Topic:

Quadrupole Mass AnalyzerCourse code: CHEM-421

Submitted To:

O Dr. Waseem Mumtaz

Submitted By:

OFaiza Hassan O11011507-023OAnalytical chemistry

majorsOSemester 8th

Mass analyzers:O It is component of mass spectrometer

that receives ions and separates them on the basis of their mass to charge ratio.

O outputs them to the detector where they are detected and later converted to a digital output.

Quadrupole Mass analyzers:

O The type of analyzer which is used to separate the ions on the basis of specified charge to mass ratio.

OrO An instrument for measuring the relative

amounts of different gases in a mixture. The gas could be atmospheric air, could be evolved from a chemical process, might be trapped inside a small mineral sample, or even be dissolved in a liquid such as sea water.

Specifications:O Mass range 10–4000 daltons (amu)O Resolution, typically 1000O Scan rate 5000 daltons/minO Accuracy .1–.2 daltons

Principle:O It consists of four cylindrical rods, set parallel

to each other provided by AC and DC source.

O Lets one mass pass through at a time.

O Can scan through all masses or sit at one fixed mass.

Quadrupoles have variable ion transmission modes

Construction:

O It consists of three components

1. The ion source2. Quadrupole mass filters3. The Detector

O 1. The Ion Source

Molecules from the gas sample are ionised by energetic electrons from a heated filament.

O 2. The Quadrupole Mass Filter

A mixture of a.c. and d.c. voltages applied to opposite pairs of cylindrical metal rods allow ions of a chosen mass to pass from the ion source to the detector. All others are rejected. Varying these voltages allows different masses to pass in turn and a scanned spectrum is produced.

O 3. The Detector

Chosen ions are detected and generate a measured current that is used to construct the mass spectrum.

O The DC bias will cause all the charged molecules to accelerate and move away from the center line, the rate being proportional to their charge to mass ratio.  If their course goes off too far they will hit the metal rods or the sides of the container and be absorbed. So the DC bias acts like the magnetic field B of the mass spec and can be tuned to specific charge to mass ratios hitting the detector.

‘tripple quadrupole’ arrangement

Q1 Q2 collision Q3

We can characterize molecules via a number of MS/MS modes:

Fragment Ion Scan: Q1 Fixed, Q2 Collide, Q3 ScanPrecursor Ion Scan: Q1 Scan, Q2 Collide, Q3 FixedNeutral Loss Scan: Q1 Scan, Q2 Collide, Q3 Scan - offset

Quadrupole Limits:O m/z limit: Depends on the maximum

RF potential that can be applied to the quadrupole rods. Normally goes to about 7000 V. The practical limit is about 10,000 – 15,000 V for electronic and arcing reasons. 7000 V translates into a limit of about 5000 m/z.

Benefits:O Classical mass spectraO Good reproducibilityO Relatively small and low-cost

systemsO Low-energy collision-induced

dissociation (CID) MS/MS spectra in triple quadrupole and hybrid mass spectrometers have efficient conversion of precursor to product

Quadrupole Limits

O Resolution: Not for high resolution mass spectra.

O in a quadrupole, higher resolution = lower sensitivity.

Sensitivity: Inversely proportional to resolution

O Mass Accuracy: Partly depends on the precision with which you can control U and V… which is highly accurate. Around .1 Da on new instruments

Applications:O Great for most organic chemistry

applications. O useful is in liquid chromatography-

mass spectrometry O Also used in gas chromatography-mass

spectrometry where they serve as exceptionally high specificity detectors.

O Used for measuring the relative amounts of different gases in a mixture.