mass spectra Flashcards

1
Q

Typical peaks in the EI mass spectra of n-alkanes are 41, 55, 69. Molecular peak has typically a high intensity.

A

no: m/z = 29, 43, 57, 71; low intensity

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2
Q

EI mass spectra of alkylated monocyclic aromatic hydrocarbons are characterized by the presence of a peak with m/z 91, which corresponds to the tropylium cation.

A

yes

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3
Q

The molecular ion is always present in EI mass spectra.

A

no

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4
Q

The EI mass spectra of polycyclic aromatic hydrocarbons (PAHs) are characterized by a doubly charged molecular ion (z=2), which has an m/z value two units lower than the singly charged molecular ion.

A

no, Doubly charged ions are rare in EI and, if present, their
m/z values would be approximately half those of singly charged ions, not “two units lower.”

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5
Q

Cycloalkanes display similar EI mass spectra patterns as alkenes.

A

yes

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6
Q

N-alkanes and i-alkanes have the same practically indistinguishable EI mass spectra.

A

no

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7
Q

Polycyclic aromatic hydrocarbons (PAHs) usually give richly fragmented EI mass spectra. A molecular ion is usually of very low intensity.

A

true

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8
Q

Mass spectra are used to determine the molecular weight of a compound.

A

yes

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9
Q

The molecular formula of the characteristic fragments in the EI mass spectra of n-alkanes is CnH2n+1.

A

yes

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10
Q

In mass spectra, the highest peak is referred to as the base peak. This peak always represents the molecular ion.

A

no

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11
Q

Do Isotopes differ in the total number of neutrons?

A

yes

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12
Q

Mass spectra are used to determine the structure of a compound

A

yes

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13
Q

In MS, cold reservoir prevents evaporation before ionization

A

yes

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14
Q

what is API?

A

atmospheric pressure ionization)

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15
Q

Ionization of the analyte occurs either under vacuum or under atmospheric pressure

A

true

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16
Q

Based on what ionization techniques are divided into2 groups: hard and soft?

A

based on the energy that is transferred to the analyte during the ionization process

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17
Q

Is electron ionization considered to be hard ionization?

A

yes

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18
Q

Is electron ionization the only example of hard ionization?

A

yes

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19
Q

What info is given about a compound during hard ionization?
1) structure of the analyte
2) molecular weight
3) molecular weight distribution

A

1) structure

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20
Q

What info is given about a compound while performing soft ionization?
1) structure
2) molecular weight

A

2) molecular weight

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21
Q

EI works best with small, volatile, and thermally stable compounds.

A

true

22
Q

EI (electron ionization) is good technique for large molacules

A

false

23
Q

Chemical ionization (CI) is a soft ionization technique that is mainly used in GC-MS.

A

true

24
Q

the main difference between CI and EI is that chemical ionization uses the presence of a so-called reaction gas

A

yes

25
Q

The ion source for chemical ionization is structurally identical to the ion source for electron
ionization. What is the source?

A

true, special component used to ionize the sample molecules using high-energy electrons.

26
Q

Is it true that in CI The analyte is
subsequently ionized by proton transfer from the reaction gas.

A

yes

27
Q

EI AND CI take place under atmospheric pressure

A

false, they take place under deep vacuum

28
Q

API (Atmospheric pressure ionization) techniques are mainly used in GC-MS

A

no, they are used in LC-MS

29
Q

What MS technique is described here:
sample is first dissolved in a suitable solvent and then converted into a spray (aerosol) form.

A

API (Atmospheric pressure ionization )

30
Q

Electrospray ionization is the most widespread ionization technique in LC-MS.

A

true

31
Q

Which is the softest of all ionization techniques in mass spectrometry?

A

Electrospray ionization

32
Q

Atmospheric pressure chemical ionization (APCI) is an extended ionization technique applicable
in LC-MS

A

true

33
Q

Thermally unstable substances cannot be analyzed in APCI (Atmospheric pressure chemical ionization)

A

true

34
Q

ESI(Electrospray ionization) ionization is soft but harder than APCI.

A

false, APCI (Atmospheric pressure chemical ionization) ionization is soft but harder than ESI.

35
Q

Matrix assisted laser desorption ionization (MALDI) is a soft ionization technique applicable in
LC-MS.

A

true

36
Q

MALDI is used mainly for biopolymers and synthetic polymers

A

true

37
Q

What are mass analyzers?

A

mass analyzers are critical components that separate ions based on their mass-to-charge ratio (
𝑚
/
𝑧
m/z).

38
Q

Is it true that detectors transform energy of ions into an electric current?

A

yes

39
Q

Molecular ion has the lowest m/z ratio in the MS spectrum

A

False, it has the highest

40
Q

If forbidden losses are present in the MS spectrum, the observed ion is not a molecular ion.

A

True

41
Q

Both in n-alkanes and iso-alkanes:
molecular ions is present, low intensity
rich fragmentation
.Is it true?

A

yes

42
Q

The most intensive peaks in n-alkanes are: m/z = 29, 43, 57, 71?

A

yes

43
Q

the mass spectra of alkenes and cycloalkanes with the same molecular weight are practically
identical, therefore they cannot be distinguished?

A

yes

44
Q

For alkenes and cycloalkanes molecular ions is present, low intensity, poor fragmentation

A

kinda false: rich fragmentation

45
Q

the most intensive peaks :56, 69, 70 (cyclopentanes) a 55 (cyclohexanes).

A

true

46
Q

In monocyclic aromatic hydrocarbons molecular ion has high intensity and kinda poor fragmentation

A

true

47
Q

alkyl-substituted benzenes are characterised by a peak m/z=91?

A

true

48
Q

Polycyclic aromatic hydrocarbons (PAH)
molecular peak has a high intensity, usually it is
also the base peak (intensity 100 %). Thus, the fragmentation is very poor.
Is it true?

A

yes

49
Q

Is it true that alcohols have mass spectra similar to alkenes?

A

yes

50
Q

How can we distinguish between alcohols and alkenes spectra?

A

alcohol can be distinguished based on the presence of the characteristic m/z 31 ion, which is not present in
alkenes

51
Q

is it true that in mass spectra of alcohols The molecular ion is very intense?

A

no, The molecular ion is very weakly intense or not present at all.

52
Q

What is the difference between
Selected ion monitoring (SIM) and Reconstructed ion chromatogram (RIC)?

A

Collects data for specific 𝑚/𝑧
m/z values during the analysis( selected) .
Collects full scan data and extracts specific ions later (reconstructed)