Electrospray interface sample types

Microbore HPLC can be coupled without modification to a conventional electrospray GC-MS type of interface for cryogenic trapping FTIR detection. A heated sheathing gas aided in solvent vaporization. A zinc selenide plate was used for sample spot collection. 

Mass spectrometers are used not only to detect the masses of proteins and peptides, but also to identify the proteins, to compare patterns of proteins and peptides, and to scan tissue sections for specific masses. MS is able to do this by giving the mass-to-charge ratio of an ionized species as well as its relative abundance. For biological sample analysis, mass spectrometers are connected to an ionizing source, which is usually matrix-assisted laser desorption ionization (MALDI) [14], surface-enhanced laser desorption/ioni-zation (SELDI, a modified form of MALDI) [15], or electrospray ionization [16]. These interfaces enable the transfer of the peptides or proteins from the solid or liquid phase, respectively, to the gas (vacuum) phase inside the mass spectrometer. Both MALDI and electrospray ionization can be connected to different types of mass analyzers, such as quadrupole, quadruple-ion-traps, time of flight (TOF), or hybrid instruments such as quadrupole-TOF or Fourier transform-ion cyclotron resonance. Each of these instruments can... 

Electrospray ionization and MALDI represent major advances in the application of mass spectrometry to analysis of biomolecules. Although in many cases the two techniques are able to provide the same information, quite frequently they are complementary. For a variety of reasons, some samples are more successfully analyzed by MALDI and other by ESI. Thus, it is highly beneficial to have access to both types of instrument for characterization of synthetic peptides. In ESI-MS, the samples are introduced in solution at flow rates from less than 1 tL/min up to 1 mL/min, depending on the design of the ESI interface. Pure samples and simple mixtures are often analyzed by direct infusion more complex mixtures (such as proteolytic digests) generally require either on-line or off-line HPLC fractionation prior to MS analysis. 

Right from the outset of the 1990s, a selection of those interfaces that could be adapted to a routine LC-MS analysis was observable. This trend had been initiated by pharmacological and pharmaceutical research, although it had the TSP interface at its disposal, which was a well-adapted and reliable type of interface that had shown its fiiU capacity in manifold appliances. The sample material, being available only in very limited quantities for such research, and improved separation techniques, as, for example, capillary electrophoresis (CE) or capillary zone electrophoresis (CZE) necessitated different types of interfaces that could be operated with considerably smaller amounts of sample than the TSP interface, which reached its optimized sensitivity with flow rates of about 2 mL min. Such a desirably lower sample demand is guaranteed by atmospheric pressure ionisation (API) interfaces, atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI) interface. 

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