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Figure 7.56 Interplate errors in 2% DOPC model (pH 7.4) over 12 months.

under those conditions [556]. When used carefully, LC/MS produces excellent results. However, when LC/MS data-taking is driven very rapidly (e.g., 20 min/ plate), disappointing results have been noted in collaborative studies [data not shown].

Figures 7.57a-c show the acceptor, donor, and reference spectra of 48 pM pro-pranolol at the end of 15 h PAMPA assay using 20% wt/vol soy lecithin in dode-cane. The sum of the donor (3 pM) and the acceptor (<1 pM) well concentrations indicates that 45 mM is lost to the membrane. In the absence of sink-creating surfactant, only a trace of propranolol reached the acceptor wells at the end of 15 h, with 94% of the compound trapped in the membrane, compared to 19% in the 2% wt/vol DOPC case (Table 7.5). The effective permeability in 20% soy dropped to 1.8 x 10~6cm/s, compared to the DOPC value of 10.2 x 10~6cm/s.

With surfactant-created sink condition in the acceptor compartment, the amount of propranolol reaching the acceptor wells is dramatically increased (Fig. 7.57d),

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