Chemical ionization HPLC-capillary

Notes LOD, limit of detection MeOH, methanol EtOH, ethanol ACN, acetonitrile EtAC, ethyl acetate SPE, solid phase extraction HLB (hydrophilic lipophilic balanced) TFA, trifluoroacetic acid GC, gas chromatography TMS, trimethylsilyl MS, mass spectrometry HPLC, high-performance liquid chromatography DAD, diode array detector NMR, nuclear magnetic resonance ESI, electrospray ionization APCI, atmospheric pressure chemical ionization CE, capillary electrophoresis ECD, electrochemical detector CD, conductivity detector TLC, thin layer chromatography PDA, photodiode array detector. 

Atmospheric-pressure chemical ionization (APCI) An ionization memod in which a liquid stream is passed through a heated capillary and a concentric flow of a nebulizing gas. Ions are formed by ion-molecule reactions between me analyte and species derived from me HPLC mobile phase. 

Figure 2.1 Mass spectrometric approach. Dl, direct inlet GC, gas chromatography HPLC, high performance liquid chromatography CZE, capillary zone electrophoresis El, electron ionization Cl, chemical ionization ESI, electrospray ionization DESI, desorption electrospray ionization APCI, atmospheric pressure chemical ionization MALDI, matrix assisted laser desorption ionization B, magnetic analyzer E, electrostatic analyzer...

Different methods are used to tackle these problems [10-13], Some of these coupling methods, such as moving-belt coupling or the particle beam (PB) interface, are based on the selective vaporization of the elution solvent before it enters the spectrometer source. Other methods such as direct liquid introduction (DLI) [14] or continuous flow FAB (CF-FAB) rely on reducing the flow of the liquid that is introduced into the interface in order to obtain a flow that can be directly pumped into the source. In order to achieve this it must be reduced to one-twentieth of the value calculated above, that is 5 pi min. These flows are obtained from HPLC capillary columns or from a flow split at the outlet of classical HPLC columns. Finally, a series of HPLC/MS coupling methods such as thermospray (TSP), electrospray (ESI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) can tolerate flow rates of about 1 ml min 1 without requiring a flow split. Introducing the eluent entirely into the interface increases the detection sensitivity of these methods. ESI can accept flow rates from 10 nl min-1 levels to... 

Modern LC/MS systems employ two ionization processes that are accomplished at atmospheric pressure, termed electrospray (ESI) and atmospheric pressure chemical ionization (APCI). In a typical ESI source, the eluent from the HPLC column composed of liquid mobile phase and analyte molecules passes through a stainless steel capillary with a high positive or negative potential applied to the end (3-5 The electric-field causes instantaneous... 

Mass Spectrometric Methods for Capillary SFC-MS. A significant advantage associated with capillary SFC-MS methods, and in contrast to all mechanical (e.g., moving ribbon) HPLC-MS interfaces, results from the flexibility in selection of ionization methods. Although initial studies were conducted using chemical ionization, and it remains the method of choice for most applications, the DFI process is also compatible with electron impact ionization (37). 

The emergence of thermospray ionization heralded a first ideal interface for a wide range of molecules [30,31]. With the introduction of this interface, LC/MS was accepted as a routine analytical technique. A major beneficiary of this interface was the pharmaceutical industry, which used this system to characterize drugs and metabolites. The construction and basic principle of thermospray ion source was discussed in Section 2.14 briefly, it consists of a heated probe, a desolvation chamber, and an ion extraction skimmer. When passed through a resistively heated capillary, the HPLC effluent, emerges as a mist of fine droplets into a heated desolvation chamber. Ionization of the solute molecules occurs by direct evaporation of the preformed ions or solvent-mediated chemical ionization. Thus, unlike the interfaces discussed above, the thermospray system acts as an ion source as well as an interface. Thermospray is ideally suited to coupling with conventional wide-bore columns. It is, however, confined primarily to reversed-phase HPLC separations, and it is less compatible with nonvolatile... 

Detection methods HPLC-DAD, HPLC with diode-array detection. HPLC-(ESI-MS), HPLC with electrospray ionization mass spectrometry. RP-HPLC, revcrsed-phase HPLC. UPLC/Q-TOFMS, UPLC with quadrupole-time of flight mass spectrometry. HPLC-APCI-MS, HPLC with atmospheric pressure chemical ionization mass spectrometry. CE-IT-MS, capillary elecliophoresis-ion-1r mass spectrometry. LC-ESI-ITMS, liquid chromatography-electrospray ionization ion trap mass spectrometry. LC-ELSD, LC with evaporative light scattering detector. DNBZ-Cl, 3,5-dinitrobenzoyl chloride. 

HPLC-MS analyses were carried out with a Waters Alliance 2690 HPLC (Milford, MA), with column heater, 996 Photodiode Array Detector, and a Micromass ZMD (Waters, Milford, MA) or Waters Integrity TMD mass spectrometer (Milford, MA). A Luna silica-2, 5 pm, 2.0 x 150 mm (Phenomenex, Torrance, CA) column was used at a temperature of 35°C. The ZMD MS was equipped widi an atmospheric pressme chemical ionization (APCI) source and parameters set as corona voltage, 3.5 kV cone voltage, 30 V source block temp, 125 C APCI heater, 400 C desolvation gas, 150 L/min cone gas flow, 100 L/min scan range, m/z 151-1000. Reversed phase LC-MS was performed using a Beckman HPLC with 126 pump, 168 PDA (Fullerton, CA), and a Thermoquest LCQ mass spectrometer (San Jose, CA). A Luna Cl8, 3 pm, 2.0 X 50 mm (Phenomenex, Torrance, CA) column was used at ambient temperature. The LCQ MS was equipped with an APCI source and parameters set as APCI vaporizer temp, 450 C source current, 5 pA sheath gas flow, 80 au aux gas flow, 20 au capillary temp, 150 C capillary voltage, 23 V scan range, m/z 250-1500. 

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