Mass SpectroscopyMass Spectroscopy

Mass SpectrometryMass Spectrometry

Most useful tool for molecular Most useful tool for molecular structure determination if you structure determination if you can get it into gas phasecan get it into gas phase

Molecular weight of parent and Molecular weight of parent and fragments that can give hints as fragments that can give hints as to the structure of the moleculeto the structure of the molecule

Early Use of Mass SpectroscopyEarly Use of Mass Spectroscopy

Quantitative methods for determination of Quantitative methods for determination of the components in complex hydrocarbon the components in complex hydrocarbon mixturesmixtures

Later used for the identification and Later used for the identification and structural analysis of complex compoundsstructural analysis of complex compounds

Principles of measurementsPrinciples of measurements

As an identification method:As an identification method: When a given molecular species is impacted When a given molecular species is impacted

with an electron beam, a family of positive with an electron beam, a family of positive particles are producedparticles are produced

The mass distribution of the particles are The mass distribution of the particles are characteristic of the parent speciescharacteristic of the parent species

How does it work?How does it work?

Sample is volatized and allowed to leak Sample is volatized and allowed to leak slowly into an ion chamberslowly into an ion chamber

Molecules of sample are ionized to mostly Molecules of sample are ionized to mostly positive ions by electron beampositive ions by electron beam

Positive ions are separated from negative Positive ions are separated from negative ionsions

How does it work?How does it work?

Positive ions are accelerated into separation Positive ions are accelerated into separation chamberchamber

The fast moving particles are subjected to a The fast moving particles are subjected to a strong magnetic field in which they travel in strong magnetic field in which they travel in a curved patha curved path

The radius depends upon their velocity and The radius depends upon their velocity and mass as well as the field strengthmass as well as the field strength

How does it work?How does it work?

ions pass through an exit slit and fall upon a ions pass through an exit slit and fall upon a collector electrodecollector electrode

the ion current that results is amplified and the ion current that results is amplified and recorded as a function of field strength or recorded as a function of field strength or accelerating potentialaccelerating potential

Magnetic sector MSMagnetic sector MS

Time of flight MSTime of flight MS

Portable TOF/MSPortable TOF/MS

ICP/MSICP/MS

QuadrupolesQuadrupoles

Quadrupole MSQuadrupole MS

Liquid ChromLiquid Chrom

GCGC

MS Instrumentation - Sample introductionMS Instrumentation - Sample introduction

Need high vacuum - 10Need high vacuum - 10 torr( torr=1 torr( torr=1 mm Hg)mm Hg)

Oil diffusion pumps, turbomolecular Oil diffusion pumps, turbomolecular pump, diffusion pumppump, diffusion pump

Gas injection through pinholeGas injection through pinhole Liquids that vaporize into vacuumLiquids that vaporize into vacuum Direct ionization of solidsDirect ionization of solids

Sample ionizationSample ionization

General ionization that causes General ionization that causes fragmentation (electron impact)fragmentation (electron impact)

Gentle ionization that favors intensity of Gentle ionization that favors intensity of molecular ion (chemical ionization with molecular ion (chemical ionization with gaseous ions)gaseous ions)

Gentle ionization for molecules that are not Gentle ionization for molecules that are not in the gas phase (eg biological molecules) in the gas phase (eg biological molecules) (Fast Atom Bombardment)(Fast Atom Bombardment)

Ionization of inorganic solidsIonization of inorganic solids

Spark source (like atomic Spark source (like atomic emission)emission)

ICP/MSICP/MSGlow discharges (hollow cathode Glow discharges (hollow cathode

lamps)lamps)Laser spallationLaser spallation

Mass analyzer - separation based on mass to charge ratioMass analyzer - separation based on mass to charge ratio

Magnetic sector (single focus)Magnetic sector (single focus) Double focus (electrostatic field to select Double focus (electrostatic field to select

energy and magnetic field for m/e)energy and magnetic field for m/e) Quadrupole (1 to 3)Quadrupole (1 to 3) Time of flight (pulsed ioization)Time of flight (pulsed ioization) Fourier transform (ion cyclotron Fourier transform (ion cyclotron

resonance)resonance)

Magnetic sector MSMagnetic sector MS

largelarge slow scans (change magnetic field with slow scans (change magnetic field with

electromagnet)electromagnet) finite spread of energies from source limit finite spread of energies from source limit

resolutionresolution R= m/R= m/m : capable of R= 600 to capable of R= 600 to

2000 which means looking at m/e 2000 which means looking at m/e of 600 with unit mass resolutionof 600 with unit mass resolution

Double focus MSDouble focus MS

Very large with electrostatic analyzer to Very large with electrostatic analyzer to eliminate differences in KE of ionseliminate differences in KE of ions

R= 40,000 is possible which means for m/e of R= 40,000 is possible which means for m/e of 100 the mass differences of 0.0025 can be 100 the mass differences of 0.0025 can be measuredmeasured

Isotopic differences: C3H7 = 43.0892Isotopic differences: C3H7 = 43.0892 C2H3O= 43.0456C2H3O= 43.0456 C2H5N= 43.0688C2H5N= 43.0688

Quadrupole MSQuadrupole MS

Electrical fields applied Electrical fields applied pairwisepairwise

DC voltage and RF DC voltage and RF oscillating voltage oscillating voltage changed so only one changed so only one value of m/e moves in a value of m/e moves in a stable path through the stable path through the fieldfield

Scans over 1000 mass Scans over 1000 mass units/secunits/sec R= 10,000 possibleR= 10,000 possible

R= 500 typicalR= 500 typical

Ion SourceIon Source Quad 1Quad 1

Quad 2 Collision chamberQuad 2 Collision chamber

Quad 3 AnalyzerQuad 3 Analyzer

DetectorDetector

MS PumpsMS Pumps

Mechanical pumps of Mechanical pumps of large capacity (for large capacity (for ion sources)ion sources)

Turbomolecular Turbomolecular pumps are expensive pumps are expensive ($7000) but smaller ($7000) but smaller and less problem and less problem than diffusion pumpsthan diffusion pumps

Ion Trap MS (like ion cyclotron)Ion Trap MS (like ion cyclotron)

Time of Flight MSTime of Flight MS

Fast scans of pulses of ionsFast scans of pulses of ionseV=1/2 mv2 How long does it eV=1/2 mv2 How long does it

take for ions to travel 1 meter.take for ions to travel 1 meter.R=400 at best R=400 at best Can store up to 20,000 spectra/sec.Can store up to 20,000 spectra/sec.

FT-MS or ICR-MSFT-MS or ICR-MS

Simultaneous measurement, multiplex, Simultaneous measurement, multiplex, mass accuracy, high throughputmass accuracy, high throughput

R= 800,000 possible but expensive as R= 800,000 possible but expensive as you need superconducting magnetyou need superconducting magnet

Different ions rotate at different Different ions rotate at different velocities so we measure the frequenciesvelocities so we measure the frequencies

m/e=H/2m/e=H/2ff

Triple Quadropole (MS-MS)Triple Quadropole (MS-MS)

Select an ion, fragment it, and then analyze Select an ion, fragment it, and then analyze the fragmentsthe fragments

DetectorDetector

SourceSource Select ionSelect ionCollisionCollisionChamberChamber AnalyzeAnalyze