Mass spectrometers detection enhancement factor

When nano LC is combined with mass spectrometer detection, attamole detection can be achieved for low abundance components in biological fluids, drug metabolites, and natural products such as Chinese herb medicines. Nano LC-MS-MS has become an essential tool for complex biological and drug metabolite studies. Nano LC-MS presents two significant differences from conventional analytical HPLC (1) large enhancement factor for sample detection and (2) direct interface to MS without flow splitting. The enhancement in MS ion counts relative to a conventional 4.6 mm ID column is proportional to the ratio of the square of the column diameter ... 

The coupling of a mass spectrometer to CE and CEC provides a powerful system for the analysis of pharmaceuticals and complex biological mixtures. This can replace or complement other conventional detection methods such as UV, electrochemical, or LIE that provide less structural information. The use of mass spectrometer as a detector enhances the usefulness of the CE and CEC and allows an efficient separation and identification of complex mixtures, obtaining structure and/or molecular mass information. The choice of mass analyzers used in CE/CEC-MS depends on factors such as sensitivity, mass resolution, requirement for structural elucidation, and the type of application (Table 5). The analyzers that have been used in CEC analysis include time-of-flight (TOE), quadrupole (Q), ion-trap (IT), fourier... 

Sensitivity with an inductively coupled plasma is further enhanced by a factor of 3-10 by observing emission along the length of the plasma instead of across the diameter of the plasma. Additional sensitivity is obtained by detecting ions with a mass spectrometer instead of by optical emission (Table 21-2), as described in Section 21-6. 

The major problem with all API techniques for mass spectrometry concerns the transfer of the ions from the atmospheric pressure ion source into the vacuum required for operation of the miz analyzer itself, a pressure drop by a factor 10 Such a transfer involves a sudden expansion of the gas at some stage and this tends to enhance the condensation of solvent molecules (particularly water) on the ions to produce clusters of various sizes that redistribute the total ion current among several species thus compUcatmg the spectra and reducing S/B values. An interface between any atmospheric pressure ionization (API) source and a mass spectrometer must be able to deal with the pressure ratio (pumping speed is a crucial factor here. Section 6.6.1) and the de-clustering of the analyte ions before m z analysis and detection. 

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