Sample Preparation and Calibration- Getting the Best Results Using XRF

8/17/2019 Sample Preparation and Calibration- Getting the Best Results Using XRF

1/101

Sample Preparation and

Calibrations: Getting the best

results using XRF

Chris Shaffer

Thermo Fisher ScientificCH-1024 Ecublens


2/101

2

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)


3/101

3


Sample preparation method

Grain size effects (ideally should be less than 50 m)



4/101

4

Sample Homogenization

Rocks, Soils and

Minerals

PolymersGlass, Ceramic andRefractories

Petroleum


5/101

5

Rocks, Soils and Minerals

How do we get a representativesample?


6/101

6



Random Sampling


7/101

7



Random Sampling

Crusher


8/101

8



Random Sampling

Crusher

Riffler

Grinding


9/101

9

Sample Grinding: Rocks, Soils, Mineral,Refractories, Ceramics, etc

Can Be• As simple as Mortar and pestle


10/101

10



• Miller Mill


11/101

11



• Miller Mill

• Planetary Mill


12/101

12



• Miller Mill

• Planetary Mill

• Puck Mill


13/101

13

Liquids (Oils, Fuel, Diesel, etc)

• Most common and easiestis using Magnetic Stirrer


14/101

14



• Conical Mixer


15/101

15



• Conical Mixer

• Wrist Action Shaker


16/101

16



• Conical Mixer

• Wrist Action Shaker

• Tabletop Shaker


17/101

17

Polymers

• Cryogenic Mill

•


18/101

18

Polymers

• Cryogenic Mill

• Shear Mill

• Extruder

• Sample Prep:

• Hot Press


19/101

19

Polymers

• Cryogenic Mill

• Shear Mill


20/101

20

Polymers

• Cryogenic Mill

• Shear Mill

• Extruder


21/101

21

Polymers

• Cryogenic Mill

• Shear Mill

• Extruder

• Sample Prep:

• Hot Press


22/101

22

Sample Preparation Conventional Solid Samples

Polymer or

Fused Glass Bead Bulk Sample(Metal, Glass or

Pressed Powder)


23/101

23

Preparation of Powders as Pressed Pellets

9499D00400

To standard holder

Briquet method

Protective ring

Apply pressure

Die

Specimen

Weigh out

Mortar or crusher

Press

Crush, grind and mix

To grain size


24/101

24

Pressed Pellets Methods

• Hydraulic Press• Manual


25/101

25



• Semi-Automatic


26/101

26



• Semi-Automatic

• Fully Automatic


27/101

27



• Semi-Automatic

• Fully Automatic


28/101

28

Preparation of Powders as Fused Beads

9499D00500

To standard holder

Melting method

Weigh outand mix

Flux + Specimen

Heat for Melting

Platinum crucible Remove bubbles

Glass diskspecimen

1000° -1100° C

Cast & Cool

The fusion of mineral, ceramic or raw materials samples into anamorphous glass disk (also called bead) allows to prevent analytical

problems due to grain size effects and mineralogical effects


29/101

29

Fusion Procedure

Step 1) Ignite:LOI

(950⁰C for 1hr)


30/101

30

Fusion Procedure

Step 2) Weigh out:

Sample

Flux

(Wetting Agent)

(Oxidizer)

Step 1) Ignite:


31/101

31

Fusion Procedure

Step 2) Weigh out:

Step 1) Ignite

Step 3) Mix:

Stir Components


32/101

32

Fusion Procedure

Step 2) Weigh out:

Step 1) Ignite:

Step 3) Mix:

Step 4) Fusion:Gas or Electric


33/101

33

Fusion Procedure

Step 2) Weigh out:

Step 1) Ignite:

Step 3) Mix:

Step 4) Fusion:

Step 5) Alternative

LOI:

Reweigh Sample

+ Crucible


34/101

34

Fusion Procedure

Step 2) Weigh out:

Step 1) Ignite:

Step 3) Mix:

Step 4) Fusion:

Step 5) Alternative

Step 6) Clean:

Ultrasonic Bath

10% HNO3 or HCl

Never Both


35/101

35

Fusion Procedure

Step 2) Weigh out:

Step 1) Ignite:

Step 3) Mix:

Step 4) Fusion:

Step 5) Alternative

LOI:

Step 6) Clean:

Step 6) Polish or

Resurface :

Element migration


36/101

36

Alternative to Fusion Instruments

• Add Sample intoGraphite Crucibles


37/101

37



• Place Crucibles into

Muffle Furnace


38/101

38




Muffle Furnace

• Grind Samples


39/101

39




Muffle Furnace

• Grind Samples

• Fuse Again in Muffle

Furnace


40/101

40




Muffle Furnace

• Grind Samples

• Fuse Again in Muffle

Furnace

• Polish on Wet Diamond

Wheel


41/101

41

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 mustsame 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


42/101

42

Loose Powders and Liquids

Loose Pellets orGranules

Liquids


43/101

43

Preparation of Liquids Standard method

9499D00600

Take up

specimen

Seal up liquid holder

Mylar film

Specimen

Polymer container

Standardcassette

Use liquid sample holder and measure underHelium atmosphere


44/101

44

Liquid Procedure

• Liquid/ Loose Powers cups


45/101

45

Liquid Procedure


• Mounting the cell

• Choosing the film

• Fill Cell:

• Pipette or

• Balance


46/101

46

Liquid Procedure





47/101

47

Liquid Procedure





48/101

48

Liquid Procedure




• Fill Cell:

• Pipette or

• Balance


49/101

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

• Loose powder

• Packing, particle size and mineralogical issues

• Escape depth through film for light elements• Possible infinite thickness issues


50/101

50


• Liquids




51/101

51


• Liquids



Analy te Li ne Graphit e Glass Iron Lead

U La1 28000 1735 154 22.4

Pb Lb1 22200 1398 125 63.9

Hg La1 10750 709 65.6 34.9W La1 6289 429 40.9 22.4

Ce Lb1 1484 113 96.1 6.72

Ba La1 893 71.3 61.3 4.4

Sn La1 399 44.8 30.2 3.34

Cd Ka 144600 8197 701 77.3

Mo Ka 60580 3600 314 36.7

Zr Ka 44130 2668 235 28.9

Sr Ka 31620 1947 173 24.6

Br Ka 18580 1183 106 55.1

As Kb 17773 1132 102 53

Zn Ka 6861 466 44.1 24

Cu Ka 5512 380 36.4 20

Ni Ka 4394 307 29.8 16.6

Fe Ka 2720 196 164 11.1

Analyte Line Graph ite Glass Iron Lead

Mn Ka 2110 155 131 9.01

Cr Ka 1619 122 104 7.23

Ti Ka 920 73.3 63 4.52

Ca Ka 495 54.3 36.5 3.41

K Ka 355 40.2 27.2 3.04

Cl Ka 172 20.9 14.3 2.19

S Ka 116 14.8 10.1 4.83

Si Ka 48.9 16.1 4.69 2.47

Al Ka 31.8 10.5 3.05 1.7

Mg Ka 20 7.08 1.92 1.13

Na Ka 12 5.56 1.15 0.728

F Ka 3.7 1.71 0.356 0.262

O Ka 1.85 2.5 0.178 0.143

N Ka 0.831 1.11 0.0802 0.0713

C Ka 13.6 0.424 0.0311 0.0312

B Ka 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)


52/101

52


• Liquids




53/101

53


• Liquids




54/101

54

Trace and Light Element Analysis in Liquids

• Filter Pad Analysis• Eliminate films

• Concentrate Sample


55/101

55




• Add by weight or

volume


56/101

56





volume

• Place dropletsuniformly over surface


57/101

57





volume


• Allow to dry

Mg LoD = 0.2 ppm


58/101

58





volume


• Allow to dry

Na LoD = 0.2 ppm


59/101

Calibrations


60/101

60

Analysis Types

• Standard Linear Regression Analysis• Factory calibrations

• Onsite calibrations

• Create your own

• Semi-Quantitative or Standard-less Analysis

• QuantAS

• UniQuant

• Qualitative Analysis

• Scans


61/101

61

Linear Regression Analysis

• Standard Concentration vs. Intensity

• Must have standards

• Calibration is matrix matched

• Empirical corrections are more accurate than Fundamental

Parameters


62/101

62

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.


63/101

63

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• 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


64/101

64

Scan Analysis

• Qualitative peak overlays

• Quick comparisons of intensities


65/101

65

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

• Similar Matrix

• Wide enough Dynamic Calibration Range of Unknowns

• Homogenous

• Constant grain size (


66/101

66


Sample preparation method Grain size effects (ideally should be less than 50 m)


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)


67/101

67

Sources of error in XRF Equipment related

Systematic errors• Sample repositioning

• Goniometer repositioning

• X-ray tube deterioration

• Short term drift

• Long term drift• Dead time correction

• Operating parameters selection


68/101

68

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


69/101

69

Step 1: Element Selection


70/101

70

Step 2: Selecting Parameter and Conditions

• Crystals

• Detectors• Collimators

• Lines

• kV• mA

• Counting times

• PBF


71/101

71

Light Elements

• 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


72/101

72

Transition Metals

• 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

• K lines

• Medium kV - medium mA

(50kV/50 mA)

• Crystals

• Either LiF200 or LiF220

• Detector

• Either FPC of SC


73/101

73

Heavy Metals and La and Ac Series

• 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

• Mostly 60 kV 40 mA

• Crystals

• Mostly Either LiF200 or LiF220

• Detector – SC

• Mostly 60 kV 40 mA

• Mostly L lines


74/101

74

Analysis Considerations

Common peak overlapsElement

V Ka

Cr Ka

Mn Ka

Fe KaCo Ka

Pb Ma

Pb La

Si Ka

Ti Ka

Al Ka

Overlaps

Ti Kb

V Kb

Cr Kb

Mn KbFe Kb

S Ka, Mo La

As Ka

W, Ta Ma

Ba La

Br La


75/101

75

Step 3: Scans and Energy Profiles

Comparison between LiF200

and LiF220

R l i S i i i i C l


76/101

76

Resolution versus Sensitivity using Crystals

Zoomed spectral areas

R l ti S iti it U i C t l


77/101

77

Resolution versus Sensitivity Using Crystals

Details on Nb and Zr

C lli t Ch i


78/101

78

Collimator Choice

M t it bl S t l Li


79/101

79

Most suitable Spectral Lines

Example Zr: Heavy overlap on ZrKa by SrKb

M t it bl S t l Li


80/101

80

Most suitable Spectral Lines

Example Zr: No overlap on ZrKb line

B k d Sit ti


81/101

81

Background Situation

Comparison of 3 different samples with LiF220

B k d Sit ti


82/101

82



Backgro nd Sit ation


83/101

83



Background Correction


84/101

84


Traditional BG correction: Example Nb



85/101

85


Traditional BG correction: Example Nb

Line Overlap Correction


86/101

86


Example Nb: Heavy overlaps by Y



87/101

87


Example Nb / Y : Overlap correction for Y

Energy Profiles


88/101

88

Energy Profiles

• Escape Peaks – Ti, V, Cr, Mn, Fe, Co

Energy Profile Second and Third Order


89/101

89

Energy Profile- Second and Third Order

• Second order overlay from Sb on S

Step 4: Instrument Drift


90/101

90

Step 4: Instrument Drift

• What is drift; Loss of intensity over time received by the instrumentdetector

• 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)

What should be used as drift standards?


91/101

91

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

75% Principle


92/101

92

75% Principle

Step 5: Linear Regression Calibration


93/101

93

Step 5: Linear Regression Calibration

• Enter concentration values for reference standard

• The values should be entered in the same chemical composition as desiredresults (i.e. elements, oxides, carbonates …)

Plot of Regression


94/101

94

Plot of Regression

Uncertainty

Standard Deviation

Detection Limits


95/101

95

Detection Limits

limits of detection

LoD = 3√(BEC/(Q*t) )

• BEC: background equivalent concentration

• Q: sensitivity

• t: time of analysis

limits of Quantification

LoQ = (3√(BEC/(Q*t) )*3)


• Q: sensitivity


Precision


96/101

96

Precision

Higher sensitivities

Precision = √[(BEC + C)/(Q*t) ]


• C: concentration in the test sample

• Q: sensitivity


Inter-Elemental Corrections


97/101

97

Inter Elemental Corrections

• Overlap and Background corrections

• Need samples with similar amounts of the analyte elements and containingvarying amounts of the overlapping element

• Can be difficult to find such standards in solids of powders, but easy in

liquids

Ti Overlap on Al

Inter-Elemental Corrections


98/101

98

Inter Elemental Corrections

• Mathematical correction models

• Additive Intensi ty (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

Inter-Elemental Corrections Continued


99/101

99

Inter Elemental Corrections Continued

• Multiplicative Intensity (MI) or Lucas Tooth

• This correction is multiplicative and is based on interferingintensities 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)

• Multipl icative 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

Inter-Elemental Corrections Continued


100/101

100

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 isfor a value near 50%

New Opportunities To Work Together, With You


101/101

New Opportunities To Work Together, With You

The world leader in serving science

Documents

Sample Preparation and Calibration- Getting the Best Results Using XRF