Atmospheric Pressure Ionization

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Information about Atmospheric Pressure Ionization
api

Published on September 25, 2013

Author: celestialsensation

Source: slideshare.net

Description

API in MS

Atmospheric Pressure IonizationAtmospheric Pressure Ionization (API)(API) Presented By: Vinitha Nair M.Sc Bioanalytical Sciences Part 2

What is MS? An instrument that separates molecules orAn instrument that separates molecules or atoms based on their mass/charge ratioatoms based on their mass/charge ratio (m/z).(m/z). – In order to control them, you need to put a charge on them. – In order to separate them, you need an “analyzer”

Why LC/MS? GC/MS required derivatization, etc. Not applicable to most biomolecules (MW, etc.) Industry wasIndustry was desperatedesperate for a decent,for a decent, ruggedrugged LC/MSLC/MS interface.interface. Because

Why API?  Revolutionized LC/MS  Desolvation and/or ionization of analytes occurs at atmospheric pressures  Gas phase ions are sampled by the high vacuum mass spectrometer.

Ion Source Interface Mass Analyzers Detection -ESI -APCI -APPI LC MS System – under vacuum Block Diagram of LCMS

API SourceAll the techniques are done at atmospheric pressure Significant change from traditional ionization methods which were all done within the vacuum chamber.

Types of API Sources

Ionization process which uses electrical fields to generate charged droplets and subsequent analyte ions by ion evaporation for MS analysis.

Gas Nebulized Spray LC Heater ESI Key Features: - Nebulized flow through capillary - Heat applied to evaporate solvent - Capillary (LC) 90o to Cone (MS) Sample Cone MS CapillaryIonization Chamber 760 torr 10-6 torr - Atmospheric pressure ion source - Voltage difference applied between capillary and cone - + - Detect (+) ions  Cap (+), Cone (-) - Detect (-) ions  Cap (-), Cone (+)

A gas phase chemical ionization (CI) process where the solvent acts as the CI reagent gas to ionize the sample.

Gas Nebulized Spray LC Heater APCI Key Features: - Nebulized flow through capillary - Heat applied to evaporate solvent - Capillary (LC) 90o to Cone (MS) MS CapillaryIonization Chamber 760 torr 10-6 torr - Atmospheric pressure ion source - No voltage applied to capillary - droplets are not charged - - Voltage still applied to cone - Detect (-) ions  Cone (+) - Detect (+) ions Cone (-) Sample Cone - Heat evaporates solvent, analytes partition into the gas-phase uncharged Corona discharge needle

The protonated analyte ions are then formed by gas-phase ion-molecule reactionsThe protonated analyte ions are then formed by gas-phase ion-molecule reactions of these charger cluster ions with the analyte molecules. This results in theof these charger cluster ions with the analyte molecules. This results in the abundant formation of [M+H]abundant formation of [M+H]++ ions.ions.

Krypton lamp producing ultraviolet light ionizes gas phase analytes or dopants with subsequent gas-phase reactions.

Gas Nebulized Spray LC Heater APPI Key Features (same as APCI): - Nebulized flow through capillary - Heat applied to evaporate solvent - Capillary (LC) 90o to Cone (MS) MS CapillaryIonization Chamber 760 torr 10-6 torr - Atmospheric pressure ion source - No voltage applied to capillary - droplets are not charged - - Voltage still applied to cone - Detect (-) ions  Cone (+) - Detect (+) ions Cone (-) Sample Cone - Heat evaporates solvent, analytes partition into the gas-phase uncharged UV lamp

Direct APPIDirect APPI M + hν ⇨ M+• + e- M + S + hν [M + H]⇨ + + [S - H]- (solvent dependent) A minority of them will be ionized directly by the UV light (photoionization). Some of the analyte molecules can be indirectly ionized with the help of the solvent molecules. You end up with two types of ions (M+• and [M + H]+ ) from one compound, which then proceed to the MS to be analyzed.

Dopant-Assisted APPIDopant-Assisted APPI D+• + M [M + H]⇨ + + [D - H]• D+• + M M⇨ +• + D The dopant ion can donate a proton to the analyte molecule. The dopant ion receives an electron from the analyte molecule. The result is an ionized sample molecule.

Relative Applicability of API Techniques MolecularWeight

References: •usd-chem730.wikispaces.com/file/view/ESI-MS.ppt •ccc.chem.pitt.edu/wipf/Agilent%20LC-MS%20primer.pdf • link.springer.com/article/10.1007%2FBF02493125 •ccc.chem.pitt.edu/wipf/Agilent%20LC-MS%20primer.pdf •137.122.232.177/NRL%20publications/2007HarrisPhytochem.pdf •usd-chem730.wikispaces.com/file/view/ESI-MS.ppt •ccc.chem.pitt.edu/wipf/Agilent%20LC-MS%20primer.pdf • link.springer.com/article/10.1007%2FBF02493125 •ccc.chem.pitt.edu/wipf/Agilent%20LC-MS%20primer.pdf •137.122.232.177/NRL%20publications/2007HarrisPhytochem.pdf •Principles & Practices of Bio-analysis – Richard Venn•Principles & Practices of Bio-analysis – Richard Venn Bibliography Webliography

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