Samsung RT34M Uživatelský manuál stáhnout pdf (Strana 31)

Dushyant Patel LC-MS/MS Method

S.K.P.C.P.E.R., Kherva 19 M .Pharm. Thesis

peak at 400 m/z. Five types of mass analyzers are currently available, i.e., magnetic

sector

, quadrupole mass filter

, quadrapole ion trap

6,7

, time-of-flight

6,8

and fourier-

transform ion-cyclotron resonance instruments

6,9

. There is not one ideal mass analyzer.

The choice depends on the application.

¾ In practice, most interfaces for coupling of LC with MS have been developed on

quadrupole instrument. The detection of ions after the mass analysis is mostly performed

by means of an electron multiplier. The signal of the electron multiplier is fed to

multichannel analyzer to perform ion counting. In most modern instruments a high-

voltage conversion dynode is used in both positive-ion and negative-ion detection. A

mass spectrometer produces an enormous amount of data. The most important type of

output are mass spectrum, mass chromatogram and total ion chromatogram. The mass

spectrum is a plot of relative intensity as a function of the m/z. It contains a base peak,

which is the peak with highest intensity used to normalize the mass spectrum. The mass

spectrum is also contains fragment peaks, isotope peak and background peak.

¾ It is an important spectrometric technique for molecular mass analysis. At present MS is

the most sensitive method for molecular analysis. Mass spectrometry could be

considered as an analytical technique that involves the study in the gas phase of ionized

molecules with the aim of one or more of the following:

• Molecular weight determination.

• Structural characterization.

• Gas phase reactivity study.

• Qualitative and quantitative analysis of components in a mixture.

¾ In analysis by LC/MS, a sample is injected onto an LC column. The sample is then

separated into its various components. The components elute from the LC column and

pass into the mass spectrometer where they are analyzed. Analysis by direct infusion or

flow injection provides no chromatographic separation of components in the sample

before it passes into the mass spectrometer. The data from the mass spectrometer are

then stored and processed by the data system. In LC-MS sample is introduce by three

ways. They are as -

• Using the syringe pump (Direct infusion).

• Using the divert/inject valve fitted with a sample loop and LC (flow injection

analysis).

• Using the divert/inject valve and HPLC fitted with column (LC-MS).

Ionization sources:

¾ In LC-MS various types of ionization sources are use. They are as-

1 2 ... 26 27 28 29 30 31 32 33 34 35 36 ... 92 93

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