mass spectrometry & process induced toxicants Flashcards
What are some applications of MS?
quantify contaminants, residues
determine isotope ratios -> geographic origin of food
detect metabolites in plants (new compounds; nontarget)
List the methods and applications for molecular MS.
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)
MS can be on a ____ or _____ level.
molecular; atomic
List the methods and applications for atomic MS.
quantify metal contaminants: use ICP-MS
determine isotope ratio: use MULTICOLLECTOR ICP-MS, or ISOTOPE RATIO MS
True/False: MS is not used for qualitative measurement
False: nontarget identification is qualitative
True/False: The atomic mass indicated on the periodic table is NOT the actual mass.
True; RELATIVE ATOMIC MASS (avg mass over natural abundances)
What is special about C in terms of atomic mass?
12 is actual mass of C12; used as reference for calculating all other atomic masses
Why would 1 molecule or atom result in multiple peaks on an MS reading?
multiple naturally occurring stable isotopes: different possible weights
True/False: all isotopes of an atom have an equal chance of appearing.
False; occur in different % (natural abundances)
True/False: you should tune your mass spectrometer for the exact mass written on the periodic table, to account for all isotopes
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
How are other atoms “filtered out” in MS?
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)
The most common isotope used for lead:
Pb208
When looking at larger molecules like dioxins, what needs to be considered for molecular mass?
isotopes; consider different forms of Cl (also diff forms of C, but less effect so don’t need to take into account)
What is the “relative abundance?”
relative % compared to HIGHEST PEAK on reading
What does a cluster of high peaks on an MS reading represent?
molecular peak - indicate AVERAGE MOL. MASS
the pattern of high peak clusters can indicate:
of Cl (or other atom) in molecule, based on calculation of % occurence of natural isotopes which correspond to peaks
The isotopes of C (do/do not) have a significant impact on molecular weight
Do not
C14 is radioactive, unstable
C13 is only 1.1% isotope abundance
MS systems must take place inside a _____. Why?
vacuum
otherwise ions will not last long enough to be read by detector (collide w/ ions in air)
describe the basic essential parts of an MS system (5)
- inlet (feed in from LC or GC
- ion source (make analyte CHARGED)
- Vacuum pump: create vacuum to maintain stability of ions
- MASS ANALYZER: filter for specific mass/charge ratio
- detector: ion arrives alone, creates electrical signal (ION TRANSDUCER)
What are the ionization methods for gas phase?
- electron impact
- negative ion chemical ionization
- desorption chemical ionization
What is electron impact ionization? How does it work
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
What is fragmentation?
breakdown of generated ion
can lose sidegroups, bonds, attachments
specific pattern to each molecule
Does ionization affect mass?
No (only adding electrons)
but: if followed by fragmentation, mass will change
Can mass-to-charge (m/z) value be negative?
No; always express as positive
