Interface Ionization cross sections

The cross-sectional area, AD, of a compound oriented in an amphiphilic gradient such as the air-water or lipid-water interface has been shown to be even more reliable for permeability predictions than the molecular weight [52]. For BBB permeation, the limiting cross-sectional area, AD, was determined as AD 73 A2, and the limiting ionization constants, p Cas, for bases and acids were determined as 9 and 4, respectively [52]. For intestinal barrier permeation, the limiting cross-sectional area was assessed as A D 100 A2, and the limiting ionization constants (pICas) for bases as 9 and for acids as 2 [53]. In this approach, the role of P-gp is again implicit [49]. 

Figure 9.7. Schematic diagram of a heated pneumatic nebulizer LC-MS interface and atmospheric pressure chemical ionization source with a cross-sectional view of the nebulizer probe.

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