Other Ionization Routes

Some types of reagent gases and their reactive ions. 

Typical Cl processes in which neutral sample molecules (M) react with NH to give either (a) a protonated ion [M + HJ or (b) an adduct ion [M + NHJ+ the quasi-molecular ions are respectively 1 and 18 mass units greater than the true mass (M). In process (c), reagent ions (CjHf) abstract hydrogen, giving a quasi-molecular ion that is 1 mass unit less than M. 

Some substances under El conditions fragment so readily that either no molecular ions survive or so few survive that it is difficult to be sure that the ones observed do not represent some impurity. Therefore, there is either no molecular mass information or it is uncertain. Under Cl conditions, very little fragmentation occurs and, depending on the reagent gas, ions [M + X]+ (X = H, NH4, NO, etc.) or [M - H] or [M - H] or [M -1- X] (X = F, Cl, OH, O, etc.) are the abundant quasi-molecular ions, which do give molecular mass information. 

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At mucosal pH where drug is 100% ionized and Eq. (4) has accounted for pH partition shifts, nonzero permeability suggests that ionized drug (Kp close to zero) permeates the membrane by a route other than via lipid partition/diffusion. A discussion of such alternative pathways follows in Section m.C. 

A characteristic feature of ESMS is the detection of multiply charged analytes. Macromolecules, such as proteins have multiple sites where protonation or deprotonation (the two most common charge inducing mechanisms in electrospray—other routes to charge induction include, ionization through adduct formation, through gas-phase reactions, and through electrochemical oxidation or reduction) occur. These are desorbed effectively in ESMS and... 

Interestingly, the flavin molecule is significantly easier to excite than the other heterocycles investigated. The first singlet excitation energy is only 3.0 eV (413 nm), and the probability of transition is intermediate. The second band with possible singlet excitation lies at 3.8 eV. Hence, if one intends to construct systems that are more readily excited, substituted flavins seem to be a more appropriate route than the furocoumarins, whereas the latter are easier to ionize. 

Absorption of phenol occurs fairly rapidly via the inhalation (Hughes and Hall 1995 Ohtsuji and Ikeda 1972 Piotrowski 1971), oral (Capel et al. 1972 Edwards et al. 1986 French et al. 1974 Hughes and Hall 1995 Kao et al. 1979 Kenyon et al. 1995), and dermal (Baranowska-Dutkiewicz 1981 Hughes and Hall 1995 Piotrowski 1971) routes. Because it is an irritant, tissue damage, inflammation, or other irritation effects may occur at the sites of absorption. Because of its high pKa, ionization will not occur within the acid environment of the gut. The action of gut microflora on phenol breakdown is not expected to be significant. 

The route of administration is determined primarily by the properties of the drug (such as water or lipid solubility, ionization, etc.) and by the therapeutic objectives (for example, the desirability of a rapid onset of action or the need for long-term administration or restriction to a local site). There are two major routes of drug administration, enteral and parenteral. (Figure 1.2 illustrates the subcategories of these routes as well as other methods of drug administration.)... 

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