Lecture 2 - Components of MS Flashcards by Jasper Sison

What are the components of a mass spectrometer?

Inlet
Ion source
Mass filter (or Ion seperation)
Detector

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What is used as inlet for MS?

Sample plate
HPLC
GC
Solids probe

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What is used as Ion source for MS?

MALDI
API/Electrospray
EI,CI

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What is used as Mass filter for MS?

TOF
Quadrupole
Ion trap

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What is used as detector for MS?

Microchannel
Plate
Electron
Multiplier

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What is the inlet of MS?

A method of introducing the sample into the MS.

Generally directly or in combination with a seperation technique

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What is the Ionisation of MS?

A method to convert neutral molecules into ions

By either a gain or loss of a proton

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What is the Mass filter (ion seperation) of MS?

A method to select target m/z ions.

Can be individually send to the detector

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What is the ion detection of MS?

A method that counts the number of ions at each m/z

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What are the types of MS?

Full scan MS

Tandem MS and MSn

Accurate mass analysis

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What is MSMS?

The use of 2 mass analyzers combined in 1 instrument to select an analyte from a mixture then fragmenting it to give structural information.

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What is MSn?

Breaking a jigsaw piece into a smaller fragments

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What does parts per million (ppm) express?

How is it calculated?

The accuracy of mass measurement

Caculation: a narrow scan/peak matching to an internal reference sample.

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What is Electron ionisation (EI)?

Bombarding gaseous molecules with high energy electron to ionise analytes.

Electrons do not impact gas molecules
Electrons disrupts bonds to remove electrons from analye(s)

1 ion produced for every 1000 molecules
sample must be in gas form
Can be linked to gas chromatography
Used for analysis of organic compounds

(M) + (e-) –> (M+) + (2e-) radical cations produced

EI uses fluorinated compounds.

Fluorinated compounds:
ESI PEG, Na trifluoroacetate, polyethylenimine (PEI).

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What is Chemical ionisation (CI)?

Reacting analye with reagent gas for ionisation.

Less energetic than electron ionisation (EI)

Typical gasses used:
Methane, isobutane, ammonia

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What is Fast atom bombardment (FAB)

Bombarding analyte with accelerated inert gas atoms (via electric field)
The analye is mixed with a matrix

Usually a peak is seen at every mass

Soft ionisation (fragmented ions are low abundance)

Good for polar compounds with high Mr

What is the first ‘desorption’ technique used by biochemists?

Fast atom bombardment (FAB)

What is Matrix Assisted Lazer Desorption Ionisation (MALDI) MS?

Bombarding ‘solid solution’ analyte+matrix mixture with a lazer (337nm)

The matrix is 200-500 fold excess relative to analyte.

Lazer is focused to a 30-50um spot size

The Matrix absorbs the energy of the lazer (>300nm)
typically 10-100 lazer shots are accumulated

The sample mixture undergoes sublimation to gas phase

Can be applied to large macromolecules

[MALDI] What is CHCA (matrix) used for?

Peptides

[MALDI] What is Sinapinic acid (matrix) used for?

Proteins, Polymers

[MALDI] What is Gentisic acid (matrix) used for?

Peptides, Proteins, Lipids, Nucleic acid, saccharides

[MALDI] What is 3-Hydroxypicolinic acid (matrix) used for?

Nucleic acid, DNA

[MALDI] What solvents are used for peptides?

0.1% TFA

Matrix in 50/50, 0.1% TFA/ACN

[MALDI] What solvents are used for proteins

0.1% TFA
Matrix in 70/30, 0.1% TFA/ACN

higher conc. will precipitate the protein

[MALDI] What solvents are used for lipids

Chloroform matrix must also be in miscible organic solvent

What is electrospray (ES)?

A method that produce ions from a liquid phase Ionisation occur at atmospheric pressure. Gas phase ions produced enter vacuum through small opening (Taylor cone) Soft ionisation process Ions produced in solution: solution chemistry Dictates whether positive or negative ions formed Process: Ionised solution (solvent) is sprayed to analyte. Analyte is mixed with solvent and solvent evaporates, until the rayleigh limit is reached. Mixture undergoes coulombic explosion Multiply charged droplet Analyte ions produced Passed through cone (counterelectrode) Vacuum gradient assists in pulling ions into the MS.

How are MS prevented from getting contaminated?

Z-Spray

[Ion separation/Mass filter] | What are quadrupoles?

4 parallel rods. Each opposite pair of rods switches between positive and negative charge. This produces continuous oscillating voltage of a set amplitude. Hence, only ions with a specific m/z ratio will achieve a stable trajectory and pass through quadrupole Tandem MS requires more than 1 quadrupole

[Ion separation/Mass filter] | What are ion traps?

An equipment that traps ions and selects using radiofrequency (Rf) applied to ring with varying voltage Injection > Trapping > Mass selective ejection MSMS/MSn: Inject and trap > Isolate ion of interest > Fragment ion of interest > Eject and detect ions

Compare the difference between Quadrupole and Ion trap for selection of ions.

Quadrupole applied to MSMS Ion trap applied to MSMS and MSn Quadrupole measures in 'space' Ion trap measures in 'time' Quadrupole has better sensitivity Quadrupole collision energy is optimised Ion trap collision energy applied to precursor ion only

What is Time of Flight? (TOF)

Uses the equation : 2 KE ____ x t^2 = m/z s^2 Ions with different mass, but same kinetic energy Ions with lighter mass will fly faster and reach detector first Flying times of the ions are proportional to m/z ratios It uses 2 detectors, linear and reflector detector Linear for better sensitivity, analyse high m/z ions Reflector for better mass accuracy (longer TOF), limited mass range

List the combinations of mass analysers

Multiple quadrupoles : triple quadrupole Quadrupole and ToF tube Quadrupole and Ion trap ToF and ToF

What equipment is used for ion detection?

Electron multiplier, counts the ions at each m/z value Each ions hits the surface of the multiplier resulting in the ejection of more particles. This cascade effect produces a charge on the anode cup. The charge represents the signal produced by the ion