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CSMLS > CHEM Mass Spec (Quizlet 262) > Flashcards

CHEM Mass Spec (Quizlet 262) Flashcards

1
Q

Define Mass Spectrometry

A
  • an analytical technique that measures the mass-to-charge (m/z) ratio of ions
  • forms gas phase ions from the sample
  • uses electric/ magnetic field to sort mixture of ions according to m/z
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2
Q

How do you calculate the mass of a cation and anion ?

A

[M+nH]^n+/-

M = molecular mass

H = proton mass

n = number of charge

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3
Q

Differentiate Accurate vs Molecular Mass

A

Accurate Mass = experimentally determined mass

Molecular Mass = calculated mass of compound based on weighted average of all isotopes

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4
Q

Define Monoisotopic Mass

A

calculated mass based on accurate masses of the most abundant stable isotopes of the elements present

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5
Q

Define Nominal Mass

A

The rounded integer value of the monoisotopic mass

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6
Q

Describe the components of a mass spectrometer and how they work

A

Inlet System

Ion Source - converts sample to ions

Mass Analyzer - filters, selects, and fragments ions

Detector - determines abundance of ions of different m:z after that have been separated

Data System - converts data into mass spectrum

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7
Q

Describe Electrospray Ionization (EI)

A
  1. Production of charged droplets - from voltage applied to Taylor cone (skimmer)
  2. Solvent evaporation - molecules become smaller in atmospheric pressure
  3. Coulombic repulsion - electrostatic forces between positive charges as they come closer together
  4. Generation of gas phase ions
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8
Q

Describe MALDI

A

WIP Matrix-assisted laser desorption ionization (MALDI)

  1. Desolvation and Ionization
  2. Proton Transfer
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9
Q

Describe Time of Flight

A
  • A type of mass analyzer
  • Ions pass through with a speed based on relative mass
  • lighter ions are accelerated to a higher velocity than heavier ions
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10
Q

Describe Quadrupole mass analyzers

A
  • A type of mass analyzer
  • Radio frequency and direct current voltages alternate between poles
  • Ions pass through based on m:z
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11
Q

Compare mass accuracy, resolution, and sensitivity between Quadropole and Time of Flight

A

Quadropole: lower mass accuracy and resolution than Time of Flight, but has similar sensitivity

Time of Flight: higher mass accuracy and resolution than Quadrupole, but has similar sensitivity

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12
Q

Describe Electron Mulitpliers

A
  • An ion detector
  1. Ion strikes the detector, producing a current
  2. Current is amplified to increase the signal attributed to ion
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13
Q

Describe tandem mass spec and scan types

A

Tandem mass analyzer: 2 mass analyzers in one space

Eg. Precursor Ion Scan

  • Product Ion Scan
  • Neutral Loss Scan
  • Multiple Reaction Monitor
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14
Q

Describe QqQ MS: Single Ion Monitoring

A

Triple Quadropole Mass Scan: Single Ion Monitoring

  • only Q1 and Q3 are used
  • Q1 is fixed with a single m/z
  • only ions with (ie. 300) m/z will exit Q1 and travel to Q3 and the detector (only green)
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15
Q

What is a neutral loss ?

A

Neutral loss: occurs when characteristic neutral fragments are produced in the collision cell and cannot be detected

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16
Q

What is a disadvantage of single mass analyzers ?

A

High potential for overlapping m/z because of molecules of similar mass and charge

17
Q

Describe QqQ MS/MS: Precursor Ion Scan

A

Triple Quadropole MS/MS: Precursor Ion Scan

  • Q1 is fixed as a range of m/z (ie. only 210 to 550 m/z will exit Q1; green and yellow)
  • Q2 is where ion fragmentation occurs
  • Q3 is fixed as a single m/z (ie. only 85 m/z will exit Q3 and is detected; only green)
18
Q

Describe QqQ MS/MS: Product Ion Scan

A

Triple Quadropole MS/MS: Product Ion Scan

  • Q1 is fixed as a single m/z (ie. only 260 m/z will exit Q1; only green)
  • Q2 is where ion fragmentation occurs
  • Q3 is fixed as a range of m/z (ie. only ions with 50 to 260 m/z will exit Q3)
19
Q

Describe QqQ MS/MS: Neutral Loss Ion Scan

A

Triple Quadropole MS/MS: Neutral Loss Ion Scan

  • mass specs do not detect neutral fragments
  • Q1 is where precursor ions are scanned with a m/z range
  • Q2 is where ion fragmentation occurs and neutral fragments are lost
  • Q3 is where product ions are scanned with a m/z range offset by the neutral lost
20
Q

Describe QqQ MS: Full Scan

A

Triple Quadropole Mass Scan: Full Scan

  • only Q1 and Q3 are used
  • Q1 is fixed with a range of m/z (ie. only ions between 100 to 300 m/z will be able to exit Q1 and travel to Q3 to the detector
  • green, yellow, and white but not purple
21
Q

Describe QqQ MS/MS: Multiple Reacting Monitoring

A

Triple Quadropole MS/MS: Multiple Reaction Monitoring

  • “multiple” = can specify for more than one precursor/ product ion pair
  • Q1 is fixed as a single m/z
  • Q2 is where ion fragmentation occurs
  • Q3 is fixed as a corresponding m/z to identify a precursor ion and product ion
  • considered gold standard
22
Q

Define base peak

A

Ion with the highest abundance (100%) in the mass spectrum

23
Q

Define ion trap

A

A component of a mass spectrometer where ions are held in a spatially confined region of space using a magnetic/ electrostatic field

  • can be manipulated to allow m/z measurements
24
Q

What is GC-MS ?

A

Gas Chromatography-Mass Spectrometry:

  • mixture of analytes is separated into individual components by gas chromatography
  • followed by ionization of separated compounds in the ion source of a mass spectrometer
25
Q

Principle of Electron Ionization

A
  • occurs in a vacuum
  • thermionic emission: gas phase molecules are bombarded by electrons from a heated filament
  • collision of electrons = radical cation
  • radical cations are electrostatically focused and introduced into the mass analyzer = mass spectrum
26
Q

Principle of Chemical Ionization

A
  • low energy; little fragmentation of ions occur
  • a proton is transferred to a gas phase analyte by a reagent gas molecule
  • useful for molecular mass determination and quantification (ie. drugs)
27
Q

Which of the following best described atmospheric pressure chemical ionization?

a. at atmospheric pressure the sample is ionized as it passes through a charged capillary

b. in a vacuum, electrons generated by thermionic emission ionize the sample

c. at atmospheric pressure a corona discharge needle is used to emit electrons which ionize the sample

d. in a vacuum, an electron beam ionizes a reagent gas which then ionizes the sample

1 - atmospheric pressure chemical ionization

2 - chemical ionization

3 - electron ionization

4 - electrospray ionization

A
  1. atmospheric pressure chemical ionization = c. at atmospheric pressure a corona discharge needle is used to emit electrons which ionize the sample
  2. chemical ionization = d. in a vacuum, an electron beam ionizes a reagent gas which then ionizes the sample
  3. electron ionization = b. in a vacuum, electrons generated by thermionic emission ionize the sample
  4. electrospray ionization = a. at atmospheric pressure the sample is ionized as it passes through a charged capillary
28
Q

Which of the following ionization techniques is most commonly used for drug screening using GCMS?

a.

chemical ionization

b.

electron ionization

c.

matrix-assisted laser desorption/ionization (MALDI)

d.

inductively coupled plasma (ICP)

A

b.

electron ionization = in a vacuum, electrons generated by thermionic emission ionize the sample

29
Q

Which of the following ionization techniques is preferred for mass spectrometry analysis of large biomolecules?

a.

inductively coupled plasma (ICP)

b.

matrix assisted laser desorption (MALDI)

c.

electrospray

d.

chemical

A

b.

matrix assisted laser desorption (MALDI)

30
Q

Which of the following techniques is primarily used for the screening and confirmation of genetic disorders?

a.

ICP-MS

b.

MALDI-TOF-MS

c.

GC-MS

d.

LC-MS

A

d.

LC-MS

CSMLS (39 decks)

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