Chemical Analysis

Fundamental Principles of X-Ray Fluorescence (XRF)The XRF method depends on fundamental principles that are common to several other

instrumental methods involving interactions between electron beams and x-rays with

samples, including: X-ray spectroscopy (e.g., SEM - EDS), X-ray diffraction (XRD), and

wavelength dispersive spectroscopy (microprobe WDS).

The analysis of major and trace elements in geological materials by x-ray fluorescence

is made possible by the behavior of atoms when they interact with radiation. When

materials are excited with high-energy, short wavelength radiation (e.g., X-rays), they

can become ionized. If the energy of the radiation is sufficient to dislodge a tightly-held

inner electron, the atom becomes unstable and an outer electron replaces the missing

inner electron. When this happens, energy is released due to the decreased binding

energy of the inner electron orbital compared with an outer one. The emitted radiation

is of lower energy than the primary incident X-rays and is termed fluorescent radiation.

Because the energy of the emitted photon is characteristic of a transition between

specific electron orbitals in a particular element, the resulting fluorescent X-rays can be

used to detect the abundances of elements that are present in the sample.

X-Ray Fluorescence (XRF) Instrumentation - How Does It Work?The analysis of major and trace elements in geological materials by XRF is made

possible by the behavior of atoms when they interact with X-radiation. An XRF

spectrometer works because if a sample is illuminated by an intense X-ray beam, known

as the incident beam, some of the energy is scattered, but some is also absorbed within

the sample in a manner that depends on its chemistry. The incident X-ray beam is

typically produced from a Rh target, although W, Mo, Cr and others can also be used,

depending on the application. 

Show Caption

When this primary X-ray beam illuminates the sample, it is said to be excited. The

excited sample in turn emits X-rays along a spectrum of wavelengths characteristic of

the types of atoms present in the sample. How does this happen? The atoms in the

sample absorb X-ray energy by ionizing, ejecting electrons from the lower (usually K

and L) energy levels. The ejected electrons are replaced by electrons from an outer,

higher energy orbital. When this happens, energy is released due to the decreased

binding energy of the inner electron orbital compared with an outer one. This energy

release is in the form of emission of characteristic X-rays indicating the type of atom

present. If a sample has many elements present, as is typical for most minerals and

rocks, the use of a Wavelength Dispersive Spectrometer much like that in

an EPMA allows the separation of a complex emitted X-ray spectrum into characteristic

wavelengths for each element present. Various types of detectors (gas flow proportional

and scintillation) are used to measure the intensity of the emitted beam. The flow

counter is commonly utilized for measuring long wavelength (>0.15 nm) X-rays that are

typical of K spectra from elements lighter than Zn. The scintillation detector is

commonly used to analyze shorter wavelengths in the X-ray spectrum (K spectra of

element from Nb to I; L spectra of Th and U). X-rays of intermediate wavelength (K

spectra produced from Zn to Zr and L spectra from Ba and the rare earth elements) are

generally measured by using both detectors in tandem. The intensity of the energy

measured by these detectors is proportional to the abundance of the element in the

sample. The exact value of this proportionality for each element is derived by

comparison to mineral or rock standards whose composition is known from prior

analyses by other techniques.

ApplicationsX-Ray fluorescence is used in a wide range of applications, including

research in igneous, sedimentary, and metamorphic petrology

soil surveys

mining (e.g., measuring the grade of ore)

cement production

ceramic and glass manufacturing

metallurgy (e.g., quality control)

environmental studies (e.g., analyses of particulate matter on air filters)

petroleum industry (e.g., sulfur content of crude oils and petroleum products)

field analysis in geological and environmental studies (using portable, hand-held

XRF spectrometers)

X-Ray fluorescence is particularly well-suited for investigations that involve

bulk chemical analyses of major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) in

rock and sediment

bulk chemical analyses of trace elements (in abundances >1 ppm; Ba, Ce, Co, Cr,

Cu, Ga, La, Nb, Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, Zn) in rock and sediment - detection

limits for trace elements are typically on the order of a few parts per million

X-ray fluorescence is limited to analysis of

relatively large samples, typically > 1 gram

materials that can be prepared in powder form and effectively homogenized

materials for which compositionally similar, well-characterized standards are

available

materials containing high abundances of elements for which absorption and

fluorescence effects are reasonably well understood

In most cases for rocks, ores, sediments and minerals, the sample is ground to a fine

powder. At this point it may be analyzed directly, especially in the case of trace element

analyses. However, the very wide range in abundances of different elements, especially

iron, and the wide range of sizes of grains in a powdered sample, makes the

proportionality comparison to the standards particularly troublesome. For this reason, it

is common practice to mix the powdered sample with a chemical flux and use a furnace

or gas burner to melt the powdered sample. Melting creates a homogenous glass that

can be analyzed and the abundances of the (now somewhat diluted) elements

calculated.

Strengths and Limitations of X-Ray Fluorescence (XRF)?

StrengthsX-Ray fluorescence is particularly well-suited for investigations that involve:

bulk chemical analyses of major elements (Si, Ti, Al, Fe, Mn, Mg, Ca, Na, K, P) in

rock and sediment

bulk chemical analyses of trace elements (>1 ppm; Ba, Ce, Co, Cr, Cu, Ga, La, Nb,

Ni, Rb, Sc, Sr, Rh, U, V, Y, Zr, Zn) in rock and sediment

LimitationsIn theory the XRF has the ability to detect X-ray emission from virtually all elements,

depending on the wavelength and intensity of incident x-rays. However...

In practice, most commercially available instruments are very limited in their

ability to precisely and accurately measure the abundances of elements with Z<11

in most natural earth materials.

XRF analyses cannot distinguish variations among isotopes of an element, so these

analyses are routinely done with other instruments (see TIMS and SIMS).

XRF analyses cannot distinguish ions of the same element in different valence

states, so these analyses of rocks and minerals are done with techniques such as

wet chemical analysis or Mossbauer spectroscopy.

User's Guide - Sample Collection and PreparationVirtually any solid or liquid material can be analyzed, if adequate standards are

available. For rocks and minerals, typical commercial instruments require a sample

constituting at least several grams of material, although the sample collected may be

much larger. For XRF chemical analyses of rocks, samples are collected that are several

times larger than the largest size grain or particle in the rock. This initial sample then

suffers a series of crushing steps to reduce it to an average grain size of a few

millimeters to a centimeter, when it can be reduced by splitting to a small

representative sample of a few tens to hundreds of grams. This small sample split is

then ground into a fine powder by any of a variety of techniques to create the XRF

sample. Care must be taken particularly at this step to be aware of the composition of

the crushing implements, which will inevitably contaminate the sample to some extent.

Data Collection, Results and Presentation

X-Ray spectrum

Data table

Detection limits

Precision

Accuracy

Database and Plotting

Evaluation of Data Quality (flyers, trends, discriminant fields)

Geochemical Plots

What is Scanning Electron Microscopy (SEM)

A typical SEM instrument, showing the electron column, sample chamber, EDS detector, electronics console, and visual

display monitors.

The scanning electron microscope (SEM) uses a focused beam of high-energy electrons

to generate a variety of signals at the surface of solid specimens. The signals that

derive from electron-sample interactions reveal information about the sample including

external morphology (texture), chemical composition, and crystalline structure and

orientation of materials making up the sample. In most applications, data are collected

over a selected area of the surface of the sample, and a 2-dimensional image is

generated that displays spatial variations in these properties. Areas ranging from

approximately 1 cm to 5 microns in width can be imaged in a scanning mode using

conventional SEM techniques (magnification ranging from 20X to approximately

30,000X, spatial resolution of 50 to 100 nm). The SEM is also capable of performing

analyses of selected point locations on the sample; this approach is especially useful in

qualitatively or semi-quantitatively determining chemical compositions (using EDS),

crystalline structure, and crystal orientations (using EBSD). The design and function of

the SEM is very similar to the EPMA and considerable overlap in capabilities exists

between the two instruments.

Fundamental Principles of Scanning Electron Microscopy (SEM)Accelerated electrons in an SEM carry significant amounts of kinetic energy, and this

energy is dissipated as a variety of signals produced byelectron-sample

interactions when the incident electrons are decelerated in the solid sample. These

signals include secondary electrons (that produce SEM images), backscattered electrons

(BSE), diffracted backscattered electrons (EBSD that are used to determine crystal

structures and orientations of minerals), photons (characteristic X-rays that are used for

elemental analysis and continuum X-rays), visible light (cathodoluminescence–CL), and

heat. Secondary electrons and backscattered electrons are commonly used for imaging

samples: secondary electrons are most valuable for showing morphology and

topography on samples and backscattered electrons are most valuable for illustrating

contrasts in composition in multiphase samples (i.e. for rapid phase discrimination). X-

ray generation is produced by inelastic collisions of the incident electrons with electrons

in discrete ortitals (shells) of atoms in the sample. As the excited electrons return to

lower energy states, they yield X-rays that are of a fixed wavelength (that is related to

the difference in energy levels of electrons in different shells for a given element). Thus,

characteristic X-rays are produced for each element in a mineral that is "excited" by the

electron beam. SEM analysis is considered to be "non-destructive"; that is, x-rays

generated by electron interactions do not lead to volume loss of the sample, so it is

possible to analyze the same materials repeatedly.

Scanning Electron Microscopy (SEM) Instrumentation - How Does It Work?

Essential components of all SEMs include the following:

Electron Source ("Gun")

Electron Lenses

Sample Stage

Detectors for all signals of interest

Display / Data output devices

Infrastructure Requirements:

o Power Supply

o Vacuum System

o Cooling system

o Vibration-free floor

o Room free of ambient magnetic and electric fields

SEMs always have at least one detector (usually a secondary electron detector), and

most have additional detectors. The specific capabilities of a particular instrument are

critically dependent on which detectors it accommodates. 

Applications

The SEM is routinely used to generate high-resolution images of shapes of objects (SEI)

and to show spatial variations in chemical compositions: 1) acquiring elemental maps or

spot chemical analyses using EDS, 2)discrimination of phases based on mean atomic

number (commonly related to relative density) using BSE, and 3) compositional maps

based on differences in trace element "activitors" (typically transition metal and Rare

Earth elements) using CL. The SEM is also widely used to identify phases based on

qualitative chemical analysis and/or crystalline structure. Precise measurement of very

small features and objects down to 50 nm in size is also accomplished using the SEM.

Backescattered electron images (BSE) can be used for rapid discrimination of phases in

multiphase samples. SEMs equipped with diffracted backscattered electron detectors

(EBSD) can be used to examine microfabric and crystallographic orientation in many

materials.

Strengths and Limitations of Scanning Electron Microscopy (SEM)?

StrengthsThere is arguably no other instrument with the breadth of applications in the study of

solid materials that compares with the SEM. The SEM is critical in all fields that require

characterization of solid materials. While this contribution is most concerned with

geological applications, it is important to note that these applications are a very small

subset of the scientific and industrial applications that exist for this instrumentation.

Most SEM's are comparatively easy to operate, with user-friendly "intuitive" interfaces.

Many applications require minimal sample preparation. For many applications, data

acquisition is rapid (less than 5 minutes/image for SEI, BSE, spot EDS analyses.) Modern

SEMs generate data in digital formats, which are highly portable.

LimitationsSamples must be solid and they must fit into the microscope chamber. Maximum size in

horizontal dimensions is usually on the order of 10 cm, vertical dimensions are generally

much more limited and rarely exceed 40 mm. For most instruments samples must be

stable in a vacuum on the order of 10-5 - 10-6 torr. Samples likely to outgas at low

pressures (rocks saturated with hydrocarbons, "wet" samples such as coal, organic

materials or swelling clays, and samples likely to decrepitate at low pressure) are

unsuitable for examination in conventional SEM's. However, "low vacuum" and

"environmental" SEMs also exist, and many of these types of samples can be

successfully examined in these specialized instruments. EDS detectors on SEM's cannot

detect very light elements (H, He, and Li), and many instruments cannot detect

elements with atomic numbers less than 11 (Na). Most SEMs use a solid state x-ray

detector (EDS), and while these detectors are very fast and easy to utilize, they have

relatively poor energy resolution and sensitivity to elements present in low abundances

when compared to wavelength dispersive x-ray detectors (WDS) on most electron probe

microanalyzers (EPMA). An electrically conductive coating must be applied to

electrically insulating samples for study in conventional SEM's, unless the instrument is

capable of operation in a low vacuum mode.

User's Guide - Sample Collection and Preparation

Sample preparation can be minimal or elaborate for SEM analysis, depending on the

nature of the samples and the data required. Minimal preparation includes acquisition of

a sample that will fit into the SEM chamber and some accommodation to prevent charge

build-up on electrically insulating samples. Most electrically insulating samples are

coated with a thin layer of conducting material, commonly carbon, gold, or some other

metal or alloy. The choice of material for conductive coatings depends on the data to be

acquired: carbon is most desirable if elemental analysis is a priority, while metal

coatings are most effective for high resolution electron imaging applications.

Alternatively, an electrically insulating sample can be examined without a conductive

coating in an instrument capable of "low vacuum" operation.

Data Collection, Results and PresentationRepresentative SEM images of asbestiform minerals from the USGS Denver Microbeam

Laboratory 

UICC Asbestos Chrysotile 'A' standard

Tremolite asbestos, Death Valley, California

Anthophyllite asbestos, Georgia

Winchite-richterite asbestos, Libby, Montana

What is Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS)

Nu plasma MC-ICPMS. Details

MC-ICPMS is an instrument that measures isotopic ratios that are used in geochemistry,

geochronology, and cosmochemistry. A MC-ICPMS is a hybrid mass spectrometer that

combines the advantages of superior ionization of an inductively coupled plasma source

and the precise measurements of a magnetic sector multicollector mass spectrometer.

The primary advantage of the MC-ICPMS is its ability to analyze a broader range of

elements, including those with high ionization potential that are difficult to analyze by

TIMS. The ICP source also allows flexibility in how samples are introduced to the mass

spectrometer and allows the analysis of samples introduced either as an aspirated

solution or as an aerosol produced by laser ablation. 

Fundamental Principles of Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS)As a hybrid mass spectrometer, MC-ICPMS combines an inductively coupled plasma

(ICP) plasma source, an energy filter, a magnetic sector analyzer, and multiple

collectors for the measurement of ions. The ions are produced by introducing the

sample into an inductively coupled plasma which strips off electrons thereby creating

positively charged ions. These ions are accelerated across an electrical potential

gradient (up to 10 KV) and focused into a beam via a series of slits and electrostatically

charged plates. This ion beam then passes through an energy filter, which results in a

consistent energy spectrum in the ion beam and then through a magnetic field where

the ions are separated on the basis of their mass to charge ratio. These mass-resolved

beams are then directed into collectors where the ions reaching the collectors are

converted into voltage. Isotope ratios are calculated by comparing voltages from the

different collectors.

Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS) Instrumentation - How Does It Work?

ThermoFinnigan MC-ICPMS. Details

Modern MC-ICPMS are composed of three primary components:

1. an inductively coupled plasma ion source, where ions are produced, accelerated,

and focused;

2. an analyzer, where a) the ions are focused and filtered to produce a beam where

the ions have the same approximate energy and can be separated based on their

mass/charge ratios; and

3. a series of collectors, where the ion beams are measured simultaneously.

The electronics of these instruments must operate to very close tolerances in order to

produce isotope ratios that are precise to 0.01-0.001%. In addition, a high vacuum

needs to be maintained along the path of the ion beam in order to avoid scattering of

the ions due to interaction with air molecules.

ApplicationsThe primary application of MC-ICPMS is to measure the isotopic ratios of elements used

in geochronologic/thermochronologic, radiogenic isotopic, and stable isotopic studies.

Geochronology/thermochronology refers to the use of radioactive decay to obtain the

time of a specific geologic event, which is referred to as an age. Tracer isotopic

applications use the natural isotopic variations in radiogenic isotopes due to decay of

radioactive elements. These isotopic variations can be used to evaluate the interaction

between geochemical systems and/or reservoirs. This application can also provide

general chronologic information, often referred to as model ages, which more loosely

constrain the timing of geologic processes and the development of, and interaction

between, geochemical reservoirs.

Separating elements on ion exchange columns in a clean laboratory. Details

For terrestrial systems, common applications in geochronology and tracer isotopic

studies involve the following isotopic systems

U-Th-Pb

Rb-Sr

Sm-Nd

Lu-Hf

Re-Os

U series disequilibrium

Sr, Nd, Hf, Os in seawater

In cosmochemistry, isotopic compositions are used to place constraints on

nucleosynthetic processes and the timing and evolution of solar system formation. This

involves use of the isotopic systems noted above, but also includes the use of extinct

radionuclides, which are nuclides that were formed during nucleosynthesis, but have

short half lives (generally < 100 m.y.) and are no longer naturally present in the solar

system. Their presence is detected by measuring isotopic variations in daughter

isotopes, as observed principally in meteorites. In addition to the systems noted above,

systems of cosmochemical interest include:

60Fe-60Ni

53Mn-53Cr

26Al-53Mg

107Pd-107Ag

92Nb-107Zr

146Sm-142Nd

182Hf-182W

Non-radiogenic (stable) isotope ratios are typically used to evaluate biologic and kinetic

processes and track reservoir interactions:

Li

B

Mg

Ca

Fe

Ni

Cu

Zn

Zr

Mo

Strengths and Limitations of Multicollector-Inductively Coupled Plasma Mass Spectrometer (MC-ICPMS)?

StrengthsThe advantages of MC-ICPMS compared to other isotope ratio techniques include:

- the ionization efficiency is very high (near 100%) for most elements which enables

analysis of most of the elements of the periodic table, including those with high

ionization potential that are difficult to analyze by TIMS

- the MC-ICPMS operates essentially as a steady state system during the analysis

resulting in time invariant mass fractionation

- there is consistent mass bias variation across the mass range which allows the use of

an adjacent element to calculate mass bias for those elements without > 2 stable

isotopes

- the MC-ICPMS permits flexibility in sample introduction systems. Solutions can be

introduced at atmospheric pressure, which allow ease in handling. Laser ablation

systems can also be coupled with the MC-ICPMS, which allows in-situ isotopic

measurements in solid materials (e.g., Hf isotopes in zircon).

LimitationsThe disadvantages of MC-ICPMS include:

- essentially all elements introduced into the plasma are ionized including doubly

charged species, oxides, and argides; in order to achieve the highest precision and

accuracy samples, need to be chemically purified (at least as pure as for TIMS).

- even with static multi-collection, plasma instability can limit precision

- even though ionization efficiency of the plasma is near 100%, transmission of ions is

lower than with TIMS because the plasma-generated ion must be transferred from

atmospheric pressure to the high vacuum of the mass spectrometer. Many ions are lost

during this difficult transfer.

- mass bias in a MC-ICPMS is not fully understood and may result from a combination of

factors, including sampling of ions in the plasma as well as during the formation of the

aerosol (from nebulizer or laser); as a result, traditional mass fractionation laws are

imperfect

- Although similar elements can be used to determine mass bias corrections in systems

with only two isotopes, (e.g., Yb for Lu; Tl for Pb) the mass bias response between the

two elements is not identical and must be accounted for

User's Guide - Sample Collection and PreparationAs for all geochemical analyses, care must be taken to preserve sample integrity from

the time of collection through analysis in all steps of physical and chemical preparation.

For the most accurate analysis, samples require complete dissolution followed by liquid

chromatography to isolate elements of interest and eliminate isobaric interferences. For

geochronologic and many tracer applications, it is necessary to "spike" with an

artificially enriched isotopic tracer in order to determine concentrations and parent-

daughter ratios by isotope dilution. For these applications, the sample is introduced as a

solution into a spray chamber that removes the majority of the liquid from the sample

and produces a fine aerosol that is injected into the plasma for ionization. The ICP

source also allows a laser to be interfaced with the instrument, which allows the

introduction of a laser generated aerosol into the plasma. This enables the in-situ

determination of isotopic ratios in certain materials enriched in the element of interest

(Sr isotopes in carbonates and plagioclase, Hf isotopes in zircon) and in some cases

allows the instrument to be used for depth profiling.

Data Collection, Results and Presentation

Lu-Hf garnet isochron with isotopic data generated by MC-ICPMS. Details

Measured isotope ratios must be properly corrected for all instrumental biases,

including mass fractionation. Once corrected, these ratios are suitable for plotting in

any diagrams requiring atomic ratios (e.g., isochron, concordia, etc.).

LiteratureThe following literature can be used to further explore Multicollector-Inductively Coupled

Plasma Mass Spectrometer (MC-ICPMS)

What is Thermal Ionization Mass Spectrometry (TIMS)

A TIMS is an instrument that measures isotopic ratios that are used in geochemistry,

geochronology, and cosmochemistry.

Fundamental Principles of Thermal Ionization Mass Spectrometry (TIMS)

A TIMS is a magnetic sector mass spectrometer that is capable of making very precise

measurements of isotope ratios of elements that can be ionized thermally, usually by

passing a current through a thin metal ribbon or ribbons under vacuum. The ions

created on the ribbon(s) are accelerated across an electrical potential gradient (up to 10

KV) and focused into a beam via a series of slits and electrostatically charged plates.

This ion beam then passes through a magnetic field and the original ion beam is

dispersed into separate beams on the basis of their mass to charge ratio. These mass-

resolved beams are then directed into collectors where the ion beam is converted into

voltage. Comparison of voltages corresponding to individual ion beams yield precise

isotope ratios. 

Thermal Ionization Mass Spectrometry (TIMS) Instrumentation - How Does It Work?Modern instruments are composed of three primary components: 1) ion source, the

region in which ions are produced, accelerated, and focused; 2) analyzer, the region in

which the beam is separated based on mass/charge ratios; and 3) collector, a region in

which the ion beams are measured either sequentially (single collector) or

simultaneously (multi-collector). The electronics of these instruments must operate to

very close tolerances in order to produce isotope ratios that are precise to 0.01-0.001%.

ApplicationsThe primary application of TIMS is to measure the isotope ratios of elements used

ingeochronology and tracer studies. Geochronology refers to the use of radioactive

decay in closed systems to obtain the time of a specific geologic event, which is

referred to as an age. Tracer applications refer to the use of the growth of daughter

isotopes from radioactive decay to evaluate the interaction between geochemical

systems and/or reservoirs. This application provides only general chronologic

information, often referred to as model ages, which more loosely constrain the timing of

geologic processes and the development of, and interaction between, geochemical

reservoirs.

For terrestrial systems, common applications in geochronology and tracer Studies

involve the following radiometric systems

U-Th-Pb

Rb-Sr

Sm-Nd

Lu-Hf

Re-Os

U series disequilibrium

Sr, Nd, Hf, Os in seawater

In cosmochemical systems, the measurement of isotopic compositions is primarily as

tracers of nucleosynthetic processes and constraining the evolution of the solar system.

This involves measurement of the systems noted above, but also includes the decay of

short lived radionuclides, as observed principally in meteorites. In addition to the

systems noted above, systems of cosmochemical interest include:

Fe-Ni

Mn-Cr

Al-Mg

Zr-Mo

Mo-Ru

Non-radiogenic (stable) isotope-isotope ratios are typically used to characterize

exchange processes, track reservoir interactions, and evaluate biologic and kinetic

processes:

Li

B

Mg

Ca

Fe

Strengths and Limitations of Thermal Ionization Mass Spectrometry (TIMS)?

StrengthsThe advantage of TIMS compared to other isotope ratio techniques include:

the chemical and physical stability of the measurement environment, which lead

to highly precise measurements,

the ability to ionize and evaporate samples at different temperatures by using

multiple filament assemblies,

lower and more consistent average mass fractionation,

the use of single element solutions to eliminate isobaric interferences,

production of ions with a restricted range of energies (eliminates need for energy

filter),

easily automated operation, and

near 100% transmission of ions from source to collector.

LimitationsThe disadvantages include:

not all elements are easily ionized, which restricts applications to elements with

low ionization potentials;

ionization is not equally efficient for all elements, and is generally less than 1%;

mass fractionation continually changes during analysis;

elementally pure solutions are required to avoid isobaric interferences, which

requires extensive preparation; and

accurate mass fractionation correction is limited to elements with 3 or more

isotopes of which at least 2 are stable.

User's Guide - Sample Collection and PreparationAs for all geochemical analyses, care must be taken to preserve sample integrity from

the time of collection through analysis in all steps of physical and chemical preparation.

Most applications require complete dissolution of the sample followed by liquid

chromatography to isolate elements of interest, which is usually done in a "clean"

laboratory (typically Class 100-1000). For geochronologic and many tracer applications,

it is necessary to "spike" samples with an artificially enriched isotopic tracer in order to

determine concentrations and parent-daughter ratios by isotope dilution. Elements are

loaded directly as acid solutions on pre-cleaned metal ribbons for analysis.

Data Collection, Results and PresentationMeasured isotope ratios must be properly corrected for all instrumental biases,

including mass fractionation. Once corrected, these ratios are suitable for plotting in

any diagrams requiring atomic ratios (e.g., isochron, concordia, etc.) or for calculating

model ages and initial isotopic ratios.

LiteratureThe following literature can be used to further explore Thermal Ionization Mass

Spectrometry (TIMS)

Related LinksFor more information about Thermal Ionization Mass Spectrometry (TIMS) follow the

links below.

Thermal Ionization - this page, from the University of Arizona SAHRA program,

offers a brief description of thermal ionization.

Geochemistry of the World Wide Web - this site, from Cornell University, provides

links to geochemistry-related websites, including professional societies, journals,

on-line geochemical data, geochemical analytical standards, government and

university laboratories, and cosmochemistry-, astronomy-, and planetology-related

sites.

Mass Spectrometry Wiki - this Wiki site provides a brief description of thermal

ionization.

Thermo Scientific Corporation - this website provides details regarding the

perchase of a Triton thermal ionization ratio MS with multicollector.

Powerpoint tutorials on Mass Spectrometry from the EARTHTIME project.