engineering

Thermal ionization mass spectrometry

Thermal ionization mass spectrometry is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Thermal ionization mass spectrometry rather than just read about it. In short: Thermal ionization mass spectrometry (TIMS), also known as surface ionization, is a highly sensitive isotope mass spectrometry characterization technique. The isotopic ratios of radionuclides are used to get an accurate measurement for the elemental analysis of a sample.

Key takeaways

Thermal ionization mass spectrometry belongs to engineering; place it in that map before memorising details.
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Connect Thermal ionization mass spectrometry to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Thermal ionization mass spectrometry from memory before moving on to harder problems.

Reference excerpt

Thermal ionization mass spectrometry (TIMS), also known as surface ionization, is a highly sensitive isotope mass spectrometry characterization technique. The isotopic ratios of radionuclides are used to get an accurate measurement for the elemental analysis of a sample. Singly charged ions of the sample are formed by the thermal ionization effect. A chemically purified liquid sample is placed on a metal filament which is then heated to evaporate the solvent. The removal of an electron from the purified sample is consequently achieved by heating the filament enough to release an electron, which then ionizes the atoms of the sample. TIMS utilizes a magnetic sector mass analyzer to separate the ions based on their mass to charge ratio. The ions gain velocity by an electrical potential gradient and are focused into a beam by electrostatic lenses. The ion beam then passes through the magnetic field of the electromagnet where it is partitioned into separate ion beams based on the ion's mass/charge ratio. These mass-resolved beams are directed into a detector where it is converted into voltage. The voltage detected is then used to calculate the isotopic ratio.

Ionization source The filaments used are made from tantalum (Ta), tungsten (W), platinum (Pt) or rhenium (Re). Conventionally, there are two filaments used in TIMS. One filament is for the sample and is called the sample filament. The liquid sample is placed on the sample filament which is then evaporated. Subsequently, these evaporated analytes land on the other filament, also known as the ionization filament, where it is ionized.

The single filament method is also possible. Once the sample evaporates, the analytes can settle back down onto the same filament to get ionized. The use of a triple filament or multifilament set-up improves ionization efficiency and provides the rate of evaporation and ionization to be controlled separately. Filaments need to be loaded with activators. An activator represses the evaporation of the desired element and can either increase or decrease the ionization potential of the filament. This results in high ionization efficiency and a higher total yield. The most common activator is silica gel/phosphoric acid for Pb. The filaments are in a vacuum that can reach temperatures anywhere from 400-2300°C. In order to prevent any damage to the filaments, they are firmly fixed onto a carousel-like sample turret which normally has 10 to 20 filament assemblies. The evaporation process is usually conducted at relatively low temperatures in exchange for long-lasting signals and minor isotopic fractionation. The ionization part requires high temperatures to ensure good ionization efficiency. The ions emitted have low spatial and energetic spread which makes a single-focusing magnetic sector mass analyzer or quadrupoles suitable. The most common detectors used for TIMS is Faraday cup, Daly detector, and electron multiplier. Customarily, TI ion sources are assembled with multicollector (MC) systems.

Thermal ionization mechanism When the hot filament heats the liquid sample, the Fermi levels within the sample reaches parity with that of the metal. In turn, this allows for an electron to tunnel from the sample to the metal filament. As a result, positive ions are formed from the sample that lost an electron. This transferring of electrons also result in the formation of negative ions. Subsequently, there are two types of thermal ionizations. One is positive thermal ionization (P-TI) and the second is negative thermal ionization (N-TI). The production of ions is parameterized by the Saha ionization equation or the Saha-Langmuir equation.

Isotope ratio measurement The relative abundances of different isotopes are then used to describe the chemical fractionation of different isotopes, travel in different reservoirs of non-radiogenic isotopes, and age or origins of solar system objects by the presence of radiogenic daughter isotopes. Elemental analysis is a predominant application of TIMS as it gives reliable isotopic ratios. Following the trend of decreasing ionization energy, elements located towards the bottom left of the periodic table are viable for TIMS. In addition, the high electron affinity seen towards the upper right of the periodic table makes these nonmetals excellent candidates. The technique is used extensively in isotope geochemistry, geochronology, and in cosmochemistry. Quantitative isotope ratio techniques include isotope dilution thermal ionization mass spectrometry (ID-TIMS) and chemical abrasion thermal ionization mass spectrometry (CA-TIMS). Isotope dilution method is used because the signal intensity in TIMS isn't proportional to the amount that is placed into TIMS. For age dating, mass spectrometers with magnetic sectors have better precision than a quadrupole mass spectrometer or quadrupole mass analyzer. Inductively coupled plasma-quadrupole mass spectrometers allows for an even higher precision of detecting the change of isotopic ratios by radioactive decay. The more precision means the higher resolution in age dating.

See also Isotope-ratio mass spectrometry

References

Illustrations

Worked examples

Example 1 — a first encounter with Thermal ionization mass spectrometry

Start with the simplest possible case. Write down what Thermal ionization mass spectrometry claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Thermal ionization mass spectrometry before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Thermal ionization mass spectrometry ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Thermal ionization mass spectrometry

In research: Thermal ionization mass spectrometry appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Thermal ionization mass spectrometry in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Thermal ionization mass spectrometry is common in secondary-school and first-year university syllabi. It links to neighbouring topics Mass spectrometry, so understanding it makes those chapters shorter.
In everyday life: Look for Thermal ionization mass spectrometry outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Thermal ionization mass spectrometry in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Thermal ionization mass spectrometry means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
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Frequently asked questions

What is Thermal ionization mass spectrometry in simple terms?

Why does Thermal ionization mass spectrometry matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Thermal ionization mass spectrometry?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Thermal ionization mass spectrometry.