Samsung RT34M Uživatelský manuál stáhnout pdf (Strana 42)

Dushyant Patel LC-MS/MS Method

S.K.P.C.P.E.R., Kherva 30 M .Pharm. Thesis

constant limiting factor is the amount of liquid that can be introduced into the ion source

of a MS prevented the wide spread development and use of LC-MS. But now many of the

difficulties associated with it have been solved and there are now several interface

designs and LC-MS is in routine use in analytical laboratories worldwide.

¾ The diversity of available interfaces: capillary inlet

12-14

, pneumatic nebulizer

interfaces

, moving belt

16-18

, direct liquid interface

19-21

, thermospray

, continuous -

flow fast atom bombardment- FAB

23-25

, particle beam

26,27

and atmospheric pressure

ionization- API

Currently API based LC/MS interfaces i.e. electrospray ionization

(ESI) and atmospheric pressure chemical ionization (APCI) are the most widely

approaches, while other has limited extent. A high electrical potential applied to a

solvent emerging from a capillary causes the solvent to break into fine threads which

disintegrate into small droplets, this phenomenon is called electrospray

28, 29

¾ In APCI the column effluent is nebulized into a heated vaporizer tube and after

desolvation the gas-vapour mixture enters the API source. In API source APCI is

initiated by electrons generated at a corona discharge needle in combination with

solvent vapours

28, 30

. More than 99% of LC-MS performed today is based on API

interfacing.

These interfaces in combination with tandem mass spectrometry of

single stage and double stage fragmentation instrument enables a LC-MS/MS

technique.

¾ ESI is one of the most exciting ionization methods due to direct ionization from

solution and therefore its use as an LC-MS/MS interface, production of multiply

charged ions that extends the effective mass range of the mass analyzer, introduction of

methods to aid in desolvation of the analyte, low background from the ionization process

are the advantages over other ionization. Extensions of the ESI interface led to

miniaturized formats, microelectrospray and nanoelectrospray.

¾ The most important application area of LC-MS is in the pharmaceutical field, where

LC-MS is involved in almost every step of drug development, testing and formulation.

Because of its specificity and sensitivity LC-MS, especially in combination with LC-

MS/MS has rapidly growing importance in other drug research area.

¾ LC-MS/MS is widely applied for drug development as well as routine analysis. In drug

discovery activities like lead identification, lead optimization, in vitro and in vivo drug

screening, preclinical activities like metabolite identification, impurity screening and

degradant screening, clinical activities like quantitative bioanalysis and metabolite

identification application of LC-MS and LC-MS/MS enhanced extensively.

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