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food toxicants and analysis > mass spectrometry & process induced toxicants > Flashcards

mass spectrometry & process induced toxicants Flashcards

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1
Q

What are some applications of MS?

A

quantify contaminants, residues
determine isotope ratios -> geographic origin of food
detect metabolites in plants (new compounds; nontarget)

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2
Q

List the methods and applications for molecular MS.

A

use LC or GC couple with quadrupole or triple quadropole, quadrupole TOF, ion trap, HRMS

  • > For quantification of MOLECULES: pesticides, POPs, antibiotics, etc
  • > for non-target identification (new molecules)
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3
Q

MS can be on a ____ or _____ level.

A

molecular; atomic

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4
Q

List the methods and applications for atomic MS.

A

quantify metal contaminants: use ICP-MS

determine isotope ratio: use MULTICOLLECTOR ICP-MS, or ISOTOPE RATIO MS

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5
Q

True/False: MS is not used for qualitative measurement

A

False: nontarget identification is qualitative

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6
Q

True/False: The atomic mass indicated on the periodic table is NOT the actual mass.

A

True; RELATIVE ATOMIC MASS (avg mass over natural abundances)

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7
Q

What is special about C in terms of atomic mass?

A

12 is actual mass of C12; used as reference for calculating all other atomic masses

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8
Q

Why would 1 molecule or atom result in multiple peaks on an MS reading?

A

multiple naturally occurring stable isotopes: different possible weights

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9
Q

True/False: all isotopes of an atom have an equal chance of appearing.

A

False; occur in different % (natural abundances)

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10
Q

True/False: you should tune your mass spectrometer for the exact mass written on the periodic table, to account for all isotopes

A

False: mass written on periodic table is not exact, it is an average!
tune for 1 specific isotope (usually most common 1) -> indicate in results what isotope was measured

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11
Q

How are other atoms “filtered out” in MS?

A

Tune for specific MASS TO CHARGE RATIO, only atoms with this ratio will make it all the way through to detector (others will deflect sideways)

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12
Q

The most common isotope used for lead:

A

Pb208

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13
Q

When looking at larger molecules like dioxins, what needs to be considered for molecular mass?

A

isotopes; consider different forms of Cl (also diff forms of C, but less effect so don’t need to take into account)

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14
Q

What is the “relative abundance?”

A

relative % compared to HIGHEST PEAK on reading

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15
Q

What does a cluster of high peaks on an MS reading represent?

A

molecular peak - indicate AVERAGE MOL. MASS

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16
Q

the pattern of high peak clusters can indicate:

A

of Cl (or other atom) in molecule, based on calculation of % occurence of natural isotopes which correspond to peaks

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17
Q

The isotopes of C (do/do not) have a significant impact on molecular weight

A

Do not
C14 is radioactive, unstable
C13 is only 1.1% isotope abundance

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18
Q

MS systems must take place inside a _____. Why?

A

vacuum

otherwise ions will not last long enough to be read by detector (collide w/ ions in air)

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19
Q

describe the basic essential parts of an MS system (5)

A
  1. inlet (feed in from LC or GC
  2. ion source (make analyte CHARGED)
  3. Vacuum pump: create vacuum to maintain stability of ions
  4. MASS ANALYZER: filter for specific mass/charge ratio
  5. detector: ion arrives alone, creates electrical signal (ION TRANSDUCER)
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20
Q

What are the ionization methods for gas phase?

A
  1. electron impact
  2. negative ion chemical ionization
  3. desorption chemical ionization
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21
Q

What is electron impact ionization? How does it work

A

ionization method for gas phase, used for almost all small molecules

filament generates electrons
bombard incoming molecule -> generate cation
usually short-lived -> followed by FRAGMENTATION

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22
Q

What is fragmentation?

A

breakdown of generated ion
can lose sidegroups, bonds, attachments
specific pattern to each molecule

23
Q

Does ionization affect mass?

A

No (only adding electrons)

but: if followed by fragmentation, mass will change

24
Q

Can mass-to-charge (m/z) value be negative?

A

No; always express as positive

25
Q

True/False: the tallest peak signifies the molecular weight

A

False; the furthest right peak is molecular weight (before fragmentation)

26
Q

What ionization methods are used for liquid phases?

A
  1. electrospray
  2. atmospheric pressure chemical ionization
  3. atmospheric pressure photoionization
27
Q

describe the process of electrospray ionization

A
  1. go through NEBULIZER (Spray through tiny needle into droplets)
  2. high voltage -> charged
  3. high temp N2 gas evaporates solvent
  4. charged molecules vaporized: burst forth into charged vapor
28
Q

What is electrospray ionization good for?

A

large molecules

charged and polar organic compounds

29
Q

ESI can be in ___ or ___ mode.

What happens in each?

A

positive; negative

positive: protonation (add H+ onto basic sites), can also be ADDUCT FORMATION (add on cation like NH4)
negative: deprotonation; can form more complex ion (lose H but gain something else)

30
Q

the 4 main types of MASS ANALYZERS:

A
  1. magnetic sensor
  2. time of flight
  3. quadrupole
  4. ion trap
31
Q

What is the mechanism of a magnetic sensor mass analyzer?

A

magnetic field: affects trajectory of particle depending on m/z

32
Q

What is the mechanism of a TOF mass analyzer?

A

particle accelerated by ELECTRIC FIELD: velocity depends on m/z
determine mass based on TIME needed to travel distance to detector (time of flight)

33
Q

What is the mechanism of a quadrupole mass analyzer?

A

4 metal rods, alternating e field (generating voltage)
only desired m/z will have stable trajectory and travel all the way to detector
(low resolution)

34
Q

What is an “isobar?”

A

2 molecules with same avg molecular mass

35
Q

what is tandem MS?

A

use two MS systems, one after the other

First MS filter out precursor ion -> fragment in INTERACTION CELL -> analyze fragment with second MS

36
Q

true/false: the same type of mass analyzers are used together for tandem MS

A

False, usually hybrid
can be triple quadrupole
hybrid quadrupole & TOF,
hybrid quadrupole & ion trap

37
Q

The various MS systems are represented as:

A

MS1, MS2,….MSn, etc

38
Q

What is “MRM?”

A

multiple reaction monitoring

monitor transition from PARENT ION (Q1) to DAUGHTER ION (Q3)
use data from precursor ion and fragmentation process to quantify molecule

39
Q

The ____ peak determines the molecular mass of the precursor ion. The ____ peak is used for quantification. The ____ peak is used for confirmation.

A

furthest right
highest
second highest

40
Q

What are process induced toxicants?

A

undesirable molecules generated during processing of food (breakdown products, reaction between components, etc) that can be harmful

41
Q

Most regulations require monitoring of at least ___ MRM transitions.

A

2

42
Q

how can process induced toxicants occur? (3)

A
  1. degradation (thermal, microbial, etc)
  2. reaction between food components
  3. reaction with additives or other components
43
Q

What are some thermal induced processing toxicants? (6)

A 
polyaromatic hydrocarbons (PAHs)
heterocyclic aromatic amines (HAAs)
furans and 5-hydroxymethylfurfural (HMF)
acrolein
acrylamide
chloropropanols
44
Q

Can boiling produce acrylamides or other toxicants?

A

No; temperature is too low (need very high temp like flame)

45
Q

What are some toxicants caused by preservation methods?

A

preservatives: benzene, n-nitrosamines
fermentation: ethyl-carbamate, biogenic amines

46
Q

Give an example of a biogenic amine

A

histamine: formed by bacteria in fish -> can trigger allergic rxn

47
Q

The main risk associated with process induced toxicants is:

A

carcinogenicity

48
Q

What are the IARC classifications of carcinogens? (5)

A

group 1: carcinogenic to humans (enough evidence)
group 2A: probably carcinogenic to humans (strong evidence but inconclusive)
group 2B: possibly carcinogenic to humans (some evidence)
group 3: unclassifiable (no evidence at present)
group 4: probably not carcinogenic (strong evidence showing no carcinogenicity)

49
Q

What are 2 compounds in IARC group 1?

A

benzene, benzo(a)pyrenes

50
Q

True/False: acrylamide is a known carcinogen

A

False: only group 2A (not yet conclusive, but strong evidence)

51
Q

How is the analytical procedure for acrylamide usually conducted?

A
  1. extraction with WATER
  2. separation and clean up with solid phase extraction
  3. analyze with LC-QqQMS/MS (triple quadrupole tandem MS)
52
Q

Why do most compounds stay at 2A or 2B classification?

A

require intensive studies and work and $$$ to absolutely prove human carcinogenicity

53
Q

What is used as a standard during acrylamide analysis?

A 
INTERNAL STANDARD
make isotope (add H+) so diff weight, distinguishable

food toxicants and analysis (11 decks)

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