2003MassSpecA

8/7/2019 2003MassSpecA

1/24

Mass Spectroscopy: Separation of Ionson the Basis of Mass to Charge Ratio

by

Kymberly Forrest, Olivia Gilbert,

Nicole Griglione, and Mary Jones


2/24

Introduction Mass spectroscopy is an effective method for determining

the weight and structure of mixtures of compounds.

It is advantageous to other methods of analysis in its abilityto separate and analyze mixtures of compounds.

It is an extremely sensitive technique with current levels of

accuracy within the range of one mass unit.


3/24

Applications General analysis of inorganic, organic, and bio-organic

chemicals

Geological Sample dating

Drug analysis and research

Process studies in the petroleum, chemical, and

pharmaceutical industries

Surface analysis

Structural resolution of proteins and genetic material


4/24

Gene

ral Se

tup

Common to all mass spectrometers are

(1) Sample Inlet (2) Ionization Source (3) Mass Analyzer

(4) Ion Detector (5) Vacuum System


5/24

MethodsofS

eparation

This presentation examines different types of Mass Analyzers,

which differ in the physical properties they manipulate.

Magnetic, which depends on Voltage

Time of Flight, which depends on Mass

Electric Quadrupole, which depends on AC/DC Currents

Common to these Mass Analyzers is the separation of particles on

the basis of mass to charge ratios (m/q).


6/24

Magnetic-SectorMass

Spe

ctrome

try


7/24

Magnetic-SectorMass

Spe

ctrome

try

THEORY:

The ion source accelerates ions to a kinetic energy given by:

KE = mv2 = qV

Where m is the mass of the ion, v is its velocity, q is the charge on

the ion, and V is the applied voltage of the ion optics.


8/24

Magnetic-SectorMass

Spe

ctrome

try

The ions enter the flight tube and are deflected by the magneticfield, B.

Only ions of mass-to-charge ratio that have equal centripetaland

centrifugalforces pass through the flight tube:

mv2 /r = BqV, where r is the radius of curvature


9/24

Magnetic-SectorMass

Spe

ctrome

try

mv2 /r = BqV

By rearranging the equation and eliminating the velocity term using

the previous equations, r = mv/qB = 1/B(2Vm/q)1/2

Therefore, m/q = B2r2/(2V)

This equation shows that the m/q ratio of the ions that reach the

detector can be varied by changing either the magnetic field (B) orthe applied voltage of the ion optics (V).


10/24

Magnetic-SectorMass

Spe

ctrome

try

In summary, by varying the voltage or magnetic field of the

magnetic-sector analyzer, the individual ion beams are separated

spatially and each has a unique radius of curvature according to itsmass/charge ratio.


11/24

TimeofFlightMass

Spe

ctrome

try (TO

F-M

S)

INTRODUCTION:

Separates ions based on flight time

Operates in pulsed mode

Ions accelerated by an electric field

Lighter ions reach the detector first


12/24

THEORY:

KE=qV when electrons are accelerated through an

electric field

KE of ion is mv2, so qV= mv2 and velocity is

inversely proportional to mass

Transit time (t) is L/v, where L is drift tube length

and v is velocity

So t=L/(2V/m/q) can be solved for charge-mass ratio

TimeofFlightMass

Spe

ctrome

try (TO

F-M

S)


13/24

TimeofFlightMass

Spe

ctrome

try (TO

F-M

S)HOW ITS DONE:

Reflectron is series of rings or grids that serves to focus

ions to improve resolution

Exact values ofL and V do not need to be known if two or

more ions of known mass are used as mass calibration points

Produces a mass spectrum as a function of time (can be

measured every 10 nsec)


14/24

TimeofFlightMass

Spe

ctrome

try (TO

F-M

S)ADVANTAGES:

Good for kinetic studies of fast reactions and for use

with gas chromatography to analyze peaks from

chromatograph

Can register molecular ions that decompose in the flight

tube


15/24

QuadrupoleM

ass Analyze

rs


16/24

BackgroundInfoQuadrupoleMass Analyzers

been in use since the 1950s

most commonly used mass spec today

sometimes referred to as mass filters because

ions of only a single mass to charge (m/q) ratio pass

through the apparatus

separate ions based on oscillations in an electric

field (the quadrupole field) using AC and DC

currents


17/24

BenefitsQuadrupol

eM

ass Analyze

rs

easy to use

simple construction

fast

low cost

can achieve unit to 0.1 m/q resolution


18/24

MoreBenefitsQuadrupol

eM

ass Analyze

rs

tolerant of relatively poor vacuums (~5 x 10-5torr),

which make them well suited to electrospray ionization

(because these ions are produced under atmosphericconditions)

quadrupoles are now capable of routinely analyzing up

to a m/q ratio of 3000, which is useful in electrosprayionization of biomolecules, which commonly produces

a charge distribution below m/z 3000


19/24

Basis ofQuadrupoleMass Filter

consists of 4 parallel metal

rods, or electrodes

opposite electrodes have

potentials of the same sign

one set of opposite electrodes

has applied potential of

[U+Vcos(t)]

other set has potential of

- [U+Vcost]

U= DC voltage, V=AC voltage,

= angular velocity of

alternating voltage


20/24

Operation ofQuadrupoleMass

Filte

r voltages applied to electrodes affecttrajectory of ions with the m/q ratioof interest as they travel down thecenter of the four rods

these ions pass through the electrodesystem

ions with other m/z ratios are thrownout of their original path

these ions are filtered out or lost tothe walls of the quadrupole, and thenejected as waste by a vacuum system

in this manner the ions of interest areseparated


21/24

ObtainingA SpectrumQuadrupol

eM

ass Analyze

rs

a mass spectrum is obtained by varying the voltages on the rods

and monitoring which ions pass through the filter

two methods for varying rod voltages: vary while holding U and V constant

vary U and V but keep the ratio U/V fixed

remember: U= DC voltage, V=AC voltage, = angular

velocity of alternating voltage

The resolution is determined by the magnitude ofU/V ratio

beam currents for individual m/q ratios may be as low as 10-13 A

and so electron multipliers are usually used


22/24

ApplicationsQuadrupol

eM

ass Analyze

rs

partial pressure analyzers

GC/MS

upper atmosphere and space research

separation of proteins and other

biomolecules with electrospray plasma diagnostics

multielement and isotopic analyses


23/24

Summary Magnetic Mass Spectroscopy shows the relationship between

voltage and mass to charge ratio:

m/q = B2r2/(2V)

Time of Flight Mass Spectroscopy shows the relationship

between tube time and mass to charge ratio:

m/q = 2Vt2

/L2

Electric Quadrupole shows the relationship between AC/DC

currents and mass to ratios.


24/24

Source

s

Dean, John A., et al. Instrumental Methods of Analysis. Belmont, CA: Wadsworth Company, 1988.

465-485.

De Laeter, John R. Toronto: John Wiley and Sons, Inc., 2001. 68-70

Sparkman, O. David. Mass Spec Desk Reference. Pittsburg: Global View, 2000. 47-48.

http://elchem.kaist.ac.kr/vt/chem-ed/ms/ms-intro.htm

http://masspec.scripps.edu/information/intro/

http://ms.mc.vanderbilt.edu/tutorials/ms/ms.htm

http://www.abrf.org/ABRFNews/1996/September1996/sep96iontrap.html

http://www.chem.arizona.edu/massspec/intro_html/intro.html

2003MassSpecA

Documents

Transcript of 2003MassSpecA