FLORIDA INTERNATIONAL UNIVERSITY

Advanced Mass Spectrometry

Piero R. Gardinali/Yong Cai/ Bruce McCord

Revised on August 23, 2009

First Steps

Introduction to mass spectrometryDefinition of common termsA generic mass spectrometerFormation of ionsThe mass spectrumWhy doing mass spectrometry?

Survey:

No previous knowledge of MS?Know basic operation but no theory?Comfortable user?I can do a manual tune!I took your MS class (did you pass?)

I will be helping with the class!

Mass spectrometry is a powerful analytical technique that is used to identify unknown compounds, to quantify known materials, and to determine the structural and chemical properties of molecules.

Detection of compounds can be accomplished with very minute quantities. (as little as 10 -12 grams).

Anode raysGoldstein

1886

Electron m/zThomson

1897 (Nobel Prize in 1906)

Magnetic deflectionPositive Ions

Wein1898

Unit of chargeMillikan & Fletcher

1909

First parabola Spectrograph

Thomson1912

Metastable ionsThomson

1913

1918

1919

1940Nier

U-235

1956

19531952

1946

1956Exact Mass

Benyon

1969

1978

1980

1981 1987

19681988

1974

1966

Develop first MS with velocity focusing,

Nobel Prize in 1922

Fenn developed ESI in 1988; Concept was proposed by Dole in 1968. Fenn received Nobel Prize in 2002

Progress in Experimental Methods and Improvements in Solution, Sensitivity, Mass

Range, and Accuracy • Resolution: m/Δm from 13 (Y1913) to 8,000,000

(Y1998)• Sensitivity: as low as 800 yoctomoles (~480

molecules)( measure peptide in solution)• Mass range: several tens of millions D (40.5 MD)• Accuracy: isotope measurement

Did you know that mass spectrometry is used to…

• Detect and identify illegal steroids in athletes • Monitor the breath of patients during surgery • Determine the composition of molecular species found in space • Determine whether honey is adulterated with corn syrup • Locate oil deposits by measuring petroleum precursors in rock • Monitor fermentation processes for the biotechnology industry • Detect dioxins in contaminated fish, water and soil • DNA Fingerprinting! • Establish the elemental composition of semiconductor materials • Speed the development of new drugs

Basic concepts

The basis of mass spectrometry (MS) is the production of ions that can be separated or filtered according to their mass to charge ratios (m/z) and detected. The resulting mass spectrum is a plot of the abundance of the produced ions as a function of the m/z ratio.

Still spectroscopy?

What is a mass spectrometer?

Illustration of the basic components of a mass spectrometry system.

IonizationSource

MassAnalzyer Detector

Inlet all ionsselected

ionsData

System

%R

elat

ive

Abu

ndan

ce

1265

.000

0321

843.

00

360

421.

0

m/z

The mass spectrum

What do I get from the instrument?

Mass spectrum of methanol by EI, presented as a graph and a table

More definitions

Base peakThe most intense peak of a mass spectrum is called base peak

• Usually mass spectra are normalized to the most intense peak by setting its intensity to 100 % relative intensity.

• This offers the advantage of being independent from absolute intensities which may extremely vary between measurements.!!!!!!

• Thus, normalization to the base peak makes comparison of spectra much easier.

More about ions and fragments

Molecular ion

The molecular ion is directly created from the corresponding neutral molecule by addition or removal of one electron

i.e. it still has the same molecular formula.

The molecular ion is usually labeled as M+. or M-., respectively.

Quasimolecular ions are different from molecular ions in that they are formed by addition or removal of some ionic particle.

Ways to define and calculate the mass of an atom, molecule or ion

• Average mass: calculated using the atomic weight, which is the weighted average of the atomic masses of the different isotopes of each element in the molecule.Often used in stoichiometric calculations.

• Nominal mass: calculated using the mass of the predominant isotopes of each element rounded to the nearest integer value that corresponds to the mass number.

• Monoisotopic mass: calculated using the extract mass of the most abundance isotope for each constituent element.Use monoisotopic mass if possible in MS

Differences between Masses

C20H42 C100H202

Nominal: (20 x 12) + (42 x1) = 282 u (100x12) + (202x1) = 1402uMonoisotopic: (20 x12) + (42 x 1.007825) = 282.33 (100x12) + (202x1.007825) = 1403.5807Average: (20 x 12.011) + (42 x 1.00794) = 282.5535 (100x12.011)+(202x1.00794) = 1404.7039

HOW DO I CREATE AN ION?

M + e- M.+ + 2e-

HOW DO I CREATE AN ION?

M + e- M.+ + 2e-

HOW DO I CREATE AN ION?

M + e- M.+ + 2e-

An then what?

HOW DO I CREATE AN ION?

M + e- M.+ + 2e-

Radical cation

•Ion free path ???

•Free mean path ???

K: Boltzmann constant, T: temperature (in K)p: pressure (in Pa): collision cross-section (in m2)

P in pascals

P in milli Torrs