xray laboratory
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EBS 325Analytical Chemistry Laboratory
Introduction To X-Ray Analysis
By
Mr. Samayamutthirian Palaniandy
School of Materials & Mineral Resources Engineering,
Engineering Campus, Universiti Sains Malaysia.
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SAMPLING
&SAMPLE
PREPARATION
XRFXRD
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SAMPLING
SAMPLE
PREPARATION
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Papers
Plastics
Glass
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X-RAY analytical errors
Sampling
Sample preparation
Instrumental
Standards
Statistical
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SAMPLE
A means by which units are taken from a
population in such a way as to represent the
characteristics of interest in that population.
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homogeneous.Well-mixed
random
accuraterepresentative
The equipment does
what we want.Our sampling
frequency is fine.
FAQ about samples and sampling
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Reasons for poor procedures,
equipment, and practices of
SAMPLING.
Lack of knowledge of the consequences of poor
sampling.
Lack of knowledge of the sampling theory.
Trying to save money.
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Questions to be answer
before sampling
WHAT is being sampled?
WHY is the sample being taken?
WHO is taking the sample?
WHERE is the sample taken?
WHEN and with what frequency is the sample
taken?
HOW is the sample taken?
HOW MUCH material is in the sample?
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EXAMPLES OF SAMPLING METHODS
Coning &
quartering
Riffle
splitter
Paper coneriffle splitter
Grab
sampling
Fractionalshoveling
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CONING AND QUATERING
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RIFFLE SPLLITING
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PAPER CONE RIFFLE SPLITTER
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Fractional Shoveling
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Grab Sampling
Consist of taking a sample using scoop or spatula
by simply inserting the sampling device into the sample
container and removing an aliquot
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Sample Mixing Flowing Liquids or Gases
A static mixer can reduce the Groupingand Segregation Error.A correct cross stream
sample may be
impossible to obtain.
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Precision of Sub-sampling Methods
Gerlach, Dobb, Raab, and Nocerino, 2002 Journal of Chemometrics Gy Sampling in
experimental studies. 1. Assessing soil splitting protocols 16, 321-328
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Your decisions are only as good as your
samples.
Your samples are only as good as your
sampling systems.
Your sampling systems are only as
good as your audit and assessment.
Summary
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X-RAY analytical errors
Sampling
Sample preparation
Instrumental
Standards
Statistical
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Analytical errorssampling
- Sample must be representative of theprocess
- Sampling must be reproducible (i.e.should be able to take identical duplicatesamples)
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Sample preparation methods
must
Simple
Low cost
Rapid
Reproducible
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The quality of sample preparation is at least asimportant as the quality of the subsequentmeasurements.
Quality of sample preparation
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Quality of sample preparation
An ideal sample would be:
- Representative of the material
- Homogenous
- Of infinite thickness
- Without surface irregularities
- With small enough particles for the
wavelengths being measured
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SAMPLES
METAL POWDER LIQUID
XRF onlyXRD and XRF
Why???
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XRD Working Concept
When a monochromatic x-ray beam with wavelength is incident on the
lattice planes in a crystal planes in a crystal at an angle , diffraction occurs
only when the distance traveled by the rays reflected from successive planes
differs by a complete number n of wavelengths. By varying the angle , the
Braggs Law conditions are satisfied by different d-spacing in polycrystalline
materials. Plotting the angular positions and intensities of the resultant
diffraction peaks produces a pattern which is characterised of the sample.
Where a mixture of different phases is present, the diffractogram is formed by
addition of the individual patterns.
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XRF Working Concept
In X-ray fluorescence spectroscopy, the process begins by exposingthe sample to a source of x-rays. As these high energy photons strike
the sample, they tend to knock electrons out of their orbits around the
nuclei of the atoms that make up the sample. When this occurs, an
electron from an outer orbit, orshell, of the atom will fall into the shell
of the missing electron. Since outer shell electrons are more energetic
than inner shell electrons, the relocated electron has an excess ofenergy that is expended as an x-ray fluorescence photon. This
fluorescence is unique to the composition of the sample. The detector
collects this spectrum and converts them to electrical impulses that
are proportional to the energies of the various x-rays in the samples
spectrum.
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METAL
CHIPS POLISHING SOLUTION
REMELT
CAST
BELT GRINDER/LATHE
INGOT
LIQUID
X-RAY ANALYSIS
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POWDER
GRINDING FUSION SOLUTION
PELLET
GLASS BEAD LIQUID
X-RAY ANALYSIS
PRESS
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LIQUID
LIQUID HOLDERDROP METHOD
SPOT ANALYSISDDTC METHOD
FILTER
X-RAY ANALYSIS
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Solids
Pressed powdersFused beads
Liquids
Sample types
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- metal alloys, plastics & glass
- relatively easy to prepare by cutting, machining,milling % fine polishing
- Avoid smearing of soft metals (e.g. Pb)- Polishing may introduce contamination from the
polishing material
- do not have particle size problems
- Surface needs to be flat- Surface needs to be homogeneous
- Surface defects are more critical for light elementsif good accuracy is required.
Solids
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- Typical samples types that are prepared as pressed powders include rocks,soil, slag, cements, alumina, fly ash, etc.
- Particle size of powder needs to be controlled for light element analysis- If necessary, powders are ground to achieve a particle size of < 50 m
- Grinding can be introduce contamination (e.g. Fe from a chrome steel mill)
- Binding agents (e.g. wax or cellulose) can be used to increase samplestrength to avoid breakage in the spectrometer
- Ground powders are pressed into a solid tablet under pressure using a
hydraulic press & 40 mm die- Relatively slow method (5 minutes per sample) but relatively low cost
- Pressed powders suffer from particle size problems for light elements
Preparation equipment needed includes:
- Grinding mill and vessel (chrome steel, zirconia, tungsten carbide, etc.)
- Hydraulic press and die (usually 40 mm)- Binding agents
Pressed powders
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- Typical samples that are prepared as fused beads include rocks, cements,iron ores, etc. when higher accuracy is required.
- Weighed sample is mixed with flux
- Sample and flux are melted at 1000 oC
- Melt is poured into a 40 mm mold
- Bead surface needs to be homogenous (constant color without cracks)
- Slow (10-15 minutes/sample)
- High cost- Important benefit is that particle size problems disappear (fusion process
results in a homogeneous glass)
- An additional benefit is that the melting flux (usually Na or Li borate)dilutes the sample, reducing matrix variations, resulting in higher accuracy
- Disadvantagereduced sensitivity for trace elements
Preparation equipment includes:
- Fusion device (manual or automatic)
- Pt/Au crucible(s) & mould(s)
- Fusion (melting) flux
- A non wetting agent (e.g. KI or LiBr) is sometimes used to help produce a
better quality bead and to assist with cleaning the Pt/Au crucible & mouldbetween samples
Fused beads
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- Typical samples include environmental (waters, mud) &oils
- Easiest to prepare
- Should have a constant volume that exceeds maximumpenetration depth
- Sample is poured into a liquid cell fitted with a thin plasticwindow
- Range of window materials to suit different liquids
- Fill to a constant height (e.g. 20 mm) to avoid errors fromvariable depth
- Choose the correct thickness and material to suit thechemistry of the sample being measured
- Na is lightest element that can be detected in liquids.
Liquids
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element Chemical % XRF % XRF %
Powder Fused bead
Na (Z=11) 0.43 0.36 0.46
Si (Z=14) 63.63 62.90 63.80
Ca (Z=20) 0.68 0.68 0.67
Ba (Z=56) 0.27 0.28 0.28
Influence of sample preparation
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Factor of errors in Sample Preparation
Grain size and surface roughness
Uniformity of sample
Contamination through the sample preparation
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Grain size and surface roughness
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Uniformity of sample
Metallic Sample
Casting condition of the sample in the molding.
Sand molding
Metal molding
X-ray intensities differ according to the molding method which comes
In the measurement of light elements.
Quenching casting which makes the metallic composition fine produces good results
Sample polishing
NiK intensity CrK intensity
50# emery paper 0.686 0.974
100# emery paper 0.699 0.983
240# emery paper 0.704 0.989
Mirror polishing 0.709 0.993
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Uniformity of sample
Contamination during polishing
Contamination effect when carbon steel and Ni-Cr alloy polish afterpolishing stainless steel.
As the contamination form the polishing belt to the sample, the re contamination from
The material of the polishing belt and from the remaining trace elements of polished
Sample.
Ni Cr Fe
% Conc 0.55 0.21 2.10
% Contamination 0.05 0.03 0.38
Powder Sample
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Powder SampleGrinding Condition
Different grinding condition cause variation in particle size distribution which
leads to variation in X-Ray intensity.
Powder Sample
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Powder SampleBrequetting
Usual forming pressure 20 tons with 40mm diameter.
X-Ray intensities varies with variation of forming pressure (especiallywhen pressure is low).
Contamination
Contamination from the grinding mill and media
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CaO,CaCO3,CaMg(CO3)2Ca(OH)2 etc.
If you are givenwith four bottles of
white powder.
What will you doto identify them?
Identification
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What is X-ray diffraction?
non-destructive analytical technique for
identification and quantitative determination
of the various crystalline forms, known asphases.
Identification is achieved by comparing theX-ray diffraction pattern
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Diffractograms and ICDD Card
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What is X-ray diffraction?
XRD able to determine :
Which phases are present?
At what concentration levels?
What are the amorphous content of thesample?
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How does XRD Works???
Every crystalline substanceproduce its own XRD pattern,which because it is dependenton the internal structure, is
characteristic of that substance.
The XRD pattern is oftenspoken as theFINGERPRINT of a mineralor a crystalline substance,
because it differs from patternof every other mineral orcrystalline substances.
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A crystal lattice is a regular three-
dimension distribution (cubic,
tetragonal, etc.) of atoms in space.
These are arrange so that they form
a series of parallel planes separated
from one another by a distance d,
which varies according to the
nature of the material. For any
crystal planes exist in a number of
different orientations- each with its
own specific d-spacing
Crystal lattice
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Fourteen (14) Bravais Lattice
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How does it work?
Diffraction
Braggs Law
n=2dsin
When a monochromatic x-ray beamwith wavelength is incident onthe lattice planes in a crystal planesin a crystal at an angle ,diffraction occurs only when thedistance traveled by the raysreflected from successive planes
differs by a complete number n ofwavelengths.
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How does it work?In powder XRD method, a sample is ground to a
powder (10m) in order to expose all possibleorientations to the X-ray beam of the crystalvalues of, dand for diffraction are achievedas follows:
1. is kept constant by using filtered X- radiationthat is approximately monochromatic. (SeeTable 1).
2. d may have value consistent with the crystalstructure (See Figure 5).
3. is the variable parameters, in terms of whichthe diffraction peaks are measured.
T bl 1 M h ti X filt
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Table 1: Monochromatic X-ray filters
Basic Component Of XRD Machine
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Basic Component Of XRD Machine
Therefore any XRD machine will
consist of three basiccomponent.
Monochromatic X-ray source
(
)
Sample-finely powdered or
polished surface-may be
rotated against the center
(goniometer).
Data collector- such as film,
strip chart or magnetic
medium/storage.
By varying the angle , the Braggs Law
conditions are satisfied by different d-
spacing in polycrystalline materials.
Plotting the angular positions and
intensities of the resultant diffraction
peaks produces a pattern which is
characterised of the sample
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Angle
(2)
d-value()
Rel. Int.(I)
27.47 3.244 26
27.82 3.204 49
28.45 3.135 100
44.87 2.018 2
46.68 1.944 30
47.11 1.928 64
55.88 1.644 41
68.89 1.362 6
76.12 1.250 10
83.19 1.160 1
87.74 1.112 10
92.49 1.067 1
94.68 1.048 13
94.99 1.045 6
106.44 0.962 2
106.78 0.960 1
113.81 0.920 5
114.26 0.917 2
127.24 0.860 4
127.82 0.858 2
Table 1: Typical experimental XRD data
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Design and Use of the Indexes for
Manual Searching of the PDF
Three search methods are used in the
indexesi.e.
The alphabetical index;
The Hanawalt index
The Finkindex.
The Alphabetical Index
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p
The Alphabetical Index
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The Alphabetical Index
Figure 3: Schematic search procedure when
chemical information is known
Hanawalt Method
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Hanawalt Method
The Fink Method
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The Fink Method
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XRF
X-Ray Fluorescence
is used to identify and measure the
concentration of
elements in a sample
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XRF instrumental parameters
x-ray tube kv
x-ray tube mA
primary beam filters
collimator masks
collimator
crystal
detector
path
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user benefits of wavelength
dispersive XRF versatile
accurate
reproducible
fast
non destructive
XRF i til
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XRF is versatile
element range is Be to U
atomic numbers (Z) of 4 to 92
concentration range covers0.1 ppm to 100 %
samples can be in the form of
solids, liquids, powders or fragments
XRF i t
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XRF is accurate
generally better than 1 % relative
(i.e. 10% 0.1%)
accuracy is limited by calibration
standards, sample preparation,
sample matrix, sampling,instrumental errors & statistics
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XRF is reproducible
generally within 0.1% relative
good reproducibility requires high
quality mechanics, stable electronics
and careful construction techniques
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XRF is fast
counting times generally between 1
& 50 seconds for each element
semi-quant analysis ofall matrix
elements in 10 to 20 minutes
overnight un-attended operation
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XRF is non-destructive
standards are permanent
measured samples can be stored and
re-analysed at a later date
precious samples are not damaged
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properties of x-rays
the following four slides list some
of the more important properties
of x-rays that contribute to the
nature of XRF analysis
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XRF analytical envelope
the following section describes the
five major areas that define theanalytical possibilities available with
wavelength dispersive XRF
spectrometers
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XRF analytical envelope
elemental range
detection limitsanalysis times
accuracyreproducibility
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elemental range
beryllium (4) to uranium (92)
in solids
fluorine (9) to uranium (92)
in liquids
range of elements in solid samples
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range of elements in solid samples
are shown in green (Be to U)
range of elements in liquid samples
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range of elements in liquid samples
are shown in green (Na to U)
detection limits (LLD)
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detection limits (LLD)
function of atomic number (Z) & themix of elements within the sample
(sample matrix)< 1 ppm for high Z in a light matrix
(e.g. Pb in petrol)
or > 10 ppm for low Z in a heavy
matrix (Na in slag)
XRF applications summary
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XRF applications summary
Na to U in all sample types Be to U in solid samples
accuracy generally 0.1 to 1 % relative
reproducibility typically < 0.5% relative
typical LLD is normally 1 - 10 ppm
(depends on element being measured andthe sample matrix)
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XRF errors
the following section describes
major source of errors in XRFanalysis, and investigates how
these errors can be minimized to
achieve maximize accuracy
overview of XRF methodology
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overview of XRF methodology
good accuracy requires careful sample preparation
fused beads for light elements
accurate standards selection of optimum instrument
parameters
collection of enough counts to avoidstatistical errors
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Methods of Analysis
the following presentation
describes the requirements for
quantitative and semi-quantitative
analysis
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overview of XRF methodology
the objective of XRF is to determine
as accurately as possible the
composition of unknown samples
measured x-ray line intensities are
converted to concentrations using anappropriate algorithm
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overview of XRF methodology
each specific application needs to
be looked at in detail to
determine which method will be
the most appropriate
XRF analytical methods
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XRF analytical methods
the atomic number (Z) of each of theelements to be determined will have
an influence on the type of samplepreparation to be used, and the
quantitative or semi-quantitativemethod that will be the most suitable
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XRF analytical methods
the quantitative method is the
most accurate, but requires calibration
standards
semi-quantitative method is less
accurate, but does not requirestandards
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overview of XRF methodology
first determine the following:
which elements are to be measured
what are their concentration ranges what accuracy is required
how many samples are to be measured are suitable standards available
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overview of XRF methodology
elements to be measured
low Z will require careful preparation
low Z may have lower accuracy low Z may require fusion of powders
semi-quant does not measure the verylight elements (Be to N)
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overview of XRF methodology
concentration ranges
as the concentration range for each
element increased, accuracy
generally decreases
large concentration ranges willrequire more standards
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overview of XRF methodology
good accuracy requires
careful sample preparation
fusion of powder samples for Z 13
longer analysis time
accurate calibration standards
careful selection of each variableinstrument parameter
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overview of XRF methodology
calibration standards
require the same sample preparation
as unknown samples accurate chemical analysis
need to cover concentration ranges mechanically stable
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XRF applications summary
Na to U in all sample types
Be to U in solid samples
accuracy typically 0.1 to 1 % relative
typical LLD is between 1 - 10 ppm
i t ( t d dl l i )
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semi-quant (standardless analysis)
accuracy is limited by
particle size
inhomogeneity
non-measured elements (H to N)
i t ( t d dl l i )
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semi-quant (standardless analysis)
accuracy of the semi-quantitative
method can be as good as 1%
relative; typically accuracy is
between 5% and 10%
quantitative analysis
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q y
calibration graph (x-ray intensity v/s %
element) is established for each
element that is to be measured
measure unknowns using the
established calibrations
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quantitative analysis - calibration
for a single element (a), the
concentration C is a function f of the
intensity I
Ca = fa x Ia
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quantitative analysis - calibration
for multiple elements (a & b) in a
sample matrix, the concentration is
related to both a & b:
Ca = f(Ia,Ib) or Ca = f(Ia, Cb)
i i l i lib i
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quantitative analysis - calibration
the object is to obtain the best fit ofexperimental data to a given algorithm
e.g. method ofleast squares fitting(CchemCcalculated)
2 = minimum
where = sum from all standardsand C = concentration
i i l i lib i
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quantitative analysis - calibration
XRF software typically includes several
quantitative methods. The most
simplistic method is a straight line
calibration where matrix (orinter-
element) effects are absent
Soalan Pramakmal
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1. Nyatakan 5 punca kesalahan analitikal analisis X-Ray.
2. Takrifkan sampel.
3. Apakah punca prosedur pensampelan yang lemah?4. Nyatakan 5 perkara yang mempengaruhi kualiti penyediaan
sampel yang ideal.
5. Terangkan prinsip kerja XRD.
6. Terangkan prinsip kerja XRF.
7. Berikan 5 contoh kaedah pensampelan.
8. Terangkan cara penyediaan fusebeads.
9. Nyatakan faktor kesilapan dalam penyediaan sampel yang
mempegaruhi analisis X-Ray.
10. Apakah maklumat yang boleh diperolehi daripada keputusanXRD.
11. Tuliskan persamaan Bragg.
12. Nyatakan komponen asas dalam mesin XRD.
S l P k l
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Soalan Pramakmal
13. Nyatakan 3 kaedah pencarian index unsur dengan manual PDF.14. Apakah perbezaan kaedah Hanawalt dan Fink?
15. Lakarkan carta alir kaedah Fink.
16. Lakarkan carta alir kaedah Hanawalt.
17. Nyatakan julat no. atom yang boleh dikesan dengan kaedah XRF
pada sampel pepejal dan cecair.
18. Apakah kaedah penyediaan sampel yang baik untuk unsur yang
mempunyai no. atom yang rendah.
19. Kejituan keputusan XRF dipengaruhi oleh 3 faktor. Nyatakan
fator-faktor itu.20. Apakah itu LOI?