Gcms Fundamentals

8/12/2019 Gcms Fundamentals

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GCMSGCMSFundamentalsFundamentals

For better understanding GCMS-QP2010


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The Aims of Chemical Analysis

Qualitative Analysis:What chemical compounds are included in thesample ?

Quantitative Analysis:What amount of the compounds are included in the

sample ?


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Measurement of Organic Compounds

Analytical Instruments for organic compounds GCHPLCGC/MSLC/MSFTIR

Tools for separation GC, HPLC

Tools for qualitative analysis MS(GC/MS, LC/MS), FTIR, NMR

Tools for quantitative analysis

GC, HPLC, GC/MS, LC/MS


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Principle of Chromatograph

Time

Detector

Column

Injector

Sample Injection

A

BAB

B

AB

A

Peak A Peak B


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Comparison of Chromatography

to Flow of a River

Riverbed

Light ObjectDirection of flow

Heavy Object


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Stationary Phase and Mobile Phase

Strong Weak

MobileMobilephasephase

Mobile phase and stationaryphase contact through phase

boundary Different solutes have different

affinities to stationary phaseand mobile phase.

Difference of movingvelocity results in separation!

StationaryStationary

PhasePhase


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Chromatography ChromatographChromatogram

Chromatography :Analytical method

Chromatograph : InstrumentChromatogram : Obtained picture

Chromatographer :Analyst


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Three States of Matter

and Chromatographic Methods

Solid

Liquid

gas

StationaryPhase

SolidLiquidgas

Mobile phase and sample

GasGas

chromatographychromatography

LiquidLiquid

chromatographychromatography


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Structure of GC (for capillarycolumn)

Disused forGC/MS

MS in case of

GC/MS

Split unit


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Injection methods of GCSplit injection

Split vent is open. Only a part of sample is introduced to column.

Used for high concentration samples

Splitless injection

Split vent is closedAlmost all amount of sample is introduced to column. Used for low concentration samples

OCI injection Samples are directly injected to column.

Used for samples including both low boiling components and high boilingcomponents. Used for thermally decomposed samples.

PTV injection Low temperature at injection port Solvent is removed at injection port.

Used for large volume injections( a few L a few tens a few hundreds L)

Most commonlyused methods


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GC Detectors

Good sensitivity for nitrogen compoundsFTD

Good sensitivity for phosphorous compounds andsulfureted compounds

FPD

Good sensitivity for high electron affinity compounds(halogenated compounds)

ECD

Organic compounds, higher sensitivity than TCDFID

Inorganic gas Low sensitivity for organic compoundsTCD


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Chromatogram

tR

t0

Signalintensityo

fdetector

Time

Peak

h

A

tR : Retention Timet0 : Dead Time of Column

A : Peak Areah : Peak Height


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Qualitative Analysis for GCSame components elute at the same retention times if

the analytical conditions are same.

Sample

Injection

Standard

Sample

(Mixed solution ofcomponent A and B)

Unknown

Sample

Component AComponent B

Analysis of standard sample (known sample)

is required


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Quantitative Analysis for GCPeak area (height) is proportional to the amount of component

entering the detector

Standard Sample 1L

(Component A 100ppm)

Component A

Unknown Sample 1LComponent A

Peak Area : 700

Peak Area : 1000

100

Concentration

(ppm)

1000Peak Area

700

70


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What is GCMS ?GCMS : Hyphenated instrument combining GC and MS

( Gas chromatograph mass spectrometer )

MS GC

GC:Gas chromatograph

MS:Mass spectrometer


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Data from MS (Mass Spectrum)

Chromatogram

Mass Spectrum :Mass distribution of ions is

specific to compounds.

Consideration of the spectral

pattern gives qualitativeinformation.

M/Z


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Good Points of GC/MS

Excellent in separation, identification and quantitation

MS (Mass Spectrometer)

Excellent in identification and quantitation

Poor in separation

GC (Gas Chromatograph)

Excellent in separation and quantitationPoor in identification

GCMS


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GCMS Applications Fields - 1Pharmaceutical

Confirmation of identity of drugs Natural products/herbal medicines

Clinical & forensic

Determination of drugs of abuse in blood, urine or otherbiological matrices

Identification of organic acids to diagnose a metabolicdisorder

Agricultural Determination of pesticide residues in agricultural

products


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GCMS Applications Fields - 2Food & beverages

Determination of contaminants in food & beverages

Identification of volatile flavor components infood/beverages

Identification of residual solvents in food packaging

Environmental Determination of pesticide residues in water

Determination of volatile organic compounds in wastewater, tap water, drinking water and environment water

Analysis of volatile organic compounds in air

Determination of volatile organic compounds in soil


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GCMS Applications Fields - 3Flavor & fragrance

Identification of fragrances used in household products,

e.g. toilet cleaner, shampoo, etc.

Polymer, plastics & rubber

Analysis of volatile residual raw materials and/or

additives in polymers Identification of polymers

Electronics & semiconductor

Identification of volatile contaminants electroniccomponents, e.g. hard disk drive

Other...


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General Sample Requirements for GC/MS Analysis

Volatility and thermal stability of the analytes

Analytes must:

have sufficient vapor pressures (volatilities) be thermally stable

at the typical GC injection port, column oven and ion source

temperatures

Suitable for analyzing organic compounds in general


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Sample Injection : GC

purge

split

carrier

purge

split

column

sample

carrierpurge

split

column

sample

splitless split

carrier gas :He

purity:99.995% or greater


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Types of Column

1. Length 0.5-5m (Max 2m)

2. Outer diameter 2-4mm

3. Filling material 0.5-25% liquid phase

(Diatom earth carrier)

4.There are many types of liquid phase.Appropriate type should be selected, because

their theoretical plate numbers are not so high.Tube

Filling material

Packed column

Capillary columnCapillary (i.d. 0.25mm, 0.5mm)

Stationary phase (Liquid coating)

1. Length 12-60m (100m on occasion)

2. Outer diameter 0.1, 0.22, 0.32, 0.53mm3. Material : fused silica, inert metal

(inert, elastic)

4. The types of liquid phase are small in number.

XX-1, 5, 10, 20

Selection of liquid phase is less important

because of high theoretical number(over 100,000)


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InterfaceInterface:introduction part from GC to MS

vacuum sealing with nut and ferrule

direct interface

columnMS

high vacuum

heater


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What is mass spectrometer ?

Ion sourceLens

system

Rod

systemDetector

ionizationion

focusing

mass

separation

ion

detection


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Overview of QP2010

Vacuum Pumps (TMP)

Rod System

Ion Source/

Lens System

Detector

Sample from GC

Vacuum


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Vacuum

- another important factor-

In only high vacuum ,

ions can move from ion source to detector.

+

ion air, water, He etc.

High vacuum ( low pressure)

+ Low vacuum ( high pressure)


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Evacuation systempressure 10-3-10-4 Pa(mean free path 5m-50m)

Ion sourceLens

system

Rod

system Detector

main

pump Fore

pump


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Comparison

Oil diffusion pump

Turbo molecular pumpRotating blade deflects gas molecules down and out the out let

Clean vacuum

Short start- up time and short shut- down time

Expensive

Heated oil from the vents collects and force down gas molecules

Inexpensive

Possibility of oil contamination

Vacuum pump (main pump)


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Single pumping and differential pumping

Differential pumping is optimum system for high flow rate

high vacuum

Ionization room Analyzing room

single pumping(QP5000series)

differential pumping(QP2010)


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Columncapillary column:long glass tube(30m,60m etc) having thinlayer of methyl silicon etc.

Inside Diameter carrier gas flow into MS

larger flow worse vacuum

I.D. of column flow

0.25mm 1-2ml/min

0.32mm 2-4ml/min

0.53mm 10-20ml/min


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What is ion?Ion:atom or molecule with charge

Ions can be electrically controlled.+

Positive ion

-Negative ion


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IonizationSample molecules are ionized in ion

source

Three ionization methods of GC/MS EI (electron impact ionization)

CI (chemical ionization) NCI (negative chemical ionization)


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EI(Electron Impact)Magnet

eee electrons from

filament

sample

molecules

Generation of molecular ion

MeM+2e

Feature of EI

Most frequently usedionization in GC/MS

Open ion source

Generation of fragment ions

sample

ions


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GCMS-QP2010 Ion Source Unit

Double filaments Increase productivity

High luminosity ion source

Increase sensitivity

Filaments

Ionization box


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Fragmentation and spectrum Molecule is broken up at the positions with weaker chemical bonds by electron

energyA-B-C-D e ABCD

(molecular ion)2e-

ABC+D+

AB+CD+

A+BCD+

A specific spectrum pattern can be obtained corresponding to a compoundEI spectrum is powerful tool for identification.

(Library search is available : Spectra accumulated in libraries are measured

at 70eV filament electron)

AD

AB

CD

ABCBCD

ABCD

base peakmolecular ion

fragment ions


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Mass of atom and mass number

Mass of an atom is represented by unit that defines mass of 12C as 12

(atomic mass unit ; denoted by u or amu)Mass number : Nearest integer of atomic mass

example

mass mass number1H 1.00782522 1

2H 2.01410222 2

12C 12.00000000 12

13C 13.00335508 13

14N 14.00307440 14

16O 15.99491502 16

18O 17.99915996 18

example:

mass number of water (H2O)

1x2+16=18

more accurate molecular weight

1.00782522x2+15.99491502=

18.01056546


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Example of Fragmentation

Methane: For internal use

CH4+

CH3+

CH2+

CH+


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Electron Impact Ionization, EI

50 60 70 800.0

25.0

50.0

75.0

100.0

%

43

6145 70

8873

50 60 70 80 900.0

25.0

50.0

75.0

100.0

%

70

61

4588

43 73

8960

70eV

14eV 40 45 50 55 60 65 70 75 80 85 m/z

0

100

200

300

400

500

600

700

800

900

Int. 43

6170

88

O O

Ethyl Acetate

NIST data base

Electronic Accelerating Voltage,


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Example of EI spectrum

m.w.78

Benzene

m.w.72

Acetone


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CI (Chemical Ionization)

e

CH4 C2H5

+

MHC2H4

Reagent gas is required

Closed type ion source ( source pressure of approx. 10Pa )

Less fragmentation ( soft ionization)

Generation of pseudo-molecular ions (e.g. hydrogenated

ion)

Effective for determination of molecular weight +

Ionization of

reagent gas

ion-molecule

reactionGeneration of pseudo-

molecular ions(In case of methane as reagent gas)


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Comparison between EI and CI spectrum

Methylstearate M.W. 298

EI

CI


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NCI (Negative Chemical Ionization)Reagent gas is required

Semi-closed type ion source ( source pressure of approx. 1Pa )Less fragmentation ( soft ionization)

High sensitivity for molecules with high electron affinity

(such as Halogenated compounds)Electron Capture Reaction

e

CH4 CH3

H

CH4

CH4

CH4

e -

High electron affinity atom or molecule ex: halogen)

Comparison of EI PCI NCI Mass Spectrum


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Comparison of EIPCINCI Mass Spectrum

EI

PCI

NCI Malathione (MW 330)


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Stable Isotopes of some elements

Elements (A+2)Elements (A+1)Elements (A)

4.4%36S0.8%33S100%32S

100%127

I

100%31P

100%19F

98.0%81Br100%79Br

32.5%37Cl100%35Cl

3.4%30Si5.1%29Si100%28Si0.20%18O0.04%17O100%16O

0.36%15N100%14N

1.08%13C100%12C

0.015%2H100%1H Pay attention toCl and Br.


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Abundance Ratios of Cl and Br.

Cl35

Cl :37

Cl = 100 : 32.5 3 : 1

1 1

Br Br2

1 2 1

Br3

13 3

1

3

1

Cl Cl2

96 1

Cl3

27 279 1

Br 79Br : 81Br = 100 : 98 1 : 1


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Example of Isotope PeaksIncl. two chlorines Incl. three chlorinesIncl. a chlorine

Incl. a bromine Incl. two bromines


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Mass separation(1)

m1+

m2+

m3+

1

1

Two opposite rods will have a

potential of +(U+Vcos(wt)) and

the other two -(U+Vcos(wt))

where U is DC voltage and

Vcos(wt) represents a radiofrequency (RF) field of

amplitude V and frequency w.

In general, for mass section U

and V are varied keeping theratio U/V constant.

M/Z and operation parameters

M/Z=K K:Constant

Varying V selects only specificm/z ions.

V

r2w2

U+Vcos(wt)

-U-Vcos(wt)

2rr : radius of inscribed circle

m1+

m2+

m3+

m1/z=KV1/r2w2

m2/z= KV2/r2w2

m3/z= KV3/r2w2

GCMS-QP2010


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Mass Filter Unit

Todetectordetector

Pre-rod (reduce contamination of main rods, can rotate)

From

ion sourceion source

main rod


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Mass Separation (2)In fact, mass filter also transfers ions withnearby masses for a

selected mass number M.Resolution

Changing set mass mass numbercontinuously:When ions with mass M enters the rod, signalgradually increases if set mass number to rodsapproaches to M from lower side. And signal ismaximum at set mass number M and decreasesabove M.

The observed result (peak profile) has a widthdespite that the mass has infinitesimal width

M

Mass number setting

:The measure how well we can distinguish ions


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:The measure how well we can distinguish ions

of very similar m/z values

ResolutionTwo peaks at m and m+ m can bedistinguished if peak has the width of m.

m

h

h/2

m

mResolution : R= m / m

Specification:R>2m means m< 0.5.

Two peaks apart by unit mass can be completely

distinguished

Detector (Electron Multiplier)


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( p )Converting ions to electrical siganal

ION Electrons

The First DynodeThe negative voltageis applied at eachdynode. Theabsolute value ofvoltage becomes

smaller at the latterdynode.

Detector system of QP2010


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y QConverting ions to electrical siganal

Electron

Multipliers

Conversion Dynode

Noise particles

Two lenses eliminate noise particles such as neutralmolecules by focusing on only ion particles.

IONSignal ions

The Role of Conversion Dynode

(1) Detection of negative ions

(2) Enhancing signal intensity of

ions at high mass region.


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Analysis Flow of GCMS

Quantitative analysis(SIM)

Creation of calibration curve

Quantitation of unknown samples

Qualitative analysis(Scan)

Peak Identification

Determination of monitor mass


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Data Acquisition mode of GC/MS

SCANAcquires mass spectra in sequence at constant intervals (eg 0.5 sec) .

All acquired mass spectra are stored in PC.

Investigation of data on PC (TIC, mass spectrum, MC etc.).Qualitative analysis / Quantitative analysis.

SIM

Detection of specific masses. Quantitative analysis.


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Data Acquisition ModeScan modeAt each chromatographic point, mass number is scanned for a mass range to obtain

a spectrum at every interval. The scan interval is to be usually set 0.5 to 1 sec.

ime

Vm/z

0.5sec 0.5sec

V35

V350

SCAN

Scan rate=Scan mass number range (amu)/Scan interval(sec)

Example: (350-35)/0.5=630

Measurement with Scan Mode


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Measurement with Scan Mode

TIC0.5sec 0.5sec 0.5sec 0.5sec 0.5sec 0.5sec 0.5sec 0.5sec 0.5sec

TIC : Total Ion Chromatogram

BG (air and breeding of liquid phase)


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MC ( Mass Chromatogram)

TIC

M/Z

Retention Time


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Mass Spectrum

TIC

M/Z

Background subtracted spectrum Library Search


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Data Search Result

If interpretation of spectrumis difficult, .

Library Search

Data Base NIST

about 200,000 spectra


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Hints on Library Search (1)

Hit data shows no m/z 78 peak

Not correct answer

Mixed components


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Single Component Peak


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Single Component Peak

Same spectrum at any position of

chromatogram peak

Double Components Peak


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Double - Components Peak

Making use of mass chromatogram (MC)

Mass Spectra in the double-

components peak

Signal? Noise?


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Signal? Noise?

Signal

Noise

Data acquisition mode


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Data acquisition mode

SIM(selected ion monitoring) mode

The SIM method is used primarily in quantitative analysis.

Only specified mass numbers are measured with SIM mode.Selection of the ion to use from the target component is very important with the SIM

method. High sensitivity analysis is possible depending on the ion selected.

Time

Vm/z

0.2sec

V112

V

V

V

SIM

SIM (Selected Ion Monitoring)


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( g)

Selecting monitoring ions of target component. Making use of mass spectrum

In general, high intensity ions with higher mass are selected

Better in quantitation

Suitable for trace analysis

50 100 150 200 250 300 350 4000

50

100%

235

165

199 23975 1761361055063 354282 319

50 100 150 200 250 300 350 4000

50

100

%

79

8277 108 263277

53243 38034517366 113 147 20919387 309

Measurement with SIM


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Measurement with SIM

M/Z X

M/Z Y0.2sec 0.2sec 0.2sec 0.2sec 0.2sec 0.2sec 0.2sec 0.2sec 0.2sec

11.0 11.5 12.0 12.5 13.0 13.5

0.5

1.0

1.5

(x100,000)

160.00 (5.43)188.10 (1.00)248.90 (82.67)285.90 (32.98)

283.90 (25.34)TIC Chlorinated Pesticide

(5ppb)

Quantitation Method


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Quantitation Method

Calibration Curve Quantitation result

Standard sample is needed to make calibration curve for eachcomponent.

Relative sensitivity is different according to each component.

Summary


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Summary

GC/MS : Mainstream of Organic compound Analysis

Documents

Gcms Fundamentals