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EBS 325 – Analytical Chemistry Laboratory Introduction To X-Ray Analysis. School of Materials & Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia. By Mr. Samayamutthirian Palaniandy. OUTLINE. SAMPLING & SAMPLE PREPARATION. XRF. XRD.

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Ebs 325 analytical chemistry laboratory introduction to x ray analysis

EBS 325 – Analytical Chemistry LaboratoryIntroduction To X-Ray Analysis

School of Materials & Mineral Resources Engineering,

Engineering Campus, Universiti Sains Malaysia.

By

Mr. Samayamutthirian Palaniandy


OUTLINE

SAMPLING

&

SAMPLE

PREPARATION

XRF

XRD


SAMPLING & SAMPLE PREPARATION

FOR X-RAY ANALYSIS


SAMPLING & SAMPLE PREPARATION

FOR X-RAY ANALYSIS

SAMPLE

PREPARATION

SAMPLING




PROPER PREPARATION FOR BEST RESULT

Glass

Plastics

Papers


X ray analytical errors
X-RAY analytical errors

Sampling

Sample preparation

Instrumental

Standards

Statistical


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.


FAQ about samples and sampling

accurate

representative

Well-mixed

homogeneous.

The equipment does

what we want.

random

Our sampling

frequency is fine.


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.


Questions to be answer SAMPLING.

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•?


EXAMPLES OF SAMPLING METHODS SAMPLING.

Coning &

quartering

Grab

sampling

Riffle

splitter

Fractional

shoveling

Paper cone

riffle splitter



RIFFLE SPLLITING SAMPLING.




Grab Sampling SAMPLING.

Consist of taking a sample using scoop or spatula

by simply inserting the sampling device into the sample

container and removing an aliquot


Sample Mixing Flowing Liquids or Gases SAMPLING.

A correct cross stream

sample may be

impossible to obtain.

A static mixer can reduce the Grouping

and Segregation Error.


Precision of Sub-sampling Methods SAMPLING.

Gerlach, Dobb, Raab, and Nocerino, 2002 Journal of Chemometrics “Gy Sampling in experimental studies. 1. Assessing soil splitting protocols” 16, 321-328


Your decisions are only as good as your samples. SAMPLING.

Your samples are only as good as your

sampling systems.

Your sampling systems are only as good as your audit and assessment.

Summary


X ray analytical errors1
X-RAY analytical errors SAMPLING.

Sampling

Sample preparation

Instrumental

Standards

Statistical


Analytical errors sampling
Analytical errors – sampling SAMPLING.

  • Sample must be representative of the process

  • Sampling must be reproducible (i.e. should be able to take identical duplicate samples)


Sample preparation methods
Sample preparation methods SAMPLING.

must

Simple

Rapid

Reproducible

Low cost


Quality of sample preparation SAMPLING.

The quality of sample preparation is at least as important as the quality of the subsequent measurements.


Quality of sample preparation
Quality of sample preparation SAMPLING.

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


SAMPLES SAMPLING.

METAL

POWDER

LIQUID

XRD and XRF

XRF only

Why???


XRD Working Concept SAMPLING.

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 Bragg’s 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.


XRF Working Concept SAMPLING.

In X-ray fluorescence spectroscopy, the process begins by exposing the 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, or “shell”, 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 of energy 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 sample’s spectrum.


METAL SAMPLING.

CHIPS

POLISHING

SOLUTION

LIQUID

REMELT

BELT GRINDER/

LATHE

CAST

INGOT

X-RAY ANALYSIS


POWDER SAMPLING.

SOLUTION

GRINDING

PRESS

FUSION

LIQUID

GLASS BEAD

PELLET

X-RAY ANALYSIS


LIQUID SAMPLING.

LIQUID HOLDER

DROP METHOD

SPOT ANALYSIS

DDTC METHOD

FILTER

X-RAY ANALYSIS


Sample types SAMPLING.

Solids

Pressed powders

Fused beads

Liquids


Solids SAMPLING.

  • 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 elements if good accuracy is required.


Pressed powders SAMPLING.

  • 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 µm

  • 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 sample strength 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


Fused beads SAMPLING.

  • 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

  • Disadvantage –reduced 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 & mould between samples


Liquids SAMPLING.

  • Typical samples include environmental (waters, mud) & oils

  • Easiest to prepare

  • Should have a constant volume that exceeds maximum penetration depth

  • Sample is poured into a liquid cell fitted with a thin plastic window

  • Range of window materials to suit different liquids

  • Fill to a constant height (e.g. 20 mm) to avoid errors from variable depth

  • Choose the correct thickness and material to suit the chemistry of the sample being measured

  • Na is lightest element that can be detected in liquids.



Factor of errors in Sample Preparation SAMPLING.

Grain size and surface roughness

Uniformity of sample

Contamination through the sample preparation



Uniformity of sample SAMPLING.

Sand molding

Metallic Sample

Metal molding

Casting condition of the sample in the 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


Uniformity of sample SAMPLING.

Contamination during polishing

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.

Contamination effect when carbon steel and Ni-Cr alloy polish after

polishing stainless steel.


Powder Sample SAMPLING.

Grinding Condition

Different grinding condition cause variation in particle size distribution which

leads to variation in X-Ray intensity.


Powder Sample SAMPLING.

Contamination

Contamination from the grinding mill and media

Brequetting

Usual forming pressure – 20 tons with 40mm diameter.

X-Ray intensities varies with variation of forming pressure (especially

when pressure is low).



Identification SAMPLING.

If you are given with four bottles of white powder. What will you do to identify them?

CaO,CaCO3,CaMg(CO3)2 Ca(OH)2 etc.


What is x ray diffraction
What is X-ray diffraction? SAMPLING.

  • non-destructive analytical technique for identification and quantitative determination of the various crystalline forms, known as ‘phases’.

  • Identification is achieved by comparing the X-ray diffraction pattern



What is x ray diffraction1
What is X-ray diffraction? SAMPLING.

XRD able to determine :

  • Which phases are present?

  • At what concentration levels?

  • What are the amorphous content of the sample?


How does xrd works
How does XRD Works??? SAMPLING.

  • Every crystalline substance produce its own XRD pattern, which because it is dependent on the internal structure, is characteristic of that substance.

  • The XRD pattern is often spoken as the “FINGERPRINT” of a mineral or a crystalline substance, because it differs from pattern of every other mineral or crystalline substances.


Crystal lattice SAMPLING.

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



How does it work
How does it work? SAMPLING.

  • Diffraction

    Bragg’s Law

    n=2dsin

    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.


How does it work1
How does it work? SAMPLING.

In powder XRD method, a sample is ground to a powder (±10µm) in order to expose all possible orientations to the X-ray beam of the crystal values of , d and  for diffraction are achieved as follows:

  •  is kept constant by using filtered X- radiation that is approximately monochromatic. (See Table 1).

  • d may have value consistent with the crystal structure (See Figure 5).

  •  is the variable parameters, in terms of which the diffraction peaks are measured.



Basic Component Of XRD Machine SAMPLING.

  • Therefore any XRD machine will consist of three basic component.

  • 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 Bragg’s 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



Design and use of the indexes for manual searching of the pdf
Design and Use of the Indexes for Manual Searching of the PDF

  • Three search methods are used in the indexes – i.e.

    • The alphabetical index;

    • The Hanawalt index

    • The Fink index.



The alphabetical index1
The Alphabetical Index PDF

Figure 3: Schematic search procedure when chemical information is known




XRF PDF

X-Ray Fluorescence

is used to identify and measure the concentration of

elements in a sample


Xrf instrumental parameters
XRF instrumental parameters PDF

  • x-ray tube kv

  • x-ray tube mA

  • primary beam filters

  • collimator masks

  • collimator

  • crystal

  • detector

  • path


User benefits of wavelength dispersive xrf
user benefits of wavelength dispersive XRF PDF

  • versatile

  • accurate

  • reproducible

  • fast

  • non destructive


Xrf is versatile
XRF is versatile PDF

  • element range is Be to U

    atomic numbers (Z) of 4 to 92

  • concentration range covers 0.1 ppm to 100 %

  • samples can be in the form of solids, liquids, powders or fragments


Xrf is accurate
XRF is accurate PDF

  • generally better than 1 % relative (i.e. 10% ± 0.1%)

  • accuracy is limited by calibration standards, sample preparation, sample matrix, sampling, instrumental errors & statistics


Xrf is reproducible
XRF is reproducible PDF

  • generally within  0.1% relative

  • good reproducibility requires high quality mechanics, stable electronics and careful construction techniques


Xrf is fast
XRF is fast PDF

  • counting times generally between 1 & 50 seconds for each element

  • semi-quant analysis of all matrix elements in 10 to 20 minutes

  • overnight un-attended operation


Xrf is non destructive
XRF is non-destructive PDF

  • standards are permanent

  • measured samples can be stored and re-analysed at a later date

  • precious samples are not damaged


Properties of x rays
properties of x-rays PDF

the following four slides list some of the more important properties of x-rays that contribute to the nature of XRF analysis


Xrf analytical envelope
XRF analytical envelope PDF

the following section describes the five major areas that define the analytical possibilities available with wavelength dispersive XRF spectrometers


Xrf analytical envelope1
XRF analytical envelope PDF

  • elemental range

  • detection limits

  • analysis times

  • accuracy

  • reproducibility


Elemental range
elemental range PDF

  • beryllium (4) to uranium (92) in solids

  • fluorine (9) to uranium (92) in liquids




Detection limits lld
detection limits (LLD) to U)

  • function of atomic number (Z) & the mix 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
XRF applications summary to U)

  • 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 and the sample matrix)


Xrf errors
XRF errors to U)

the following section describes major source of errors in XRF analysis, and investigates how these errors can be minimized to achieve maximize accuracy


Overview of xrf methodology
overview of XRF methodology to U)

good accuracy requires

  • careful sample preparation

  • fused beads for light elements

  • accurate standards

  • selection of optimum instrument parameters

  • collection of enough counts to avoid statistical errors


Methods of analysis

Methods of Analysis to U)

the following presentation describes the requirements for quantitative and semi-quantitative analysis


Overview of xrf methodology1
overview of XRF methodology to U)

  • 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 an appropriate algorithm


Overview of xrf methodology2
overview of XRF methodology to U)

each specific application needs to be looked at in detail to determine which method will be the most appropriate


Xrf analytical methods
XRF analytical methods to U)

the atomic number (Z) of each of the elements to be determined will have

an influence on the type of sample preparation to be used, and the quantitative or semi-quantitative method that will be the most suitable


Xrf analytical methods1
XRF analytical methods to U)

  • the quantitative method is the most accurate, but requires calibration standards

  • semi-quantitative method is less accurate, but does not require standards


Overview of xrf methodology3
overview of XRF methodology to U)

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


Overview of xrf methodology4
overview of XRF methodology to U)

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 very light elements (Be to N)


Overview of xrf methodology5
overview of XRF methodology to U)

concentration ranges

  • as the concentration range for each element increased, accuracy generally decreases

  • large concentration ranges will require more standards


Overview of xrf methodology6
overview of XRF methodology to U)

good accuracy requires

  • careful sample preparation

  • fusion of powder samples for Z  13

  • longer analysis time

  • accurate calibration standards

  • careful selection of each variable instrument parameter


Overview of xrf methodology7
overview of XRF methodology to U)

calibration standards

  • require the same sample preparation as unknown samples

  • accurate chemical analysis

  • need to cover concentration ranges

  • mechanically stable


Xrf applications summary1
XRF applications summary to U)

  • 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


Semi quant standardless analysis
semi-quant (standardless analysis) to U)

accuracy is limited by

  • particle size

  • inhomogeneity

  • non-measured elements (H to N)


Semi quant standardless analysis1
semi-quant (standardless analysis) to U)

accuracy of the semi-quantitative method can be as good as 1% relative; typically accuracy is between 5% and 10%


Quantitative analysis
quantitative analysis to U)

  • calibration graph (x-ray intensity v/s % element) is established for each element that is to be measured

  • measure unknowns using the established calibrations


Quantitative analysis calibration
quantitative analysis - calibration to U)

for a single element (a), the concentration C is a function f of the intensity I

Ca = fa x Ia


Quantitative analysis calibration1
quantitative analysis - calibration to U)

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)


Quantitative analysis calibration2
quantitative analysis - calibration to U)

the object is to obtain the best fit of experimental data to a given algorithm

e.g. method of least squares fitting

Σ(Cchem – Ccalculated)2 = minimum

where Σ = sum from all standards

and C = concentration


Quantitative analysis calibration3
quantitative analysis - calibration to U)

XRF software typically includes several quantitative methods. The most simplistic method is a straight line calibration where matrix (or inter-element) effects are absent


Soalan Pramakmal to U)

  • Nyatakan 5 punca kesalahan analitikal analisis X-Ray.

  • Takrifkan sampel.

  • Apakah punca prosedur pensampelan yang lemah?

  • Nyatakan 5 perkara yang mempengaruhi kualiti penyediaan sampel yang ideal.

  • Terangkan prinsip kerja XRD.

  • Terangkan prinsip kerja XRF.

  • Berikan 5 contoh kaedah pensampelan.

  • Terangkan cara penyediaan “fuse beads”.

  • Nyatakan faktor kesilapan dalam penyediaan sampel yang mempegaruhi analisis X-Ray.

  • Apakah maklumat yang boleh diperolehi daripada keputusan XRD.

  • Tuliskan persamaan Bragg.

  • Nyatakan komponen asas dalam mesin XRD.


Soalan Pramakmal to U)

  • Nyatakan 3 kaedah pencarian index unsur dengan manual PDF.

  • Apakah perbezaan kaedah Hanawalt dan Fink?

  • Lakarkan carta alir kaedah Fink.

  • Lakarkan carta alir kaedah Hanawalt.

  • Nyatakan julat no. atom yang boleh dikesan dengan kaedah XRF pada sampel pepejal dan cecair.

  • Apakah kaedah penyediaan sampel yang baik untuk unsur yang mempunyai no. atom yang rendah.

  • Kejituan keputusan XRF dipengaruhi oleh 3 faktor. Nyatakan fator-faktor itu.

  • Apakah itu LOI?


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