Unit 7- Mass Spectrometry

explain basic principle of MS

A mass spectrum is a plot of ion abundance versus mass-to-charge ratio or just mass for singly charged ions. ( used to identify MASS of molecules)

—> will produce a mass spectrum

explain overview of how MS works

1.      Analyte is converted to ions by applying energy (create charged particle)

2.      Ions formed are separated based on their mass to charge ratio

3.      Ions are directed to a transducer that converts the number of ions into an electrical signal

when can mass to charge be shorten to mass

only for singly charged ions

Atomic mass scale

used to express atomic and molecular masses based on specific isotope of carbon

unified atomic mass unit

exact mass

refers to the precise mass of a specific isotope of an element or compound that contains particular isotopes.

Average atomic mass

the weighted average of the masses of all naturally occurring isotopes of an element, considering their fractional abundances.

what are the different components of MS

inlet system

ion source

mass analyzer

detector

signal processor

readout

what are the different types of Mass analyzers

magnetic

double focusing

quadrupole

ion trap

ion cyclotron

time of flight

what are double focusing MS

elector sector procedes magnetic sector

—> focus beam of ions

A double focusing mass spectrometer uses two types of analyzers in sequence:

1. Electric field (electrostatic sector)

2. Magnetic field (magnetic sector)

how does quadrupole work

mass filters that only allow ions of a certain mass-to-charfe ratio to pass

—>scan voltage applied to the rods

—> low resolution

Time of flight?

of mass analyzer that separates ions based on how long they take to travel down a flight tube to the detector after being accelerated.

what are the different ion sources for MS

1. ICP —>Q

2. direct current plasma—>Q

3. microwave induced—>Q

4. sparked—> DF

5. glow discharge—>DF

hwo does ICPMS work

Ions formed in the plasma are introduced into the mass analyzer, often a
quadrupole, where they are sorted by m/z ratio and detected

what is sparked source MS

used for solid samples, not easily dissolved by ICPMS

how are analyte ions drawn into the MS

differential pumping—>

what are the different ion sources

gas=phase: EI, CI

Desorptopn: FAB< MALBI< ESI

explain gasp=phase source of ions

sample is vaporized and ionzied

explain desorption

sample in a solid or liquid state is converted directly into gaseous ions

works by nonvolatiles and unstable soucre

what is energy ionization

molecules bombarded with high energy beam of electrons

positive ions—> electrostatic repulsion

what are inlet systems used for

to introduce a representative sample to the ion source
with minimal loss of vacuum

what are the different types of inlet sources

batch inlets, direct probe inlets, chromatographic inlets, and electrophoretic inlets.

BDEC

what mass analyzer used in GC/MS

quadrupole

what is tandem ms

do ms twice use two mass analyzers

explain ms-ms

1. ms 1 produces fragment ion

2. precurose ion reacts

3. decomposes to product ions

4. product ions gets ms 2

applications of MS

molecular mass

fragmentation patterns

identity based on comparing to data

pesticides in foods

structures of compounds

what is a good technique for non volaties

LC/MS

what is a sector analyzer

Separation in these devices is
based on their deflection of ions in
a magnetic field

general design of MS

Inlet: interface with GC, LC, IC, CE.
Ion source: region in a mass spectrometer where gas-phase ions are
produced
Mass analyzer: region in a mass spectrometer where ions are separated
according to their mass-to-charge ratio (m/z) values
Detector: collect and convert ions (with a particular m/z) into an electrical
signal by an ion transducer.
Vacuum pumps keep the mass spectrometer devoid from interferences
A computer usually pilot the system, collect the data (e.g. mass spectrum)
and allow for their analysis (qualitative or quantitative).

what can teh mass analyzer do

1. continously look for signal over m/z range

2. ook at specific m/z

what is precursor ion

selected frgament in the first mass analyzer

what is daughter ion

fragmenattion of precursor

Parent daughter ion

Q1>Q3

Resolution in MS?

Ability to distinguish two peaks of a mass spectrum with a difference
of mass-to-charge ratios ΔM

what mass analyzer lowest resolution

quad

highest resolution MS

time of flight