APPLICATION OF LC-MS

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The APCI interface (Fig. 2) vaporizes the mobile phase first, then uses a corona discharge to add a charge to the analyte in the gas phase. This technique isused for compounds that do not ionize well with ESI (often more stable, smaller- molecular-weight compounds and some nonpolar compounds), but uses harsher conditions, so it is more likely than ESI to cause sample degradation, especially with heat-labile compounds.

Also, APCI has been shown to have fewer matrix ion- ization problems than ESI. APCI and ESI have different ionization mechanisms, so the response and selectivity may vary significantly between the two interfaces. Either interface can be operated in the positive or negative ion mode, resulting in the generation of positively or negatively charged sample ions (most commonly achieved by adding or removing a proton from

the analyte molecule.[Snyder, L.R, Dolan, J.W]

Table summaries major type of lcms interface which is used:

[Watson D. G]

APPLICATION:
LC/MS plays a key role in the drug discovery and drug development process. Since the introduction of electrospray ionization a variety of LC/MS applications for the pharmaceutical industry have been developed for compound identification and quantification.

LC/MS is suitable for many applications, from pharmaceutical development to environmental analysis. Its ability to detect a wide range of compounds with great sensitivity and speci- ficity has made it popular in a variety of fields.

LCMS is always the method of choice when liquid chromatography is an essential step in an analytical procedure anyway, namely for the determination of highly polar, chemically or thermally labile compounds. It is also the best method, when the detector has to be more sensitive, more specific or unknowns have to be identified. An advantage is that, at least for some of the LC/MS techniques, the development of a method needs no compromise for adaptation to mass spectrometry.

Molecular Weight Determination
One fundamental application of LC/MS is the determination of molecular weights. This information is key to determining identity.

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