Spectrometer analytical characterization

Atmospheric pressure chemical ionization, like electrospray ionization, is a mass spectrometer ionization source in which ionization occurs not in a vacuum but at atmospheric pressure. In contrast to electrospray ionization, in which the ionization process occurs in solution phase, atmospheric pressure chemical ionization is a gas-phase ionization process whereby gas-phase molecules are isolated from the carrier solvent before ionization [6]. Because the ionization mechanisms of APCI and electrospray are fundamentally different (gas-phase and liquid-phase ionization, respectively) the two methods have the potential to provide complimentary analyte characterization. To generalize, electrospray ionization is more... 

Consequently, a more fundamental question arises Why should one apply mass spectrometry to supramolecules What is the motivation and what is the added value of using this method together with other techniques that are maybe more commonly used in supramolecular chemistry The present chapter elaborates on the hypothesis that the potential of mass spectrometry goes far beyond the analytical characterization of complexes with respect to their exact masses, charge states, stoichiometries, or purity. In fact, the information that can be gained is complementary to other methods such as NMR spectroscopy and includes structural aspects, reactivity, and even thermochemistry. Examination of supramolecules by mass spectrometry involves their transfer into the high vacuum of the mass spectrometer and thus implies that isolated particles are investigated. There is no... 

Mass spectrometry (MS) has played an increasingly important role in drug discovery including analytical characterization of potential drug molecules and metabolic identification. A mass spectrophotometer consists of three components (1) an ionization source, (2) a mass analyzer, and (3) a detector. Mass spectral analysis requires that the analyte be introduced into the mass spectrometer as a gaseous ion. 

Beyer, C., Feldmann, I., Gilmour, D., Hoffmann, V, Jakubowski, N. (2002) Development and analytical characterization of a Grimm-type glow discharge ion source operated with high gas flow rates and coupled to a mass spectrometer with high mass resolution. Spectrochimica Acta Part B Atomic Spectroscopy, 57,1521-1533. 

Fig. 11.1. In addition, one area that has yet to be characterized is the use of sequential RP columns with large dead volumes. It seems unlikely that peptides eluting from the RP trap would reconcentrate on the RP column directly in front of the mass spectrometer diminishing the value of the second RP column. This needs further analytical investigation.

One of the best tools for metabolite profiling is the hybrid QTRAP MS/MS system (Applied Biosystems).119-121 While the hybrid QTRAP MS/MS was initially considered a premier tool for metabolite identification, it has more recently been seen as a tool for quantitation and metabolite profiling. Li et al.122 described the use of a hybrid QTRAP MS/MS system for discovery PK assays plus metabolite profiling in the same analytical procedure. Because QTRAP MS/MS may be used as a triple quadrupole MS system, it can be used as part of a quantitative HPLC/MS/MS system. Because QTRAP MS/MS also has linear ion trap capabilities, it can be used for metabolite screening and characterization—essentially it combines the capabilities of a triple quadrupole mass spectrometer and a linear ion trap mass spectrometer. 

Once a starting point has been identified, the analyst should evaluate the appropriateness of the procedure for impurities applications by first examining the pnrity of the analyte peak using a mnltidimensional detector snch as a photodiode array or mass spectrometer. The time to complete these initial evalnations can be accelerated by working with samples that have not been pnrified to the level intended for clinical application (also known as dirty samples.) Any impurities that are found shonld be identified by relative retention time and peak area so that they can nndergo additional characterization at a later date. 

Mass spectrometry is a sensitive analytical technique which is able to quantify known analytes and to identify unknown molecules at the picomoles or femto-moles level. A fundamental requirement is that atoms or molecules are ionized and analyzed as gas phase ions which are characterized by their mass (m) and charge (z). A mass spectrometer is an instrument which measures precisely the abundance of molecules which have been converted to ions. In a mass spectrum m/z is used as the dimensionless quantity that is an independent variable. There is still some ambiguity how the x-axis of the mass spectrum should be defined. Mass to charge ratio should not lo longer be used because the quantity measured is not the quotient of the ion s mass to its electric charge. Also, the use of the Thomson unit (Th) is considered obsolete [15, 16]. Typically, a mass spectrometer is formed by the following components (i) a sample introduction device (direct probe inlet, liquid interface), (ii) a source to produce ions, (iii) one or several mass analyzers, (iv) a detector to measure the abundance of ions, (v) a computerized system for data treatment (Fig. 1.1). 

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