Ion source

Key takeaways

Ion source belongs to physics; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Ion source to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Ion source from memory before moving on to harder problems.

Reference excerpt

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

Electron ionization

Electron ionization is widely used in mass spectrometry, particularly for organic molecules. The gas phase reaction producing electron ionization is

M

+ e − ⟶ M + ∙

+ 2 e − {\displaystyle {\ce {M{}+e^{-}->M^{+\bullet }{}+2e^{-}}}}

where M is the atom or molecule being ionized, e − {\displaystyle {\ce {e^-}}} is the electron, and M + ∙ {\displaystyle {\ce {M^{+\bullet }}}} is the resulting ion. The electrons may be created by an arc discharge between a cathode and an anode. An electron beam ion source (EBIS) is used in atomic physics to produce highly charged ions by bombarding atoms with a powerful electron beam. Its principle of operation is shared by the electron beam ion trap.

Electron capture ionization Electron capture ionization (ECI) is the ionization of a gas phase atom or molecule by attachment of an electron to create an ion of the form A−•. The reaction is

A + e − → M A − {\displaystyle {\ce {A + e^- ->[M] A^-}}}

where the M over the arrow denotes that to conserve energy and momentum a third body is required (the molecularity of the reaction is three). Electron capture can be used in conjunction with chemical ionization. An electron capture detector is used in some gas chromatography systems.

Chemical ionization

Chemical ionization (CI) is a lower energy process than electron ionization because it involves ion/molecule reactions rather than electron removal. The lower energy yields less fragmentation, and usually a simpler spectrum. A typical CI spectrum has an easily identifiable molecular ion. In a CI experiment, ions are produced through the collision of the analyte with ions of a reagent gas in the ion source. Some common reagent gases include: methane, ammonia, and isobutane. Inside the ion source, the reagent gas is present in large excess compared to the analyte. Electrons entering the source will preferentially ionize the reagent gas. The resultant collisions with other reagent gas molecules will create an ionization plasma. Positive and negative ions of the analyte are formed by reactions with this plasma. For example, protonation occurs by

CH 4 + e − ⟶ CH 4 + + 2 e − {\displaystyle {\ce {CH4 + e^- -> CH4+ + 2e^-}}} (primary ion formation),

CH 4 + CH 4 + ⟶ CH 5 + + CH 3 {\displaystyle {\ce {CH4 + CH4+ -> CH5+ + CH3}}} (reagent ion formation),

M + CH 5 + ⟶ CH 4 + [ M + H ] + {\displaystyle {\ce {M + CH5+ -> CH4 + [M + H]+}}} (product ion formation, e.g. protonation).

Charge exchange ionization

Charge-exchange ionization (also known as charge-transfer ionization) is a gas phase reaction between an ion and an atom or molecule in which the charge of the ion is transferred to the neutral species.

A + + B ⟶ A + B + {\displaystyle {\ce {A+ + B -> A + B+}}}

Chemi-ionization Chemi-ionization is the formation of an ion through the reaction of a gas phase atom or molecule with an atom or molecule in an excited state. Chemi-ionization can be represented by

G ∗

+ M ⟶ G

+ M + ∙

+ e − {\displaystyle {\ce {G^{\ast }{}+M->G{}+M^{+\bullet }{}+e^{-}}}}

… excerpt ends here. Continue reading the full article.

Illustrations

Ion source: Electron ionization source schematic — Electron ionization source schematic

Worked examples

Example 1 — a first encounter with Ion source

Start with the simplest possible case. Write down what Ion source claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In physics, 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 Ion source 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 Ion source 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 Ion source

In research: Ion source appears in physics 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 Ion source 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: Ion source is common in secondary-school and first-year university syllabi. It links to neighbouring topics Accelerator physics, Ion source, Ions, so understanding it makes those chapters shorter.
In everyday life: Look for Ion source 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.

How to study Ion source in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Ion source 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.
Explain Ion source out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Ion source in simple terms?

An ion source is a device that creates atomic and molecular ions. Ion sources are used to form ions for mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters and ion engines.

Why does Ion source matter?

Because it connects several physics 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 Ion source?

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 Ion source.