Morphine, base ionization

Fig. 2.1. Lipophilicity profiles for diclofenac (acid), propranolol (base) and morphine (ampholyte). Dashed lines indicate the pH range where molecule may partition in its ionized form.

Example Morphine is a weak base (pKa 8.0). What percentage will be in the ionized form in the urine at a pH of 6.0 ... 

Dissociation constants and corresponding pK values of the drugs were obtained from measured free-base solubilities (determined at high pH s) and the concentrations of saturated solutions at intermediate pH s. Morphine, fentanyl, and sufentanil exhibited pJCa values of 8.08,8.99, and 8.51, respectively. Over the pH range of 5 to 12.5 the apparent solubilities are determined by the intrinsic solubility of the free base plus the concentration of ionized drug necessary to satisfy the dissociation equilibrium at a given pH."... 

Chemical ionization MS, with various deuterated reagent gases, has been used to probe the number and nature of active hydrogens in a molecule. For example, based on the mass shifts of the protonated ions that are observed when switching from ammonia (NH3) to deuterated ammonia (ND3), the number of active hydrogens in morphine and several other drugs have been demonstrated. 

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