THE COMBINED TECHNOLOGY OF CHROMATOGRAPHY AND SPECTROSCOPY , HERE THE PROCES AND INSTRUMENTATION WITH EXAMPLES ARE DISCUSSED

1. LIQUID CHROMATOGRAPHY-MASS SPECTROMETRY
(LC/MS)

2. Principle:
• LC/MS is a technique that combines physical separation
capabilities of liquid chromatography with mass analysis
capabilityofMassspectrometry.
• ItisamethodthatcombinesseparationpowerofHPLCwith
detectionpowerofMassspectrometry.
• InLC-MSweremovethedetectorfromthecolumnofLCandfit the
columntointerfaceofMS.
• InthemostofthecasestheinterfaceusedinLC-MSareionization source.
INTRODUCTION

3. • HPLCisamethod for separatingacomplexmixture in to its
components.
• Highsensitivityof massspectroscopy provides theinformation
for identification of compoundsor structural elucidation of
compounds.
• Combination of thesetwotechniques isLC-MS.
• Asthe metabolitesappearfrom the endof the column they
enter the massdetector, where the solvent isremovedand the
metabolitesareionized.
Theory of LC/MS

4. LC-MS System Components
• Mass spectrometers work by ionizing molecules and then
sorting and identifying the ions according to their mass-
to-charge (m/z) ratios.

5. HPLC
• Liquidphaseoperation
• 25- 50deg.C
• Nomassrange
limitations
• Inorganicbuffers
• 1ml/min eluent flowis
equivalent to 500 ml/min
ofgas
MS
• Vacuumoperation
200- 300deg.C
• Upto 4000Dafor
quadrupole MS
• Requiresvolatile
buffers
• Accepts10ml/min gas
flow
PROBLEMS IN COMBINING HPLC AND MS

6. Themobile phaseisthe solvent that movesthe solute throughout
column.
Generalrequirements:-
(1) Lowcost,UVtransparency,high purity.
(2) Lowviscosity,low toxicity, nonflammability.
(3) Noncorrosiveto LCsystemcomponent.
Solventstrength andselectivity:-
It isthe abilityof solvent to elute solutesfromacolumn.
MOBILE PHASE

7. • The use of di-functional or tri-functional silanes to create bonded
groups with two or three attachment points leading to phases
with higher stability in low or higher pHandlower bleedfor LC-MS
• Most widely usedcolumnsfor LC-MSare :-
(1) fast LC column :-
the useof short column.(15-50mm)
(2) Micro LC column :-
the useof largecolumn. (20-150mm)
COLUMN

8. • Samplepreparation generally consists of concentrating the analyte
and removing compounds that can cause background ion or
suppressionization.
• Exampleof samplepreparationinclude:-
• OnColumnconcentration -to increaseanalyteconcentration.
• Desalting - to reduce the sodium and potassium adduct
formation that commonlyoccursin electrospray.
• Filtration- to separate a low molecular-weight drug from
proteins in plasma,milk, ortissue.
Sample preparation

9. • LC-MSsystemsinclude adevicefor introducing samples(suchas an
HPLC)aninterface for connectingsuchdevice,anion source that
ionizessamples,anelectrostatic lensthat efficiently introduces
the generatedions, amassanalyzerunit that separatesions based
on their mass-to-charge(m/z) ratio, anda detector unit that
detectstheseparatedions.
• In anLC-MSsystem,however, if the LCunit issimplyconnected
directlyto the MSunit, the liquid mobile phasewould vaporize,
resulting in large amountsof gasbeingintroduced into the MS
unit.
• Thiswould decreasethe vacuumlevel andprevent the targetions
from reachingthe detector. Sointerfaces are tobeused.
INTERFACES

10. • It isdifficult to interface aliquid chromatographyto amass-
spectrometercauseof the necessityto removethe solvent.
• Thecommonlyusedinterfacesare:-
(1) Electrosprayionization(ESI)
(2) Thermosprayionization(TSI)
(3) Atmosphericpressurechemicalionization(APCI)
(4) Atmosphericpressurephotoionization(APPI)
TYPES OF INTERFACES

11. • ESIdrawssamplesolutions to the tip of acapillarytube,
whereit appliesahighvoltage of about 3to 5kV.
• A nebulizer gas flows from outside the capillary to spray the
sample.Thiscreatesafine mist of chargeddroplets with the same
polarity asthe appliedvoltage.
• Asthischargedparticles move,the solvent continuesto evaporate,
thereby increasingthe electricfield onthe droplet surface.When
the mutual repulsive force of the charges exceedsthe liquid
surfacetension, then fissionoccurs.
• Asthis evaporation andfissioncycleisrepeated, thedroplets
eventually becomesmallenoughthat the sampleionsare
liberated into the gasphase.
ElectroSprayIonization(ESI)

12. • ESIprovides the softest ionization method available, which
meansit canbeusedfor highly polar, least volatile, or
thermally unstablecompounds.
ElectroSprayIonization(ESI)

13. • APCIvaporizessolvent andsamplemoleculesbysprayingthe
samplesolution into aheater (heatedtoabout 400C)usinga gas,
suchasN2.
• Solventmoleculesareionizedbycoronadischargetogenerate stable
reactionions.
Atmospheric pressurechemical ionization
(APCI)

14. • Theyareof 2type:
• a)Real-TSPionization
• b) Dischargeelectrode for external ionizationandrepeller
electrode
Thermospray ionization (TSI)

15. • TheLC eluent isvaporizedusingaheater at atmospheric pressure.
Theresulting gas ismadeto pass through a beamof photons
generated byadischargelamp(UVlamp) which ionizesthe gas
molecules.
Atmospheric pressurephotoionization(APPI)

16. • Theydeflect ionsdown acurvedtubes in amagnetic fields based
on theirkinetic energydetermined bythe mass,charge and
velocity.
• Themagnetic field isscannedto measuredifferentions.
• Typesof massanalyzer:-
(1) Quadrapolemassfilter.
(2) Timeof flight
(3) Iontrap
(4) Fourier transform ion cyclotron resonance(FT-ICR)
Mass Analyser

17. • A Quadrupolemassfilter consistsof four parallelmetal rodswith different
charges
• Twooppositerodshaveanapplied +potential andthe othertwo
rodshavea-potential
• Theappliedvoltages affect the trajectory of ionstravelingdown the flight
path
• ForgivenDC andAC voltages,only ionsof acertain mass-to-charge ratio pass
through the quadrupole filter and all other ionsare thrownout of their
originalpath.
QuadrupoleMassAnalyzer

18. • TOFAnalyzersseparateionsbytime without the useofan
electric or magneticfield.
• In acrude sense,TOF issimilar to chromatography, except there is
no stationary/ mobile phase,insteadtheseparationis basedon
the kineticenergyandvelocityof the ions.
TOF (Time of Flight)Mass Analyzer

19. • It usesanelectricfield for the separationof the ionbymass to
chargeratios.
• Theelectricfield in the cavitydueto the electrodescauses the
ionsof certainm/z valuesto orbit in the space.
Ion TrapMass Analyzer

20. • Usesamagneticfield in orderto trap ionsinto anor bit inside of it.
• Inthisanalyzerthereisnoseparationthat occursrather all the
ionsof aparticular rangearetrapped inside,andan applied
external electric field helpstogenerate asignal.
Fourier Transform ion cyclotron
resonance (FT-ICR)

21.  PharmaceuticalApplications:
 Rapidchromatographyofbenzodiazepines
 Identificationofbileacidmetabolite
 BiochemicalApplications:
 Rapid protein identification using capillary LC/MS/MS and
databasesearching.
 ClinicalApplications:
 High-sensitivitydetectionoftrimipramineandthioridazine
Applications of LC-MS

22.  Food Applications:
 Identificationofaflatoxinsinfood
 DeterminationofvitaminD3inpoultryfeedsupplements
 EnvironmentalApplications:
 Detectionofphenylureaherbicides
 Detectionoflowlevelsofcarbarylin food
 Forensic Applications:
 illegalsubstances,toxicagents
 Explosives
Applications of LC-MS