction: Example Nb
85
Line Overlap Correction
Example Nb: Heavy overlaps by Y
86
Line Overlap Correction
Example Nb / Y : Overlap correction for Y
87
Energy Profiles
• Escape Peaks – Ti, V, Cr, Mn, Fe, Co
88
Energy Profile- Second and Third Order
• Second order overlay from Sb on S
89
Step 4: Instrument Drift
• What is drift; Loss of intensity over time received by the instrument
detector
• X-ray source loss due to Rh filament tube decay
• Think if a light bulb filament
• Powder sample dusting of breaking
• Can block or reduce intensity of X-ray tube
• Crystal decay and decomposition
• Chemical attacks ( as discussed above)
90
What should be used as drift standards?
• Stable Solid Sample
• Glass
• Polish metal
• Drift samples do not
have to be same as
standards
• Only concerned about
elemental intensities
91
75% Principle
92
Step 5: Linear Regression Calibration
• Enter concentration values for reference standard
• The values should be entered in the same chemical composition as desired
results (i.e. elements, oxides, carbonates …)
93
Plot of Regression
Uncertainty
Standard Deviation
94
Detection Limits
limits of detection
limits of Quantification
LoD = 3√(BEC/(Q*t)
)
LoQ = (3√(BEC/(Q*t)
)*3)
•
•
•
95
BEC: background equivalent
concentration
• BEC:
background equivalent concentration
Q: sensitivity
• Q: sensitivity
t: time of analysis
• t: time of analysis
Precision
Higher sensitivities
Precision = √[(BEC + C)/(Q*t) ]
•
•
•
•
96
BEC: background equivalent concentration
C: concentration in the test sample
Q: sensitivity
t: time of analysis
Inter-Elemental Corrections
• Overlap and Background corrections
• Need samples with similar amounts of the analyte elements and containing
varying amounts of the overlapping element
• Can be difficult to find such standards in solids of powders, but easy in
liquids
Ti Overlap on Al
97
Inter-Elemental Corrections
• Mathematical correction models
• Additive Intensity (AI)
• Correction based on Intensity ( should only be used investigate
line overlaps)
• Should use binary samples for correction instead
• Additive Concentration (AC)
• Correction based on Intensity ( should only be used investigate
line overlaps
• Should use binary samples for correction instead
98
Inter-Elemental Corrections Continued
• Multiplicative Intensity (MI) or Lucas Tooth
• This correction is multiplicative and is based on interfering
intensities and used in situations were interfering element
concentrations are unknown
• Only good when net intensities are in a limited range of
concentration (10% to 20% range)
• Multiplicative Concentration (MC) or Traill Lachance
• Most commonly used matrix correction model
• Similar to MI but uses concentration instead of intensity
• ARL has made changes to allow for self correction
99
Inter-Elemental Corrections Continued
• COLA (COmprehensive LAchance).
• Uses theoretical alphas determined by the integrated
fundamental program NBSGSC
• Calculates theoretical inter-elemental correction factor for Metal,
Powders and Fused Beads
• α1 is for a value near 100%, α2 is for a value near 0%, and α3 is
for a value near 50%
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